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CL-HTTP2-PROTOCOL

What This Is

This is HTTP/2 draft-14 (a.k.a. "h2-14") interopability test code written in Common Lisp. It has only been tested against SBCL 1.1.8.0 to 1.1.14 on Ubuntu Linux on x86, but it should be possible to make it work on other Common Lisp implementations, subject to some editing in util.lisp and possibly example.lisp.

The code offers a pure Common Lisp transport agnostic implementation of the HTTP/2 protocol at draft-14. An example client and server are included for a "Hello, World" style test, which employ TLS using CL+SSL and OpenSSL.

Networking examples have been based on the CL-ASYNC library. Some alterations to functions in CL+SSL and CL-ASYNC were necessary and are included in the source tree. (Prior versions of this library were based on homemade event loops based on USOCKET and SB-BSD-SOCKETS but this has now been removed.)

The current implementation is based on:

Support for:

Binary framing parsing and encoding
Stream multiplexing and prioritization
Connection and stream flow control
Header compression
Server push
Connection and stream management

Copyright

Copyright (c) 2014 Akamai Technologies, Inc. Published under MIT License.
Contains design and text from http-2 which contains this notice: "(MIT License) - Copyright (c) 2013 Ilya Grigorik"
Contains code from CL+SSL which contains this notice: "This library is a fork of SSL-CMUCL. The original SSL-CMUCL source code was written by Eric Marsden and includes contributions by Jochen Schmidt. Development into CL+SSL was done by David Lichteblau. License: MIT-style."
Contains code from CL-ASYNC which contains this notice: "As always, my code is MIT licenced. Do whatever the hell you want with it. Enjoy!"

Notes on Port

This code began life as a port from the draft-06 Ruby interopability code written by Ilya Grigorik released under MIT license. This code has since diverged to support subsequent working group drafts (up to draft-14 currently), to allow queueing and multiplexing support with a prioritization algorithm, and to move away from some Ruby idioms towards Lisp idioms over time.

The following are notes only of interest to folks who followed along since the beginning or have some interest in comparing the code revisions. Others may skip this section.

util.lisp defines several general purpose forms that give us some capabilities similar to calls in Ruby, as well as convenience calls that are stylistic Lisp choices.
buffer.lisp is much longer than buffer.rb in order to allow us to build up various primitives that Ruby offers in the String class for free.
ssl.lisp redefines some items in the CL+SSL package (based on the cl+ssl-20140316-git version) and tcp-ssl.lisp overrides some items in the CL-ASYNC-SSL package (based on the cl-async-20140616-git version), mostly to add support for NPN, SNI, and DH parameters, all of which are neecessary to establish the TLS connection as required by HTTP/2. See the comments in those files for more information.
tcp.lisp redefines some items in the CL-ASYNC package (based on the cl-async-20140616-git version) mostly to fix a couple issues encountered in corner cases.
The code in the example folder is contained in example.lisp in the form of functions. The examples in Lisp fire up CL-ASYNC event loops.
The Ruby code uses arrays and hashes which in the CL code are variously ported as alists, plists, and hashes depending on the specifics of access required.
The error conditions are largely the same, but are prefixed with HTTP2- and an additional one is added named HTTP2-NOT-STARTED as it is very convenient in debugging (when NPN fails, etc). In addition, the Lisp code defines various restarts in the normal manner, so that during debugging certain failures do not require the instant transaction to be aborted entirely.
Classes are matched one-to-one but module/package organization is different. Use the HTTP2 package for most functions and the HTTP2-EXAMPLE package for the examples.

This Common Lisp code was produced by Martin Flack, a Principal Architect on the Foundry team in the Web Experience business at Akamai.

Our team's mission is innovative applied R&D, and accordingly we explore new technologies close to the mission of excellent web experience. Note that this code is intended to be used against the other HTTP/2 interopability client/server code linked above, and not necessarily any part of the Akamai network; nor is any feature herein indicative of any planned or actual feature of Akamai products or services.

This system was named CL-HTTP2-PROTOCOL to avoid misunderstanding that it was related to CL-HTTP, a Common Lisp web server. Apologies for the redundant word.

Server Setup and Example

To run this on a fresh Ubuntu Linux 13.10 or 14.04 server, follow these instructions. A non-root user of "ubuntu" with sudo access is assumed.

