Golang server, how to receive TCP JSON packet?

Question

I'm new to Golang and am using the "Server" code here as a starting point: http://www.golang-book.com/13/index.htm#section7

I've attempted to use JSON instead of Gob decoding (since I am required to write the client in C#), and I'm sending the JSON TCP data client data in a separate script from the code below.

I'm stuck on the part where I'm actually receiving the JSON TCP data and storing it in a variable for it to be decoded. It looks like I can decode it with json.Unmarshal, but I can't find any examples where json.Unmarshal is being used to decode TCP data. I can only find examples where json.Unmarshal is being used to decode JSON strings.

My code is below:

package main

import (
  "encoding/json"
  "fmt"
  "net"
)

type coordinate struct {
  X float64 `json:"x"`
  Y float64 `json:"y"`
  Z float64 `json:"z"`
}

func server() {
  // listen on a port
  ln, err := net.Listen("tcp", ":9999")
  if err != nil {
    fmt.Println(err)
    return
  }
  for {
    // accept a connection
    c, err := ln.Accept()
    if err != nil {
      fmt.Println(err)
      continue
    }
    // handle the connection
    go handleServerConnection(c)
  }
}

func handleServerConnection(c net.Conn) {
  // receive the message
  var msg coordinate

Stuck on the line below. What could I set the rawJSON variable equal to?

  err := json.Unmarshal([]byte(rawJSON), &msg)
  if err != nil {
    fmt.Println(err)
  } else {
    fmt.Println("Received", msg)
  }

  c.Close()
}

func main() {
  go server()

  //let the server goroutine run forever
  var input string
  fmt.Scanln(&input)
}

Solution

You can patch a json.Decoder directly to the connection:

func handleServerConnection(c net.Conn) {

    // we create a decoder that reads directly from the socket
    d := json.NewDecoder(c)

    var msg coordinate

    err := d.Decode(&msg)
    fmt.Println(msg, err)

    c.Close()

}

Comments

[JimB]

Decoder can read multiple messages, in the same way that Encoder writes multiple messages. They use a simple newline delimiter between objects.

[Joseph Smitty]

This code/explanation helps me a lot, thank you. My goal is to create a client that sends coordinates in an online game to a Golang server, so I do need to send constant streams of data. I'll look into the EOF some more, thanks.

[Not_a_Golfer]

@jimb thanks, I wasn't aware of that. I'll change my answer when I'm not on my phone :)