Test change e2e skip true

instead of finding the block at the beginning of the weak subjectivity
epoch.

.buildkite-bazelrc

@@ -44,3 +44,6 @@ build --flaky_test_attempts=5
 # Better caching
 build:nostamp --nostamp
 build:nostamp --workspace_status_command=./hack/workspace_status_ci.sh
+
+# E2E test config, to add this --config=e2e
+test:e2e --test_keep_going=true

api/client/beacon/checkpoint.go

@@ -26,69 +26,126 @@ type OriginData struct {
 	bb  []byte
 	st  state.BeaconState
 	b   interfaces.SignedBeaconBlock
-	cf  *detect.VersionedUnmarshaler
-}
-
-// CheckpointString returns the standard string representation of a Checkpoint for the block root and epoch for the
-// SignedBeaconBlock value found by DownloadOriginData.
-// The format is a a hex-encoded block root, followed by the epoch of the block, separated by a colon. For example:
-// "0x1c35540cac127315fabb6bf29181f2ae0de1a3fc909d2e76ba771e61312cc49a:74888"
-func (od *OriginData) CheckpointString() string {
-	return fmt.Sprintf("%#x:%d", od.wsd.BlockRoot, od.wsd.Epoch)
+	vu  *detect.VersionedUnmarshaler
+	br  [32]byte
+	sr  [32]byte
 }
 
 // SaveBlock saves the downloaded block to a unique file in the given path.
 // For readability and collision avoidance, the file name includes: type, config name, slot and root
-func (od *OriginData) SaveBlock(dir string) (string, error) {
-	blockPath := path.Join(dir, fname("block", od.cf, od.b.Block().Slot(), od.wsd.BlockRoot))
-	return blockPath, file.WriteFile(blockPath, od.BlockBytes())
+func (o *OriginData) SaveBlock(dir string) (string, error) {
+	blockPath := path.Join(dir, fname("block", o.vu, o.b.Block().Slot(), o.br))
+	return blockPath, file.WriteFile(blockPath, o.BlockBytes())
 }
 
 // SaveState saves the downloaded state to a unique file in the given path.
 // For readability and collision avoidance, the file name includes: type, config name, slot and root
-func (od *OriginData) SaveState(dir string) (string, error) {
-	statePath := path.Join(dir, fname("state", od.cf, od.st.Slot(), od.wsd.StateRoot))
-	return statePath, file.WriteFile(statePath, od.StateBytes())
+func (o *OriginData) SaveState(dir string) (string, error) {
+	statePath := path.Join(dir, fname("state", o.vu, o.st.Slot(), o.sr))
+	return statePath, file.WriteFile(statePath, o.StateBytes())
 }
 
 // StateBytes returns the ssz-encoded bytes of the downloaded BeaconState value.
-func (od *OriginData) StateBytes() []byte {
-	return od.sb
+func (o *OriginData) StateBytes() []byte {
+	return o.sb
 }
 
 // BlockBytes returns the ssz-encoded bytes of the downloaded SignedBeaconBlock value.
-func (od *OriginData) BlockBytes() []byte {
-	return od.bb
+func (o *OriginData) BlockBytes() []byte {
+	return o.bb
 }
 
-func fname(prefix string, cf *detect.VersionedUnmarshaler, slot types.Slot, root [32]byte) string {
-	return fmt.Sprintf("%s_%s_%s_%d-%#x.ssz", prefix, cf.Config.ConfigName, version.String(cf.Fork), slot, root)
+func fname(prefix string, vu *detect.VersionedUnmarshaler, slot types.Slot, root [32]byte) string {
+	return fmt.Sprintf("%s_%s_%s_%d-%#x.ssz", prefix, vu.Config.ConfigName, version.String(vu.Fork), slot, root)
 }
 
-// this method downloads the head state, which can be used to find the correct chain config
-// and use prysm's helper methods to compute the latest weak subjectivity epoch.
-func getWeakSubjectivityEpochFromHead(ctx context.Context, client *Client) (types.Epoch, error) {
-	headBytes, err := client.GetState(ctx, IdHead)
+// DownloadFinalizedData downloads the most recently finalized state, and the block most recently applied to that state.
+// This pair can be used to initialize a new beacon node via checkpoint sync.
+func DownloadFinalizedData(ctx context.Context, client *Client) (*OriginData, error) {
+	sb, err := client.GetState(ctx, IdFinalized)
 	if err != nil {
-		return 0, err
+		return nil, err
 	}
-	cf, err := detect.FromState(headBytes)
+	vu, err := detect.FromState(sb)
 	if err != nil {
-		return 0, errors.Wrap(err, "error detecting chain config for beacon state")
+		return nil, errors.Wrap(err, "error detecting chain config for finalized state")
 	}
-	log.Printf("detected supported config in remote head state, name=%s, fork=%s", cf.Config.ConfigName, version.String(cf.Fork))
-	headState, err := cf.UnmarshalBeaconState(headBytes)
+	log.Printf("detected supported config in remote finalized state, name=%s, fork=%s", vu.Config.ConfigName, version.String(vu.Fork))
+	s, err := vu.UnmarshalBeaconState(sb)
 	if err != nil {
-		return 0, errors.Wrap(err, "error unmarshaling state to correct version")
+		return nil, errors.Wrap(err, "error unmarshaling finalized state to correct version")
 	}
 
-	epoch, err := helpers.LatestWeakSubjectivityEpoch(ctx, headState, cf.Config)
+	sr, err := s.HashTreeRoot(ctx)
 	if err != nil {
-		return 0, errors.Wrap(err, "error computing the weak subjectivity epoch from head state")
+		return nil, errors.Wrapf(err, "failed to compute htr for finalized state at slot=%d", s.Slot())
+	}
+	header := s.LatestBlockHeader()
+	header.StateRoot = sr[:]
+	br, err := header.HashTreeRoot()
+	if err != nil {
+		return nil, errors.Wrap(err, "error while computing block root using state data")
 	}
 
