Table of Contents

• Needed software
• The observation track
  • With Chrome
  • With Firefox
• The low-level client track
  • Establishing a connection
  • GOAWAY frames
  • PING frames
  • HPACK
• The server track
  • H2O frame handling
  • Using H2O as a library

Needed software

• git clone [email protected]:deweerdt/h2o-exercise.git
• git clone [email protected]:h2o/h2o.git
• git clone [email protected]:deweerdt/h2get.git
• Wireshark: https://www.wireshark.org/download.html
• Chrome
• nghttp2
• curl
  • Linux: https://serversforhackers.com/video/curl-with-http2-support
  • Mac OS X: https://simonecarletti.com/blog/2016/01/http2-curl-macosx/
• openssl
• libuv (macosx only)

The observation track

With Chrome

Using chrome://net-internals#http2 . Note that you can use "Flush Sockets" in the upper right corner to force Chrome to re-establish an HTTP/2 connection.

• Observe connection coalescing:
  • https://www.vox.com
  • Verify that they share the same IP:

    dig cdn.vox-cdn.com
    dig fonts.voxmedia.com
    

  • Check the SAN: openssl s_client -connect fonts.voxmedia.com:443 2>&1 | openssl x509 -text | grep -A1 'Subject Alternative Name'
• Observer pushes
  • https://seekingalpha.com/
  • find HTTP2_SESSION_RECV_PUSH_PROMISE
  • observe how H2O replicated some of the headers for the request that originated the push

With Firefox

• Use wireshark (https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format):

  $ export SSLKEYLOGFILE=$HOME/sslkeylogs/keylog.log
  $ /Applications/Firefox.app/Contents/MacOS/firefox &
  $ wireshark
  

• Observe how Firefox sends PRIORITY frames and then attaches requests to them

The low-level client track

Build h2get:

• cmake -DOPENSSL_ROOT_DIR=/usr/local/Cellar/[email protected]/1.1.0f .

h2get embeds a Ruby interpreter, it can be used as following: ./h2get script.rb

Establishing a connection

• Dump the different settings that different servers send:
  • www.fastly.com
  • www.google.com
  • www.facebook.com

GOAWAY frames

An endpoint that encounters a connection error SHOULD first send a GOAWAY frame (Section 6.8) with the stream identifier of the last stream that it successfully received from its peer

• Send invalid values in the SETTINGS frame in order to obtain a response from the server (search for PROTOCOL_ERROR in the RFC)
• Send an invalid stream id -- use send_headers

PING frames

Have a client sending send PING frames (https://www.google.com or https://www.fastly.com respond to PING)

HPACK

Implement decode_int https://tools.ietf.org/html/rfc7541#section-5.1

Checkout the no-decode-int branch, use ./test_decode_int to check the implementation.

The server track

H2O frame handling

H2O core frame handling function is lib/http2/connection.c::expect_default. This function dispatches the received frame depending on its type. Apply 0001-Output-priorities.patch in order to have priority information about the requests output to stderr.

Following the same model, instrument handle_window_update_frame in order to understand how browsers send WINDOW_UPDATE frames.

www/ has a directory that can be used as a root directory to serve different type of contents.

Using H2O as a library

This assumes that you've built and installed h2o. This repository comes with a small C server that uses libh2o that we will customize.

• install and compile h2o:
  • cmake -DOPENSSL_ROOT_DIR=/usr/local/Cellar/[email protected]/1.1.0f/ .
  • make -j 4 && make install
• Build the sample server in this directory:
  • make
• Add a handler that sends a JS file Make that JS of variable size, denpending on an URL parameter, use h2o_req_t to find the path of the request .
• Add a handler that sends a CSS file Make this of variable size
• Add a handler that sends an HTML file Reference the js and css, multiple times
• Add a 'Link: preload' header
  • See the upcoming critical keyword: h2o/h2o#1436