default validator client rest mode to ssz for post block (#15645)

* wip

* fixing tests

* updating unit tests for coverage

* gofmt

* changelog

* consolidated propose beacon block tests and improved code coverage

* gaz

* partial review feedback

* continuation fixing feedback on functions

* adding log

* only fall back on 406

* fixing broken tests

* Update validator/client/beacon-api/propose_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/client/beacon-api/propose_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/client/beacon-api/propose_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/client/beacon-api/propose_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* Update validator/client/beacon-api/propose_beacon_block.go

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

* radek review feedback

* more feedback

* radek suggestion

* fixing unit tests

---------

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

changelog/james-prysm_post-block-ssz.md

@@ -0,0 +1,3 @@
+### Changed
+
+- Switching default of validator client rest call for submit block from JSON to SSZ. Fallback json will be attempted.

validator/client/beacon-api/BUILD.bazel

@@ -91,18 +91,6 @@ go_test(
         "index_test.go",
         "prepare_beacon_proposer_test.go",
         "propose_attestation_test.go",
-        "propose_beacon_block_altair_test.go",
-        "propose_beacon_block_bellatrix_test.go",
-        "propose_beacon_block_blinded_bellatrix_test.go",
-        "propose_beacon_block_blinded_capella_test.go",
-        "propose_beacon_block_blinded_deneb_test.go",
-        "propose_beacon_block_blinded_electra_test.go",
-        "propose_beacon_block_blinded_fulu_test.go",
-        "propose_beacon_block_capella_test.go",
-        "propose_beacon_block_deneb_test.go",
-        "propose_beacon_block_electra_test.go",
-        "propose_beacon_block_fulu_test.go",
-        "propose_beacon_block_phase0_test.go",
         "propose_beacon_block_test.go",
         "propose_exit_test.go",
         "prysm_beacon_chain_client_test.go",

validator/client/beacon-api/beacon_api_validator_client_test.go

@@ -1,14 +1,18 @@
 package beacon_api
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
+	"net/http"
 	"testing"
 
 	"github.com/OffchainLabs/prysm/v6/api/server/structs"
+	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
 	"github.com/OffchainLabs/prysm/v6/config/params"
 	"github.com/OffchainLabs/prysm/v6/consensus-types/primitives"
 	"github.com/OffchainLabs/prysm/v6/encoding/bytesutil"
+	"github.com/OffchainLabs/prysm/v6/network/httputil"
 	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
 	"github.com/OffchainLabs/prysm/v6/testing/assert"
 	"github.com/OffchainLabs/prysm/v6/testing/require"
@@ -136,15 +140,14 @@ func TestBeaconApiValidatorClient_ProposeBeaconBlockValid(t *testing.T) {
 	ctx := t.Context()
 
 	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-	jsonRestHandler.EXPECT().Post(
+	jsonRestHandler.EXPECT().PostSSZ(
 		gomock.Any(),
 		"/eth/v2/beacon/blocks",
-		map[string]string{"Eth-Consensus-Version": "phase0"},
 		gomock.Any(),
-		nil,
+		gomock.Any(),
 	).Return(
-		nil,
+		nil, nil, nil,
-	).Times(2)
+	).Times(1)
 
 	validatorClient := beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
 	expectedResp, expectedErr := validatorClient.proposeBeaconBlock(
@@ -153,34 +156,38 @@ func TestBeaconApiValidatorClient_ProposeBeaconBlockValid(t *testing.T) {
 			Block: generateSignedPhase0Block(),
 		},
 	)
-
+	require.NoError(t, expectedErr)
-	resp, err := validatorClient.ProposeBeaconBlock(
+	require.NotNil(t, expectedResp)
-		ctx,
-		&ethpb.GenericSignedBeaconBlock{
-			Block: generateSignedPhase0Block(),
-		},
-	)
-
-	assert.DeepEqual(t, expectedErr, err)
-	assert.DeepEqual(t, expectedResp, resp)
 }
 
-func TestBeaconApiValidatorClient_ProposeBeaconBlockError(t *testing.T) {
+func TestBeaconApiValidatorClient_ProposeBeaconBlockError_ThenPass(t *testing.T) {
 	ctrl := gomock.NewController(t)
 	defer ctrl.Finish()
 
 	ctx := t.Context()
 
 	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+	jsonRestHandler.EXPECT().PostSSZ(
+		gomock.Any(),
+		"/eth/v2/beacon/blocks",
+		gomock.Any(),
+		gomock.Any(),
+	).Return(
+		nil, nil, &httputil.DefaultJsonError{
+			Code:    http.StatusNotAcceptable,
+			Message: "SSZ not supported",
+		},
+	).Times(1)
+
 	jsonRestHandler.EXPECT().Post(
 		gomock.Any(),
 		"/eth/v2/beacon/blocks",
-		map[string]string{"Eth-Consensus-Version": "phase0"},
 		gomock.Any(),
-		nil,
+		gomock.Any(),
+		gomock.Any(),
 	).Return(
-		errors.New("foo error"),
+		nil,
-	).Times(2)
+	).Times(1)
 
 	validatorClient := beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
 	expectedResp, expectedErr := validatorClient.proposeBeaconBlock(
@@ -189,16 +196,351 @@ func TestBeaconApiValidatorClient_ProposeBeaconBlockError(t *testing.T) {
 			Block: generateSignedPhase0Block(),
 		},
 	)
+	require.NoError(t, expectedErr)
+	require.NotNil(t, expectedResp)
+}
 
-	resp, err := validatorClient.ProposeBeaconBlock(
+func TestBeaconApiValidatorClient_ProposeBeaconBlockAllTypes(t *testing.T) {
-		ctx,
+	tests := []struct {
-		&ethpb.GenericSignedBeaconBlock{
+		name          string
-			Block: generateSignedPhase0Block(),
+		block         *ethpb.GenericSignedBeaconBlock
+		expectedPath  string
+		wantErr       bool
+		errorMessage string
+	}{
+		{
+			name: "Phase0 block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedPhase0Block(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
 		},
-	)
+		{
+			name: "Altair block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedAltairBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Bellatrix block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBellatrixBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Capella block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedCapellaBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Bellatrix block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedBellatrixBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Blinded Capella block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedCapellaBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Deneb block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedDenebBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Deneb block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedDenebBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Electra block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedElectraBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Electra block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedElectraBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Fulu block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedFuluBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Fulu block",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedFuluBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Unsupported block type",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: nil,
+			},
+			wantErr:      true,
+			errorMessage: "unsupported block type",
+		},
+	}
 
-	assert.ErrorContains(t, expectedErr.Error(), err)
+	for _, tt := range tests {
-	assert.DeepEqual(t, expectedResp, resp)
+		t.Run(tt.name, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+			defer ctrl.Finish()
+
+			ctx := t.Context()
+			jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+			if !tt.wantErr {
+				jsonRestHandler.EXPECT().PostSSZ(
+					gomock.Any(),
+					tt.expectedPath,
+					gomock.Any(),
+					gomock.Any(),
+				).Return(nil, nil, nil).Times(1)
+			}
+
+			validatorClient := beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+			resp, err := validatorClient.proposeBeaconBlock(ctx, tt.block)
+
+			if tt.wantErr {
+				require.ErrorContains(t, tt.errorMessage, err)
+				assert.Equal(t, (*ethpb.ProposeResponse)(nil), resp)
+			} else {
+				require.NoError(t, err)
+				require.NotNil(t, resp)
+			}
+		})
+	}
+}
+
+func TestBeaconApiValidatorClient_ProposeBeaconBlockHTTPErrors(t *testing.T) {
+	tests := []struct {
+		name         string
+		sszError     error
+		expectJSON   bool
+		errorMessage string
+	}{
+		{
+			name: "HTTP 202 Accepted - block broadcast but failed validation",
+			sszError: &httputil.DefaultJsonError{
+				Code:    http.StatusAccepted,
+				Message: "block broadcast but failed validation",
+			},
+			expectJSON:   false, // No fallback for non-406 errors
+			errorMessage: "failed to submit block ssz",
+		},
+		{
+			name: "Other HTTP error",
+			sszError: &httputil.DefaultJsonError{
+				Code:    http.StatusBadRequest,
+				Message: "bad request",
+			},
+			expectJSON:   false, // No fallback for non-406 errors
+			errorMessage: "failed to submit block ssz",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+			defer ctrl.Finish()
+
+			ctx := t.Context()
+			jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+			jsonRestHandler.EXPECT().PostSSZ(
+				gomock.Any(),
+				"/eth/v2/beacon/blocks",
+				gomock.Any(),
+				gomock.Any(),
+			).Return(nil, nil, tt.sszError).Times(1)
+			
+			if tt.expectJSON {
+				// When SSZ fails, it falls back to JSON
+				jsonRestHandler.EXPECT().Post(
+					gomock.Any(),
+					"/eth/v2/beacon/blocks",
+					gomock.Any(),
+					gomock.Any(),
+					gomock.Any(),
+				).Return(tt.sszError).Times(1)
+			}
+
+			validatorClient := beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+			_, err := validatorClient.proposeBeaconBlock(
+				ctx,
+				&ethpb.GenericSignedBeaconBlock{
+					Block: generateSignedPhase0Block(),
+				},
+			)
+			require.ErrorContains(t, tt.errorMessage, err)
+		})
+	}
+}
+
+func TestBeaconApiValidatorClient_ProposeBeaconBlockJSONFallback(t *testing.T) {
+	tests := []struct {
+		name         string
+		block        *ethpb.GenericSignedBeaconBlock
+		expectedPath string
+		jsonError    error
+		wantErr      bool
+	}{
+		{
+			name: "Phase0 block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedPhase0Block(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Altair block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedAltairBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Bellatrix block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBellatrixBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Capella block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedCapellaBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Bellatrix block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedBellatrixBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Blinded Capella block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedCapellaBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Deneb block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedDenebBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Deneb block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedDenebBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Electra block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedElectraBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Electra block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedElectraBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "Fulu block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedFuluBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+		},
+		{
+			name: "Blinded Fulu block JSON fallback success",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedBlindedFuluBlock(),
+			},
+			expectedPath: "/eth/v2/beacon/blinded_blocks",
+		},
+		{
+			name: "JSON fallback fails",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedPhase0Block(),
+			},
+			expectedPath: "/eth/v2/beacon/blocks",
+			jsonError:    errors.New("json post failed"),
+			wantErr:      true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+			defer ctrl.Finish()
+
+			ctx := t.Context()
+			jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+			// SSZ call fails with 406 to trigger JSON fallback
+			jsonRestHandler.EXPECT().PostSSZ(
+				gomock.Any(),
+				tt.expectedPath,
+				gomock.Any(),
+				gomock.Any(),
+			).Return(nil, nil, &httputil.DefaultJsonError{
+				Code:    http.StatusNotAcceptable,
+				Message: "SSZ not supported",
+			}).Times(1)
+
+			// JSON fallback
+			jsonRestHandler.EXPECT().Post(
+				gomock.Any(),
+				tt.expectedPath,
+				gomock.Any(),
+				gomock.Any(),
+				gomock.Any(),
+			).Return(tt.jsonError).Times(1)
+
+			validatorClient := beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+			resp, err := validatorClient.proposeBeaconBlock(ctx, tt.block)
+
+			if tt.wantErr {
+				assert.NotNil(t, err)
+				assert.Equal(t, (*ethpb.ProposeResponse)(nil), resp)
+			} else {
+				require.NoError(t, err)
+				require.NotNil(t, resp)
+			}
+		})
+	}
 }
 