-	log.Printf("(computed client-side) weak subjectivity epoch = %d", epoch)
-	return epoch, nil
+	bb, err := client.GetBlock(ctx, IdFromRoot(br))
+	if err != nil {
+		return nil, errors.Wrapf(err, "error requesting block by root = %#x", br)
+	}
+	b, err := vu.UnmarshalBeaconBlock(bb)
+	if err != nil {
+		return nil, errors.Wrap(err, "unable to unmarshal block to a supported type using the detected fork schedule")
+	}
+	realBlockRoot, err := b.Block().HashTreeRoot()
+	if err != nil {
+		return nil, errors.Wrap(err, "error computing hash_tree_root of retrieved block")
+	}
+
+	log.Printf("BeaconState slot=%d, Block slot=%d", s.Slot(), b.Block().Slot())
+	log.Printf("BeaconState htr=%#xd, Block state_root=%#x", sr, b.Block().StateRoot())
+	log.Printf("BeaconState latest_block_header htr=%#xd, block htr=%#x", br, realBlockRoot)
+	return &OriginData{
+		st: s,
+		b:  b,
+		sb: sb,
+		bb: bb,
+		vu: vu,
+		br: br,
+		sr: sr,
+	}, nil
+}
+
+// WeakSubjectivityData represents the state root, block root and epoch of the BeaconState + SignedBeaconBlock
+// that falls at the beginning of the current weak subjectivity period. These values can be used to construct
+// a weak subjectivity checkpoint beacon node flag to be used for validation.
+type WeakSubjectivityData struct {
+	BlockRoot [32]byte
+	StateRoot [32]byte
+	Epoch     types.Epoch
+}
+
+// CheckpointString returns the standard string representation of a Checkpoint.
+// The format is a a hex-encoded block root, followed by the epoch of the block, separated by a colon. For example:
+// "0x1c35540cac127315fabb6bf29181f2ae0de1a3fc909d2e76ba771e61312cc49a:74888"
+func (wsd *WeakSubjectivityData) CheckpointString() string {
+	return fmt.Sprintf("%#x:%d", wsd.BlockRoot, wsd.Epoch)
+}
+
+// ComputeWeakSubjectivityCheckpoint attempts to use the prysm weak_subjectivity api
+// to obtain the current weak_subjectivity checkpoint.
+// For non-prysm nodes, the same computation will be performed with extra steps,
+// using the head state downloaded from the beacon node api.
+func ComputeWeakSubjectivityCheckpoint(ctx context.Context, client *Client) (*WeakSubjectivityData, error) {
+	ws, err := client.GetWeakSubjectivity(ctx)
+	if err != nil {
+		// a 404/405 is expected if querying an endpoint that doesn't support the weak subjectivity checkpoint api
+		if !errors.Is(err, ErrNotOK) {
+			return nil, errors.Wrap(err, "unexpected API response for prysm-only weak subjectivity checkpoint API")
+		}
+		// fall back to vanilla Beacon Node API method
+		return computeBackwardsCompatible(ctx, client)
+	}
+	log.Printf("server weak subjectivity checkpoint response - epoch=%d, block_root=%#x, state_root=%#x", ws.Epoch, ws.BlockRoot, ws.StateRoot)
+	return ws, nil
 }
 
 const (
@@ -96,8 +153,8 @@ const (
 	prysmImplementationName = "Prysm"
 )
 
-// ErrUnsupportedPrysmCheckpointVersion indicates remote beacon node can't be used for checkpoint retrieval.
-var ErrUnsupportedPrysmCheckpointVersion = errors.New("node does not meet minimum version requirements for checkpoint retrieval")
+// errUnsupportedPrysmCheckpointVersion indicates remote beacon node can't be used for checkpoint retrieval.
+var errUnsupportedPrysmCheckpointVersion = errors.New("node does not meet minimum version requirements for checkpoint retrieval")
 
 // for older endpoints or clients that do not support the weak_subjectivity api method
 // we gather the necessary data for a checkpoint sync by:
@@ -105,14 +162,14 @@ var ErrUnsupportedPrysmCheckpointVersion = errors.New("node does not meet minimu
 // - requesting the state at the first slot of the epoch
 // - using hash_tree_root(state.latest_block_header) to compute the block the state integrates
 // - requesting that block by its root
-func downloadBackwardsCompatible(ctx context.Context, client *Client) (*OriginData, error) {
+func computeBackwardsCompatible(ctx context.Context, client *Client) (*WeakSubjectivityData, error) {
 	log.Print("falling back to generic checkpoint derivation, weak_subjectivity API not supported by server")
 	nv, err := client.GetNodeVersion(ctx)
 	if err != nil {
 		return nil, errors.Wrap(err, "unable to proceed with fallback method without confirming node version")
 	}
 	if nv.implementation == prysmImplementationName && semver.Compare(nv.semver, prysmMinimumVersion) < 0 {
-		return nil, errors.Wrapf(ErrUnsupportedPrysmCheckpointVersion, "%s < minimum (%s)", nv.semver, prysmMinimumVersion)
+		return nil, errors.Wrapf(errUnsupportedPrysmCheckpointVersion, "%s < minimum (%s)", nv.semver, prysmMinimumVersion)
 	}
 	epoch, err := getWeakSubjectivityEpochFromHead(ctx, client)
 	if err != nil {
@@ -127,136 +184,78 @@ func downloadBackwardsCompatible(ctx context.Context, client *Client) (*OriginDa
 
 	log.Printf("requesting checkpoint state at slot %d", slot)
 	// get the state at the first slot of the epoch
-	stateBytes, err := client.GetState(ctx, IdFromSlot(slot))
+	sb, err := client.GetState(ctx, IdFromSlot(slot))
 	if err != nil {
 		return nil, errors.Wrapf(err, "failed to request state by slot from api, slot=%d", slot)
 	}
 
 	// ConfigFork is used to unmarshal the BeaconState so we can read the block root in latest_block_header
-	cf, err := detect.FromState(stateBytes)
+	vu, err := detect.FromState(sb)
 	if err != nil {
 		return nil, errors.Wrap(err, "error detecting chain config for beacon state")
 	}
-	log.Printf("detected supported config in checkpoint state, name=%s, fork=%s", cf.Config.ConfigName, version.String(cf.Fork))
+	log.Printf("detected supported config in checkpoint state, name=%s, fork=%s", vu.Config.ConfigName, version.String(vu.Fork))
 
