[Golang] JSONP Server Implementation Code
My previous posts [4] shows how to use JSONP in front-end to request data from a server in different domain. In this post, we will show how to implement the back-end server that returns data (HTTP request headers) with Go programming language.
You need to have some basic knowledge about writing web applications in Go. Please refer to [2] if you have no idea about Go web applications.
The basic idea of JSONP server is as follows:
- Get the name of front-end callback function from the query string in HTTP request.
- Encode the data to be returned to the client in JSON format. In this case, it's the HTTP headers encoded in JSON.
- Set the Content-Type as application/javascript in HTTP response.
- return the string callbackName(JSONString); to the client, where callbackName is the name of callback in query string, and JSONString is the JSON-encoded data in step 2.
The complete implementation in Go is as follows:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 | package main
import (
"encoding/json"
"fmt"
"net/http"
)
func handler(w http.ResponseWriter, r *http.Request) {
fmt.Fprintf(w, indexHtml)
}
func jsonpHandler(w http.ResponseWriter, r *http.Request) {
callbackName := r.URL.Query().Get("callback")
if callbackName == "" {
fmt.Fprintf(w, "Please give callback name in query string")
return
}
b, err := json.Marshal(r.Header)
if err != nil {
fmt.Fprintf(w, "json encode error")
return
}
w.Header().Set("Content-Type", "application/javascript")
// return `callbackName(jsonString);`
fmt.Fprintf(w, "%s(%s);", callbackName, b)
}
func main() {
http.HandleFunc("/jsonp", jsonpHandler)
http.HandleFunc("/", handler)
http.ListenAndServe(":8000", nil)
}
|
The front-end code for this JSONP server is as follows:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | package main
const indexHtml = `<!DOCTYPE html>
<html>
<head><title>Go JSONP Server</title></head>
<body>
<button id="btn">Click to get HTTP header via JSONP</button>
<pre id="result"></pre>
<script>
'use strict';
var btn = document.getElementById("btn");
var result = document.getElementById("result");
function myCallback(acptlang) {
result.innerHTML = JSON.stringify(acptlang, null, 2);
}
function jsonp() {
result.innerHTML = "Loading ...";
var tag = document.createElement("script");
tag.src = "/jsonp?callback=myCallback";
document.querySelector("head").appendChild(tag);
}
btn.addEventListener("click", jsonp);
</script>
</body>
</html>`
|
Tested on:
- Ubuntu Linux 16.10
- Go 1.8
- Chromium Version 56.0.2924.76 Built on Ubuntu , running on Ubuntu 16.10 (64-bit)
References:
| [1] |
| [2] |
| [3] | JSON and Go - The Go Blog |
| [4] |