 func TestBeaconApiValidatorClient_Host(t *testing.T) {
@@ -229,3 +571,88 @@ func TestBeaconApiValidatorClient_Host(t *testing.T) {
 	host = validatorClient.Host()
 	require.Equal(t, hosts[1], host)
 }
+
+// Helper functions for generating test blocks for newer consensus versions
+func generateSignedDenebBlock() *ethpb.GenericSignedBeaconBlock_Deneb {
+	var blockContents structs.SignedBeaconBlockContentsDeneb
+	if err := json.Unmarshal([]byte(rpctesting.DenebBlockContents), &blockContents); err != nil {
+		panic(err)
+	}
+	genericBlock, err := blockContents.ToGeneric()
+	if err != nil {
+		panic(err)
+	}
+	return &ethpb.GenericSignedBeaconBlock_Deneb{
+		Deneb: genericBlock.GetDeneb(),
+	}
+}
+
+func generateSignedBlindedDenebBlock() *ethpb.GenericSignedBeaconBlock_BlindedDeneb {
+	var blindedBlock structs.SignedBlindedBeaconBlockDeneb
+	if err := json.Unmarshal([]byte(rpctesting.BlindedDenebBlock), &blindedBlock); err != nil {
+		panic(err)
+	}
+	genericBlock, err := blindedBlock.ToGeneric()
+	if err != nil {
+		panic(err)
+	}
+	return &ethpb.GenericSignedBeaconBlock_BlindedDeneb{
+		BlindedDeneb: genericBlock.GetBlindedDeneb(),
+	}
+}
+
+func generateSignedElectraBlock() *ethpb.GenericSignedBeaconBlock_Electra {
+	var blockContents structs.SignedBeaconBlockContentsElectra
+	if err := json.Unmarshal([]byte(rpctesting.ElectraBlockContents), &blockContents); err != nil {
+		panic(err)
+	}
+	genericBlock, err := blockContents.ToGeneric()
+	if err != nil {
+		panic(err)
+	}
+	return &ethpb.GenericSignedBeaconBlock_Electra{
+		Electra: genericBlock.GetElectra(),
+	}
+}
+
+func generateSignedBlindedElectraBlock() *ethpb.GenericSignedBeaconBlock_BlindedElectra {
+	var blindedBlock structs.SignedBlindedBeaconBlockElectra
+	if err := json.Unmarshal([]byte(rpctesting.BlindedElectraBlock), &blindedBlock); err != nil {
+		panic(err)
+	}
+	genericBlock, err := blindedBlock.ToGeneric()
+	if err != nil {
+		panic(err)
+	}
+	return &ethpb.GenericSignedBeaconBlock_BlindedElectra{
+		BlindedElectra: genericBlock.GetBlindedElectra(),
+	}
+}
+
+func generateSignedFuluBlock() *ethpb.GenericSignedBeaconBlock_Fulu {
+	var blockContents structs.SignedBeaconBlockContentsFulu
+	if err := json.Unmarshal([]byte(rpctesting.FuluBlockContents), &blockContents); err != nil {
+		panic(err)
+	}
+	genericBlock, err := blockContents.ToGeneric()
+	if err != nil {
+		panic(err)
+	}
+	return &ethpb.GenericSignedBeaconBlock_Fulu{
+		Fulu: genericBlock.GetFulu(),
+	}
+}
+
+func generateSignedBlindedFuluBlock() *ethpb.GenericSignedBeaconBlock_BlindedFulu {
+	var blindedBlock structs.SignedBlindedBeaconBlockFulu
+	if err := json.Unmarshal([]byte(rpctesting.BlindedFuluBlock), &blindedBlock); err != nil {
+		panic(err)
+	}
+	genericBlock, err := blindedBlock.ToGeneric()
+	if err != nil {
+		panic(err)
+	}
+	return &ethpb.GenericSignedBeaconBlock_BlindedFulu{
+		BlindedFulu: genericBlock.GetBlindedFulu(),
+	}
+}

validator/client/beacon-api/mock/json_rest_handler_mock.go

@@ -114,6 +114,22 @@ func (mr *MockJsonRestHandlerMockRecorder) Post(ctx, endpoint, headers, data, re
 	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Post", reflect.TypeOf((*MockJsonRestHandler)(nil).Post), ctx, endpoint, headers, data, resp)
 }
 
+// Post mocks base method.
+func (m *MockJsonRestHandler) PostSSZ(ctx context.Context, endpoint string, headers map[string]string, data *bytes.Buffer) ([]byte, http.Header, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "PostSSZ", ctx, endpoint, headers, data)
+	ret0, _ := ret[0].([]byte)
+	ret1, _ := ret[1].(http.Header)
+	ret2, _ := ret[2].(error)
+	return ret0,ret1,ret2
+}
+
+// Post indicates an expected call of Post.
+func (mr *MockJsonRestHandlerMockRecorder) PostSSZ(ctx, endpoint, headers, data any) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "PostSSZ", reflect.TypeOf((*MockJsonRestHandler)(nil).PostSSZ), ctx, endpoint, headers, data)
+}
+
 // SetHost mocks base method.
 func (m *MockJsonRestHandler) SetHost(host string) {
 	m.ctrl.T.Helper()

validator/client/beacon-api/propose_beacon_block.go

@@ -15,8 +15,10 @@ import (
 type blockProcessingResult struct {
 	consensusVersion string
 	beaconBlockRoot  [32]byte
-	marshalledJSON   []byte
+	marshalledSSZ    []byte
 	blinded          bool
+	// Function to marshal JSON on demand
+	marshalJSON func() ([]byte, error)
 }
 
 func (c *beaconApiValidatorClient) proposeBeaconBlock(ctx context.Context, in *ethpb.GenericSignedBeaconBlock) (*ethpb.ProposeResponse, error) {
@@ -62,17 +64,54 @@ func (c *beaconApiValidatorClient) proposeBeaconBlock(ctx context.Context, in *e
 	}
 
 	headers := map[string]string{"Eth-Consensus-Version": res.consensusVersion}
-	err = c.jsonRestHandler.Post(ctx, endpoint, headers, bytes.NewBuffer(res.marshalledJSON), nil)
+
-	errJson := &httputil.DefaultJsonError{}
+	// Try PostSSZ first with SSZ data
-	if err != nil {
+	if res.marshalledSSZ != nil {
-		if !errors.As(err, &errJson) {
+		_, _, err = c.jsonRestHandler.PostSSZ(ctx, endpoint, headers, bytes.NewBuffer(res.marshalledSSZ))
-			return nil, err
+		if err != nil {
+			errJson := &httputil.DefaultJsonError{}
+			// If PostSSZ fails with 406 (Not Acceptable), fall back to JSON
+			if !errors.As(err, &errJson) {
+				return nil, err
+			}
+			if errJson.Code == http.StatusNotAcceptable && res.marshalJSON != nil {
+				log.WithError(err).Warn("Failed to submit block ssz, falling back to JSON")
+				jsonData, jsonErr := res.marshalJSON()
+				if jsonErr != nil {
+					return nil, errors.Wrap(jsonErr, "failed to marshal JSON")
+				}
+				// Reset headers for JSON
+				err = c.jsonRestHandler.Post(ctx, endpoint, headers, bytes.NewBuffer(jsonData), nil)
+				// If JSON also fails, return that error
+				if err != nil {
+					return nil, errors.Wrap(err, "failed to submit block via JSON fallback")
+				}
+			} else {
+				// For non-406 errors or when no JSON fallback is available, return the SSZ error
+				return nil, errors.Wrap(errJson, "failed to submit block ssz")
+			}
 		}
-		// Error 202 means that the block was successfully broadcast, but validation failed
+	} else if res.marshalJSON == nil {
-		if errJson.Code == http.StatusAccepted {
+		return nil, errors.New("no marshalling functions available")
-			return nil, errors.New("block was successfully broadcast but failed validation")
+	} else {
+		// No SSZ data available, marshal and use JSON
+		jsonData, jsonErr := res.marshalJSON()
+		if jsonErr != nil {
+			return nil, errors.Wrap(jsonErr, "failed to marshal JSON")
+		}
+		// Reset headers for JSON
+		err = c.jsonRestHandler.Post(ctx, endpoint, headers, bytes.NewBuffer(jsonData), nil)
+		errJson := &httputil.DefaultJsonError{}
+		if err != nil {
+			if !errors.As(err, &errJson) {
+				return nil, err
+			}
+			// Error 202 means that the block was successfully broadcast, but validation failed
+			if errJson.Code == http.StatusAccepted {
+				return nil, errors.New("block was successfully broadcast but failed validation")
+			}
+			return nil, errJson
 		}
-		return nil, errJson
 	}
 
 	return &ethpb.ProposeResponse{BlockRoot: res.beaconBlockRoot[:]}, nil
@@ -89,11 +128,19 @@ func handlePhase0Block(block *ethpb.GenericSignedBeaconBlock_Phase0) (*blockProc
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock := structs.SignedBeaconBlockPhase0FromConsensus(block.Phase0)
+	// Marshal SSZ
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	ssz, err := block.Phase0.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall phase0 beacon block to json")
+		return nil, errors.Wrap(err, "failed to serialize block for phase0 beacon block")
 	}
+	res.marshalledSSZ = ssz
+
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock := structs.SignedBeaconBlockPhase0FromConsensus(block.Phase0)
+		return json.Marshal(signedBlock)
+	}
+
 	return &res, nil
 }
 
