Go中读取整体网络PDU的方法

Question

I am developing a simple Go server program which receives client's request and process it. And the code is simplified as this:

package main

import (
    "fmt"
    "net"
    "os"
)

const (
    pduLen = 32
)

func checkError(err error) {
    if err != nil {
        fmt.Println(err)
        os.Exit(1)
    }
}

func main() {
    var buffer [4096]byte
    var count int

    conn, err := net.Dial("tcp", fmt.Sprintf("%s:%s", os.Args[1], os.Args[2]))
    checkError(err)

    for count < pduLen {
        n, err := conn.Read(buffer[count:])
        checkError(err)
        count += n
    }
    ......

}

I assume every request's length is 32 bytes (just an example). Because the TCP is a stream protocol, I need to use a loop to check whether an integral PDU is read:

for count < pduLen {
    n, err := conn.Read(buffer[count:])
    checkError(err)
    count += n
}

Is there any method to assure that an integral PDU is read? Personally, I think the loop code is a little ugly.

Answer 1

It can depend on the exact nature of the PDU you are receiving, but this example will look for the size, and then read everything (using io.ReadFul()).

func read(conn net.Conn, key string) string {
  fmt.Fprintf(conn, GenerateCommand(OP_GET, key))
  if verify(conn) {
    var size uint16
    binary.Read(conn, binary.LittleEndian, &size)
    b := make([]byte, size)
    // _, err := conn.Read(b)
    _, err := io.ReadFull(conn, b)
    if err == nil {
      return string(b)
    }
  }
  return ""
}

func verify(conn net.Conn) bool {
  b := make([]byte, 1)
  conn.Read(b)
  return b[0] == ERR_NO_ERROR
}

Used in:

conn, err := net.Dial("tcp", ":12345")
if err != nil {
  t.Error(err)
}
write(conn, "foo", "bar")
if !verify(conn) {
  t.Error("Bad write!")
}
if r := read(conn, "foo"); r != "bar" {
  t.Errorf("Bad read! Got %v", r)
}