HTTP MITM Proxy

HTTP Man In The Middle (MITM) Proxy written in node.js. Supports capturing and modifying the request and response data.

Install

npm install --save http-mitm-proxy

Node.js Compatibility

The library should work starting Node.js 8.x, but testing is only expected for currently supported LTS versions of Node.js starting Node.js 12.x . use on your own risk with non LTS Node.js versions.

Typescript

type definitions are now included in this project, no extra steps required.

Example

This example will modify any search results coming from google and replace all the result titles with "Pwned!".

const Proxy = require('http-mitm-proxy').Proxy;
// or using import/module (package.json -> "type": "module")
// import { Proxy } from "http-mitm-proxy";
const proxy = new Proxy();

proxy.onError(function(ctx, err) {
  console.error('proxy error:', err);
});

proxy.onRequest(function(ctx, callback) {
  if (ctx.clientToProxyRequest.headers.host == 'www.google.com'
    && ctx.clientToProxyRequest.url.indexOf('/search') == 0) {
    ctx.use(Proxy.gunzip);

    ctx.onResponseData(function(ctx, chunk, callback) {
      chunk = Buffer.from(chunk.toString().replace(/<h3.*?<\/h3>/g, '<h3>Pwned!</h3>'));
      return callback(null, chunk);
    });
  }
  return callback();
});

console.log('begin listening on 8081')
proxy.listen({port: 8081});

You can find more examples in the examples directory

SSL

Using node-forge allows the automatic generation of SSL certificates within the proxy. After running your app you will find options.sslCaDir + '/certs/ca.pem' which can be imported to your browser, phone, etc.

API

Proxy

• listen(options)
• close
• onError(fn)
• onCertificateRequired
• onCertificateMissing
• onRequest(fn)
• onRequestData(fn)
• onRequestEnd(fn)
• onResponse(fn)
• onResponseData(fn)
• onResponseEnd(fn)
• onWebSocketConnection(fn)
• onWebSocketSend(fn)
• onWebSocketMessage(fn)
• onWebSocketFrame(fn)
• onWebSocketError(fn)
• onWebSocketClose(fn)
• use(fn)

Context

Context functions only effect the current request/response. For example you may only want to gunzip requests made to a particular host.

• isSSL: boolean,
• clientToProxyRequest: IncomingMessage,
• proxyToClientResponse: ServerResponse,
• proxyToServerRequest: ClientRequest,
• serverToProxyResponse: IncomingMessage,
• onError(fn)
• onRequest(fn)
• onRequestData(fn)
• onRequestEnd(fn)
• addRequestFilter(fn)
• onResponse(fn)
• onResponseData(fn)
• onResponseEnd(fn)
• addResponseFilter(fn)
• use(mod)

WebSocket Context

The context available in websocket handlers is a bit different

• isSSL: boolean,
• clientToProxyWebSocket: WebSocket,
• proxyToServerWebSocket: WebSocket,
• onWebSocketConnection(fn)
• onWebSocketSend(fn)
• onWebSocketMessage(fn)
• onWebSocketFrame(fn)
• onWebSocketError(fn)
• onWebSocketClose(fn)
• use(mod)

Proxy

proxy.listen

Starts the proxy listening on the given port.

Arguments

• options - An object with the following options:
• port - The port or named socket to listen on (default: 8080).
• host - The hostname or local address to listen on (default: 'localhost'). Pass '::' to listen on all IPv4/IPv6 interfaces.
• sslCaDir - Path to the certificates cache directory (default: process.cwd() + '/.http-mitm-proxy')
• keepAlive - enable HTTP persistent connection
• timeout - The number of milliseconds of inactivity before a socket is presumed to have timed out. Defaults to no timeout.
• httpAgent - The http.Agent to use when making http requests. Useful for chaining proxys. (default: internal Agent)
• httpsAgent - The https.Agent to use when making https requests. Useful for chaining proxys. (default: internal Agent)
• forceSNI - force use of SNI by the client. Allow node-http-mitm-proxy to handle all HTTPS requests with a single internal server.
• httpsPort - The port or named socket for https server to listen on. (forceSNI must be enabled)
• forceChunkedRequest - Setting this option will remove the content-length from the proxy to server request, forcing chunked encoding.

Example

proxy.listen({ port: 80 });

proxy.close

Stops the proxy listening.

Example

proxy.close();

proxy.onError(fn) or ctx.onError(fn)

Adds a function to the list of functions to get called if an error occures.

Arguments

• fn(ctx, err, errorKind) - The function to be called on an error.