@@ -108,11 +155,19 @@ func handleAltairBlock(block *ethpb.GenericSignedBeaconBlock_Altair) (*blockProc
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock := structs.SignedBeaconBlockAltairFromConsensus(block.Altair)
+	// Marshal SSZ
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	ssz, err := block.Altair.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall altair beacon block to json")
+		return nil, errors.Wrap(err, "failed to serialize block for altair beacon block")
 	}
+	res.marshalledSSZ = ssz
+
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock := structs.SignedBeaconBlockAltairFromConsensus(block.Altair)
+		return json.Marshal(signedBlock)
+	}
+
 	return &res, nil
 }
 
@@ -127,13 +182,20 @@ func handleBellatrixBlock(block *ethpb.GenericSignedBeaconBlock_Bellatrix) (*blo
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBeaconBlockBellatrixFromConsensus(block.Bellatrix)
+	// Marshal SSZ
+	ssz, err := block.Bellatrix.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall bellatrix beacon block")
+		return nil, errors.Wrap(err, "failed to serialize block for bellatrix beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall bellatrix beacon block to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBeaconBlockBellatrixFromConsensus(block.Bellatrix)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert bellatrix beacon block")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -150,13 +212,20 @@ func handleBlindedBellatrixBlock(block *ethpb.GenericSignedBeaconBlock_BlindedBe
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBlindedBeaconBlockBellatrixFromConsensus(block.BlindedBellatrix)
+	// Marshal SSZ
+	ssz, err := block.BlindedBellatrix.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall blinded bellatrix beacon block")
+		return nil, errors.Wrap(err, "failed to serialize block for bellatrix beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall blinded bellatrix beacon block to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBlindedBeaconBlockBellatrixFromConsensus(block.BlindedBellatrix)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert blinded bellatrix beacon block")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -173,13 +242,20 @@ func handleCapellaBlock(block *ethpb.GenericSignedBeaconBlock_Capella) (*blockPr
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBeaconBlockCapellaFromConsensus(block.Capella)
+	// Marshal SSZ
+	ssz, err := block.Capella.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall capella beacon block")
+		return nil, errors.Wrap(err, "failed to serialize capella beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall capella beacon block to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBeaconBlockCapellaFromConsensus(block.Capella)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert capella beacon block")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -196,13 +272,20 @@ func handleBlindedCapellaBlock(block *ethpb.GenericSignedBeaconBlock_BlindedCape
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBlindedBeaconBlockCapellaFromConsensus(block.BlindedCapella)
+	// Marshal SSZ
+	ssz, err := block.BlindedCapella.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall blinded capella beacon block")
+		return nil, errors.Wrap(err, "failed to serialize blinded capella beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall blinded capella beacon block to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBlindedBeaconBlockCapellaFromConsensus(block.BlindedCapella)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert blinded capella beacon block")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -219,13 +302,20 @@ func handleDenebBlockContents(block *ethpb.GenericSignedBeaconBlock_Deneb) (*blo
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBeaconBlockContentsDenebFromConsensus(block.Deneb)
+	// Marshal SSZ
+	ssz, err := block.Deneb.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall deneb beacon block contents")
+		return nil, errors.Wrap(err, "failed to serialize deneb beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall deneb beacon block contents to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBeaconBlockContentsDenebFromConsensus(block.Deneb)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert deneb beacon block contents")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -242,13 +332,20 @@ func handleBlindedDenebBlock(block *ethpb.GenericSignedBeaconBlock_BlindedDeneb)
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBlindedBeaconBlockDenebFromConsensus(block.BlindedDeneb)
+	// Marshal SSZ
+	ssz, err := block.BlindedDeneb.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall deneb blinded beacon block ")
+		return nil, errors.Wrap(err, "failed to serialize blinded deneb  beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall deneb blinded beacon block to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBlindedBeaconBlockDenebFromConsensus(block.BlindedDeneb)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert deneb blinded beacon block")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -265,13 +362,20 @@ func handleElectraBlockContents(block *ethpb.GenericSignedBeaconBlock_Electra) (
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBeaconBlockContentsElectraFromConsensus(block.Electra)
+	// Marshal SSZ
+	ssz, err := block.Electra.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall electra beacon block contents")
+		return nil, errors.Wrap(err, "failed to serialize electra beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall electra beacon block contents to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBeaconBlockContentsElectraFromConsensus(block.Electra)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert electra beacon block contents")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -288,13 +392,20 @@ func handleBlindedElectraBlock(block *ethpb.GenericSignedBeaconBlock_BlindedElec
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBlindedBeaconBlockElectraFromConsensus(block.BlindedElectra)
+	// Marshal SSZ
+	ssz, err := block.BlindedElectra.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall electra blinded beacon block")
+		return nil, errors.Wrap(err, "failed to serialize blinded electra beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall electra blinded beacon block to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBlindedBeaconBlockElectraFromConsensus(block.BlindedElectra)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert electra blinded beacon block")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -311,13 +422,20 @@ func handleFuluBlockContents(block *ethpb.GenericSignedBeaconBlock_Fulu) (*block
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBeaconBlockContentsFuluFromConsensus(block.Fulu)
+	// Marshal SSZ
+	ssz, err := block.Fulu.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall fulu beacon block contents")
+		return nil, errors.Wrap(err, "failed to serialize fulu beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall fulu beacon block contents to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBeaconBlockContentsFuluFromConsensus(block.Fulu)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert fulu beacon block contents")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil
@@ -334,13 +452,20 @@ func handleBlindedFuluBlock(block *ethpb.GenericSignedBeaconBlock_BlindedFulu) (
 	}
 	res.beaconBlockRoot = beaconBlockRoot
 
-	signedBlock, err := structs.SignedBlindedBeaconBlockFuluFromConsensus(block.BlindedFulu)
+	// Marshal SSZ
+	ssz, err := block.BlindedFulu.MarshalSSZ()
 	if err != nil {
-		return nil, errors.Wrap(err, "failed to marshall fulu blinded beacon block")
+		return nil, errors.Wrap(err, "failed to serialize blinded fulu beacon block")
 	}
-	res.marshalledJSON, err = json.Marshal(signedBlock)
+	res.marshalledSSZ = ssz
-	if err != nil {
+
-		return nil, errors.Wrap(err, "failed to marshall fulu blinded beacon block to json")
+	// Set up JSON marshalling function for fallback
+	res.marshalJSON = func() ([]byte, error) {
+		signedBlock, err := structs.SignedBlindedBeaconBlockFuluFromConsensus(block.BlindedFulu)
+		if err != nil {
+			return nil, errors.Wrap(err, "failed to convert fulu blinded beacon block")
+		}
+		return json.Marshal(signedBlock)
 	}
 
 	return &res, nil

validator/client/beacon-api/propose_beacon_block_altair_test.go

@@ -1,63 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	testhelpers "github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/test-helpers"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_Altair(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	altairBlock := generateSignedAltairBlock()
-
-	genericSignedBlock := &ethpb.GenericSignedBeaconBlock{}
-	genericSignedBlock.Block = altairBlock
-
-	jsonAltairBlock := structs.SignedBeaconBlockAltairFromConsensus(altairBlock.Altair)
-
-	marshalledBlock, err := json.Marshal(jsonAltairBlock)
-	require.NoError(t, err)
-
-	ctx := t.Context()
-
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "altair"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blocks",
-		headers,
-		bytes.NewBuffer(marshalledBlock),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(ctx, genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := altairBlock.Altair.Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}
-
-func generateSignedAltairBlock() *ethpb.GenericSignedBeaconBlock_Altair {
-	return &ethpb.GenericSignedBeaconBlock_Altair{
-		Altair: &ethpb.SignedBeaconBlockAltair{
-			Block:     testhelpers.GenerateProtoAltairBeaconBlock(),
-			Signature: testhelpers.FillByteSlice(96, 112),
-		},
-	}
-}

validator/client/beacon-api/propose_beacon_block_bellatrix_test.go

@@ -1,64 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	testhelpers "github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/test-helpers"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_Bellatrix(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	bellatrixBlock := generateSignedBellatrixBlock()
-
-	genericSignedBlock := &ethpb.GenericSignedBeaconBlock{}
-	genericSignedBlock.Block = bellatrixBlock
-
-	jsonBellatrixBlock, err := structs.SignedBeaconBlockBellatrixFromConsensus(bellatrixBlock.Bellatrix)
-	require.NoError(t, err)
-
-	marshalledBlock, err := json.Marshal(jsonBellatrixBlock)
-	require.NoError(t, err)
-
-	ctx := t.Context()
-
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "bellatrix"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blocks",
-		headers,
-		bytes.NewBuffer(marshalledBlock),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(ctx, genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := bellatrixBlock.Bellatrix.Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}
-
-func generateSignedBellatrixBlock() *ethpb.GenericSignedBeaconBlock_Bellatrix {
-	return &ethpb.GenericSignedBeaconBlock_Bellatrix{
-		Bellatrix: &ethpb.SignedBeaconBlockBellatrix{
-			Block:     testhelpers.GenerateProtoBellatrixBeaconBlock(),
-			Signature: testhelpers.FillByteSlice(96, 127),
-		},
-	}
-}

