ethclient/lightclient: more comments and minor changes

ethclient/lightclient/blocks.go

@@ -54,6 +54,7 @@ func (c *Client) closeBlocksAndHeaders() {
 	c.blockRequests.close()
 }
 
+// getHeader returns the header with the given block hash.
 func (c *Client) getHeader(ctx context.Context, hash common.Hash) (*types.Header, error) {
 	if header, ok := c.headerCache.Get(hash); ok {
 		return header, nil
@@ -84,15 +85,25 @@ func (c *Client) getHeader(ctx context.Context, hash common.Hash) (*types.Header
 	return header, err
 }
 
+// getPayloadHeader returns the payload header with the given block hash.
+// Note that types.Header and the CL execution payload header (btypes.ExecutionHeader)
+// both contain the information relevant to the light client but they are not
+// interchangeable. Payload headers are received from head/finality updates and
+// are cached but they are not obtainable later on demand as they are not directly
+// chained to each other by hash reference. If reverse syncing is required then
+// EL headers should be used.
 func (c *Client) getPayloadHeader(hash common.Hash) *btypes.ExecutionHeader {
 	pheader, _ := c.payloadHeaderCache.Get(hash)
 	return pheader
 }
 
+// addPayloadHeader caches the given payload header.
 func (c *Client) addPayloadHeader(header *btypes.ExecutionHeader) {
 	c.payloadHeaderCache.Add(header.BlockHash(), header)
 }
 
+// getBlock returns the block with the given hash. If the block has been retrieved
+// from the server then the transaction inclusion positions are also cached.
 func (c *Client) getBlock(ctx context.Context, hash common.Hash) (*types.Block, error) {
 	if block, ok := c.blockCache.Get(hash); ok {
 		return block, nil
@@ -149,7 +160,8 @@ func (c *Client) requestBlock(ctx context.Context, hash common.Hash) (*types.Blo
 	return block, nil
 }
 
-//TODO de-duplicate json block decoding
+// decodeBlock decodes a JSON encoded block.
+//TODO de-duplicate
 func decodeBlock(raw json.RawMessage) (*types.Block, error) {
 	// Decode header and transactions.
 	var head *types.Header

ethclient/lightclient/canonical.go

@@ -31,6 +31,8 @@ import (
 	"github.com/ethereum/go-ethereum/rpc"
 )
 
+// recentCanonicalLength specifies the maximum number of most recent number to hash
+// associations stored in the recent map
 const recentCanonicalLength = 256
 
 // canonicalChainFields defines Client fields related to canonical chain tracking.
@@ -40,13 +42,13 @@ type canonicalChainFields struct {
 	recent               map[uint64]common.Hash // nil while head == nil
 	recentTail           uint64                 // if recent != nil then recent hashes are available from recentTail to head
 	tailFetchCh, closeCh chan struct{}
-	finalized            *lru.Cache[uint64, common.Hash]  // finalized but not recent hashes
+	cache                *lru.Cache[uint64, common.Hash]  // older than recentTail
-	requests             *requestMap[uint64, common.Hash] // requested; neither recent nor cached finalized
+	requests             *requestMap[uint64, common.Hash] // requested; neither recent nor cached
 }
 
 // initCanonicalChain initializes the structures related to canonical chain tracking.
 func (c *Client) initCanonicalChain() {
-	c.finalized = lru.NewCache[uint64, common.Hash](10000)
+	c.cache = lru.NewCache[uint64, common.Hash](10000)
 	c.requests = newRequestMap[uint64, common.Hash](nil)
 	c.tailFetchCh = make(chan struct{})
 	c.closeCh = make(chan struct{})
@@ -59,6 +61,8 @@ func (c *Client) closeCanonicalChain() {
 	close(c.closeCh)
 }
 
+// setHead sets a new head for the canonical chain. It also updates the recent
+// hash associations and takes care of state cache invalidation if necessary.
 func (c *Client) setHead(head *btypes.ExecutionHeader) bool {
 	c.chainLock.Lock()
 	defer c.chainLock.Unlock()
@@ -68,9 +72,15 @@ func (c *Client) setHead(head *btypes.ExecutionHeader) bool {
 		return false
 	}
 	if c.recent == nil || c.head == nil || c.head.BlockNumber()+1 != headNum || c.head.BlockHash() != head.ParentHash() {
-		// initialize recent canonical hash map when first head is added or when
+		// new head is not a descendant of the previous one; everything that was
-		// it is not a descendant of the previous head
+		// not finalized should be invalidated.
+		if c.finality == nil || c.recentTail > c.finality.BlockNumber()+1 {
+			// purge cache if the previous contents were not all finalized
+			c.cache.Purge()
+		}
+		// state proofs are cached by number
 		c.clearStateCache()
+		// initialize recent canonical hash map
 		c.recent = make(map[uint64]common.Hash)
 		if headNum > 0 {
 			c.recent[headNum-1] = head.ParentHash()
@@ -82,9 +92,7 @@ func (c *Client) setHead(head *btypes.ExecutionHeader) bool {
 	c.head = head
 	c.recent[headNum] = headHash
 	for headNum >= c.recentTail+recentCanonicalLength {
-		if c.finality != nil && c.recentTail <= c.finality.BlockNumber() {
+		c.cache.Add(c.recentTail, c.recent[c.recentTail])
-			c.finalized.Add(c.recentTail, c.recent[c.recentTail])
-		}
 		delete(c.recent, c.recentTail)
 		c.recentTail++
 	}
@@ -93,6 +101,7 @@ func (c *Client) setHead(head *btypes.ExecutionHeader) bool {
 	return true
 }
 
