mitmproxy-node

Node bindings for mitmproxy. Based on https://github.com/jvilk/mitmproxy-node (v2.1.2).

Why?

It is far easier to rewrite JavaScript/HTML/etc using JavaScript than Python, but mitmproxy only accepts Python plugins. There are no decent alternatives to mitmproxy, so this package lets me use mitmproxy with Node.js-based rewriting code.

What can I use this for?

For transparently rewriting HTTP/HTTPS responses. The mitmproxy plugin lets every HTTP request go through to the server uninhibited, and then passes it to Node.js via a WebSocket for rewriting. You can optionally specify a list of paths that should be directly intercepted without being passed to the server.

How does it work?

A Python plugin for mitmproxy starts a WebSocket server, and mitmproxy-node talks with it over WebSocket messages. The two communicate via binary messages to reduce marshaling-related overhead.

Using

You can either start mitmproxy manually with mitmdump --anticache -s scripts/proxy.py, or mitmproxy-node will do so automatically for you. mitmproxy-node auto-detects if mitmproxy is already running. If you frequently start/stop the proxy, it may be best to start it manually.

import MITMProxy from '@oxygenhq/mitmproxy-node';

// Returns Promise<MITMProxy>
async function makeProxy() {
  // Note: Your interceptor can also be asynchronous and return a Promise!
  return MITMProxy.Create(function(interceptedMsg) {
    const req = interceptedMsg.request;
    const res = interceptedMsg.response;
    if (req.rawUrl.contains("target.js") && res.getHeader('content-type').indexOf("javascript") !== -1) {
      interceptedMsg.setResponseBody(Buffer.from(`Hacked!`, 'utf8'));
    }
  }, ['/eval'] /* list of paths to directly intercept -- don't send to server */,
  true /* Be quiet; turn off for debug messages */,
  true /* Only intercept text or potentially-text requests (all mime types with *application* and *text* in them, plus responses with no mime type) */
  );
}

async function main() {
  const proxy = await makeProxy();
  // when done:
  await proxy.shutdown();
}

Without fancy async/await:

import MITMProxy from '@oxygenhq/mitmproxy-node';

// Returns Promise<MITMProxy>
function makeProxy() {
  return MITMProxy.Create(function(interceptedMsg) {
    const req = interceptedMsg.request;
    const res = interceptedMsg.response;
    if (req.rawUrl.contains("target.js") && res.getHeader('content-type').indexOf("javascript") !== -1) {
      interceptedMsg.setResponseBody(Buffer.from(`Hacked!`, 'utf8'));
    }
  }, ['/eval'], true, true);
}

function main() {
  makeProxy().then((proxy) => {
    // when done
    proxy.shutdown.then(() => {
      // Proxy is closed!
    });
  });
}