validator/client/beacon-api/propose_beacon_block_blinded_bellatrix_test.go

@@ -1,291 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	enginev1 "github.com/OffchainLabs/prysm/v6/proto/engine/v1"
-	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	testhelpers "github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/test-helpers"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_BlindedBellatrix(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	blindedBellatrixBlock := generateSignedBlindedBellatrixBlock()
-
-	genericSignedBlock := &ethpb.GenericSignedBeaconBlock{}
-	genericSignedBlock.Block = blindedBellatrixBlock
-
-	jsonBlindedBellatrixBlock, err := structs.SignedBlindedBeaconBlockBellatrixFromConsensus(blindedBellatrixBlock.BlindedBellatrix)
-	require.NoError(t, err)
-
-	marshalledBlock, err := json.Marshal(jsonBlindedBellatrixBlock)
-	require.NoError(t, err)
-
-	ctx := t.Context()
-
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "bellatrix"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blinded_blocks",
-		headers,
-		bytes.NewBuffer(marshalledBlock),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(ctx, genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := blindedBellatrixBlock.BlindedBellatrix.Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}
-
-func generateSignedBlindedBellatrixBlock() *ethpb.GenericSignedBeaconBlock_BlindedBellatrix {
-	return &ethpb.GenericSignedBeaconBlock_BlindedBellatrix{
-		BlindedBellatrix: &ethpb.SignedBlindedBeaconBlockBellatrix{
-			Block: &ethpb.BlindedBeaconBlockBellatrix{
-				Slot:          1,
-				ProposerIndex: 2,
-				ParentRoot:    testhelpers.FillByteSlice(32, 3),
-				StateRoot:     testhelpers.FillByteSlice(32, 4),
-				Body: &ethpb.BlindedBeaconBlockBodyBellatrix{
-					RandaoReveal: testhelpers.FillByteSlice(96, 5),
-					Eth1Data: &ethpb.Eth1Data{
-						DepositRoot:  testhelpers.FillByteSlice(32, 6),
-						DepositCount: 7,
-						BlockHash:    testhelpers.FillByteSlice(32, 8),
-					},
-					Graffiti: testhelpers.FillByteSlice(32, 9),
-					ProposerSlashings: []*ethpb.ProposerSlashing{
-						{
-							Header_1: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          10,
-									ProposerIndex: 11,
-									ParentRoot:    testhelpers.FillByteSlice(32, 12),
-									StateRoot:     testhelpers.FillByteSlice(32, 13),
-									BodyRoot:      testhelpers.FillByteSlice(32, 14),
-								},
-								Signature: testhelpers.FillByteSlice(96, 15),
-							},
-							Header_2: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          16,
-									ProposerIndex: 17,
-									ParentRoot:    testhelpers.FillByteSlice(32, 18),
-									StateRoot:     testhelpers.FillByteSlice(32, 19),
-									BodyRoot:      testhelpers.FillByteSlice(32, 20),
-								},
-								Signature: testhelpers.FillByteSlice(96, 21),
-							},
-						},
-						{
-							Header_1: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          22,
-									ProposerIndex: 23,
-									ParentRoot:    testhelpers.FillByteSlice(32, 24),
-									StateRoot:     testhelpers.FillByteSlice(32, 25),
-									BodyRoot:      testhelpers.FillByteSlice(32, 26),
-								},
-								Signature: testhelpers.FillByteSlice(96, 27),
-							},
-							Header_2: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          28,
-									ProposerIndex: 29,
-									ParentRoot:    testhelpers.FillByteSlice(32, 30),
-									StateRoot:     testhelpers.FillByteSlice(32, 31),
-									BodyRoot:      testhelpers.FillByteSlice(32, 32),
-								},
-								Signature: testhelpers.FillByteSlice(96, 33),
-							},
-						},
-					},
-					AttesterSlashings: []*ethpb.AttesterSlashing{
-						{
-							Attestation_1: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{34, 35},
-								Data: &ethpb.AttestationData{
-									Slot:            36,
-									CommitteeIndex:  37,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 39,
-										Root:  testhelpers.FillByteSlice(32, 40),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 41,
-										Root:  testhelpers.FillByteSlice(32, 42),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 43),
-							},
-							Attestation_2: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{44, 45},
-								Data: &ethpb.AttestationData{
-									Slot:            46,
-									CommitteeIndex:  47,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 49,
-										Root:  testhelpers.FillByteSlice(32, 50),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 51,
-										Root:  testhelpers.FillByteSlice(32, 52),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 53),
-							},
-						},
-						{
-							Attestation_1: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{54, 55},
-								Data: &ethpb.AttestationData{
-									Slot:            56,
-									CommitteeIndex:  57,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 59,
-										Root:  testhelpers.FillByteSlice(32, 60),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 61,
-										Root:  testhelpers.FillByteSlice(32, 62),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 63),
-							},
-							Attestation_2: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{64, 65},
-								Data: &ethpb.AttestationData{
-									Slot:            66,
-									CommitteeIndex:  67,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 69,
-										Root:  testhelpers.FillByteSlice(32, 70),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 71,
-										Root:  testhelpers.FillByteSlice(32, 72),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 73),
-							},
-						},
-					},
-					Attestations: []*ethpb.Attestation{
-						{
-							AggregationBits: testhelpers.FillByteSlice(4, 74),
-							Data: &ethpb.AttestationData{
-								Slot:            75,
-								CommitteeIndex:  76,
-								BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-								Source: &ethpb.Checkpoint{
-									Epoch: 78,
-									Root:  testhelpers.FillByteSlice(32, 79),
-								},
-								Target: &ethpb.Checkpoint{
-									Epoch: 80,
-									Root:  testhelpers.FillByteSlice(32, 81),
-								},
-							},
-							Signature: testhelpers.FillByteSlice(96, 82),
-						},
-						{
-							AggregationBits: testhelpers.FillByteSlice(4, 83),
-							Data: &ethpb.AttestationData{
-								Slot:            84,
-								CommitteeIndex:  85,
-								BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-								Source: &ethpb.Checkpoint{
-									Epoch: 87,
-									Root:  testhelpers.FillByteSlice(32, 88),
-								},
-								Target: &ethpb.Checkpoint{
-									Epoch: 89,
-									Root:  testhelpers.FillByteSlice(32, 90),
-								},
-							},
-							Signature: testhelpers.FillByteSlice(96, 91),
-						},
-					},
-					Deposits: []*ethpb.Deposit{
-						{
-							Proof: testhelpers.FillByteArraySlice(33, testhelpers.FillByteSlice(32, 92)),
-							Data: &ethpb.Deposit_Data{
-								PublicKey:             testhelpers.FillByteSlice(48, 94),
-								WithdrawalCredentials: testhelpers.FillByteSlice(32, 95),
-								Amount:                96,
-								Signature:             testhelpers.FillByteSlice(96, 97),
-							},
-						},
-						{
-							Proof: testhelpers.FillByteArraySlice(33, testhelpers.FillByteSlice(32, 98)),
-							Data: &ethpb.Deposit_Data{
-								PublicKey:             testhelpers.FillByteSlice(48, 100),
-								WithdrawalCredentials: testhelpers.FillByteSlice(32, 101),
-								Amount:                102,
-								Signature:             testhelpers.FillByteSlice(96, 103),
-							},
-						},
-					},
-					VoluntaryExits: []*ethpb.SignedVoluntaryExit{
-						{
-							Exit: &ethpb.VoluntaryExit{
-								Epoch:          104,
-								ValidatorIndex: 105,
-							},
-							Signature: testhelpers.FillByteSlice(96, 106),
-						},
-						{
-							Exit: &ethpb.VoluntaryExit{
-								Epoch:          107,
-								ValidatorIndex: 108,
-							},
-							Signature: testhelpers.FillByteSlice(96, 109),
-						},
-					},
-					SyncAggregate: &ethpb.SyncAggregate{
-						SyncCommitteeBits:      testhelpers.FillByteSlice(64, 110),
-						SyncCommitteeSignature: testhelpers.FillByteSlice(96, 111),
-					},
-					ExecutionPayloadHeader: &enginev1.ExecutionPayloadHeader{
-						ParentHash:       testhelpers.FillByteSlice(32, 112),
-						FeeRecipient:     testhelpers.FillByteSlice(20, 113),
-						StateRoot:        testhelpers.FillByteSlice(32, 114),
-						ReceiptsRoot:     testhelpers.FillByteSlice(32, 115),
-						LogsBloom:        testhelpers.FillByteSlice(256, 116),
-						PrevRandao:       testhelpers.FillByteSlice(32, 117),
-						BlockNumber:      118,
-						GasLimit:         119,
-						GasUsed:          120,
-						Timestamp:        121,
-						ExtraData:        testhelpers.FillByteSlice(32, 122),
-						BaseFeePerGas:    testhelpers.FillByteSlice(32, 123),
-						BlockHash:        testhelpers.FillByteSlice(32, 124),
-						TransactionsRoot: testhelpers.FillByteSlice(32, 125),
-					},
-				},
-			},
-			Signature: testhelpers.FillByteSlice(96, 126),
-		},
-	}
-}

