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HTTPlab

A reverse web-proxy and backend server setup for easy packet capture of clear-text HTTP/1.1, HTTP/2, and Websocket traffic. Sample pcaps included.

Background

For implementing protocol parsers or simply to learn about modern web traffic it's still handy to have pcaps of HTTP traffic that's normally transferred over TLS, particularly via http/2. This repo provides a docker-compose application that runs a reverse proxy terminating TLS with a self-signed certificate, forwarding traffic to two node.js servers that speak unencrypted http/1.1 and http/2. They serve the socket.io chat application, adding websocket use on top of HTTP. You can easily serve other content as well. A tcpdump of the web server traffic provides pcaps with unencrypted flows.

Network topology

This project uses the following containers:

Topology

An HAProxy instance in the proxy container offers three TCP ports to the host: plain HTTP/1.1., HTTP/1.1 over TLS, and HTTP/2 over TLS. It acts as a TLS terminator with a self-signed cert. It forwards the plain HTTP payload over unencrypted connections to two node.js servers, one speaking HTTP/1.1 (http11), the other HTTP/2 (http2).

The following URLs are live once docker-compose is up:

Note that the TLS certificate in use is self-signed, so you'll need to click through your browser's warning dialog once.

Protocol details

For http/1.1, the WebSocket traffic happens over the usual connection-level upgrade mechanism outlined in RFC6455. For http/2, it uses the SETTINGS_ENABLE_CONNECT_PROTOCOL value in a settings frame, with a subsequent CONNECT as specified in RFC8441.

NOTE: the web server currently seems to reject the websocket CONNECT over http/2 with a 405. Patches to improve this are welcome. The chat application itself works because socket.io falls back on polling.

Launching the servers

To start the network, say docker-compose up from this folder. You'll see something like this:

proxy_1   | Note: setting global.maxconn to 493.
proxy_1   | Available polling systems :
proxy_1   |       epoll : pref=300,  test result OK
proxy_1   |        poll : pref=200,  test result OK
proxy_1   |      select : pref=150,  test result OK
proxy_1   | Total: 3 (3 usable), will use epoll.
proxy_1   |
proxy_1   | Available filters :
proxy_1   |     [SPOE] spoe
proxy_1   |     [CACHE] cache
proxy_1   |     [FCGI] fcgi-app
proxy_1   |     [TRACE] trace
proxy_1   |     [COMP] compression
proxy_1   | Using epoll() as the polling mechanism.
http11_1  | speaking http on *:80
http2_1   | speaking http2 on *:80

At this point you can visit any of the three localhost URLs shown above with your browser, and you should see a basic but functional chat app. Note that the backend between the plaintext and HTTP/1.1-over-TLS URLs is shared, so you'll see chat messages broadcast across them.

Capturing pcaps

To capture raw traffic you'll need to know the IP addresses of the backend servers and the right interface on your local host to sniff on. Let's cover them in turn. To learn about the network, say docker network inspect httplab_default, which is the name docker-compose chooses for your network. The output includes IP addresses for the two web servers, e.g. as follows:

"Containers": {
    "05e497beddfc22c74a57d055ab9d1fd9183f375bf296146ee7fb30eb20e279dc": {
        "Name": "httplab_http2_1",
        "EndpointID": "b83ce30ddc2d0d63741fbebd40654adc5ed43084c06e8b27f5665cbf7a45d986",
        "MacAddress": "02:42:ac:13:00:04",
        "IPv4Address": "172.19.0.4/16",
        "IPv6Address": ""
    },
    "d698292f026090bf6a1942f14c225b97aa11df98962cf00462ce77d6bb7dea9f": {
        "Name": "httplab_http11_1",
        "EndpointID": "576939974e7afc5cb1b429bc347c031ac10d1e16df8cfa90011bee650f517ba4",
        "MacAddress": "02:42:ac:13:00:03",
        "IPv4Address": "172.19.0.3/16",
        "IPv6Address": ""
    },
    ...

At this point a tcpdump of port 80 on the http11 or http2 addresses (172.19.0.3 or 172.19.0.4 in the above) will show you unencrypted HTTP/1.1 or HTTP/2 traffic, respectively. The interface to sniff on depends on your Docker setup. Most likely it's a bridge device spun up by docker-compose. You can identify it from the output of docker network ls:

$ docker network ls | grep httplab_default
500b158c17e5        httplab_default     bridge              local

In my case, ifconfig shows a corresponding bridge device called br-500b158c17e5. So, piecing it all together, the following captures clear-text http/2 traffic:

# tcpdump -n -s0 -i br-500b158c17e5 -w http2.pcap host 172.19.0.4

Those pcaps likely have invalid checksums due to checksum offloading, so to make life easier for people consuming your pcaps, clean them up by running them through tcprewrite -C.

Sample pcaps

The pcaps folder has sample captures for websockets over HTTP/1.1 and HTTP/2, recorded as described above.

Serving additional web content

The node webservers serve up anything in /opt/webserver, so to change that you can simply copy additional content into the relevant container. For example, after saying

docker cp foo.html httplab_http11_1:/opt/webserver

you'll see the contents of foo.html at http://127.0.0.1/foo.html.

Using other protocols

There's nothing HTTP-specific in the HAProxy configuration, so you can easily extend this setup to other protocols carried over TLS. You just need an endpoint serving the protocol unencrypted.