requestcontext

Installation

Run "go get" pointing to a package.

$ go get github.com/goodfoo/requestcontext

Features

Package requestcontext is a contention free http.Request adapter for golang.org/x/net/context for Go.

Handy for passing request level context through middleware to your handlers, plus all the other context goodness.

Our team was frustrated by contention related performance issues with other context packages.

Motivated by Go context package and James Abley Gorilla Context pull request

Not limited to string -> string !

Use any comparable type as a key and any value type.

Leverage all the awesomeness of the golang.org/x/net/context using traditional http.Handler's

Usage

There are only two public functions, Get and Set

Always call Get() first. Get() returns the context or establishes a new chain if needed.

c := requestcontext.Get(r) assuming r is a valid *http.Request

Use or enhance the golang.org/x/net/context

v := c.Value(key)

c, cancelFunc := context.WithTimeout(c, 2 * duration.Second)
c = context.WithValue(c, key, value)

Set() it back to the request if enhanced

requestcontext.Set(r, c)

Example

package main

import (
	"fmt"
	"net/http"

	"github.com/codegangsta/negroni"
	"github.com/goodfoo/requestcontext"
	"golang.org/x/net/context"
)

// arbitrary value type
type blah struct {
	s    string
	rune rune
	out  int
}

// any comparable
var comparable = "key"

// MyMiddleware assigns a value into the request
// any number of middleware may be nested
// it could register a Cancel func(), a Timeout or Deadline
func MyMiddleware(rw http.ResponseWriter, r *http.Request, next http.HandlerFunc) {
	// arbitrary value type
	value := blah{
		"a☻☺b", '☺', 4,
	}

	// always Get the context, will be populated if needed
	parent := requestcontext.Get(r)

	// this could be any of the google context extensions
	// WithCancel, WithDeadline, WithTimeout,
	// or the ever popular WithValue
	c := context.WithValue(parent, comparable, value)

	// no contention here ever
	requestcontext.Set(r, c)

	// good luck little buddy
	next(rw, r)
}

func MyHandler(w http.ResponseWriter, r *http.Request) {
	// get the context - no contention here
	c := requestcontext.Get(r)

	// could call Deadline(), or Done() or Err()
	// call Value and convert the response to arbitrary type
	if b, ok := c.Value(comparable).(blah); ok {
		fmt.Fprintf(w, "Context value %s %c %d!", b.s, b.rune, b.out)
	}
}

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/", MyHandler)

	n := negroni.Classic()
	n.Use(negroni.HandlerFunc(MyMiddleware))
	n.UseHandler(mux)
	n.Run(":3000")
}