Ensure WAL payload is less than max uint32

wal/record.go

@@ -10,17 +10,25 @@ import (
 	"fmt"
 	"hash/crc64"
 	"io"
+	"math"
 )
 
 const (
 	recordSizeLen     = 4
 	recordChecksumLen = 8
 )
 
-var ErrInvalidCRC = errors.New("invalid CRC checksum")
+var (
+	ErrInvalidCRC      = errors.New("invalid CRC checksum")
+	ErrPayloadTooLarge = errors.New("payload too large for record length field")
+)
 
 // writeRecord writes a length-prefixed and check-summed record to the writer.
 func writeRecord(w io.Writer, payload []byte) error {
+	if uint64(len(payload)) > math.MaxUint32 {
+		return fmt.Errorf("%w: %d bytes", ErrPayloadTooLarge, len(payload))
+	}
+
 	checksumIndex := recordSizeLen + len(payload)
 	buff := make([]byte, checksumIndex+recordChecksumLen)
 	crc := crc64.New(crc64.MakeTable(crc64.ECMA))

wal/record_test.go

@@ -29,6 +29,16 @@ func TestWriteRecord(t *testing.T) {
 	)
 }
 
+// TestWriteRecordRejectsOversizedPayload ensures a payload whose length does not fit in the
+// 32 bit length field is rejected before anything is written.
+func TestWriteRecordRejectsOversizedPayload(t *testing.T) {
+	payload := make([]byte, math.MaxUint32+1)
+
+	var buff bytes.Buffer
+	require.ErrorIs(t, writeRecord(&buff, payload), ErrPayloadTooLarge)
+	require.Zero(t, buff.Len())
+}
+
 func TestReadRecord(t *testing.T) {
 	require := require.New(t)