正确的惯用字节缓冲区读写

Question

I have a net/socket open. I need to read a structured protocol off the wire. Ie I have

messagelength|type|value|type|value ...

where messagelength is 4 bytes, type one byte, value depends on type,...

I am trying to work out the no-brainer way of doing this in go. I am swamped by io,bufio,encoding... I cant find the right place to start and cant find samples. Looking for ReadInt32, ReadByte,....

Next thing - i need to assemble a reply -> WriteInt32, WriteString, WriteByte,....

Trying to convert python to go, python code uses struct.unpack / pack

Answer 1

You can use the package encoding/binary. The only functions you will need are Read() and Write(). Here is how you use them:

The Read() function has the following signature:

func Read(r io.Reader, order ByteOrder, data interface{}) error

This function reads from r in order ByteOrder into data. data must be a pointer to a fixed-size value (e.g. an int32, a byte or a struct with only fixed size members) or a slice of such values. If you pass a pointer to a struct, struct fields are read in without padding, data corresponding for blank fields (i.e. those named _) is read and discarded (ideal for padding).

For your specific problem, declare a struct that matches the header of your data stream.

type Header struct {
    Length uint32
    Type   uint8
}

Consume the header of a packet (assume big endian):

var hdr Header
if err = Read(connection, binary.BigEndian, &hdr); err != nil {
    // deal with read error
}

Switch over the type byte:

switch hdr.Type {
// for each type, read into a type-specific struct
// ...
}

Write() is similar but writes instead of reading.