A comment server written in Golang for the FB react.js tutorial

comment_server.go

// A comment server for the FB react.js tutorial at:
// https://facebook.github.io/react/docs/tutorial.html

package main

import (
	"encoding/json"
	"io/ioutil"
	"log"
	"net/http"
	"strings"
)

const max = 2048

var (
	commentsPut     = make(chan Comment)
	commentsGet     = make(chan *[max]Comment)
	count       int = 0
)

type Comment struct {
	Id     int    `json:"id"`
	Author string `json:"author"`
	Text   string `json:"text"`
}

func failOnError(err error, msg string) {
	if err != nil {
		log.Fatalf("%s: %s", msg, err)
	}
}

func initialize() {
	var err error
	var cs []Comment

	jsn, err := ioutil.ReadFile("./comments.json")
	failOnError(err, "Failed to read data file")
	err = json.Unmarshal(jsn, &cs)
	failOnError(err, "Failed to parse data from file")

	go commentsProcessor()

	for _, c := range cs {
		commentsPut <- c
	}
}

// commentsProcessor synchronizes access to the comments array.
//
// New comments to be stored come in via the commentsPut
// channel. Existing comments (pointer to the array) are made
// available on the commentsGet channel. Since both operations are
// wrapped in the same select, access to the comments array is
// synchronized.
func commentsProcessor() {
	var comments [max]Comment

	for {
		select {
		case c := <-commentsPut:
			if count < max {
				if c.Id == 0 {
					if count == 0 {
						c.Id = 0
					} else {
						c.Id = comments[count-1].Id + 1
					}
				}
				comments[count] = c
				count++
			}
		case commentsGet <- &comments:
		}
	}
}

func commentsHandler(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Access-Control-Allow-Origin", "*")
	w.Header().Set("Content-Type", "application/json; charset=utf-8")

	if strings.ToUpper(r.Method) == "POST" {
		newComment := Comment{
			Author: r.FormValue("author"),
			Text:   r.FormValue("text"),
		}
		commentsPut <- newComment
		w.WriteHeader(201)
	}

	// We fall through to here in case of POST, too (POST requests
	// expect a list of comments in return).
	cs := <-commentsGet
	jsn, err := json.Marshal(cs[:count])
	failOnError(err, "Error serializing comments")
	w.Write(jsn)
}

func main() {
	initialize()

	http.HandleFunc("/api/comments", commentsHandler)
	log.Fatal(http.ListenAndServe(":3000", nil))
}

/*
 * Local variables:
 * compile-command: "go run comment_server.go":
 * End:
 */