Go HTTP proxy server library

go get -u github.com/go-httpproxy/httpproxy
# or
go get -u gopkg.in/httpproxy.v1

// Proxy defines parameters for running an HTTP Proxy. It implements
// http.Handler interface for ListenAndServe function. If you need, you must
// set Proxy struct before handling requests.
type Proxy struct {
	// Session number of last proxy request.
	SessionNo int64

	// RoundTripper interface to obtain remote response.
	// By default, it uses &http.Transport{}.
	Rt http.RoundTripper

	// Certificate key pair.
	Ca tls.Certificate

	// User data to use free.
	UserData interface{}

	// Error callback.
	OnError func(ctx *Context, where string, err *Error, opErr error)

	// Accept callback. It greets proxy request like ServeHTTP function of
	// http.Handler.
	// If it returns true, stops processing proxy request.
	OnAccept func(ctx *Context, w http.ResponseWriter, r *http.Request) bool

	// Auth callback. If you need authentication, set this callback.
	// If it returns true, authentication succeeded.
	OnAuth func(ctx *Context, authType string, user string, pass string) bool

	// Connect callback. It sets connect action and new host.
	// If len(newhost) > 0, host changes.
	OnConnect func(ctx *Context, host string) (ConnectAction ConnectAction,
		newHost string)

	// Request callback. It greets remote request.
	// If it returns non-nil response, stops processing remote request.
	OnRequest func(ctx *Context, req *http.Request) (resp *http.Response)

	// Response callback. It greets remote response.
	// Remote response sends after this callback.
	OnResponse func(ctx *Context, req *http.Request, resp *http.Response)

	// If ConnectAction is ConnectMitm, it sets chunked to Transfer-Encoding.
	// By default, true.
	MitmChunked bool

	// HTTP Authentication type. If it's not specified (""), uses "Basic".
	// By default, "".
	AuthType string
}

// Context keeps context of each proxy request.
type Context struct {
	// Pointer of Proxy struct handled this context.
	// It's using internally. Don't change in Context struct!
	Prx *Proxy

	// Session number of this context obtained from Proxy struct.
	SessionNo int64

	// Sub session number of processing remote connection.
	SubSessionNo int64

	// Original Proxy request.
	// It's using internally. Don't change in Context struct!
	Req *http.Request

	// Original Proxy request, if proxy request method is CONNECT.
	// It's using internally. Don't change in Context struct!
	ConnectReq *http.Request

	// Action of after the CONNECT, if proxy request method is CONNECT.
	// It's using internally. Don't change in Context struct!
	ConnectAction ConnectAction

	// Remote host, if proxy request method is CONNECT.
	// It's using internally. Don't change in Context struct!
	ConnectHost string

	// User data to use free.
	UserData interface{}
}

package main

import (
	"log"
	"net/http"

	"github.com/go-httpproxy/httpproxy"
)

func OnError(ctx *httpproxy.Context, where string,
	err *httpproxy.Error, opErr error) {
	// Log errors.
	log.Printf("ERR: %s: %s [%s]", where, err, opErr)
}

func OnAccept(ctx *httpproxy.Context, w http.ResponseWriter,
	r *http.Request) bool {
	// Handle local request has path "/info"
	if r.Method == "GET" && !r.URL.IsAbs() && r.URL.Path == "/info" {
		w.Write([]byte("This is go-httpproxy."))
		return true
	}
	return false
}

func OnAuth(ctx *httpproxy.Context, authType string, user string, pass string) bool {
	// Auth test user.
	if user == "test" && pass == "1234" {
		return true
	}
	return false
}

func OnConnect(ctx *httpproxy.Context, host string) (
	ConnectAction httpproxy.ConnectAction, newHost string) {
	// Apply "Man in the Middle" to all ssl connections. Never change host.
	return httpproxy.ConnectMitm, host
}

func OnRequest(ctx *httpproxy.Context, req *http.Request) (
	resp *http.Response) {
	// Log proxying requests.
	log.Printf("INFO: Proxy: %s %s", req.Method, req.URL.String())
	return
}

func OnResponse(ctx *httpproxy.Context, req *http.Request,
	resp *http.Response) {
	// Add header "Via: go-httpproxy".
	resp.Header.Add("Via", "go-httpproxy")
}

func main() {
	// Create a new proxy with default certificate pair.
	prx, _ := httpproxy.NewProxy()

	// Set handlers.
	prx.OnError = OnError
	prx.OnAccept = OnAccept
	prx.OnAuth = OnAuth
	prx.OnConnect = OnConnect
	prx.OnRequest = OnRequest
	prx.OnResponse = OnResponse

	// Listen...
	http.ListenAndServe(":8080", prx)
}