+// setFinality sets a new finality slot.
 func (c *Client) setFinality(finality *btypes.ExecutionHeader) {
 	c.chainLock.Lock()
 	defer c.chainLock.Unlock()
@@ -100,11 +109,12 @@ func (c *Client) setFinality(finality *btypes.ExecutionHeader) {
 	c.finality = finality
 	finalNum := finality.BlockNumber()
 	if finalNum < c.recentTail {
-		c.finalized.Add(finalNum, finality.BlockHash())
+		c.cache.Add(finalNum, finality.BlockHash())
 	}
 	c.requests.tryDeliver(finalNum, finality.BlockHash())
 }
 
+// getHead returns the current local canonical chain head.
 func (c *Client) getHead() *btypes.ExecutionHeader {
 	c.chainLock.Lock()
 	defer c.chainLock.Unlock()
@@ -112,6 +122,7 @@ func (c *Client) getHead() *btypes.ExecutionHeader {
 	return c.head
 }
 
+// getFinality returns the current finality header
 func (c *Client) getFinality() *btypes.ExecutionHeader {
 	c.chainLock.Lock()
 	defer c.chainLock.Unlock()
@@ -119,6 +130,8 @@ func (c *Client) getFinality() *btypes.ExecutionHeader {
 	return c.finality
 }
 
+// addRecentTail tries to add the given header to the tail of the recent canonical
+// section and returns true if successful.
 func (c *Client) addRecentTail(tail *types.Header) bool {
 	c.chainLock.Lock()
 	defer c.chainLock.Unlock()
@@ -136,6 +149,7 @@ func (c *Client) addRecentTail(tail *types.Header) bool {
 	return true
 }
 
+// tailFetcher reverse syncs canonical hashes until all requested items are present.
 func (c *Client) tailFetcher() {
 	for {
 		c.chainLock.Lock()
@@ -173,6 +187,7 @@ func (c *Client) tailFetcher() {
 	}
 }
 
+// getHash returns the requested number -> hash association.
 func (c *Client) getHash(ctx context.Context, number uint64) (common.Hash, error) {
 	if hash, ok := c.getCachedHash(number); ok {
 		return hash, nil
@@ -186,6 +201,8 @@ func (c *Client) getHash(ctx context.Context, number uint64) (common.Hash, error
 	return req.waitForResult(ctx)
 }
 
+// getCachedHash returns the requested number -> hash association if it is already
+// in memory cache.
 func (c *Client) getCachedHash(number uint64) (common.Hash, bool) {
 	c.chainLock.Lock()
 	hash, ok := c.recent[number]
@@ -193,9 +210,11 @@ func (c *Client) getCachedHash(number uint64) (common.Hash, bool) {
 	if ok {
 		return hash, true
 	}
-	return c.finalized.Get(number)
+	return c.cache.Get(number)
 }
 
+// resolveBlockNumber resolves an RPC block number into uint64 and also returns
+// the payload header in case of special (negative) RPC numbers.
 func (c *Client) resolveBlockNumber(number *big.Int) (uint64, *btypes.ExecutionHeader, error) {
 	if !number.IsInt64() {
 		return 0, nil, errors.New("Invalid block number")
@@ -220,6 +239,10 @@ func (c *Client) resolveBlockNumber(number *big.Int) (uint64, *btypes.ExecutionH
 	return uint64(num), nil, nil
 }
 
+// blockNumberToHash returns the canonical hash belonging to the given RPC block
+// number. Note that requesting older canonical hashes might trigger a reverse
+// header sync process which might take a very long time depending on the age
+// of the specified block.
 func (c *Client) blockNumberToHash(ctx context.Context, number *big.Int) (common.Hash, error) {
 	num, pheader, err := c.resolveBlockNumber(number)
 	if err != nil {
@@ -231,6 +254,7 @@ func (c *Client) blockNumberToHash(ctx context.Context, number *big.Int) (common
 	return c.getHash(ctx, num)
 }
 
+// blockNumberOrHashToHash resolves rpc.BlockNumberOrHash into a block hash.
 func (c *Client) blockNumberOrHashToHash(ctx context.Context, blockNrOrHash rpc.BlockNumberOrHash) (common.Hash, error) {
 	if blockNrOrHash.BlockNumber != nil {
 		return c.blockNumberToHash(ctx, big.NewInt(int64(*blockNrOrHash.BlockNumber)))

ethclient/lightclient/transactions.go

@@ -370,6 +370,7 @@ func (c *Client) sendTransaction(ctx context.Context, tx *types.Transaction) err
 	return c.TrackTransaction(tx)
 }
 
+// TrackTransaction adds a transaction to the set of tracked transactions.
 func (c *Client) TrackTransaction(tx *types.Transaction) error {
 	sender, err := types.Sender(c.signer, tx)
 	if err != nil {