-	st, err := cf.UnmarshalBeaconState(stateBytes)
+	s, err := vu.UnmarshalBeaconState(sb)
 	if err != nil {
 		return nil, errors.Wrap(err, "error using detected config fork to unmarshal state bytes")
 	}
 
 	// compute state and block roots
-	stateRoot, err := st.HashTreeRoot(ctx)
+	sr, err := s.HashTreeRoot(ctx)
 	if err != nil {
 		return nil, errors.Wrap(err, "error computing hash_tree_root of state")
 	}
 
-	header := st.LatestBlockHeader()
-	header.StateRoot = stateRoot[:]
-	computedBlockRoot, err := header.HashTreeRoot()
+	h := s.LatestBlockHeader()
+	h.StateRoot = sr[:]
+	br, err := h.HashTreeRoot()
 	if err != nil {
 		return nil, errors.Wrap(err, "error while computing block root using state data")
 	}
 
-	blockBytes, err := client.GetBlock(ctx, IdFromRoot(computedBlockRoot))
+	bb, err := client.GetBlock(ctx, IdFromRoot(br))
 	if err != nil {
-		return nil, errors.Wrapf(err, "error requesting block by root = %d", computedBlockRoot)
+		return nil, errors.Wrapf(err, "error requesting block by root = %d", br)
 	}
-	block, err := cf.UnmarshalBeaconBlock(blockBytes)
+	b, err := vu.UnmarshalBeaconBlock(bb)
 	if err != nil {
 		return nil, errors.Wrap(err, "unable to unmarshal block to a supported type using the detected fork schedule")
 	}
-	blockRoot, err := block.Block().HashTreeRoot()
+	br, err = b.Block().HashTreeRoot()
 	if err != nil {
 		return nil, errors.Wrap(err, "error computing hash_tree_root for block obtained via root")
 	}
 
-	log.Printf("BeaconState slot=%d, Block slot=%d", st.Slot(), block.Block().Slot())
-	log.Printf("BeaconState htr=%#xd, Block state_root=%#x", stateRoot, block.Block().StateRoot())
-	log.Printf("BeaconBlock root computed from state=%#x, Block htr=%#x", computedBlockRoot, blockRoot)
-
-	return &OriginData{
-		wsd: &WeakSubjectivityData{
-			BlockRoot: blockRoot,
-			StateRoot: stateRoot,
-			Epoch:     epoch,
-		},
-		st: st,
-		sb: stateBytes,
-		b:  block,
-		bb: blockBytes,
-		cf: cf,
+	return &WeakSubjectivityData{
+		Epoch:     epoch,
+		BlockRoot: br,
+		StateRoot: sr,
 	}, nil
 }
 
-// DownloadOriginData attempts to use the proposed weak_subjectivity beacon node api
-// to obtain the weak_subjectivity metadata (epoch, block_root, state_root) needed to sync
-// a beacon node from the canonical weak subjectivity checkpoint. As this is a proposed API
-// that will only be supported by prysm at first, in the event of a 404 we fallback to using a
-// different technique where we first download the head state which can be used to compute the
-// weak subjectivity epoch on the client side.
-func DownloadOriginData(ctx context.Context, client *Client) (*OriginData, error) {
-	ws, err := client.GetWeakSubjectivity(ctx)
+// this method downloads the head state, which can be used to find the correct chain config
+// and use prysm's helper methods to compute the latest weak subjectivity epoch.
+func getWeakSubjectivityEpochFromHead(ctx context.Context, client *Client) (types.Epoch, error) {
+	headBytes, err := client.GetState(ctx, IdHead)
 	if err != nil {
-		// a 404/405 is expected if querying an endpoint that doesn't support the weak subjectivity checkpoint api
-		if !errors.Is(err, ErrNotOK) {
-			return nil, errors.Wrap(err, "unexpected API response for prysm-only weak subjectivity checkpoint API")
-		}
-		// fall back to vanilla Beacon Node API method
-		return downloadBackwardsCompatible(ctx, client)
+		return 0, err
 	}
-	log.Printf("server weak subjectivity checkpoint response - epoch=%d, block_root=%#x, state_root=%#x", ws.Epoch, ws.BlockRoot, ws.StateRoot)
-
-	// use first slot of the epoch for the block slot
-	slot, err := slots.EpochStart(ws.Epoch)
+	vu, err := detect.FromState(headBytes)
 	if err != nil {
-		return nil, errors.Wrapf(err, "error computing first slot of epoch=%d", ws.Epoch)
+		return 0, errors.Wrap(err, "error detecting chain config for beacon state")
 	}
-	log.Printf("requesting checkpoint state at slot %d", slot)
-
-	stateBytes, err := client.GetState(ctx, IdFromSlot(slot))
+	log.Printf("detected supported config in remote head state, name=%s, fork=%s", vu.Config.ConfigName, version.String(vu.Fork))
+	headState, err := vu.UnmarshalBeaconState(headBytes)
 	if err != nil {
-		return nil, errors.Wrapf(err, "failed to request state by slot from api, slot=%d", slot)
-	}
-	cf, err := detect.FromState(stateBytes)
-	if err != nil {
-		return nil, errors.Wrap(err, "error detecting chain config for beacon state")
-	}
-	log.Printf("detected supported config in checkpoint state, name=%s, fork=%s", cf.Config.ConfigName, version.String(cf.Fork))
-
-	state, err := cf.UnmarshalBeaconState(stateBytes)
-	if err != nil {
-		return nil, errors.Wrap(err, "error using detected config fork to unmarshal state bytes")
-	}
-	stateRoot, err := state.HashTreeRoot(ctx)
-	if err != nil {
-		return nil, errors.Wrapf(err, "failed to compute htr for state at slot=%d", slot)
+		return 0, errors.Wrap(err, "error unmarshaling state to correct version")
 	}
 
