accounts/abi/bind: handle UnpackLog with zero topics (ethereum#26920)

Adds error handling for the case that UnpackLog or UnpackLogIntoMap is called with a log that has zero topics.

---------

Co-authored-by: Sina Mahmoodi <itz.s1na@gmail.com>

Author: aaronbuchwald

accounts/abi/bind/base.go

@@ -34,6 +34,11 @@ import (
 
 const basefeeWiggleMultiplier = 2
 
+var (
+	errNoEventSignature       = errors.New("no event signature")
+	errEventSignatureMismatch = errors.New("event signature mismatch")
+)
+
 // SignerFn is a signer function callback when a contract requires a method to
 // sign the transaction before submission.
 type SignerFn func(common.Address, *types.Transaction) (*types.Transaction, error)
@@ -488,8 +493,12 @@ func (c *BoundContract) WatchLogs(opts *WatchOpts, name string, query ...[]inter
 
 // UnpackLog unpacks a retrieved log into the provided output structure.
 func (c *BoundContract) UnpackLog(out interface{}, event string, log types.Log) error {
+	// Anonymous events are not supported.
+	if len(log.Topics) == 0 {
+		return errNoEventSignature
+	}
 	if log.Topics[0] != c.abi.Events[event].ID {
-		return fmt.Errorf("event signature mismatch")
+		return errEventSignatureMismatch
 	}
 	if len(log.Data) > 0 {
 		if err := c.abi.UnpackIntoInterface(out, event, log.Data); err != nil {
@@ -507,8 +516,12 @@ func (c *BoundContract) UnpackLog(out interface{}, event string, log types.Log)
 
 // UnpackLogIntoMap unpacks a retrieved log into the provided map.
 func (c *BoundContract) UnpackLogIntoMap(out map[string]interface{}, event string, log types.Log) error {
+	// Anonymous events are not supported.
+	if len(log.Topics) == 0 {
+		return errNoEventSignature
+	}
 	if log.Topics[0] != c.abi.Events[event].ID {
-		return fmt.Errorf("event signature mismatch")
+		return errEventSignatureMismatch
 	}
 	if len(log.Data) > 0 {
 		if err := c.abi.UnpackIntoMap(out, event, log.Data); err != nil {

accounts/abi/bind/base_test.go

@@ -186,6 +186,23 @@ func TestUnpackIndexedStringTyLogIntoMap(t *testing.T) {
 	unpackAndCheck(t, bc, expectedReceivedMap, mockLog)
 }
 
+func TestUnpackAnonymousLogIntoMap(t *testing.T) {
+	mockLog := newMockLog(nil, common.HexToHash("0x0"))
+
+	abiString := `[{"anonymous":false,"inputs":[{"indexed":false,"name":"amount","type":"uint256"}],"name":"received","type":"event"}]`
+	parsedAbi, _ := abi.JSON(strings.NewReader(abiString))
+	bc := bind.NewBoundContract(common.HexToAddress("0x0"), parsedAbi, nil, nil, nil)
+
+	var received map[string]interface{}
+	err := bc.UnpackLogIntoMap(received, "received", mockLog)
+	if err == nil {
+		t.Error("unpacking anonymous event is not supported")
+	}
+	if err.Error() != "no event signature" {
+		t.Errorf("expected error 'no event signature', got '%s'", err)
+	}
+}
+
 func TestUnpackIndexedSliceTyLogIntoMap(t *testing.T) {
 	sliceBytes, err := rlp.EncodeToBytes([]string{"name1", "name2", "name3", "name4"})
 	if err != nil {