validator/client/beacon-api/propose_beacon_block_blinded_capella_test.go

@@ -1,310 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	enginev1 "github.com/OffchainLabs/prysm/v6/proto/engine/v1"
-	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	testhelpers "github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/test-helpers"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_BlindedCapella(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	blindedCapellaBlock := generateSignedBlindedCapellaBlock()
-
-	genericSignedBlock := &ethpb.GenericSignedBeaconBlock{}
-	genericSignedBlock.Block = blindedCapellaBlock
-
-	jsonBlindedCapellaBlock, err := structs.SignedBlindedBeaconBlockCapellaFromConsensus(blindedCapellaBlock.BlindedCapella)
-	require.NoError(t, err)
-
-	marshalledBlock, err := json.Marshal(jsonBlindedCapellaBlock)
-	require.NoError(t, err)
-
-	ctx := t.Context()
-
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "capella"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blinded_blocks",
-		headers,
-		bytes.NewBuffer(marshalledBlock),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(ctx, genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := blindedCapellaBlock.BlindedCapella.Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}
-
-func generateSignedBlindedCapellaBlock() *ethpb.GenericSignedBeaconBlock_BlindedCapella {
-	return &ethpb.GenericSignedBeaconBlock_BlindedCapella{
-		BlindedCapella: &ethpb.SignedBlindedBeaconBlockCapella{
-			Block: &ethpb.BlindedBeaconBlockCapella{
-				Slot:          1,
-				ProposerIndex: 2,
-				ParentRoot:    testhelpers.FillByteSlice(32, 3),
-				StateRoot:     testhelpers.FillByteSlice(32, 4),
-				Body: &ethpb.BlindedBeaconBlockBodyCapella{
-					RandaoReveal: testhelpers.FillByteSlice(96, 5),
-					Eth1Data: &ethpb.Eth1Data{
-						DepositRoot:  testhelpers.FillByteSlice(32, 6),
-						DepositCount: 7,
-						BlockHash:    testhelpers.FillByteSlice(32, 8),
-					},
-					Graffiti: testhelpers.FillByteSlice(32, 9),
-					ProposerSlashings: []*ethpb.ProposerSlashing{
-						{
-							Header_1: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          10,
-									ProposerIndex: 11,
-									ParentRoot:    testhelpers.FillByteSlice(32, 12),
-									StateRoot:     testhelpers.FillByteSlice(32, 13),
-									BodyRoot:      testhelpers.FillByteSlice(32, 14),
-								},
-								Signature: testhelpers.FillByteSlice(96, 15),
-							},
-							Header_2: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          16,
-									ProposerIndex: 17,
-									ParentRoot:    testhelpers.FillByteSlice(32, 18),
-									StateRoot:     testhelpers.FillByteSlice(32, 19),
-									BodyRoot:      testhelpers.FillByteSlice(32, 20),
-								},
-								Signature: testhelpers.FillByteSlice(96, 21),
-							},
-						},
-						{
-							Header_1: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          22,
-									ProposerIndex: 23,
-									ParentRoot:    testhelpers.FillByteSlice(32, 24),
-									StateRoot:     testhelpers.FillByteSlice(32, 25),
-									BodyRoot:      testhelpers.FillByteSlice(32, 26),
-								},
-								Signature: testhelpers.FillByteSlice(96, 27),
-							},
-							Header_2: &ethpb.SignedBeaconBlockHeader{
-								Header: &ethpb.BeaconBlockHeader{
-									Slot:          28,
-									ProposerIndex: 29,
-									ParentRoot:    testhelpers.FillByteSlice(32, 30),
-									StateRoot:     testhelpers.FillByteSlice(32, 31),
-									BodyRoot:      testhelpers.FillByteSlice(32, 32),
-								},
-								Signature: testhelpers.FillByteSlice(96, 33),
-							},
-						},
-					},
-					AttesterSlashings: []*ethpb.AttesterSlashing{
-						{
-							Attestation_1: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{34, 35},
-								Data: &ethpb.AttestationData{
-									Slot:            36,
-									CommitteeIndex:  37,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 39,
-										Root:  testhelpers.FillByteSlice(32, 40),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 41,
-										Root:  testhelpers.FillByteSlice(32, 42),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 43),
-							},
-							Attestation_2: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{44, 45},
-								Data: &ethpb.AttestationData{
-									Slot:            46,
-									CommitteeIndex:  47,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 49,
-										Root:  testhelpers.FillByteSlice(32, 50),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 51,
-										Root:  testhelpers.FillByteSlice(32, 52),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 53),
-							},
-						},
-						{
-							Attestation_1: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{54, 55},
-								Data: &ethpb.AttestationData{
-									Slot:            56,
-									CommitteeIndex:  57,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 59,
-										Root:  testhelpers.FillByteSlice(32, 60),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 61,
-										Root:  testhelpers.FillByteSlice(32, 62),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 63),
-							},
-							Attestation_2: &ethpb.IndexedAttestation{
-								AttestingIndices: []uint64{64, 65},
-								Data: &ethpb.AttestationData{
-									Slot:            66,
-									CommitteeIndex:  67,
-									BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-									Source: &ethpb.Checkpoint{
-										Epoch: 69,
-										Root:  testhelpers.FillByteSlice(32, 70),
-									},
-									Target: &ethpb.Checkpoint{
-										Epoch: 71,
-										Root:  testhelpers.FillByteSlice(32, 72),
-									},
-								},
-								Signature: testhelpers.FillByteSlice(96, 73),
-							},
-						},
-					},
-					Attestations: []*ethpb.Attestation{
-						{
-							AggregationBits: testhelpers.FillByteSlice(4, 74),
-							Data: &ethpb.AttestationData{
-								Slot:            75,
-								CommitteeIndex:  76,
-								BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-								Source: &ethpb.Checkpoint{
-									Epoch: 78,
-									Root:  testhelpers.FillByteSlice(32, 79),
-								},
-								Target: &ethpb.Checkpoint{
-									Epoch: 80,
-									Root:  testhelpers.FillByteSlice(32, 81),
-								},
-							},
-							Signature: testhelpers.FillByteSlice(96, 82),
-						},
-						{
-							AggregationBits: testhelpers.FillByteSlice(4, 83),
-							Data: &ethpb.AttestationData{
-								Slot:            84,
-								CommitteeIndex:  85,
-								BeaconBlockRoot: testhelpers.FillByteSlice(32, 38),
-								Source: &ethpb.Checkpoint{
-									Epoch: 87,
-									Root:  testhelpers.FillByteSlice(32, 88),
-								},
-								Target: &ethpb.Checkpoint{
-									Epoch: 89,
-									Root:  testhelpers.FillByteSlice(32, 90),
-								},
-							},
-							Signature: testhelpers.FillByteSlice(96, 91),
-						},
-					},
-					Deposits: []*ethpb.Deposit{
-						{
-							Proof: testhelpers.FillByteArraySlice(33, testhelpers.FillByteSlice(32, 92)),
-							Data: &ethpb.Deposit_Data{
-								PublicKey:             testhelpers.FillByteSlice(48, 94),
-								WithdrawalCredentials: testhelpers.FillByteSlice(32, 95),
-								Amount:                96,
-								Signature:             testhelpers.FillByteSlice(96, 97),
-							},
-						},
-						{
-							Proof: testhelpers.FillByteArraySlice(33, testhelpers.FillByteSlice(32, 98)),
-							Data: &ethpb.Deposit_Data{
-								PublicKey:             testhelpers.FillByteSlice(48, 100),
-								WithdrawalCredentials: testhelpers.FillByteSlice(32, 101),
-								Amount:                102,
-								Signature:             testhelpers.FillByteSlice(96, 103),
-							},
-						},
-					},
-					VoluntaryExits: []*ethpb.SignedVoluntaryExit{
-						{
-							Exit: &ethpb.VoluntaryExit{
-								Epoch:          104,
-								ValidatorIndex: 105,
-							},
-							Signature: testhelpers.FillByteSlice(96, 106),
-						},
-						{
-							Exit: &ethpb.VoluntaryExit{
-								Epoch:          107,
-								ValidatorIndex: 108,
-							},
-							Signature: testhelpers.FillByteSlice(96, 109),
-						},
-					},
-					SyncAggregate: &ethpb.SyncAggregate{
-						SyncCommitteeBits:      testhelpers.FillByteSlice(64, 110),
-						SyncCommitteeSignature: testhelpers.FillByteSlice(96, 111),
-					},
-					ExecutionPayloadHeader: &enginev1.ExecutionPayloadHeaderCapella{
-						ParentHash:       testhelpers.FillByteSlice(32, 112),
-						FeeRecipient:     testhelpers.FillByteSlice(20, 113),
-						StateRoot:        testhelpers.FillByteSlice(32, 114),
-						ReceiptsRoot:     testhelpers.FillByteSlice(32, 115),
-						LogsBloom:        testhelpers.FillByteSlice(256, 116),
-						PrevRandao:       testhelpers.FillByteSlice(32, 117),
-						BlockNumber:      118,
-						GasLimit:         119,
-						GasUsed:          120,
-						Timestamp:        121,
-						ExtraData:        testhelpers.FillByteSlice(32, 122),
-						BaseFeePerGas:    testhelpers.FillByteSlice(32, 123),
-						BlockHash:        testhelpers.FillByteSlice(32, 124),
-						TransactionsRoot: testhelpers.FillByteSlice(32, 125),
-						WithdrawalsRoot:  testhelpers.FillByteSlice(32, 126),
-					},
-					BlsToExecutionChanges: []*ethpb.SignedBLSToExecutionChange{
-						{
-							Message: &ethpb.BLSToExecutionChange{
-								ValidatorIndex:     127,
-								FromBlsPubkey:      testhelpers.FillByteSlice(48, 128),
-								ToExecutionAddress: testhelpers.FillByteSlice(20, 129),
-							},
-							Signature: testhelpers.FillByteSlice(96, 130),
-						},
-						{
-							Message: &ethpb.BLSToExecutionChange{
-								ValidatorIndex:     131,
-								FromBlsPubkey:      testhelpers.FillByteSlice(48, 132),
-								ToExecutionAddress: testhelpers.FillByteSlice(20, 133),
-							},
-							Signature: testhelpers.FillByteSlice(96, 134),
-						},
-					},
-				},
-			},
-			Signature: testhelpers.FillByteSlice(96, 135),
-		},
-	}
-}

validator/client/beacon-api/propose_beacon_block_blinded_deneb_test.go

@@ -1,49 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_BlindedDeneb(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	var block structs.SignedBlindedBeaconBlockDeneb
-	err := json.Unmarshal([]byte(rpctesting.BlindedDenebBlock), &block)
-	require.NoError(t, err)
-	genericSignedBlock, err := block.ToGeneric()
-	require.NoError(t, err)
-
-	denebBytes, err := json.Marshal(block)
-	require.NoError(t, err)
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "deneb"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blinded_blocks",
-		headers,
-		bytes.NewBuffer(denebBytes),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := genericSignedBlock.GetBlindedDeneb().HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}

validator/client/beacon-api/propose_beacon_block_blinded_electra_test.go

@@ -1,49 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_BlindedElectra(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	var block structs.SignedBlindedBeaconBlockElectra
-	err := json.Unmarshal([]byte(rpctesting.BlindedElectraBlock), &block)
-	require.NoError(t, err)
-	genericSignedBlock, err := block.ToGeneric()
-	require.NoError(t, err)
-
-	electraBytes, err := json.Marshal(block)
-	require.NoError(t, err)
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "electra"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blinded_blocks",
-		headers,
-		bytes.NewBuffer(electraBytes),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := genericSignedBlock.GetBlindedElectra().HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}

validator/client/beacon-api/propose_beacon_block_blinded_fulu_test.go

@@ -1,49 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_BlindedFulu(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	var block structs.SignedBlindedBeaconBlockFulu
-	err := json.Unmarshal([]byte(rpctesting.BlindedFuluBlock), &block)
-	require.NoError(t, err)
-	genericSignedBlock, err := block.ToGeneric()
-	require.NoError(t, err)
-
-	fuluBytes, err := json.Marshal(block)
-	require.NoError(t, err)
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "fulu"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blinded_blocks",
-		headers,
-		bytes.NewBuffer(fuluBytes),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := genericSignedBlock.GetBlindedFulu().HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}

validator/client/beacon-api/propose_beacon_block_capella_test.go

@@ -1,62 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	testhelpers "github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/test-helpers"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_Capella(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	capellaBlock := generateSignedCapellaBlock()
-
-	genericSignedBlock := &ethpb.GenericSignedBeaconBlock{}
-	genericSignedBlock.Block = capellaBlock
-
-	jsonCapellaBlock, err := structs.SignedBeaconBlockCapellaFromConsensus(capellaBlock.Capella)
-	require.NoError(t, err)
-
-	marshalledBlock, err := json.Marshal(jsonCapellaBlock)
-	require.NoError(t, err)
-
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "capella"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blocks",
-		headers,
-		bytes.NewBuffer(marshalledBlock),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := capellaBlock.Capella.Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}
-
-func generateSignedCapellaBlock() *ethpb.GenericSignedBeaconBlock_Capella {
-	return &ethpb.GenericSignedBeaconBlock_Capella{
-		Capella: &ethpb.SignedBeaconBlockCapella{
-			Block:     testhelpers.GenerateProtoCapellaBeaconBlock(),
-			Signature: testhelpers.FillByteSlice(96, 127),
-		},
-	}
-}

validator/client/beacon-api/propose_beacon_block_deneb_test.go

@@ -1,49 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_Deneb(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	var blockContents structs.SignedBeaconBlockContentsDeneb
-	err := json.Unmarshal([]byte(rpctesting.DenebBlockContents), &blockContents)
-	require.NoError(t, err)
-	genericSignedBlock, err := blockContents.ToGeneric()
-	require.NoError(t, err)
-
-	denebBytes, err := json.Marshal(blockContents)
-	require.NoError(t, err)
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "deneb"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blocks",
-		headers,
-		bytes.NewBuffer(denebBytes),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := genericSignedBlock.GetDeneb().Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}