-	blockRoot, err := state.LatestBlockHeader().HashTreeRoot()
+	epoch, err := helpers.LatestWeakSubjectivityEpoch(ctx, headState, vu.Config)
 	if err != nil {
-		return nil, errors.Wrap(err, "error computing hash_tree_root of latest_block_header")
+		return 0, errors.Wrap(err, "error computing the weak subjectivity epoch from head state")
 	}
-	blockBytes, err := client.GetBlock(ctx, IdFromRoot(ws.BlockRoot))
-	if err != nil {
-		return nil, errors.Wrapf(err, "error requesting block by slot = %d", slot)
-	}
-	block, err := cf.UnmarshalBeaconBlock(blockBytes)
-	if err != nil {
-		return nil, errors.Wrap(err, "unable to unmarshal block to a supported type using the detected fork schedule")
-	}
-	realBlockRoot, err := block.Block().HashTreeRoot()
-	if err != nil {
-		return nil, errors.Wrap(err, "error computing hash_tree_root of retrieved block")
-	}
-	log.Printf("BeaconState slot=%d, Block slot=%d", state.Slot(), block.Block().Slot())
-	log.Printf("BeaconState htr=%#xd, Block state_root=%#x", stateRoot, block.Block().StateRoot())
-	log.Printf("BeaconState latest_block_header htr=%#xd, block htr=%#x", blockRoot, realBlockRoot)
-	return &OriginData{
-		wsd: ws,
-		st:  state,
-		b:   block,
-		sb:  stateBytes,
-		bb:  blockBytes,
-		cf:  cf,
-	}, nil
+
+	log.Printf("(computed client-side) weak subjectivity epoch = %d", epoch)
+	return epoch, nil
 }

api/client/beacon/checkpoint_test.go

@@ -93,8 +93,8 @@ func TestFallbackVersionCheck(t *testing.T) {
 	}}
 
 	ctx := context.Background()
-	_, err := DownloadOriginData(ctx, c)
-	require.ErrorIs(t, err, ErrUnsupportedPrysmCheckpointVersion)
+	_, err := ComputeWeakSubjectivityCheckpoint(ctx, c)
+	require.ErrorIs(t, err, errUnsupportedPrysmCheckpointVersion)
 }
 
 func TestFname(t *testing.T) {
@@ -120,9 +120,9 @@ func TestFname(t *testing.T) {
 	require.Equal(t, expected, actual)
 }
 
-func TestDownloadOriginData(t *testing.T) {
+func TestDownloadWeakSubjectivityCheckpoint(t *testing.T) {
 	ctx := context.Background()
-	cfg := params.MainnetConfig()
+	cfg := params.MainnetConfig().Copy()
 
 	epoch := cfg.AltairForkEpoch - 1
 	// set up checkpoint state, using the epoch that will be computed as the ws checkpoint state based on the head state
@@ -204,19 +204,15 @@ func TestDownloadOriginData(t *testing.T) {
 		baseURL: &url.URL{Host: "localhost:3500", Scheme: "http"},
 	}
 
-	od, err := DownloadOriginData(ctx, c)
+	wsd, err := ComputeWeakSubjectivityCheckpoint(ctx, c)
 	require.NoError(t, err)
-	require.Equal(t, expectedWSD.Epoch, od.wsd.Epoch)
-	require.Equal(t, expectedWSD.StateRoot, od.wsd.StateRoot)
-	require.Equal(t, expectedWSD.BlockRoot, od.wsd.BlockRoot)
-	require.DeepEqual(t, wsSerialized, od.sb)
-	require.DeepEqual(t, serBlock, od.bb)
-	require.DeepEqual(t, wst.Fork().CurrentVersion, od.cf.Version[:])
-	require.DeepEqual(t, version.Phase0, od.cf.Fork)
+	require.Equal(t, expectedWSD.Epoch, wsd.Epoch)
+	require.Equal(t, expectedWSD.StateRoot, wsd.StateRoot)
+	require.Equal(t, expectedWSD.BlockRoot, wsd.BlockRoot)
 }
 
-// runs downloadBackwardsCompatible directly
-// and via DownloadOriginData with a round tripper that triggers the backwards compatible code path
+// runs computeBackwardsCompatible directly
+// and via ComputeWeakSubjectivityCheckpoint with a round tripper that triggers the backwards compatible code path
 func TestDownloadBackwardsCompatibleCombined(t *testing.T) {
 	ctx := context.Background()
 	cfg := params.MainnetConfig()
@@ -297,16 +293,12 @@ func TestDownloadBackwardsCompatibleCombined(t *testing.T) {
 		baseURL: &url.URL{Host: "localhost:3500", Scheme: "http"},
 	}
 
-	odPub, err := DownloadOriginData(ctx, c)
+	wsPub, err := ComputeWeakSubjectivityCheckpoint(ctx, c)
 	require.NoError(t, err)
 
-	odPriv, err := downloadBackwardsCompatible(ctx, c)
+	wsPriv, err := computeBackwardsCompatible(ctx, c)
 	require.NoError(t, err)
-	require.DeepEqual(t, odPriv.wsd, odPub.wsd)
-	require.DeepEqual(t, odPriv.sb, odPub.sb)
-	require.DeepEqual(t, odPriv.bb, odPub.bb)
-	require.DeepEqual(t, odPriv.cf.Fork, odPub.cf.Fork)
-	require.DeepEqual(t, odPriv.cf.Version, odPub.cf.Version)
+	require.DeepEqual(t, wsPriv, wsPub)
 }
 
 func TestGetWeakSubjectivityEpochFromHead(t *testing.T) {
@@ -402,3 +394,94 @@ func populateValidators(cfg *params.BeaconChainConfig, st state.BeaconState, val
 
