How to create an HTTP Proxy?

Questions / Help
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1

Which library / approach would be advisable for building an MITM-style HTTP(s) Proxy, i.e. for intercepting outgoing web traffic? Effectively inspect (and do side effects) based on outgoing traffic.

I found GitHub - houli/http-proxy: A HTTP(S) Proxy written in Elixir (9 years old, work in progress) and GitHub - KazuCocoa/http_proxy: http proxy with Elixir. wait request with multi port and forward to each URIs, but there’s no real getting-started sample. Given that a proxy isn’t just a regular web server, I’m not sure this thing can easily be plugged into a web server like Cowboy/Bandit/Phoenix…

Thanks, Christian

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How so? The requirements may widely wary, however I can see how you could have a combination of phoenix and a http client.

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do you know https://github.com/tallarium/reverse_proxy_plug?
we use it for “shielding” an old website and injecting css into the page

kind regards, robert

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Not sure if this is helpful, but I use this service a lot for finding Elixir packages:

https://elixir-toolbox.dev/packages/search?query=proxy

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Thanks @sorax . I had a look at that, but it seems targeted as “reverse proxy”, like NGINX, right? That looked like a component I can put in front of my web server application, and route incoming requests different ways, like an API Gateway.

I’m looking for a component used by a web browser, before going out to the Internet. Is reverse_proxy_plug usable for that, too? The proxy protocol looks slightly different than HTTP

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Fully agree that I want the proxy server to run on a solid foundation (like Phoenix). The thing that’s unclear is how to host a component that talks the proxy protocol to the client, instead of plain HTTP.

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Thanks for the link, wasn’t aware of the search capabilities of elixir-toolbox.dev… However, as far as I can see, all these are either proxies for special protocols (SIP, Kafka, Telegram MProto) or are ‘reverse proxies’ (like nginx).

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I guess the confusion is reverse_proxy_plug could be considered a forward proxy given that it would be used to access an external website. However, it can still be considered a “reverse proxy” between the user & the elixir server.

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It sounds like you’re looking for an http server that supports the CONNECT protocol, such as the standalone app squid.

I haven’t personally seen any Erlang or Elixir http servers that have explicit documented support of HTTP CONNECT for proxying, but cowboy does appear to support enable_connect_protocol for Websockets on HTTP2. Might take a bit of experimentation with cowboy’s configuration to determine if it suits your need.