Example

proxy.onError(function(ctx, err, errorKind) {
  // ctx may be null
  var url = (ctx && ctx.clientToProxyRequest) ? ctx.clientToProxyRequest.url : "";
  console.error(errorKind + ' on ' + url + ':', err);
});

proxy.onCertificateRequired = function(hostname, callback)

Allows the default certificate name/path computation to be overwritten.

The default behavior expects keys/{hostname}.pem and certs/{hostname}.pem files to be at self.sslCaDir.

Arguments

• hostname - Requested hostname.
• callback - The function to be called when certificate files' path were already computed.

Example 1

proxy.onCertificateRequired = function(hostname, callback) {
  return callback(null, {
    keyFile: path.resolve('/ca/certs/', hostname + '.key'),
    certFile: path.resolve('/ca/certs/', hostname + '.crt')
  });
};

Example 2: Wilcard certificates

proxy.onCertificateRequired = function(hostname, callback) {
  return callback(null, {
    keyFile: path.resolve('/ca/certs/', hostname + '.key'),
    certFile: path.resolve('/ca/certs/', hostname + '.crt'),
    hosts: ["*.mydomain.com"]
  });
};

proxy.onCertificateMissing = function(ctx, files, callback)

Allows you to handle missing certificate files for current request, for example, creating them on the fly.

Arguments

• ctx - Context with the following properties
• hostname - The hostname which requires certificates
• data.keyFileExists - Whether key file exists or not
• data.certFileExists - Whether certificate file exists or not
• files - missing files names (files.keyFile, files.certFile and optional files.hosts)
• callback - The function to be called to pass certificate data back (keyFileData and certFileData)

Example 1

proxy.onCertificateMissing = function(ctx, files, callback) {
  console.log('Looking for "%s" certificates',   ctx.hostname);
  console.log('"%s" missing', ctx.files.keyFile);
  console.log('"%s" missing', ctx.files.certFile);

  // Here you have the last chance to provide certificate files data
  // A tipical use case would be creating them on the fly
  //
  // return callback(null, {
  //   keyFileData: keyFileData,
  //   certFileData: certFileData
  // });
  };

Example 2: Wilcard certificates

proxy.onCertificateMissing = function(ctx, files, callback) {
  return callback(null, {
    keyFileData: keyFileData,
    certFileData: certFileData,
    hosts: ["*.mydomain.com"]
  });
};

proxy.onRequest(fn) or ctx.onRequest(fn)

Adds a function to get called at the beginning of a request.

Arguments

• fn(ctx, callback) - The function that gets called on each request.

Example

proxy.onRequest(function(ctx, callback) {
  console.log('REQUEST:', ctx.clientToProxyRequest.url);
  return callback();
});

proxy.onRequestData(fn) or ctx.onRequestData(fn)

Adds a function to get called for each request data chunk (the body).

Arguments

• fn(ctx, chunk, callback) - The function that gets called for each data chunk.

Example

proxy.onRequestData(function(ctx, chunk, callback) {
  console.log('REQUEST DATA:', chunk.toString());
  return callback(null, chunk);
});

proxy.onRequestEnd(fn) or ctx.onRequestEnd(fn)

Adds a function to get called when all request data (the body) was sent.

Arguments

• fn(ctx, callback) - The function that gets called when all request data (the body) was sent.

Example

var chunks = [];

proxy.onRequestData(function(ctx, chunk, callback) {
  chunks.push(chunk);
  return callback(null, chunk);
});

proxy.onRequestEnd(function(ctx, callback) {
  console.log('REQUEST END', (Buffer.concat(chunks)).toString());
  return callback();
});

proxy.onResponse(fn) or ctx.onResponse(fn)

Adds a function to get called at the beginning of the response.

Arguments

• fn(ctx, callback) - The function that gets called on each response.

Example

proxy.onResponse(function(ctx, callback) {
  console.log('BEGIN RESPONSE');
  return callback();
});

proxy.onResponseData(fn) or ctx.onResponseData(fn)

Adds a function to get called for each response data chunk (the body).

Arguments

• fn(ctx, chunk, callback) - The function that gets called for each data chunk.

Example

proxy.onResponseData(function(ctx, chunk, callback) {
  console.log('RESPONSE DATA:', chunk.toString());
  return callback(null, chunk);
});

proxy.onResponseEnd(fn) or ctx.onResponseEnd(fn)

Adds a function to get called when the proxy request to server has ended.

Arguments

• fn(ctx, callback) - The function that gets called when the proxy request to server as ended.

Example

proxy.onResponseEnd(function(ctx, callback) {
  console.log('RESPONSE END');
  return callback();
});

proxy.onWebSocketConnection(fn) or ctx.onWebSocketConnection(fn)

Adds a function to get called at the beginning of websocket connection

Arguments

• fn(ctx, callback) - The function that gets called for each data chunk.