 	return nil
 }
+
+func TestDownloadFinalizedData(t *testing.T) {
+	ctx := context.Background()
+	cfg := params.MainnetConfig().Copy()
+
+	// avoid the altair zone because genesis tests are easier to set up
+	epoch := cfg.AltairForkEpoch - 1
+	// set up checkpoint state, using the epoch that will be computed as the ws checkpoint state based on the head state
+	slot, err := slots.EpochStart(epoch)
+	require.NoError(t, err)
+	st, err := util.NewBeaconState()
+	require.NoError(t, err)
+	fork, err := forkForEpoch(cfg, epoch)
+	require.NoError(t, st.SetFork(fork))
+
+	// set up checkpoint block
+	b, err := wrapper.WrappedSignedBeaconBlock(util.NewBeaconBlock())
+	require.NoError(t, wrapper.SetBlockParentRoot(b, cfg.ZeroHash))
+	require.NoError(t, wrapper.SetBlockSlot(b, slot))
+	require.NoError(t, wrapper.SetProposerIndex(b, 0))
+
+	// set up state header pointing at checkpoint block - this is how the block is downloaded by root
+	header, err := b.Header()
+	require.NoError(t, err)
+	require.NoError(t, st.SetLatestBlockHeader(header.Header))
+
+	// order of operations can be confusing here:
+	// - when computing the state root, make sure block header is complete, EXCEPT the state root should be zero-value
+	// - before computing the block root (to match the request route), the block should include the state root
+	//   *computed from the state with a header that does not have a state root set yet*
+	sr, err := st.HashTreeRoot(ctx)
+	require.NoError(t, err)
+
+	require.NoError(t, wrapper.SetBlockStateRoot(b, sr))
+	mb, err := b.MarshalSSZ()
+	require.NoError(t, err)
+	br, err := b.Block().HashTreeRoot()
+	require.NoError(t, err)
+
+	ms, err := st.MarshalSSZ()
+	require.NoError(t, err)
+
+	hc := &http.Client{
+		Transport: &testRT{rt: func(req *http.Request) (*http.Response, error) {
+			res := &http.Response{Request: req}
+			switch req.URL.Path {
+			case renderGetStatePath(IdFinalized):
+				res.StatusCode = http.StatusOK
+				res.Body = io.NopCloser(bytes.NewBuffer(ms))
+			case renderGetBlockPath(IdFromRoot(br)):
+				res.StatusCode = http.StatusOK
+				res.Body = io.NopCloser(bytes.NewBuffer(mb))
+			default:
+				res.StatusCode = http.StatusInternalServerError
+				res.Body = io.NopCloser(bytes.NewBufferString(""))
+			}
+
+			return res, nil
+		}},
+	}
+	c := &Client{
+		hc:      hc,
+		baseURL: &url.URL{Host: "localhost:3500", Scheme: "http"},
+	}
+
+	// sanity check before we go through checkpoint
+	// make sure we can download the state and unmarshal it with the VersionedUnmarshaler
+	sb, err := c.GetState(ctx, IdFinalized)
+	require.NoError(t, err)
+	require.Equal(t, true, bytes.Equal(sb, ms))
+	vu, err := detect.FromState(sb)
+	require.NoError(t, err)
+	us, err := vu.UnmarshalBeaconState(sb)
+	require.NoError(t, err)
+	ushtr, err := us.HashTreeRoot(ctx)
+	require.NoError(t, err)
+	require.Equal(t, sr, ushtr)
+
+	expected := &OriginData{
+		sb: ms,
+		bb: mb,
+		br: br,
+		sr: sr,
+	}
+	od, err := DownloadFinalizedData(ctx, c)
+	require.NoError(t, err)
+	require.Equal(t, true, bytes.Equal(expected.sb, od.sb))
+	require.Equal(t, true, bytes.Equal(expected.bb, od.bb))
+	require.Equal(t, expected.br, od.br)
+	require.Equal(t, expected.sr, od.sr)
+}

api/client/beacon/client.go

@@ -46,8 +46,9 @@ const (
 type StateOrBlockId string
 
 const (
-	IdGenesis StateOrBlockId = "genesis"
-	IdHead    StateOrBlockId = "head"
+	IdGenesis   StateOrBlockId = "genesis"
+	IdHead      StateOrBlockId = "head"
+	IdFinalized StateOrBlockId = "finalized"
 )
 
 var ErrMalformedHostname = errors.New("hostname must include port, separated by one colon, like example.com:3500")
@@ -344,16 +345,6 @@ func (c *Client) GetWeakSubjectivity(ctx context.Context) (*WeakSubjectivityData
 	}, nil
 }
 
-// WeakSubjectivityData represents the state root, block root and epoch of the BeaconState + SignedBeaconBlock
-// that falls at the beginning of the current weak subjectivity period. These values can be used to construct
-// a weak subjectivity checkpoint, or to download a BeaconState+SignedBeaconBlock pair that can be used to bootstrap
-// a new Beacon Node using Checkpoint Sync.
-type WeakSubjectivityData struct {
-	BlockRoot [32]byte
-	StateRoot [32]byte
-	Epoch     types.Epoch
-}
-
 func non200Err(response *http.Response) error {
 	bodyBytes, err := io.ReadAll(response.Body)
 	var body string

beacon-chain/sync/checkpoint/api.go

@@ -27,7 +27,7 @@ func NewAPIInitializer(beaconNodeHost string) (*APIInitializer, error) {
 // Initialize downloads origin state and block for checkpoint sync and initializes database records to
 // prepare the node to begin syncing from that point.
 func (dl *APIInitializer) Initialize(ctx context.Context, d db.Database) error {
-	od, err := beacon.DownloadOriginData(ctx, dl.c)
+	od, err := beacon.DownloadFinalizedData(ctx, dl.c)
 	if err != nil {
 		return errors.Wrap(err, "Error retrieving checkpoint origin state and block")
 	}

cmd/prysmctl/checkpoint/latest.go

@@ -44,12 +44,12 @@ func cliActionLatest(_ *cli.Context) error {
 		return err
 	}
 
-	od, err := beacon.DownloadOriginData(ctx, client)
+	ws, err := beacon.ComputeWeakSubjectivityCheckpoint(ctx, client)
 	if err != nil {
 		return err
 	}
 	fmt.Println("\nUse the following flag when starting a prysm Beacon Node to ensure the chain history " +
 		"includes the Weak Subjectivity Checkpoint: ")
-	fmt.Printf("--weak-subjectivity-checkpoint=%s\n\n", od.CheckpointString())
+	fmt.Printf("--weak-subjectivity-checkpoint=%s\n\n", ws.CheckpointString())
 	return nil
 }

cmd/prysmctl/checkpoint/save.go

@@ -17,7 +17,7 @@ var saveFlags = struct {
 
 var saveCmd = &cli.Command{
 	Name:   "save",
-	Usage:  "Query for the current weak subjectivity period epoch, then download the corresponding state and block. To be used for checkpoint sync.",
+	Usage:  "Save the latest finalized header and the most recent block it integrates. To be used for checkpoint sync.",
 	Action: cliActionSave,
 	Flags: []cli.Flag{
 		&cli.StringFlag{
@@ -50,7 +50,7 @@ func cliActionSave(_ *cli.Context) error {
 		return err
 	}
 