sudo apt-get update && sudo apt-get dist-upgrade -y && sudo reboot
# ...if prompted about grub choose "install package maintainer's version"
#
# ...login again
sudo apt-get install -y git sbcl
git clone https://github.com/akamai/cl-http2-protocol.git
wget http://beta.quicklisp.org/quicklisp.lisp
sbcl --script <<EOF
(load "quicklisp.lisp")
(quicklisp-quickstart:install)
(ql:quickload :swank)
(ql:quickload :alexandria)
(ql:quickload :anaphora)
(ql:quickload :babel)
(ql:quickload :puri)
(ql:quickload :usocket)
(ql:quickload :cl+ssl)
(ql:quickload :cl-async)
(ql:quickload :cl-async-ssl)
EOF
#
# ...optionally run screen if you're familiar with it and you want to
# quickly test server/client on one system:
screen
#
# ...start the server:
sbcl --script <<EOF
(load "quicklisp/setup.lisp")
(load "cl-http2-protocol/cl-http2-protocol.asd")
(require :cl-http2-protocol)
(in-package :http2-example)
(example-server)
EOF
#
# ...now you have an HTTP/2 server, secured with TLS, on port 8080
# (note the server is ONLY HTTP/2; there is no HTTP/1.1 fallback)
# (note that port 8080 is chosen only to allow a non-root user to
# run the Lisp image and launch the server)
#
# ...to stop the server, CTRL+C followed by ABORT at the handler
#
# ...if you prefer to have less output and keep exceptions from
# stopping the program, break the server, set these globals and rerun
# the server:
(setf *verbose-mode* nil)
(setf *debug-mode* nil)
(setf *dump-bytes* nil)
(example-server)
#
# ...if you ran screen, press CTRL-A CTRL-C, else open a new terminal
# to the server in order to run the example client
#
# ...run a client:
sbcl --script <<EOF
(load "quicklisp/setup.lisp")
(load "cl-http2-protocol/cl-http2-protocol.asd")
(require :cl-http2-protocol)
(in-package :http2-example)
(example-client "https://localhost:8080/")
EOF

Please note that the files mykey.pem, mycert.pem, and dhparams.2048.pem are used for the example server, so it is recommended that you regenerate them. You will then remove security warnings from real browsers. Please note that EXAMPLE-CLIENT does absolutely no sensible checking of the TLS certificate, etc.

openssl genrsa -out mykey.pem 2048
openssl req -new -key mykey.pem -out mycert.csr
# CN should be set to the hostname you will use to reach the server
openssl req -noout -text -in mycert.csr
openssl x509 -req -days 365 -in mycert.csr -signkey mykey.pem -out mycert.pem
openssl dhparam -outform pem -out dhparams.2048.pem 2048

At the time of writing (Sep 10, 2014), Firefox Nightly and Chrome Canary will be compatible with your HTTP/2 server started above as well. The address bar in Firefox Nightly should be https://HOST:8080/ where HOST is the hostname used to reach your server.

Getting Started

(load "cl-http2-protocol/cl-http2-protocol.asd")
(require :cl-http2-protocol)

(defvar socket #|  provide a transport...  |#)

(defvar conn (make-instance 'client))
(on conn :frame (lambda (bytes) #|  send the bytes...  |#))

(loop for bytes = #|  read some bytes...  |#
      if bytes (connection<< conn bytes) else (return))

Check out EXAMPLE-CLIENT and EXAMPLE-SERVER in HTTP2-EXAMPLE for basic examples that perform complete HTTP request/responses. These functions use CL+SSL for secure connections, or USOCKET / SB-BSD-SOCKETS for plain connections.

Connection lifecycle management

Depending on the role of the endpoint you must initialize either a CLIENT or a SERVER object. Doing so picks the appropriate header compression / decompression algorithms and stream management logic. From there, you can subscribe to connection level events, or invoke appropriate APIs to allocate new streams and manage the lifecycle. For example:

;;; server

(in-package :http2-example)

(defvar server (make-instance 'server))

(on server :stream (lambda (stream) ...))  ; process inbound stream
(on server :frame (lambda (bytes) ...))  ; encoded HTTP/2 frames

(ping server (lambda (payload) ...))  ; send ping, process pong

(goaway server)  ; send goaway frame to the client

;;; client

(in-package :http2-example)

(defvar client (make-instance 'client))

(on client :promise (lambda (stream) ...))  ; process push promise

(defparameter stream (new-stream client))  ; allocate new stream
(headers stream '((":method" . "post")) :end-stream: nil)
(data stream (buffer-simple "Hello") :end-stream t)

Events emitted by the CONNECTION object:

<table> <tr> <td>:promise</td> <td>client role only, fires once for each new push promise</td> </tr> <tr> <td>:stream</td> <td>server role only, fires once for each new client stream</td> </tr> <tr> <td>:frame</td> <td>fires once for every encoded HTTP/2 frame that needs to be sent to the peer</td> </tr> </table>

Stream lifecycle management

A single HTTP/2 connection can multiplex multiple streams in parallel: multiple requests and responses can be in flight simultaneously and stream data can be interleaved and prioritized. Further, the specification provides a well-defined lifecycle for each stream (see below).

The good news is, all of the stream management, and state transitions, and error checking is handled by the library. All you have to do is subscribe to appropriate events (marked with ":" prefix in diagram below) and provide your application logic to handle request and response processing.

