mitm v1.7.3
Mitm.js
Mitm.js is a library for Node.js (and Io.js) to intercept and mock outgoing
network TCP and HTTP connections. Mitm.js intercepts and gives you
a Net.Socket
to communicate as if you were the remote server. For HTTP
requests it even gives you Http.IncomingMessage
and Http.ServerResponse
— just like you're used to when writing Node.js servers. Except there's no
actual server running, it's all just In-Process Interception™.
Intercepting connections and requests is extremely useful to test and ensure your code does what you expect. Assert on request parameters and send back various responses to your code without ever having to hit the real network. Fast as hell and a lot easier to develop with than external test servers.
Mitm.js works on all Node versions: ancient v0.10, v0.11 and v0.12 versions, previous and current LTS versions like v4 to v12 and the newest v22 and beyond. For all it has automated tests to ensure it will stay that way.
I've developed Mitm.js on a need-to basis for testing Monday Calendar's syncing, so if you find a use-case I haven't come across, please fling me an email, a tweet or create an issue on GitHub.
Tour
Intercept both TCP socket connections (
Net.connect
) and HTTP requests (Http.request
andHttps.request
).Hooks to Node.js's network functions at a very low level with the goal of not having to patch existing classes and have everything behave as if bytes were arriving from the network.
Does not have any kitchen sink features or yet another API to assert on intercepted connections.
That's a different responsibility handled better by assertion libraries (you'll do no better than to pick Must.js for that ;-).Use an API you already know to assert or respond to requests — Mitm.js gives you access to a vanilla
Net.Socket
to respond with:mitm.on("connection", function(socket) { socket.write("Hello back!") }) var socket = Net.connect(22, "example.org") socket.write("Hello!") socket.setEncoding("utf8") socket.on("data", console.log) // => "Hello back!"
When you do HTTP or HTTPS requests, Mitm.js gives you both a
Http.IncomingMessage
andHttp.ServerResponse
to play the server with. That means you'll be using an API you're already familiar with rather than yet another idiosyncratic domain specific language.Mitm.js comes very handy to ensure your code makes requests with the appropriate parameters:
mitm.on("request", function(req, res) { req.headers.authorization.must.equal("OAuth DEADBEEF") }) Http.get("http://example.org")
It's also useful to see if your code behaves as you'd expect if everything is not
200 OK
:mitm.on("request", function(req, res) { res.statusCode = 402 res.end("Pay up, sugar!") }) Http.get("http://example.org", function(res) { res.setEncoding("utf8") res.statusCode // => 402 res.on("data", console.log) // => "Pay up, sugar!" })
Http.IncomingMessage
andHttp.ServerResponse
are the same objects you get when you write Node.js HTTP servers withNet.Server
or use a library like Express.js.Bypass interception selectively for some connections (such as your SQL server) and let them connect as usual.
mitm.on("connect", function(socket, opts) { if (opts.host == "sql.example.org" && opts.port == 5432) socket.bypass() })
Developed with automated tests. Yeah, I know, why should one list this a feature when writing tests is just a sign of professionalism and respect towards other developers? But in a world where so many libraries and "production" software are released without any tests, I like to point out that I even write tests for testing libraries. ;-)
Installing
npm install mitm
From v1.0.0 Mitm.js will follow semantic versioning, but until then, breaking changes may appear between minor versions (the middle number).
Using
Require Mitm.js and invoke it as a function to both create an instance of Mitm
and enable intercepting:
var Mitm = require("mitm")
var mitm = Mitm()
Mitm.js will then intercept all requests until you disable it:
mitm.disable()
Intercepting in tests
In tests, it's best to use the before and after hooks to enable and disable intercepting for each test case:
beforeEach(function() { this.mitm = Mitm() })
afterEach(function() { this.mitm.disable() })
Intercepting TCP connections
After you've called Mitm()
, Mitm.js will intercept and emit connection
on
itself for each new connection.
The connection
event will be given a server side Net.Socket
for you to reply
with:
mitm.on("connection", function(socket) { socket.write("Hello back!") })
var socket = Net.connect(22, "example.org")
socket.write("Hello!")
socket.setEncoding("utf8")
socket.on("data", console.log) // => "Hello back!"
Intercepting HTTP/HTTPS requests
After you've called Mitm()
, Mitm.js will intercept and emit request
on itself for each new HTTP or HTTPS request.
The request
event will be given a server side Http.IncomingMessage
and
Http.ServerResponse
.
For example, asserting on HTTP requests would look something like this:
mitm.on("request", function(req, res) {
req.headers.authorization.must.equal("OAuth DEADBEEF")
})
Http.get("http://example.org")
Responding to requests is just as easy and exactly like you're used to from using Node.js HTTP servers (or from libraries like Express.js):
mitm.on("request", function(req, res) {
res.statusCode = 402
res.end("Pay up, sugar!")
})
Http.get("http://example.org", function(res) {
res.statusCode // => 402
res.setEncoding("utf8")
res.on("data", console.log) // => "Pay up, sugar!"
})
Please note that HTTPS requests are currently "morphed" into HTTP requests. That's to save us from having to set up certificates and disable their verification. But if you do need to test this, please ping me and we'll see if we can get Mitm.js to support that.
Custom HTTP Methods
Unfortunately because Node.js's web server doesn't seem to support custom HTTP methods (that is, ones beyond require("http").METHODS
), Mitm.js doesn't support them out of the box either. The Node.js HTTP parser throws an error given a request with an unsupported method. However, as Mitm.js also supports intercepting at the TCP level, you could hook in your own HTTP parser. I've briefly alluded to it in issue #63.
Bypassing interception
You can bypass connections listening to the connect
event on the Mitm instance
and then calling bypass
on the given socket. To help you do
so selectively, connect
is given the options
object that was given to
Net.connect
:
mitm.on("connect", function(socket, opts) {
if (opts.host == "sql.example.org" && opts.port == 5432) socket.bypass()
})
Bypassed connections do not emit connection
or request
events. They're
ignored by Mitm.js.
In most cases you don't need to bypass because by the time you call Mitm
in
your tests to start intercepting, all of the long-running connections, such as
database or cache connections, are already made.
You might need to bypass connections you make to localhost when you're running
integration tests against the HTTP server you started in the test process, but
still want to intercept some other connections that this request might invoke.
The following should suffice:
mitm.on("connect", function(socket, opts) {
if (opts.host == "localhost") socket.bypass()
})
Events
All events that Mitm will emit on an instance of itself (see Using Mitm.js for examples):
Event | Description |
---|---|
connect | Emitted when a TCP connection is made. Given the client side Net.Socket and options from Net.connect . |
connection | Emitted when a TCP connection is made. Given the server side Net.Socket and options from Net.connect . |
request | Emitted when a HTTP/HTTPS request is made. Given the server side Http.IncomingMessage and Http.ServerResponse . |
License
Mitm.js is released under a Lesser GNU Affero General Public License, which in summary means:
- You can use this program for no cost.
- You can use this program for both personal and commercial reasons.
- You do not have to share your own program's code which uses this program.
- You have to share modifications (e.g. bug-fixes) you've made to this program.
For more convoluted language, see the LICENSE
file.
About
Andri Möll typed this and the code.
Monday Calendar supported the engineering work.
If you find Mitm.js needs improving, please don't hesitate to type to me now at andri@dot.ee or create an issue online.
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