-	od, err := beacon.DownloadOriginData(ctx, client)
+	od, err := beacon.DownloadFinalizedData(ctx, client)
 	if err != nil {
 		return err
 	}

testing/endtoend/BUILD.bazel

@@ -36,6 +36,7 @@ go_test(
         "requires-network",
     ],
     deps = [
+        "//api/client/beacon:go_default_library",
         "//beacon-chain/blockchain/testing:go_default_library",
         "//beacon-chain/core/transition:go_default_library",
         "//beacon-chain/db/testing:go_default_library",
@@ -44,6 +45,10 @@ go_test(
         "//config/params:go_default_library",
         "//consensus-types/primitives:go_default_library",
         "//crypto/bls:go_default_library",
+        "//encoding/bytesutil:go_default_library",
+        "//io/file:go_default_library",
+        "//proto/eth/service:go_default_library",
+        "//proto/eth/v1:go_default_library",
         "//proto/prysm/v1alpha1:go_default_library",
         "//testing/assert:go_default_library",
         "//testing/endtoend/components:go_default_library",
@@ -59,6 +64,8 @@ go_test(
         "@com_github_sirupsen_logrus//:go_default_library",
         "@com_github_sirupsen_logrus//hooks/test:go_default_library",
         "@org_golang_google_grpc//:go_default_library",
+        "@org_golang_google_grpc//codes:go_default_library",
+        "@org_golang_google_grpc//status:go_default_library",
         "@org_golang_google_protobuf//types/known/emptypb:go_default_library",
         "@org_golang_x_sync//errgroup:go_default_library",
     ],

testing/endtoend/component_handler_test.go

@@ -129,6 +129,9 @@ func (c *componentHandler) setup() {
 		return nil
 	})
 
+	if config.TestCheckpointSync {
+		appendDebugEndpoints(config)
+	}
 	// Beacon nodes.
 	beaconNodes := components.NewBeaconNodes(config)
 	g.Go(func() error {
@@ -201,3 +204,11 @@ func (c *componentHandler) required() []e2etypes.ComponentRunner {
 	}
 	return requiredComponents
 }
+
+func appendDebugEndpoints(cfg *e2etypes.E2EConfig) {
+	debug := []string{
+		"--enable-debug-rpc-endpoints",
+		"--grpc-max-msg-size=65568081",
+	}
+	cfg.BeaconFlags = append(cfg.BeaconFlags, debug...)
+}

testing/endtoend/components/beacon_node.go

@@ -175,6 +175,9 @@ func (node *BeaconNode) Start(ctx context.Context) error {
 	if node.config.TestSync {
 		expectedNumOfPeers += 1
 	}
+	if node.config.TestCheckpointSync {
+		expectedNumOfPeers += 1
+	}
 	jwtPath := path.Join(e2e.TestParams.TestPath, "eth1data/"+strconv.Itoa(node.index)+"/")
 	if index == 0 {
 		jwtPath = path.Join(e2e.TestParams.TestPath, "eth1data/miner/")

testing/endtoend/endtoend_setup_test.go

@@ -14,7 +14,7 @@ import (
 	"github.com/prysmaticlabs/prysm/testing/require"
 )
 
-func e2eMinimal(t *testing.T, useWeb3RemoteSigner bool, extraEpochs uint64) *testRunner {
+func e2eMinimal(t *testing.T, cfgo ...types.E2EConfigOpt) *testRunner {
 	params.SetupTestConfigCleanup(t)
 	params.OverrideBeaconConfig(params.E2ETestConfig().Copy())
 	require.NoError(t, e2eParams.Init(e2eParams.StandardBeaconCount))
@@ -74,12 +74,13 @@ func e2eMinimal(t *testing.T, useWeb3RemoteSigner bool, extraEpochs uint64) *tes
 		TestDeposits:        true,
 		UsePrysmShValidator: false,
 		UsePprof:            !longRunning,
-		UseWeb3RemoteSigner: useWeb3RemoteSigner,
 		TracingSinkEndpoint: tracingEndpoint,
 		Evaluators:          evals,
 		EvalInterceptor:     defaultInterceptor,
 		Seed:                int64(seed),
-		ExtraEpochs:         extraEpochs,
+	}
+	for _, o := range cfgo {
+		o(testConfig)
 	}
 
 	return newTestRunner(t, testConfig)

testing/endtoend/endtoend_test.go

@@ -14,6 +14,14 @@ import (
 	"testing"
 	"time"
 
+	"github.com/prysmaticlabs/prysm/api/client/beacon"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	"github.com/prysmaticlabs/prysm/io/file"
+	"github.com/prysmaticlabs/prysm/proto/eth/service"
+	v1 "github.com/prysmaticlabs/prysm/proto/eth/v1"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
 	"github.com/pkg/errors"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	"github.com/prysmaticlabs/prysm/config/params"
@@ -211,9 +219,101 @@ func (r *testRunner) testTxGeneration(ctx context.Context, g *errgroup.Group, ke
 	})
 }
 