validator/client/beacon-api/propose_beacon_block_electra_test.go

@@ -1,49 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_Electra(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	var blockContents structs.SignedBeaconBlockContentsElectra
-	err := json.Unmarshal([]byte(rpctesting.ElectraBlockContents), &blockContents)
-	require.NoError(t, err)
-	genericSignedBlock, err := blockContents.ToGeneric()
-	require.NoError(t, err)
-
-	electraBytes, err := json.Marshal(blockContents)
-	require.NoError(t, err)
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "electra"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blocks",
-		headers,
-		bytes.NewBuffer(electraBytes),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := genericSignedBlock.GetElectra().Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}

validator/client/beacon-api/propose_beacon_block_fulu_test.go

@@ -1,49 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_Fulu(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	var blockContents structs.SignedBeaconBlockContentsFulu
-	err := json.Unmarshal([]byte(rpctesting.FuluBlockContents), &blockContents)
-	require.NoError(t, err)
-	genericSignedBlock, err := blockContents.ToGeneric()
-	require.NoError(t, err)
-
-	fuluBytes, err := json.Marshal(blockContents)
-	require.NoError(t, err)
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "fulu"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blocks",
-		headers,
-		bytes.NewBuffer(fuluBytes),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := genericSignedBlock.GetFulu().Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}

validator/client/beacon-api/propose_beacon_block_phase0_test.go

@@ -1,63 +0,0 @@
-package beacon_api
-
-import (
-	"bytes"
-	"encoding/json"
-	"testing"
-
-	"github.com/OffchainLabs/prysm/v6/api/server/structs"
-	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
-	"github.com/OffchainLabs/prysm/v6/testing/assert"
-	"github.com/OffchainLabs/prysm/v6/testing/require"
-	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
-	testhelpers "github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/test-helpers"
-	"go.uber.org/mock/gomock"
-)
-
-func TestProposeBeaconBlock_Phase0(t *testing.T) {
-	ctrl := gomock.NewController(t)
-	defer ctrl.Finish()
-	jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
-
-	phase0Block := generateSignedPhase0Block()
-
-	genericSignedBlock := &ethpb.GenericSignedBeaconBlock{}
-	genericSignedBlock.Block = phase0Block
-
-	jsonPhase0Block := structs.SignedBeaconBlockPhase0FromConsensus(phase0Block.Phase0)
-
-	marshalledBlock, err := json.Marshal(jsonPhase0Block)
-	require.NoError(t, err)
-
-	ctx := t.Context()
-
-	// Make sure that what we send in the POST body is the marshalled version of the protobuf block
-	headers := map[string]string{"Eth-Consensus-Version": "phase0"}
-	jsonRestHandler.EXPECT().Post(
-		gomock.Any(),
-		"/eth/v2/beacon/blocks",
-		headers,
-		bytes.NewBuffer(marshalledBlock),
-		nil,
-	)
-
-	validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
-	proposeResponse, err := validatorClient.proposeBeaconBlock(ctx, genericSignedBlock)
-	assert.NoError(t, err)
-	require.NotNil(t, proposeResponse)
-
-	expectedBlockRoot, err := phase0Block.Phase0.Block.HashTreeRoot()
-	require.NoError(t, err)
-
-	// Make sure that the block root is set
-	assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
-}
-
-func generateSignedPhase0Block() *ethpb.GenericSignedBeaconBlock_Phase0 {
-	return &ethpb.GenericSignedBeaconBlock_Phase0{
-		Phase0: &ethpb.SignedBeaconBlock{
-			Block:     testhelpers.GenerateProtoPhase0BeaconBlock(),
-			Signature: testhelpers.FillByteSlice(96, 110),
-		},
-	}
-}

validator/client/beacon-api/propose_beacon_block_test.go

@@ -1,43 +1,42 @@
 package beacon_api
 
 import (
+	"bytes"
+	"encoding/json"
 	"errors"
 	"net/http"
 	"testing"
 
+	"github.com/OffchainLabs/prysm/v6/api/server/structs"
+	rpctesting "github.com/OffchainLabs/prysm/v6/beacon-chain/rpc/eth/shared/testing"
 	"github.com/OffchainLabs/prysm/v6/network/httputil"
+	engine "github.com/OffchainLabs/prysm/v6/proto/engine/v1"
 	ethpb "github.com/OffchainLabs/prysm/v6/proto/prysm/v1alpha1"
 	"github.com/OffchainLabs/prysm/v6/testing/assert"
+	"github.com/OffchainLabs/prysm/v6/testing/require"
 	"github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/mock"
+	testhelpers "github.com/OffchainLabs/prysm/v6/validator/client/beacon-api/test-helpers"
 	"go.uber.org/mock/gomock"
 )
 
-func TestProposeBeaconBlock_Error(t *testing.T) {
+func TestProposeBeaconBlock_SSZ_Error(t *testing.T) {
 	testSuites := []struct {
 		name                 string
 		returnedError        error
 		expectedErrorMessage string
 	}{
-		{
-			name:                 "error 202",
-			expectedErrorMessage: "block was successfully broadcast but failed validation",
-			returnedError: &httputil.DefaultJsonError{
-				Code:    http.StatusAccepted,
-				Message: "202 error",
-			},
-		},
 		{
 			name:                 "error 500",
-			expectedErrorMessage: "HTTP request unsuccessful (500: foo error)",
+			expectedErrorMessage: "failed to submit block ssz",
 			returnedError: &httputil.DefaultJsonError{
 				Code:    http.StatusInternalServerError,
-				Message: "foo error",
+				Message: "failed to submit block ssz",
 			},
 		},
 		{
 			name:                 "other error",
-			expectedErrorMessage: "foo error",
+			expectedErrorMessage: "failed to submit block ssz",
-			returnedError:        errors.New("foo error"),
+			returnedError:        errors.New("failed to submit block ssz"),
 		},
 	}
 
@@ -106,17 +105,21 @@ func TestProposeBeaconBlock_Error(t *testing.T) {
 				ctx := t.Context()
 				jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
 
-				headers := map[string]string{"Eth-Consensus-Version": testCase.consensusVersion}
+				// Expect PostSSZ to be called first with SSZ data
-				jsonRestHandler.EXPECT().Post(
+				headers := map[string]string{
+					"Eth-Consensus-Version": testCase.consensusVersion,
+				}
+				jsonRestHandler.EXPECT().PostSSZ(
 					gomock.Any(),
 					testCase.endpoint,
 					headers,
 					gomock.Any(),
-					nil,
 				).Return(
-					testSuite.returnedError,
+					nil, nil, testSuite.returnedError,
 				).Times(1)
 
