grpc/grpc-go · error

received frame with size %v which is shorter than message ty

Error message

received frame with size %v which is shorter than message type field size %v

What it means

In conn.ReadOnReady (record.go:267-269), after a complete frame is parsed, the payload after the 4-byte length header must still contain the 4-byte message-type field (msgTypeFieldSize). If the declared frame length is so small that less than 4 bytes of payload remain, the frame is malformed and the connection errors. This is a defensive check on ALTS record framing.

Source

Thrown at credentials/alts/internal/conn/record.go:269

				}
				p.protectedHandle = newBuf
				protected = (*newBuf)[:nRead]
			} else {
				nRead, err := p.Conn.Read(protected[len(protected):cap(protected)])
				if err != nil {
					return nil, 0, err
				}
				protected = protected[:len(protected)+nRead]
			}
			framedMsg, p.nextFrame, err = ParseFramedMsg(protected, altsRecordLengthLimit)
			if err != nil {
				return nil, 0, err
			}
		}
		// Now we have a complete frame, decrypted it.
		msg := framedMsg[MsgLenFieldSize:]
		if len(msg) < msgTypeFieldSize {
			return nil, 0, fmt.Errorf("received frame with size %v which is shorter than message type field size %v", len(msg), msgTypeFieldSize)
		}
		msgType := binary.LittleEndian.Uint32(msg[:msgTypeFieldSize])
		if msgType&0xff != altsRecordMsgType {
			return nil, 0, fmt.Errorf("received frame with incorrect message type %v, expected lower byte %v",
				msgType, altsRecordMsgType)
		}
		ciphertext := msg[msgTypeFieldSize:]

		// Decrypt directly into the buffer, avoiding a copy from p.buf if
		// possible.
		if bufSize >= len(ciphertext) {
			allocatedBuf := pool.Get(bufSize)
			dec, err := p.crypto.Decrypt((*allocatedBuf)[:0], ciphertext)
			if err != nil {
				pool.Put(allocatedBuf)
				return nil, 0, err
			}
			p.dropProtectedIfEmtpy()

View on GitHub (pinned to 03255a9237)

Solutions

1. Ensure the peer implements ALTS record framing correctly (length covers >= msgTypeFieldSize).
2. Treat as connection-fatal: close the ALTS connection and reconnect.
3. In tests, build frames with at least MsgLenFieldSize+msgTypeFieldSize bytes.

Example fix

// before: test frame declares length 2
binary.LittleEndian.PutUint32(buf, 2)
// after: declare length >= 4 (msgTypeFieldSize)
binary.LittleEndian.PutUint32(buf, 4)

n, err := altsConn.Read(buf)
if err != nil {
    if strings.Contains(err.Error(), "shorter than message type field size") {
        log.Printf("malformed ALTS frame; closing connection")
        altsConn.Close()
    }
    return n, err
}

When it happens

Trigger: A peer (or corrupted stream) sends an ALTS record whose length header indicates a payload smaller than the 4-byte message-type sub-field — e.g. a frame length of 0–3. Encountered during conn.Read/ReadOnReady.

Common situations: A non-conformant or malicious peer; stream corruption; a fuzz test feeding truncated frames; an ALTS implementation bug producing zero-length records.

Related errors

• received the frame length %d larger than the limit %d
• received frame with incorrect message type %v, expected lowe
• no error details for status with code OK
• duplicated name
• wrr: errorUtilizationPenalty must be non-negative

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/f4b47a2af7096178. Report an issue: GitHub.