Function ReadFrame

agent/boundarylogproxy/codec/codec.go:96–133

ReadFrame reads a framed message, returning the decoded tag and data. If the message size exceeds MaxMessageSizeV1, ErrMessageTooLarge is returned. The provided buf is used if it has sufficient capacity; otherwise a new buffer is allocated. To reuse the buffer across calls, pass in the returned data

(r io.Reader, buf []byte)

//	    _, buf, _ = ReadFrame(r, buf)
//	}
func ReadFrame(r io.Reader, buf []byte) (Tag, []byte, error) {
	var header uint32
	if err := binary.Read(r, binary.BigEndian, &header); err != nil {
		return 0, nil, xerrors.Errorf("read header error: %w", err)
	}

	const lengthMask = (1 << DataLength) - 1
	length := header & lengthMask
	const tagMask = (1 << tagLength) - 1 // 0xFF
	shifted := (header >> DataLength) & tagMask
	if shifted > tagMask {
		// This is really only here to satisfy the gosec linter. We know from above that
		// shifted <= tagMask.
		return 0, nil, xerrors.Errorf("invalid tag: %d", shifted)
	}
	tag := Tag(shifted)

	maxSize, err := maxSizeForTag(tag)
	if err != nil {
		return 0, nil, err
	}

	if length > maxSize {
		return 0, nil, ErrMessageTooLarge
	}

	if cap(buf) < int(length) {
		buf = make([]byte, length)
	} else {
		buf = buf[:length:cap(buf)]
	}

	if _, err := io.ReadFull(r, buf[:length]); err != nil {
		return 0, nil, xerrors.Errorf("read full error: %w", err)
	}

	return tag, buf[:length], nil
}

// maxSizeForTag returns the maximum payload size for the given tag.
func maxSizeForTag(tag Tag) (uint32, error) {