Add comment about Iter

Signed-off-by: Matt Lord <[email protected]>

go/mysql/binlog_event_compression.go

@@ -212,7 +212,8 @@ func (tp *TransactionPayload) decode() error {
 	if decompressedFile != nil {
 		fstat, err := decompressedFile.Stat()
 		if err != nil {
-			return vterrors.New(vtrpcpb.Code_INTERNAL, fmt.Sprintf("error getting stats on temporary file used to store uncompressed transaction payload: %v", err))
+			return vterrors.New(vtrpcpb.Code_INTERNAL, fmt.Sprintf("error getting stats on temporary file %s used to store the uncompressed transaction payload: %v",
+				decompressedFile.Name(), err))
 		}
 		log.Errorf("DEBUG: Decompressed transaction payload to temporary file %s of size %d MiB", decompressedFile.Name(), fstat.Size()/1024/1024)
 		// Read from the temporary file.
@@ -238,7 +239,7 @@ func (tp *TransactionPayload) decode() error {
 			eventData := make([]byte, eventLen)
 			// The event includes the header, so we move back to the start of the event.
 			if _, err := decompressedFile.Seek(-headerLen, 1); err != nil {
-				return nil, vterrors.Wrapf(err, "error seeking to the beginning of the event in the %s file", decompressedFile.Name())
+				return nil, vterrors.Wrapf(err, "error seeking to the beginning of the %s file", decompressedFile.Name())
 			}
 			i, err = decompressedFile.Read(eventData)
 			if err != nil && err != io.EOF {
@@ -296,7 +297,7 @@ func (tp *TransactionPayload) decompress() ([]byte, *os.File, error) {
 			return nil, nil, vterrors.New(vtrpcpb.Code_INTERNAL, fmt.Sprintf("error creating temporary file to store uncompressed transaction payload: %v", err))
 		}
 		// Delete the file path on the FS. It will then be fully removed when we
-		// close our open file descriptor.
+		// close our open file descriptor after trying to read it in decode().
 		defer os.Remove(tmpFile.Name())
 		in := bytes.NewReader(tp.payload)
 		streamDecoder, err := zstd.NewReader(in)
@@ -319,9 +320,19 @@ func (tp *TransactionPayload) decompress() ([]byte, *os.File, error) {
 	}
 
 	if uint64(len(decompressedBytes)) != tp.uncompressedSize {
-		return []byte{}, nil, vterrors.New(vtrpcpb.Code_INVALID_ARGUMENT,
+		return nil, nil, vterrors.New(vtrpcpb.Code_INVALID_ARGUMENT,
 			fmt.Sprintf("decompressed size %d does not match expected size %d", len(decompressedBytes), tp.uncompressedSize))
 	}
 
 	return decompressedBytes, nil, nil
 }
+
+// Events returns an iterator over the internal binlog events that
+// were contained within the compressed transaction payload/event.
+// It returns a single-use iterator.
+// TODO: come back to this when main is on go 1.23. See:
+// - https://tip.golang.org/wiki/RangefuncExperiment
+// - https://github.com/golang/go/blob/release-branch.go1.23/src/iter/iter.go
+//func (tp *TransactionPayload) Events() iter.Seq[BinlogEvent] {
+//	return tp.iterator
+//}