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elazarl
4.0K Stars 772 Forks BSD 3-Clause "New" or "Revised" License 293 Commits 159 Opened issues

Description

An HTTP proxy library for Go

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Introduction

GoDoc Join the chat at https://gitter.im/elazarl/goproxy Status

Package goproxy provides a customizable HTTP proxy library for Go (golang),

It supports regular HTTP proxy, HTTPS through CONNECT, and "hijacking" HTTPS connection using "Man in the Middle" style attack.

The intent of the proxy is to be usable with reasonable amount of traffic, yet customizable and programmable.

The proxy itself is simply a

net/http
handler.

In order to use goproxy, one should set their browser to use goproxy as an HTTP proxy. Here is how you do that in Chrome and in Firefox.

For example, the URL you should use as proxy when running

./bin/basic
is
localhost:8080
, as this is the default binding for the basic proxy.

Mailing List

New features will be discussed on the mailing list before their development.

Latest Stable Release

Get the latest goproxy from

gopkg.in/elazarl/goproxy.v1
.

Why not Fiddler2?

Fiddler is an excellent software with similar intent. However, Fiddler is not as customizable as goproxy intends to be. The main difference is, Fiddler is not intended to be used as a real proxy.

A possible use case that suits goproxy but not Fiddler, is gathering statistics on page load times for a certain website over a week. With goproxy you could ask all your users to set their proxy to a dedicated machine running a goproxy server. Fiddler is a GUI app not designed to be run like a server for multiple users.

A taste of goproxy

To get a taste of

goproxy
, a basic HTTP/HTTPS transparent proxy
package main

import ( "github.com/elazarl/goproxy" "log" "net/http" )

func main() { proxy := goproxy.NewProxyHttpServer() proxy.Verbose = true log.Fatal(http.ListenAndServe(":8080", proxy)) }

This line will add

X-GoProxy: yxorPoG-X
header to all requests sent through the proxy
proxy.OnRequest().DoFunc(
    func(r *http.Request,ctx *goproxy.ProxyCtx)(*http.Request,*http.Response) {
        r.Header.Set("X-GoProxy","yxorPoG-X")
        return r,nil
    })

DoFunc
will process all incoming requests to the proxy. It will add a header to the request and return it. The proxy will send the modified request.

Note that we returned nil value as the response. Had we returned a response, goproxy would have discarded the request and sent the new response to the client.

In order to refuse connections to reddit at work time

proxy.OnRequest(goproxy.DstHostIs("www.reddit.com")).DoFunc(
    func(r *http.Request,ctx *goproxy.ProxyCtx)(*http.Request,*http.Response) {
        if h,_,_ := time.Now().Clock(); h >= 8 && h <= 17 {
            return r,goproxy.NewResponse(r,
                    goproxy.ContentTypeText,http.StatusForbidden,
                    "Don't waste your time!")
        }
        return r,nil
})

DstHostIs
returns a
ReqCondition
, that is a function receiving a
Request
and returning a boolean. We will only process requests that match the condition.
DstHostIs("www.reddit.com")
will return a
ReqCondition
accepting only requests directed to "www.reddit.com".

DoFunc
will receive a function that will preprocess the request. We can change the request, or return a response. If the time is between 8:00am and 17:00pm, we will reject the request, and return a precanned text response saying "do not waste your time".

See additional examples in the examples directory.

Type of handlers for manipulating connect/req/resp behavior

There are 3 kinds of useful handlers to manipulate the behavior, as follows:

// handler called after receiving HTTP CONNECT from the client, and before proxy establish connection 
// with destination host
httpsHandlers   []HttpsHandler

// handler called before proxy send HTTP request to destination host reqHandlers []ReqHandler

// handler called after proxy receives HTTP Response from destination host, and before proxy forward // the Response to the client. respHandlers []RespHandler

Depending on what you want to manipulate, the ways to add handlers to each handler list are:

// Add handlers to httpsHandlers 
proxy.OnRequest(Some ReqConditions).HandleConnect(YourHandlerFunc())

// Add handlers to reqHandlers proxy.OnRequest(Some ReqConditions).Do(YourReqHandlerFunc())

// Add handlers to respHandlers proxy.OnResponse(Some RespConditions).Do(YourRespHandlerFunc())

For example:

// This rejects the HTTPS request to *.reddit.com during HTTP CONNECT phase
proxy.OnRequest(goproxy.ReqHostMatches(regexp.MustCompile("reddit.*:443$"))).HandleConnect(goproxy.RejectConnect)

// This will NOT reject the HTTPS request with URL ending with gif, due to the fact that proxy // only got the URL.Hostname and URL.Port during the HTTP CONNECT phase if the scheme is HTTPS, which is // quiet common these days. proxy.OnRequest(goproxy.UrlMatches(regexp.MustCompile(.*gif$))).HandleConnect(goproxy.RejectConnect)

// The correct way to manipulate the HTTP request using URL.Path as condition is: proxy.OnRequest(goproxy.UrlMatches(regexp.MustCompile(.*gif$))).Do(YourReqHandlerFunc())

What's New

  1. Ability to
    Hijack
    CONNECT requests. See the eavesdropper example
  2. Transparent proxy support for http/https including MITM certificate generation for TLS. See the transparent example.

License

I put the software temporarily under the Go-compatible BSD license. If this prevents someone from using the software, do let me know and I'll consider changing it.

At any rate, user feedback is very important for me, so I'll be delighted to know if you're using this package.

Beta Software

I've received positive feedback from a few people who use goproxy in production settings. I believe it is good enough for usage.

I'll try to keep reasonable backwards compatibility. In case of a major API change, I'll change the import path.

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