Implement GetValidator RPC Endpoint (#4188)

* include new patch targeting latest ethapis master
* ensure project builds
* Merge branch 'master' into update-all-api
* fix up committees
* Merge branch 'update-all-api' of github.com:prysmaticlabs/prysm into update-all-api
* include latest eth apis
* Merge branch 'master' into update-all-api
* update block tests
* Merge branch 'update-all-api' of github.com:prysmaticlabs/prysm into update-all-api
* Merge branch 'master' into update-all-api
* add todos
* implement get validator rpc
* add test for get validator
* table driven test
* fix up test
* fix confs
* tests for more cases
* fix up tests and add out of range

beacon-chain/rpc/beacon/validators.go

@@ -1,6 +1,7 @@
 package beacon
 
 import (
+	"bytes"
 	"context"
 	"sort"
 	"strconv"
@@ -248,11 +249,45 @@ func (bs *Server) ListValidators(
 }
 
 // GetValidator information from any validator in the registry by index or public key.
-// TODO(#4177): Implement.
 func (bs *Server) GetValidator(
-	_ context.Context, _ *ethpb.GetValidatorRequest,
+	ctx context.Context, req *ethpb.GetValidatorRequest,
 ) (*ethpb.Validator, error) {
-	return nil, status.Error(codes.Unimplemented, "Not yet implemented")
+	var requestingIndex bool
+	var index uint64
+	var pubKey []byte
+	switch q := req.QueryFilter.(type) {
+	case *ethpb.GetValidatorRequest_Index:
+		index = q.Index
+		requestingIndex = true
+	case *ethpb.GetValidatorRequest_PublicKey:
+		pubKey = q.PublicKey
+	default:
+		return nil, status.Error(
+			codes.InvalidArgument,
+			"Need to specify either validator index or public key in request",
+		)
+	}
+	headState, err := bs.HeadFetcher.HeadState(ctx)
+	if err != nil {
+		return nil, status.Error(codes.Internal, "Could not get head state")
+	}
+	if requestingIndex {
+		if index >= uint64(len(headState.Validators)) {
+			return nil, status.Errorf(
+				codes.OutOfRange,
+				"Requesting index %d, but there are only %d validators",
+				index,
+				len(headState.Validators),
+			)
+		}
+		return headState.Validators[index], nil
+	}
+	for i := 0; i < len(headState.Validators); i++ {
+		if bytes.Equal(headState.Validators[i].PublicKey, pubKey) {
+			return headState.Validators[i], nil
+		}
+	}
+	return nil, status.Error(codes.NotFound, "No validator matched filter criteria")
 }
 
 // GetValidatorActiveSetChanges retrieves the active set changes for a given epoch.

beacon-chain/rpc/beacon/validators_test.go

@@ -806,6 +806,97 @@ func TestServer_ListValidators_FromOldEpoch(t *testing.T) {
 	}
 }
 
+func TestServer_GetValidator(t *testing.T) {
+	db := dbTest.SetupDB(t)
+	defer dbTest.TeardownDB(t, db)
+
+	count := 30
+	validators := make([]*ethpb.Validator, count)
+	for i := 0; i < count; i++ {
+		validators[i] = &ethpb.Validator{
+			ActivationEpoch: uint64(i),
+			PublicKey:       []byte(strconv.Itoa(i)),
+		}
+	}
+
+	bs := &Server{
+		HeadFetcher: &mock.ChainService{
+			State: &pbp2p.BeaconState{
+				Validators: validators,
+			},
+		},
+	}
+
+	tests := []struct {
+		req     *ethpb.GetValidatorRequest
+		res     *ethpb.Validator
+		wantErr bool
+		err     string
+	}{
+		{
+			req: &ethpb.GetValidatorRequest{
+				QueryFilter: &ethpb.GetValidatorRequest_Index{
+					Index: 0,
+				},
+			},
+			res:     validators[0],
+			wantErr: false,
+		},
+		{
+			req: &ethpb.GetValidatorRequest{
+				QueryFilter: &ethpb.GetValidatorRequest_Index{
+					Index: uint64(count - 1),
+				},
+			},
+			res:     validators[count-1],
+			wantErr: false,
+		},
+		{
+			req: &ethpb.GetValidatorRequest{
+				QueryFilter: &ethpb.GetValidatorRequest_PublicKey{
+					PublicKey: []byte(strconv.Itoa(5)),
+				},
+			},
+			res:     validators[5],
+			wantErr: false,
+		},
+		{
+			req: &ethpb.GetValidatorRequest{
+				QueryFilter: &ethpb.GetValidatorRequest_PublicKey{
+					PublicKey: []byte("bad-key"),
+				},
+			},
+			res:     nil,
+			wantErr: true,
+			err:     "No validator matched filter criteria",
+		},
+		{
+			req: &ethpb.GetValidatorRequest{
+				QueryFilter: &ethpb.GetValidatorRequest_Index{
+					Index: uint64(len(validators)),
+				},
+			},
+			res:     nil,
+			wantErr: true,
+			err:     fmt.Sprintf("there are only %d validators", len(validators)),
+		},
+	}
+
+	for _, test := range tests {
+		res, err := bs.GetValidator(context.Background(), test.req)
+		if test.wantErr && err != nil {
+			if !strings.Contains(err.Error(), test.err) {
+				t.Fatalf("Wanted %v, received %v", test.err, err)
+			}
+		} else if err != nil {
+			t.Fatal(err)
+		}
+		if !reflect.DeepEqual(test.res, res) {
+			t.Errorf("Wanted %v, got %v", test.res, res)
+		}
+	}
+}
+
 func TestServer_GetValidatorActiveSetChanges_CannotRequestFutureEpoch(t *testing.T) {
 	db := dbTest.SetupDB(t)
 	defer dbTest.TeardownDB(t, db)