+				// No JSON fallback expected for non-406 errors
+
 				validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
 				_, err := validatorClient.proposeBeaconBlock(ctx, testCase.block)
 				assert.ErrorContains(t, testSuite.expectedErrorMessage, err)
@@ -130,3 +133,546 @@ func TestProposeBeaconBlock_UnsupportedBlockType(t *testing.T) {
 	_, err := validatorClient.proposeBeaconBlock(t.Context(), &ethpb.GenericSignedBeaconBlock{})
 	assert.ErrorContains(t, "unsupported block type", err)
 }
+
+func TestProposeBeaconBlock_SSZSuccess_NoFallback(t *testing.T) {
+	testCases := []struct {
+		name             string
+		consensusVersion string
+		endpoint         string
+		block            *ethpb.GenericSignedBeaconBlock
+	}{
+		{
+			name:             "phase0",
+			consensusVersion: "phase0",
+			endpoint:         "/eth/v2/beacon/blocks",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedPhase0Block(),
+			},
+		},
+		{
+			name:             "altair",
+			consensusVersion: "altair",
+			endpoint:         "/eth/v2/beacon/blocks",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedAltairBlock(),
+			},
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+			defer ctrl.Finish()
+
+			ctx := t.Context()
+			jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+			// Expect PostSSZ to be called and succeed
+			headers := map[string]string{
+				"Eth-Consensus-Version": testCase.consensusVersion,
+			}
+			jsonRestHandler.EXPECT().PostSSZ(
+				gomock.Any(),
+				testCase.endpoint,
+				headers,
+				gomock.Any(),
+			).Return(
+				nil, nil, nil,
+			).Times(1)
+
+			// Post should NOT be called when PostSSZ succeeds
+			jsonRestHandler.EXPECT().Post(
+				gomock.Any(),
+				gomock.Any(),
+				gomock.Any(),
+				gomock.Any(),
+				gomock.Any(),
+			).Times(0)
+
+			validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+			_, err := validatorClient.proposeBeaconBlock(ctx, testCase.block)
+			assert.NoError(t, err)
+		})
+	}
+}
+
+func TestProposeBeaconBlock_NewerTypes_SSZMarshal(t *testing.T) {
+	t.Run("deneb", func(t *testing.T) {
+		ctrl := gomock.NewController(t)
+		defer ctrl.Finish()
+		jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+		var blockContents structs.SignedBeaconBlockContentsDeneb
+		err := json.Unmarshal([]byte(rpctesting.DenebBlockContents), &blockContents)
+		require.NoError(t, err)
+		genericSignedBlock, err := blockContents.ToGeneric()
+		require.NoError(t, err)
+
+		denebBytes, err := genericSignedBlock.GetDeneb().MarshalSSZ()
+		require.NoError(t, err)
+
+		jsonRestHandler.EXPECT().PostSSZ(
+			gomock.Any(),
+			"/eth/v2/beacon/blocks",
+			gomock.Any(),
+			bytes.NewBuffer(denebBytes),
+		)
+
+		validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+		proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
+		assert.NoError(t, err)
+		require.NotNil(t, proposeResponse)
+
+		expectedBlockRoot, err := genericSignedBlock.GetDeneb().Block.HashTreeRoot()
+		require.NoError(t, err)
+		assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
+	})
+
+	t.Run("blinded_deneb", func(t *testing.T) {
+		ctrl := gomock.NewController(t)
+		defer ctrl.Finish()
+		jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+		var blindedBlock structs.SignedBlindedBeaconBlockDeneb
+		err := json.Unmarshal([]byte(rpctesting.BlindedDenebBlock), &blindedBlock)
+		require.NoError(t, err)
+		genericSignedBlock, err := blindedBlock.ToGeneric()
+		require.NoError(t, err)
+
+		blindedDenebBytes, err := genericSignedBlock.GetBlindedDeneb().MarshalSSZ()
+		require.NoError(t, err)
+
+		jsonRestHandler.EXPECT().PostSSZ(
+			gomock.Any(),
+			"/eth/v2/beacon/blinded_blocks",
+			gomock.Any(),
+			bytes.NewBuffer(blindedDenebBytes),
+		)
+
+		validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+		proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
+		assert.NoError(t, err)
+		require.NotNil(t, proposeResponse)
+
+		expectedBlockRoot, err := genericSignedBlock.GetBlindedDeneb().HashTreeRoot()
+		require.NoError(t, err)
+		assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
+	})
+
+	t.Run("electra", func(t *testing.T) {
+		ctrl := gomock.NewController(t)
+		defer ctrl.Finish()
+		jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+		var blockContents structs.SignedBeaconBlockContentsElectra
+		err := json.Unmarshal([]byte(rpctesting.ElectraBlockContents), &blockContents)
+		require.NoError(t, err)
+		genericSignedBlock, err := blockContents.ToGeneric()
+		require.NoError(t, err)
+
+		electraBytes, err := genericSignedBlock.GetElectra().MarshalSSZ()
+		require.NoError(t, err)
+
+		jsonRestHandler.EXPECT().PostSSZ(
+			gomock.Any(),
+			"/eth/v2/beacon/blocks",
+			gomock.Any(),
+			bytes.NewBuffer(electraBytes),
+		)
+
+		validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+		proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
+		assert.NoError(t, err)
+		require.NotNil(t, proposeResponse)
+
+		expectedBlockRoot, err := genericSignedBlock.GetElectra().Block.HashTreeRoot()
+		require.NoError(t, err)
+		assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
+	})
+
+	t.Run("blinded_electra", func(t *testing.T) {
+		ctrl := gomock.NewController(t)
+		defer ctrl.Finish()
+		jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+		var blindedBlock structs.SignedBlindedBeaconBlockElectra
+		err := json.Unmarshal([]byte(rpctesting.BlindedElectraBlock), &blindedBlock)
+		require.NoError(t, err)
+		genericSignedBlock, err := blindedBlock.ToGeneric()
+		require.NoError(t, err)
+
+		blindedElectraBytes, err := genericSignedBlock.GetBlindedElectra().MarshalSSZ()
+		require.NoError(t, err)
+
+		jsonRestHandler.EXPECT().PostSSZ(
+			gomock.Any(),
+			"/eth/v2/beacon/blinded_blocks",
+			gomock.Any(),
+			bytes.NewBuffer(blindedElectraBytes),
+		)
+
+		validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+		proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
+		assert.NoError(t, err)
+		require.NotNil(t, proposeResponse)
+
+		expectedBlockRoot, err := genericSignedBlock.GetBlindedElectra().HashTreeRoot()
+		require.NoError(t, err)
+		assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
+	})
+
+	t.Run("fulu", func(t *testing.T) {
+		ctrl := gomock.NewController(t)
+		defer ctrl.Finish()
+		jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+		var blockContents structs.SignedBeaconBlockContentsFulu
+		err := json.Unmarshal([]byte(rpctesting.FuluBlockContents), &blockContents)
+		require.NoError(t, err)
+		genericSignedBlock, err := blockContents.ToGeneric()
+		require.NoError(t, err)
+
+		fuluBytes, err := genericSignedBlock.GetFulu().MarshalSSZ()
+		require.NoError(t, err)
+
+		jsonRestHandler.EXPECT().PostSSZ(
+			gomock.Any(),
+			"/eth/v2/beacon/blocks",
+			gomock.Any(),
+			bytes.NewBuffer(fuluBytes),
+		)
+
+		validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+		proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
+		assert.NoError(t, err)
+		require.NotNil(t, proposeResponse)
+
+		expectedBlockRoot, err := genericSignedBlock.GetFulu().Block.HashTreeRoot()
+		require.NoError(t, err)
+		assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
+	})
+
+	t.Run("blinded_fulu", func(t *testing.T) {
+		ctrl := gomock.NewController(t)
+		defer ctrl.Finish()
+		jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+		var blindedBlock structs.SignedBlindedBeaconBlockFulu
+		err := json.Unmarshal([]byte(rpctesting.BlindedFuluBlock), &blindedBlock)
+		require.NoError(t, err)
+		genericSignedBlock, err := blindedBlock.ToGeneric()
+		require.NoError(t, err)
+
+		blindedFuluBytes, err := genericSignedBlock.GetBlindedFulu().MarshalSSZ()
+		require.NoError(t, err)
+
+		jsonRestHandler.EXPECT().PostSSZ(
+			gomock.Any(),
+			"/eth/v2/beacon/blinded_blocks",
+			gomock.Any(),
+			bytes.NewBuffer(blindedFuluBytes),
+		)
+
+		validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+		proposeResponse, err := validatorClient.proposeBeaconBlock(t.Context(), genericSignedBlock)
+		assert.NoError(t, err)
+		require.NotNil(t, proposeResponse)
+
+		expectedBlockRoot, err := genericSignedBlock.GetBlindedFulu().HashTreeRoot()
+		require.NoError(t, err)
+		assert.DeepEqual(t, expectedBlockRoot[:], proposeResponse.BlockRoot)
+	})
+}
+
+// Generator functions for test blocks
+func generateSignedPhase0Block() *ethpb.GenericSignedBeaconBlock_Phase0 {
+	return &ethpb.GenericSignedBeaconBlock_Phase0{
+		Phase0: &ethpb.SignedBeaconBlock{
+			Block:     testhelpers.GenerateProtoPhase0BeaconBlock(),
+			Signature: testhelpers.FillByteSlice(96, 110),
+		},
+	}
+}
+
+func generateSignedAltairBlock() *ethpb.GenericSignedBeaconBlock_Altair {
+	return &ethpb.GenericSignedBeaconBlock_Altair{
+		Altair: &ethpb.SignedBeaconBlockAltair{
+			Block:     testhelpers.GenerateProtoAltairBeaconBlock(),
+			Signature: testhelpers.FillByteSlice(96, 112),
+		},
+	}
+}
+
+func generateSignedBellatrixBlock() *ethpb.GenericSignedBeaconBlock_Bellatrix {
+	return &ethpb.GenericSignedBeaconBlock_Bellatrix{
+		Bellatrix: &ethpb.SignedBeaconBlockBellatrix{
+			Block:     testhelpers.GenerateProtoBellatrixBeaconBlock(),
+			Signature: testhelpers.FillByteSlice(96, 127),
+		},
+	}
+}
+
+func generateSignedBlindedBellatrixBlock() *ethpb.GenericSignedBeaconBlock_BlindedBellatrix {
+	return &ethpb.GenericSignedBeaconBlock_BlindedBellatrix{
+		BlindedBellatrix: &ethpb.SignedBlindedBeaconBlockBellatrix{
+			Block: &ethpb.BlindedBeaconBlockBellatrix{
+				Slot:          1,
+				ProposerIndex: 2,
+				ParentRoot:    testhelpers.FillByteSlice(32, 3),
+				StateRoot:     testhelpers.FillByteSlice(32, 4),
+				Body: &ethpb.BlindedBeaconBlockBodyBellatrix{
+					RandaoReveal: testhelpers.FillByteSlice(96, 5),
+					Eth1Data: &ethpb.Eth1Data{
+						DepositRoot:  testhelpers.FillByteSlice(32, 6),
+						DepositCount: 7,
+						BlockHash:    testhelpers.FillByteSlice(32, 8),
+					},
+					Graffiti: testhelpers.FillByteSlice(32, 9),
+					ProposerSlashings: []*ethpb.ProposerSlashing{
+						{
+							Header_1: &ethpb.SignedBeaconBlockHeader{
+								Header: &ethpb.BeaconBlockHeader{
+									Slot:          10,
+									ProposerIndex: 11,
+									ParentRoot:    testhelpers.FillByteSlice(32, 12),
+									StateRoot:     testhelpers.FillByteSlice(32, 13),
+									BodyRoot:      testhelpers.FillByteSlice(32, 14),
+								},
+								Signature: testhelpers.FillByteSlice(96, 15),
+							},
+							Header_2: &ethpb.SignedBeaconBlockHeader{
+								Header: &ethpb.BeaconBlockHeader{
+									Slot:          16,
+									ProposerIndex: 17,
+									ParentRoot:    testhelpers.FillByteSlice(32, 18),
+									StateRoot:     testhelpers.FillByteSlice(32, 19),
+									BodyRoot:      testhelpers.FillByteSlice(32, 20),
+								},
+								Signature: testhelpers.FillByteSlice(96, 21),
+							},
+						},
+					},
+					AttesterSlashings: []*ethpb.AttesterSlashing{},
+					Attestations:      []*ethpb.Attestation{},
+					Deposits:          []*ethpb.Deposit{},
+					VoluntaryExits:    []*ethpb.SignedVoluntaryExit{},
+					SyncAggregate: &ethpb.SyncAggregate{
+						SyncCommitteeBits:      testhelpers.FillByteSlice(64, 100),
+						SyncCommitteeSignature: testhelpers.FillByteSlice(96, 101),
+					},
+					ExecutionPayloadHeader: &engine.ExecutionPayloadHeader{
+						ParentHash:       testhelpers.FillByteSlice(32, 102),
+						FeeRecipient:     testhelpers.FillByteSlice(20, 103),
+						StateRoot:        testhelpers.FillByteSlice(32, 104),
+						ReceiptsRoot:     testhelpers.FillByteSlice(32, 105),
+						LogsBloom:        testhelpers.FillByteSlice(256, 106),
+						PrevRandao:       testhelpers.FillByteSlice(32, 107),
+						BlockNumber:      108,
+						GasLimit:         109,
+						GasUsed:          110,
+						Timestamp:        111,
+						ExtraData:        testhelpers.FillByteSlice(32, 112),
+						BaseFeePerGas:    testhelpers.FillByteSlice(32, 113),
+						BlockHash:        testhelpers.FillByteSlice(32, 114),
+						TransactionsRoot: testhelpers.FillByteSlice(32, 115),
+					},
+				},
+			},
+			Signature: testhelpers.FillByteSlice(96, 116),
+		},
+	}
+}
+
+func generateSignedCapellaBlock() *ethpb.GenericSignedBeaconBlock_Capella {
+	return &ethpb.GenericSignedBeaconBlock_Capella{
+		Capella: &ethpb.SignedBeaconBlockCapella{
+			Block:     testhelpers.GenerateProtoCapellaBeaconBlock(),
+			Signature: testhelpers.FillByteSlice(96, 127),
+		},
+	}
+}
+
+func generateSignedBlindedCapellaBlock() *ethpb.GenericSignedBeaconBlock_BlindedCapella {
+	return &ethpb.GenericSignedBeaconBlock_BlindedCapella{
+		BlindedCapella: &ethpb.SignedBlindedBeaconBlockCapella{
+			Block: &ethpb.BlindedBeaconBlockCapella{
+				Slot:          1,
+				ProposerIndex: 2,
+				ParentRoot:    testhelpers.FillByteSlice(32, 3),
+				StateRoot:     testhelpers.FillByteSlice(32, 4),
+				Body: &ethpb.BlindedBeaconBlockBodyCapella{
+					RandaoReveal: testhelpers.FillByteSlice(96, 5),
+					Eth1Data: &ethpb.Eth1Data{
+						DepositRoot:  testhelpers.FillByteSlice(32, 6),
+						DepositCount: 7,
+						BlockHash:    testhelpers.FillByteSlice(32, 8),
+					},
+					Graffiti: testhelpers.FillByteSlice(32, 9),
+					ProposerSlashings: []*ethpb.ProposerSlashing{
+						{
+							Header_1: &ethpb.SignedBeaconBlockHeader{
+								Header: &ethpb.BeaconBlockHeader{
+									Slot:          10,
+									ProposerIndex: 11,
+									ParentRoot:    testhelpers.FillByteSlice(32, 12),
+									StateRoot:     testhelpers.FillByteSlice(32, 13),
+									BodyRoot:      testhelpers.FillByteSlice(32, 14),
+								},
+								Signature: testhelpers.FillByteSlice(96, 15),
+							},
+							Header_2: &ethpb.SignedBeaconBlockHeader{
+								Header: &ethpb.BeaconBlockHeader{
+									Slot:          16,
+									ProposerIndex: 17,
+									ParentRoot:    testhelpers.FillByteSlice(32, 18),
+									StateRoot:     testhelpers.FillByteSlice(32, 19),
+									BodyRoot:      testhelpers.FillByteSlice(32, 20),
+								},
+								Signature: testhelpers.FillByteSlice(96, 21),
+							},
+						},
+					},
+					AttesterSlashings: []*ethpb.AttesterSlashing{},
+					Attestations:      []*ethpb.Attestation{},
+					Deposits:          []*ethpb.Deposit{},
+					VoluntaryExits:    []*ethpb.SignedVoluntaryExit{},
+					SyncAggregate: &ethpb.SyncAggregate{
+						SyncCommitteeBits:      testhelpers.FillByteSlice(64, 37),
+						SyncCommitteeSignature: testhelpers.FillByteSlice(96, 38),
+					},
+					ExecutionPayloadHeader: &engine.ExecutionPayloadHeaderCapella{
+						ParentHash:       testhelpers.FillByteSlice(32, 39),
+						FeeRecipient:     testhelpers.FillByteSlice(20, 40),
+						StateRoot:        testhelpers.FillByteSlice(32, 41),
+						ReceiptsRoot:     testhelpers.FillByteSlice(32, 42),
+						LogsBloom:        testhelpers.FillByteSlice(256, 43),
+						PrevRandao:       testhelpers.FillByteSlice(32, 44),
+						BlockNumber:      45,
+						GasLimit:         46,
+						GasUsed:          47,
+						Timestamp:        48,
+						ExtraData:        testhelpers.FillByteSlice(32, 49),
+						BaseFeePerGas:    testhelpers.FillByteSlice(32, 50),
+						BlockHash:        testhelpers.FillByteSlice(32, 51),
+						TransactionsRoot: testhelpers.FillByteSlice(32, 52),
+						WithdrawalsRoot:  testhelpers.FillByteSlice(32, 53),
+					},
+					BlsToExecutionChanges: []*ethpb.SignedBLSToExecutionChange{},
+				},
+			},
+			Signature: testhelpers.FillByteSlice(96, 54),
+		},
+	}
+}
+
+func TestProposeBeaconBlock_SSZFails_406_FallbackToJSON(t *testing.T) {
+	testCases := []struct {
+		name             string
+		consensusVersion string
+		endpoint         string
+		block            *ethpb.GenericSignedBeaconBlock
+	}{
+		{
+			name:             "phase0",
+			consensusVersion: "phase0",
+			endpoint:         "/eth/v2/beacon/blocks",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedPhase0Block(),
+			},
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+			defer ctrl.Finish()
+
+			ctx := t.Context()
+			jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+			// Expect PostSSZ to be called first and fail
+			jsonRestHandler.EXPECT().PostSSZ(
+				gomock.Any(),
+				testCase.endpoint,
+				gomock.Any(),
+				gomock.Any(),
+			).Return(
+				nil, nil, &httputil.DefaultJsonError{
+					Code:    http.StatusNotAcceptable,
+					Message: "SSZ not supported",
+				},
+			).Times(1)
+
+			jsonRestHandler.EXPECT().Post(
+				gomock.Any(),
+				testCase.endpoint,
+				gomock.Any(),
+				gomock.Any(),
+				nil,
+			).Return(
+				nil,
+			).Times(1)
+
+			validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+			_, err := validatorClient.proposeBeaconBlock(ctx, testCase.block)
+			assert.NoError(t, err)
+		})
+	}
+}
+
+func TestProposeBeaconBlock_SSZFails_Non406_NoFallback(t *testing.T) {
+	testCases := []struct {
+		name             string
+		consensusVersion string
+		endpoint         string
+		block            *ethpb.GenericSignedBeaconBlock
+	}{
+		{
+			name:             "phase0",
+			consensusVersion: "phase0",
+			endpoint:         "/eth/v2/beacon/blocks",
+			block: &ethpb.GenericSignedBeaconBlock{
+				Block: generateSignedPhase0Block(),
+			},
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			ctrl := gomock.NewController(t)
+			defer ctrl.Finish()
+
+			ctx := t.Context()
+			jsonRestHandler := mock.NewMockJsonRestHandler(ctrl)
+
+			// Expect PostSSZ to be called first and fail with non-406 error
+			sszHeaders := map[string]string{
+				"Eth-Consensus-Version": testCase.consensusVersion,
+			}
+			jsonRestHandler.EXPECT().PostSSZ(
+				gomock.Any(),
+				testCase.endpoint,
+				sszHeaders,
+				gomock.Any(),
+			).Return(
+				nil, nil, &httputil.DefaultJsonError{
+					Code:    http.StatusInternalServerError,
+					Message: "Internal server error",
+				},
+			).Times(1)
+
+			// Post should NOT be called for non-406 errors
+			jsonRestHandler.EXPECT().Post(
+				gomock.Any(),
+				gomock.Any(),
+				gomock.Any(),
+				gomock.Any(),
+				gomock.Any(),
+			).Times(0)
+
+			validatorClient := &beaconApiValidatorClient{jsonRestHandler: jsonRestHandler}
+			_, err := validatorClient.proposeBeaconBlock(ctx, testCase.block)
+			require.ErrorContains(t, "Internal server error", err)
+		})
+	}
+}