+func (r *testRunner) waitForMatchingHead(ctx context.Context, check, ref *grpc.ClientConn) error {
+	// sleep hack copied from testBeaconChainSync
+	// Sleep a second for every 4 blocks that need to be synced for the newly started node.
+	secondsPerEpoch := uint64(params.BeaconConfig().SlotsPerEpoch.Mul(params.BeaconConfig().SecondsPerSlot))
+	extraSecondsToSync := (r.config.EpochsToRun) * secondsPerEpoch
+	deadline := time.Now().Add(time.Second * time.Duration(extraSecondsToSync))
+	dctx, cancel := context.WithDeadline(ctx, deadline)
+	defer cancel()
+	checkClient := service.NewBeaconChainClient(check)
+	refClient := service.NewBeaconChainClient(ref)
+	for {
+		select {
+		case <-dctx.Done():
+			// deadline ensures that the test eventually exits when beacon node fails to sync in a resonable timeframe
+			return fmt.Errorf("deadline exceeded waiting for known good block to appear in checkpoint-synced node")
+		default:
+			cResp, err := checkClient.GetBlockRoot(ctx, &v1.BlockRequest{BlockId: []byte("head")})
+			if err != nil {
+				errStatus, ok := status.FromError(err)
+				// in the happy path we expect NotFound results until the node has synced
+				if ok && errStatus.Code() == codes.NotFound {
+					continue
+				}
+				return fmt.Errorf("error requesting head from 'check' beacon node")
+			}
+			rResp, err := refClient.GetBlockRoot(ctx, &v1.BlockRequest{BlockId: []byte("head")})
+			if err != nil {
+				return errors.Wrap(err, "unexpected error requesting head block root from 'ref' beacon node")
+			}
+			if bytesutil.ToBytes32(cResp.Data.Root) == bytesutil.ToBytes32(rResp.Data.Root) {
+				return nil
+			}
+		}
+	}
+}
+
+func (r *testRunner) testCheckpointSync(ctx context.Context, g *errgroup.Group, i int, conns []*grpc.ClientConn, bnAPI, enr, minerEnr string) error {
+	ethNode := eth1.NewNode(i, minerEnr)
+	g.Go(func() error {
+		return ethNode.Start(ctx)
+	})
+	if err := helpers.ComponentsStarted(ctx, []e2etypes.ComponentRunner{ethNode}); err != nil {
+		return fmt.Errorf("sync beacon node not ready: %w", err)
+	}
+
+	client, err := beacon.NewClient(bnAPI)
+	if err != nil {
+		return err
+	}
+	gb, err := client.GetState(ctx, beacon.IdGenesis)
+	if err != nil {
+		return err
+	}
+	genPath := path.Join(e2e.TestParams.TestPath, "genesis.ssz")
+	err = file.WriteFile(genPath, gb)
+	if err != nil {
+		return err
+	}
+
+	flags := append([]string{}, r.config.BeaconFlags...)
+	flags = append(flags, fmt.Sprintf("--checkpoint-sync-url=%s", bnAPI))
+	flags = append(flags, fmt.Sprintf("--genesis-beacon-api-url=%s", bnAPI))
+
+	cfgcp := new(e2etypes.E2EConfig)
+	*cfgcp = *r.config
+	cfgcp.BeaconFlags = flags
+	cpsyncer := components.NewBeaconNode(cfgcp, i, enr)
+	g.Go(func() error {
+		return cpsyncer.Start(ctx)
+	})
+	if err := helpers.ComponentsStarted(ctx, []e2etypes.ComponentRunner{cpsyncer}); err != nil {
+		return fmt.Errorf("checkpoint sync beacon node not ready: %w", err)
+	}
+	c, err := grpc.Dial(fmt.Sprintf("127.0.0.1:%d", e2e.TestParams.Ports.PrysmBeaconNodeRPCPort+i), grpc.WithInsecure())
+	require.NoError(r.t, err, "Failed to dial")
+
+	// this is so that the syncEvaluators checks can run on the checkpoint sync'd node
+	conns = append(conns, c)
+	err = r.waitForMatchingHead(ctx, c, conns[0])
+	if err != nil {
+		return err
+	}
+
+	syncEvaluators := []e2etypes.Evaluator{ev.FinishedSyncing, ev.AllNodesHaveSameHead}
+	for _, evaluator := range syncEvaluators {
+		r.t.Run(evaluator.Name, func(t *testing.T) {
+			assert.NoError(t, evaluator.Evaluation(conns...), "Evaluation failed for sync node")
+		})
+	}
+	return nil
+}
+
 // testBeaconChainSync creates another beacon node, and tests whether it can sync to head using previous nodes.
 func (r *testRunner) testBeaconChainSync(ctx context.Context, g *errgroup.Group,
-	conns []*grpc.ClientConn, tickingStartTime time.Time, bootnodeEnr, minerEnr string) (*grpc.ClientConn, error) {
+	conns []*grpc.ClientConn, tickingStartTime time.Time, bootnodeEnr, minerEnr string) error {
 	t, config := r.t, r.config
 	index := e2e.TestParams.BeaconNodeCount + e2e.TestParams.LighthouseBeaconNodeCount
 	ethNode := eth1.NewNode(index, minerEnr)
@@ -221,14 +321,14 @@ func (r *testRunner) testBeaconChainSync(ctx context.Context, g *errgroup.Group,
 		return ethNode.Start(ctx)
 	})
 	if err := helpers.ComponentsStarted(ctx, []e2etypes.ComponentRunner{ethNode}); err != nil {
-		return nil, fmt.Errorf("sync beacon node not ready: %w", err)
+		return fmt.Errorf("sync beacon node not ready: %w", err)
 	}
 	syncBeaconNode := components.NewBeaconNode(config, index, bootnodeEnr)
 	g.Go(func() error {
 		return syncBeaconNode.Start(ctx)
 	})
 	if err := helpers.ComponentsStarted(ctx, []e2etypes.ComponentRunner{syncBeaconNode}); err != nil {
-		return nil, fmt.Errorf("sync beacon node not ready: %w", err)
+		return fmt.Errorf("sync beacon node not ready: %w", err)
 	}
 	syncConn, err := grpc.Dial(fmt.Sprintf("127.0.0.1:%d", e2e.TestParams.Ports.PrysmBeaconNodeRPCPort+index), grpc.WithInsecure())
 	require.NoError(t, err, "Failed to dial")
@@ -247,7 +347,7 @@ func (r *testRunner) testBeaconChainSync(ctx context.Context, g *errgroup.Group,
 		assert.NoError(t, helpers.WaitForTextInFile(syncLogFile, "Synced up to"), "Failed to sync")
 	})
 	if t.Failed() {
-		return nil, errors.New("cannot sync beacon node")
+		return errors.New("cannot sync beacon node")
 	}
 
 	// Sleep a slot to make sure the synced state is made.
@@ -258,7 +358,7 @@ func (r *testRunner) testBeaconChainSync(ctx context.Context, g *errgroup.Group,
 			assert.NoError(t, evaluator.Evaluation(conns...), "Evaluation failed for sync node")
 		})
 	}
-	return syncConn, nil
+	return nil
 }
 
 func (r *testRunner) testDoppelGangerProtection(ctx context.Context) error {
@@ -365,18 +465,29 @@ func (r *testRunner) defaultEndToEndRun() error {
 		return errors.Wrap(err, "one or more evaluators failed")
 	}
 
