func()

in conn.go [990:1035]

• 32 lines of code
• 10 McCabe index (conditional complexity)

func (c *Conn) readProtoHeader() (protoHeader, error) {
	const protoHeaderSize = 8

	// only read from the network once our buffer has been exhausted.
	// TODO: this preserves existing behavior as some tests rely on this
	// implementation detail (it lets you replay a stream of bytes). we
	// might want to consider removing this and fixing the tests as the
	// protocol doesn't actually work this way.
	if c.rxBuf.Len() == 0 {
		for {
			err := c.rxBuf.ReadFromOnce(c.net)
			if err != nil {
				return protoHeader{}, err
			}

			// read more if buf doesn't contain enough to parse the header
			if c.rxBuf.Len() >= protoHeaderSize {
				break
			}
		}
	}

	buf, ok := c.rxBuf.Next(protoHeaderSize)
	if !ok {
		return protoHeader{}, errors.New("invalid protoHeader")
	}
	// bounds check hint to compiler; see golang.org/issue/14808
	_ = buf[protoHeaderSize-1]

	if !bytes.Equal(buf[:4], []byte{'A', 'M', 'Q', 'P'}) {
		return protoHeader{}, fmt.Errorf("unexpected protocol %q", buf[:4])
	}

	p := protoHeader{
		ProtoID:  protoID(buf[4]),
		Major:    buf[5],
		Minor:    buf[6],
		Revision: buf[7],
	}

	if p.Major != 1 || p.Minor != 0 || p.Revision != 0 {
		return protoHeader{}, fmt.Errorf("unexpected protocol version %d.%d.%d", p.Major, p.Minor, p.Revision)
	}

	return p, nil
}