validator/client/beacon-api/rest_handler_client.go

@@ -25,6 +25,7 @@ type RestHandler interface {
 	Get(ctx context.Context, endpoint string, resp interface{}) error
 	GetSSZ(ctx context.Context, endpoint string) ([]byte, http.Header, error)
 	Post(ctx context.Context, endpoint string, headers map[string]string, data *bytes.Buffer, resp interface{}) error
+	PostSSZ(ctx context.Context, endpoint string, headers map[string]string, data *bytes.Buffer) ([]byte, http.Header, error)
 	HttpClient() *http.Client
 	Host() string
 	SetHost(host string)
@@ -179,6 +180,75 @@ func (c *BeaconApiRestHandler) Post(
 	return decodeResp(httpResp, resp)
 }
 
+// PostSSZ sends a POST request and prefers an SSZ (application/octet-stream) response body.
+func (c *BeaconApiRestHandler) PostSSZ(
+	ctx context.Context,
+	apiEndpoint string,
+	headers map[string]string,
+	data *bytes.Buffer,
+) ([]byte, http.Header, error) {
+	if data == nil {
+		return nil, nil, errors.New("data is nil")
+	}
+	url := c.host + apiEndpoint
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, data)
+	if err != nil {
+		return nil, nil, errors.Wrapf(err, "failed to create request for endpoint %s", url)
+	}
+
+	// Accept header: prefer octet-stream (SSZ), fall back to JSON
+	primaryAcceptType := fmt.Sprintf("%s;q=%s", api.OctetStreamMediaType, "0.95")
+	secondaryAcceptType := fmt.Sprintf("%s;q=%s", api.JsonMediaType, "0.9")
+	acceptHeaderString := fmt.Sprintf("%s,%s", primaryAcceptType, secondaryAcceptType)
+	req.Header.Set("Accept", acceptHeaderString)
+
+	// User-supplied headers
+	for headerKey, headerValue := range headers {
+		req.Header.Set(headerKey, headerValue)
+	}
+
+	for _, o := range c.reqOverrides {
+		o(req)
+	}
+	req.Header.Set("Content-Type", api.OctetStreamMediaType)
+	req.Header.Set("User-Agent", version.BuildData())
+	httpResp, err := c.client.Do(req)
+	if err != nil {
+		return nil, nil, errors.Wrapf(err, "failed to perform request for endpoint %s", url)
+	}
+	defer func() {
+		if err := httpResp.Body.Close(); err != nil {
+			return
+		}
+	}()
+
+	accept := req.Header.Get("Accept")
+	contentType := httpResp.Header.Get("Content-Type")
+	body, err := io.ReadAll(httpResp.Body)
+	if err != nil {
+		return nil, nil, errors.Wrapf(err, "failed to read response body for %s", httpResp.Request.URL)
+	}
+
+	if !apiutil.PrimaryAcceptMatches(accept, contentType) {
+		log.WithFields(logrus.Fields{
+			"Accept":       accept,
+			"Content-Type": contentType,
+		}).Debug("Server responded with non primary accept type")
+	}
+
+	// non-2XX codes are a failure
+	if !strings.HasPrefix(httpResp.Status, "2") {
+		decoder := json.NewDecoder(bytes.NewBuffer(body))
+		errorJson := &httputil.DefaultJsonError{}
+		if err = decoder.Decode(errorJson); err != nil {
+			return nil, nil, errors.Wrapf(err, "failed to decode response body into error json for %s", httpResp.Request.URL)
+		}
+		return nil, nil, errorJson
+	}
+
+	return body, httpResp.Header, nil
+}
+
 func decodeResp(httpResp *http.Response, resp interface{}) error {
 	body, err := io.ReadAll(httpResp.Body)
 	if err != nil {