-	// If requested, run sync test.
-	if !config.TestSync {
-		return nil
+	index := e2e.TestParams.BeaconNodeCount + e2e.TestParams.LighthouseBeaconNodeCount
+	if config.TestSync {
+		// using g.Go to run these methods that start after the main tests so that they can run in parallel
+		g.Go(func() error {
+			return r.testBeaconChainSync(ctx, g, conns, tickingStartTime, bootNode.ENR(), eth1Miner.ENR())
+		})
+		index += 1
 	}
-	syncConn, err := r.testBeaconChainSync(ctx, g, conns, tickingStartTime, bootNode.ENR(), eth1Miner.ENR())
 	if err != nil {
 		return errors.Wrap(err, "beacon chain sync test failed")
 	}
-	conns = append(conns, syncConn)
 	if err := r.testDoppelGangerProtection(ctx); err != nil {
 		return errors.Wrap(err, "doppel ganger protection check failed")
 	}
+	if config.TestCheckpointSync {
+		httpEndpoints := helpers.BeaconAPIHostnames(e2e.TestParams.BeaconNodeCount)
+		menr := eth1Miner.ENR()
+		benr := bootNode.ENR()
+		if err := r.testCheckpointSync(ctx, g, index, conns, httpEndpoints[0], benr, menr); err != nil {
+			return errors.Wrap(err, "checkpoint sync test failed")
+		}
+		index += 1
+	}
 
 	if config.ExtraEpochs > 0 {
 		if err := r.waitExtra(ctx, types.Epoch(config.EpochsToRun+config.ExtraEpochs), conns[0], types.Epoch(config.ExtraEpochs)); err != nil {

testing/endtoend/evaluators/node.go

@@ -136,7 +136,7 @@ func allNodesHaveSameHead(conns ...*grpc.ClientConn) error {
 		beaconClient := eth.NewBeaconChainClient(conn)
 		chainHead, err := beaconClient.GetChainHead(context.Background(), &emptypb.Empty{})
 		if err != nil {
-			return err
+			return errors.Wrapf(err, "connection number=%d", i)
 		}
 		headEpochs[i] = chainHead.HeadEpoch
 		justifiedRoots[i] = chainHead.JustifiedBlockRoot

testing/endtoend/helpers/helpers.go

@@ -7,10 +7,12 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"net"
 	"net/http"
 	"os"
 	"path"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -269,6 +271,16 @@ func NewLocalConnections(ctx context.Context, numConns int) ([]*grpc.ClientConn,
 	}, nil
 }
 
+// BeaconAPIHostnames constructs a hostname:port string for the
+func BeaconAPIHostnames(numConns int) []string {
+	hostnames := make([]string, 0)
+	for i := 0; i < numConns; i++ {
+		port := e2e.TestParams.Ports.PrysmBeaconNodeGatewayPort + i
+		hostnames = append(hostnames, net.JoinHostPort("127.0.0.1", strconv.Itoa(port)))
+	}
+	return hostnames
+}
+
 // ComponentsStarted checks, sequentially, each provided component, blocks until all of the components are ready.
 func ComponentsStarted(ctx context.Context, comps []e2etypes.ComponentRunner) error {
 	for _, comp := range comps {

testing/endtoend/minimal_e2e_test.go

@@ -2,12 +2,18 @@ package endtoend
 
 import (
 	"testing"
+
+	"github.com/prysmaticlabs/prysm/testing/endtoend/types"
 )
 
 func TestEndToEnd_MinimalConfig(t *testing.T) {
-	e2eMinimal(t, false, 3).run()
+	e2eMinimal(t).run()
 }
 
 func TestEndToEnd_MinimalConfig_Web3Signer(t *testing.T) {
-	e2eMinimal(t, true, 0).run()
+	e2eMinimal(t, types.WithRemoteSigner()).run()
+}
+
+func TestEndToEnd_MinimalConfig_CheckpointSync(t *testing.T) {
+	e2eMinimal(t, types.WithCheckpointSync()).run()
 }

testing/endtoend/minimal_scenario_e2e_test.go

@@ -3,7 +3,7 @@ package endtoend
 import "testing"
 
 func TestEndToEnd_ScenarioRun_BeaconOffline(t *testing.T) {
-	runner := e2eMinimal(t, false, 0)
+	runner := e2eMinimal(t)
 
 	runner.config.Evaluators = scenarioEvals()
 	runner.config.EvalInterceptor = runner.singleNodeOffline
@@ -11,7 +11,7 @@ func TestEndToEnd_ScenarioRun_BeaconOffline(t *testing.T) {
 }
 
 func TestEndToEnd_ScenarioRun_AllvalidatorsOffline(t *testing.T) {
-	runner := e2eMinimal(t, false, 0)
+	runner := e2eMinimal(t)
 
 	runner.config.Evaluators = scenarioEvals()
 	runner.config.EvalInterceptor = runner.allValidatorsOffline
@@ -20,7 +20,7 @@ func TestEndToEnd_ScenarioRun_AllvalidatorsOffline(t *testing.T) {
 
 func TestEndToEnd_ScenarioRun_EEOffline(t *testing.T) {
 	t.Skip("TODO(#10242) Prysm is current unable to handle an offline e2e")
-	runner := e2eMinimal(t, false, 0)
+	runner := e2eMinimal(t)
 
 	runner.config.Evaluators = scenarioEvals()
 	runner.config.EvalInterceptor = runner.eeOffline

testing/endtoend/types/types.go

@@ -9,8 +9,29 @@ import (
 	"google.golang.org/grpc"
 )
 
+type E2EConfigOpt func(*E2EConfig)
+
+func WithExtraEpochs(extra uint64) E2EConfigOpt {
+	return func(cfg *E2EConfig) {
+		cfg.ExtraEpochs = extra
+	}
+}
+
+func WithRemoteSigner() E2EConfigOpt {
+	return func(cfg *E2EConfig) {
+		cfg.UseWeb3RemoteSigner = true
+	}
+}
+
+func WithCheckpointSync() E2EConfigOpt {
+	return func(cfg *E2EConfig) {
+		cfg.TestCheckpointSync = true
+	}
+}
+
 // E2EConfig defines the struct for all configurations needed for E2E testing.
 type E2EConfig struct {
+	TestCheckpointSync      bool
 	TestSync                bool
 	TestFeature             bool
 	UsePrysmShValidator     bool