                         +--------+
                    PP   |        |   PP
                ,--------|  idle  |--------.
               /         |        |         \
              v          +--------+          v
       +----------+          |           +----------+
       |          |          | H         |          |
   ,---|:reserved |          |           |:reserved |---.
   |   | (local)  |          v           | (remote) |   |
   |   +----------+      +--------+      +----------+   |
   |      | :active      |        |      :active |      |
   |      |      ,-------|:active |-------.      |      |
   |      | H   /   ES   |        |   ES   \   H |      |
   |      v    v         +--------+         v    v      |
   |   +-----------+          |          +-_---------+  |
   |   |:half_close|          |          |:half_close|  |
   |   |  (remote) |          |          |  (local)  |  |
   |   +-----------+          |          +-----------+  |
   |        |                 v                |        |
   |        |    ES/R    +--------+    ES/R    |        |
   |        `----------->|        |<-----------'        |
   | R                   | :close |                   R |
   `-------------------->|        |<--------------------'
                         +--------+

For sake of example, let's take a look at a simple server implementation:

(defvar conn (make-instance 'server))

; emits new streams opened by the client
(on conn :stream
  (lambda (stream)
    (on stream :active
      (lambda () ))  ; fires when stream transitions to open
    (on stream :close
      (lambda (err) ))  ; stream is closed by client and server

    (on stream :headers
      (lambda (head) ))  ; header callback
    (on stream :data
      (lambda (chunk) ))  ; body payload callback
	  
    (on stream :half-close
	  (lambda ()
	    ; ... generate response ...
		; send response
		(headers stream '((":status" . "200")
		                  ("content-type" . "text/plain")))
						  
        ; split response between multiple DATA frames
		(let ((chunk1 (buffer-simple "stuff "))
		      (chunk2 (buffer-simple "more stuff")))
		  (data stream chunk1 :end-stream nil)
		  (data stream chunk2))))))

Events emitted by the STREAM object:

<table> <tr> <td>:reserved</td> <td>fires exactly once when a push stream is initialized</td> </tr> <tr> <td>:active</td> <td>fires exactly once when the stream become active and is counted towards the open stream limit</td> </tr> <tr> <td>:headers</td> <td>fires once for each received header block (multi-frame blocks are reassembled before emitting this event)</td> </tr> <tr> <td>:data</td> <td>fires once for every DATA frame (no buffering)</td> </tr> <tr> <td>:half_close</td> <td>fires exactly once when the opposing peer closes its end of connection (e.g. client indicating that request is finished, or server indicating that response is finished)</td> </tr> <tr> <td>:close</td> <td>fires exactly once when both peers close the stream, or if the stream is reset</td> </tr> <tr> <td>:priority</td> <td>fires once for each received priority update (server only)</td> </tr> </table>

Flow control

Multiplexing multiple streams over the same TCP connection introduces contention for shared bandwidth resources. Stream priorities can help determine the relative order of delivery, but priorities alone are insufficient to control how the resource allocation is performed between multiple streams. To address this, HTTP/2 provides a simple mechanism for stream and connection flow control.

Connection and stream flow control is handled by the library: all streams are initialized with the default window size (64KB), and send/receive window updates are automatically processed - i.e. window is decremented on outgoing data transfers, and incremented on receipt of window frames. Similarly, if the window is exceeded, then data frames are automatically buffered until window is updated.

The only thing left is for your application to specify the logic as to when to emit window updates:

(buffered-amount conn)      ; check amount of buffered data
(conn-window conn)          ; check current window size
(window-update conn 1024)   ; increment connection window by 1024 bytes

(buffered-amount stream)    ; check amount of buffered data
(stream-window stream)      ; check current window size
(window-update stream 2048) ; increment stream window by 2048 bytes

Server push

An HTTP/2 server can send multiple replies to a single client request. To do so, first it emits a "push promise" frame which contains the headers of the promised resource, followed by the response to the original request, as well as promised resource payloads (which may be interleaved). A simple example is in order:

(defvar conn (make-instance 'server))

(on conn :stream
  (lambda (stream)
    (on stream :headers
	  (lambda (head) ... ))
    (on stream :data
	  (lambda (chunk) ... ))

    ; fires when client terminates its request (i.e. request finished)
    (on stream :half-close
	  (lambda ()
	    (let ((head '((":status" . "200")
		              (":path" . "/other_resource")
					  ("content-type" . "text/plain")))
              promise)
          (promise stream head
		    (lambda (push)
			  (headers push ...)
			  (setf promise push))))
			  
        (headers stream '((":status" . "200")
		                  ("content-type" . "text/plain")))
        (data stream response-chunk :end-stream nil)
		(data promise payload)
		(data stream last-chunk))))))

When a new push promise stream is sent by the server, the client is notified via the :promise event:

(defvar conn (make-instance 'client))
(on conn :promise
  (lambda (push)
    ; process push stream
	))

The client can cancel any given push stream (via STREAM-CLOSE), or disable server push entirely by sending the appropriate settings frame (note that below setting only impacts server > client direction):

(settings client :streams 0)  ; setting max limit to 0 disables server push