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github.com/elazarl/goproxy

Taken from $GOROOT/src/pkg/net/http/chunked needed to write https responses to client. Package goproxy provides a customizable HTTP proxy, supporting hijacking HTTPS connection. The intent of the proxy, is to be usable with reasonable amount of traffic yet, customizable and programmable. The proxy itself is simply an `net/http` handler. Typical usage is Adding a header to each request For printing the content type of all incoming responses note that we used the ProxyCtx context variable here. It contains the request and the response (Req and Resp, Resp is nil if unavailable) of this specific client interaction with the proxy. To print the content type of all responses from a certain url, we'll add a ReqCondition to the OnResponse function: We can write the condition ourselves, conditions can be set on request and on response Caution! If you give a RespCondition to the OnRequest function, you'll get a run time panic! It doesn't make sense to read the response, if you still haven't got it! Finally, we have convenience function to throw a quick response we close the body of the original response, and return a new 403 response with a short message. Example use cases: 1. https://github.com/elazarl/goproxy/tree/master/examples/goproxy-avgsize To measure the average size of an Html served in your site. One can ask all the QA team to access the website by a proxy, and the proxy will measure the average size of all text/html responses from your host. 2. [not yet implemented] All requests to your web servers should be directed through the proxy, when the proxy will detect html pieces sent as a response to AJAX request, it'll send a warning email. 3. https://github.com/elazarl/goproxy/blob/master/examples/goproxy-httpdump/ Generate a real traffic to your website by real users using through proxy. Record the traffic, and try it again for more real load testing. 4. https://github.com/elazarl/goproxy/tree/master/examples/goproxy-no-reddit-at-worktime Will allow browsing to reddit.com between 8:00am and 17:00pm 5. https://github.com/elazarl/goproxy/tree/master/examples/goproxy-jquery-version Will warn if multiple versions of jquery are used in the same domain. 6. https://github.com/elazarl/goproxy/blob/master/examples/goproxy-upside-down-ternet/ Modifies image files in an HTTP response via goproxy's image extension found in ext/.

    v0.0.0-20231117061959-7cc037d33fb5

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# Introduction

[![GoDoc](https://godoc.org/github.com/elazarl/goproxy?status.svg)](https://godoc.org/github.com/elazarl/goproxy)
[![Join the chat at https://gitter.im/elazarl/goproxy](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/elazarl/goproxy?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
![Status](https://github.com/elazarl/goproxy/workflows/Go/badge.svg)

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](https://support.google.com/chrome/answer/96815?hl=en)
and [in Firefox](http://www.wikihow.com/Enter-Proxy-Settings-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](https://groups.google.com/forum/#!forum/goproxy-dev)
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

```go
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

```go
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

```go
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 pre-canned 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:

```go
// 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:

```go
// 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:

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

// 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.AlwaysReject)

// 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](https://github.com/elazarl/goproxy/blob/master/examples/goproxy-eavesdropper/main.go#L27)
2. Transparent proxy support for http/https including MITM certificate generation for TLS.  See the [transparent example.](https://github.com/elazarl/goproxy/tree/master/examples/goproxy-transparent)

# 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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Last updated on 17 Nov 2023

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