op-program: hints/oracle comms io style changes

Co-authored-by: Adrian Sutton <adrian@oplabs.co>

op-program/preimage/hints.go

@@ -20,8 +20,8 @@ func NewHintWriter(w io.Writer) *HintWriter {
 
 func (hw *HintWriter) Hint(v Hint) {
 	hint := v.Hint()
-	hintBytes := make([]byte, 4, 4+len(hint)+1)
-	binary.BigEndian.PutUint32(hintBytes[:4], uint32(len(hint)))
+	var hintBytes []byte
+	hintBytes = binary.BigEndian.AppendUint32(hintBytes, uint32(len(hint)))
 	hintBytes = append(hintBytes, []byte(hint)...)
 	hintBytes = append(hintBytes, 0) // to block writing on
 	_, err := hw.w.Write(hintBytes)
@@ -41,14 +41,13 @@ func NewHintReader(r io.Reader) *HintReader {
 }
 
 func (hr *HintReader) NextHint(router func(hint string) error) error {
-	var lengthPrefix [4]byte
-	if _, err := io.ReadFull(hr.r, lengthPrefix[:]); err != nil {
+	var length uint32
+	if err := binary.Read(hr.r, binary.BigEndian, &length); err != nil {
 		if err == io.EOF {
 			return io.EOF
 		}
 		return fmt.Errorf("failed to read hint length prefix: %w", err)
 	}
-	length := binary.BigEndian.Uint32(lengthPrefix[:])
 	payload := make([]byte, length)
 	if length > 0 {
 		if _, err := io.ReadFull(hr.r, payload); err != nil {

op-program/preimage/oracle.go

@@ -26,15 +26,10 @@ func (o *OracleClient) Get(key Key) []byte {
 		panic(fmt.Errorf("failed to write key %s (%T) to pre-image oracle: %w", key, key, err))
 	}
 
-	var lengthPrefix [8]byte
-	if _, err := io.ReadFull(o.rw, lengthPrefix[:]); err != nil {
+	var length uint64
+	if err := binary.Read(o.rw, binary.BigEndian, &length); err != nil {
 		panic(fmt.Errorf("failed to read pre-image length of key %s (%T) from pre-image oracle: %w", key, key, err))
 	}
-
-	length := binary.BigEndian.Uint64(lengthPrefix[:])
-	if length == 0 { // don't read empty payloads
-		return nil
-	}
 	payload := make([]byte, length)
 	if _, err := io.ReadFull(o.rw, payload); err != nil {
 		panic(fmt.Errorf("failed to read pre-image payload (length %d) of key %s (%T) from pre-image oracle: %w", length, key, key, err))
@@ -65,10 +60,8 @@ func (o *OracleServer) NextPreimageRequest(getPreimage func(key common.Hash) ([]
 		return fmt.Errorf("failed to serve pre-image %s request: %w", key, err)
 	}
 
-	var lengthPrefix [8]byte
-	binary.BigEndian.PutUint64(lengthPrefix[:], uint64(len(value)))
-	if _, err := o.rw.Write(lengthPrefix[:]); err != nil {
-		return fmt.Errorf("failed to write length-prefix %x: %w", lengthPrefix, err)
+	if err := binary.Write(o.rw, binary.BigEndian, uint64(len(value))); err != nil {
+		return fmt.Errorf("failed to write length-prefix %d: %w", len(value), err)
 	}
 	if len(value) == 0 {
 		return nil