use context with http handlers

http-handler-with-context.go

package main

import (
	"io"
	"log"
	. "net/http"
	"time"

	"code.google.com/p/go-uuid/uuid"

	"golang.org/x/net/context"
)

type CtxHandlerFunc func(context.Context, ResponseWriter, *Request)

func duration(h CtxHandlerFunc) HandlerFunc {
	return func(w ResponseWriter, r *Request) {
		s := time.Now()
		var (
			ctx    context.Context
			cancel context.CancelFunc
		)
		ctx, cancel = context.WithTimeout(context.Background(), 100*time.Millisecond)
		defer cancel()
		h(ctx, w, r)
		log.Println("req server in ", time.Since(s))
	}

}

// middleware to mark request
func identify(h CtxHandlerFunc) CtxHandlerFunc {
	return func(ctx context.Context, w ResponseWriter, r *Request) {
		h(context.WithValue(ctx, "req_uuid", uuid.New()), w, r)
	}
}

func hello(ctx context.Context, w ResponseWriter, r *Request) {
	reqID := ctx.Value("req_uuid").(string)
	io.WriteString(w, "this is response to request id "+reqID+"\n")
}

func slow(ctx context.Context, w ResponseWriter, r *Request) {
	c := make(chan string, 1)
	// do it async
	go func() {
		time.Sleep(90 * time.Millisecond)
		reqID := ctx.Value("req_uuid").(string)
		c <- "this is response to request id " + reqID + "\n"

	}()
	// wait to finish or stop by timeout
	select {
	case res := <-c:
		io.WriteString(w, res)

	case <-ctx.Done():
		io.WriteString(w, "this response canceled by timeout")
	}

}

func main() {
	HandleFunc("/", duration(identify(hello)))
	HandleFunc("/slow", duration(identify(slow)))
	log.Fatalln(ListenAndServe(":8080", nil))
}