Example

proxy.onWebSocketConnection(function(ctx, callback) {
  console.log('WEBSOCKET CONNECT:', ctx.clientToProxyWebSocket.upgradeReq.url);
  return callback();
});

proxy.onWebSocketSend(fn) or ctx.onWebSocketSend(fn)

Adds a function to get called for each WebSocket message sent by the client.

Arguments

• fn(ctx, message, flags, callback) - The function that gets called for each WebSocket message sent by the client.

Example

proxy.onWebSocketSend(function(ctx, message, flags, callback) {
  console.log('WEBSOCKET SEND:', ctx.clientToProxyWebSocket.upgradeReq.url, message);
  return callback(null, message, flags);
});

proxy.onWebSocketMessage(fn) or ctx.onWebSocketMessage(fn)

Adds a function to get called for each WebSocket message received from the server.

Arguments

• fn(ctx, message, flags, callback) - The function that gets called for each WebSocket message received from the server.

Example

proxy.onWebSocketMessage(function(ctx, message, flags, callback) {
  console.log('WEBSOCKET MESSAGE:', ctx.clientToProxyWebSocket.upgradeReq.url, message);
  return callback(null, message, flags);
});

proxy.onWebSocketFrame(fn) or ctx.onWebSocketFrame(fn)

Adds a function to get called for each WebSocket frame exchanged (message, ping or pong).

Arguments

• fn(ctx, type, fromServer, data, flags, callback) - The function that gets called for each WebSocket frame exchanged.

Example

proxy.onWebSocketFrame(function(ctx, type, fromServer, data, flags, callback) {
  console.log('WEBSOCKET FRAME ' + type + ' received from ' + (fromServer ? 'server' : 'client'), ctx.clientToProxyWebSocket.upgradeReq.url, data);
  return callback(null, data, flags);
});

proxy.onWebSocketError(fn) or ctx.onWebSocketError(fn)

Adds a function to the list of functions to get called if an error occures in WebSocket.

Arguments

• fn(ctx, err) - The function to be called on an error in WebSocket.

Example

proxy.onWebSocketError(function(ctx, err) {
  console.log('WEBSOCKET ERROR:', ctx.clientToProxyWebSocket.upgradeReq.url, err);
});

proxy.onWebSocketClose(fn) or ctx.onWebSocketClose(fn)

Adds a function to get called when a WebSocket connection is closed

Arguments

• fn(ctx, code, message, callback) - The function that gets when a WebSocket is closed.

Example

proxy.onWebSocketClose(function(ctx, code, message, callback) {
  console.log('WEBSOCKET CLOSED BY '+(ctx.closedByServer ? 'SERVER' : 'CLIENT'), ctx.clientToProxyWebSocket.upgradeReq.url, code, message);
  callback(null, code, message);
});

proxy.use(module) or ctx.use(module)

Adds a module into the proxy. Modules encapsulate multiple life cycle processing functions into one object.

Arguments

• module - The module to add. Modules contain a hash of functions to add.

Example

proxy.use({
  onError: function(ctx, err) { },
  onCertificateRequired: function(hostname, callback) { return callback(); },
  onCertificateMissing: function(ctx, files, callback) { return callback(); },
  onRequest: function(ctx, callback) { return callback(); },
  onRequestData: function(ctx, chunk, callback) { return callback(null, chunk); },
  onResponse: function(ctx, callback) { return callback(); },
  onResponseData: function(ctx, chunk, callback) { return callback(null, chunk); },
  onWebSocketConnection: function(ctx, callback) { return callback(); },
  onWebSocketSend: function(ctx, message, flags, callback) { return callback(null, message, flags); },
  onWebSocketMessage: function(ctx, message, flags, callback) { return callback(null, message, flags); },
  onWebSocketError: function(ctx, err) {  },
  onWebSocketClose: function(ctx, code, message, callback) {  },
});

node-http-mitm-proxy provide some ready to use modules:

• Proxy.gunzip Gunzip response filter (uncompress gzipped content before onResponseData and compress back after)
• Proxy.wildcard Generates wilcard certificates by default (so less certificates are generated)

Context

ctx.addRequestFilter(stream)

Adds a stream into the request body stream.

Arguments

• stream - The read/write stream to add in the request body stream.

Example

ctx.addRequestFilter(zlib.createGunzip());

ctx.addResponseFilter(stream)

Adds a stream into the response body stream.

Arguments

• stream - The read/write stream to add in the response body stream.

Example

ctx.addResponseFilter(zlib.createGunzip());

License

Copyright (c) 2015 Joe Ferner

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:



The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.



THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.