Pure Ruby, framework and transport agnostic, implementation of HTTP/2 protocol and HPACK header compression with support for:
- Binary framing parsing and encoding
- Stream multiplexing and prioritization
- Connection and stream flow control
- Header compression and server push
- Connection and stream management
- And more... see API docs
Protocol specifications:
$> gem install http-2This implementation makes no assumptions as how the data is delivered: it could be a regular Ruby TCP socket, your custom eventloop, or whatever other transport you wish to use - e.g. ZeroMQ, avian carriers, etc.
Your code is responsible for feeding data into the parser, which performs all of the necessary HTTP/2 decoding, state management and the rest, and vice versa, the parser will emit bytes (encoded HTTP/2 frames) that you can then route to the destination. Roughly, this works as follows:
require 'http/2'
socket = YourTransport.new
conn = HTTP2::Client.new
conn.on(:frame) {|bytes| socket << bytes }
while bytes = socket.read
conn << bytes
endCheckout provided client and server implementations for basic examples.
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 ---------------
server = HTTP2::Server.new
server.on(:stream) { |stream| ... } # process inbound stream
server.on(:frame) { |bytes| ... } # encoded HTTP/2 frames
server.ping { ... } # run liveness check, process pong response
server.goaway # send goaway frame to the client
# - Client ---------------
client = HTTP2::Client.new
client.on(:promise) { |stream| ... } # process push promise
stream = client.new_stream # allocate new stream
stream.headers({':method' => 'post', ...}, end_stream: false)
stream.data(payload, end_stream: true)Events emitted by the connection object:
| :promise | client role only, fires once for each new push promise |
| :stream | server role only, fires once for each new client stream |
| :frame | fires once for every encoded HTTP/2 frame that needs to be sent to the peer |
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:
conn = HTTP2::Server.new
# emits new streams opened by the client
conn.on(:stream) do |stream|
stream.on(:active) { } # fires when stream transitions to open state
stream.on(:close) { } # stream is closed by client and server
stream.on(:headers) { |head| ... } # header callback
stream.on(:data) { |chunk| ... } # body payload callback
# fires when client terminates its request (i.e. request finished)
stream.on(:half_close) do
# ... generate_response
# send response
stream.headers({
":status" => 200,
"content-type" => "text/plain"
})
# split response between multiple DATA frames
stream.data(response_chunk, end_stream: false)
stream.data(last_chunk)
end
endEvents emitted by the Stream object:
| :reserved | fires exactly once when a push stream is initialized |
| :active | fires exactly once when the stream become active and is counted towards the open stream limit |
| :headers | fires once for each received header block (multi-frame blocks are reassembled before emitting this event) |
| :data | fires once for every DATA frame (no buffering) |
| :half_close | 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) |
| :close | fires exactly once when both peers close the stream, or if the stream is reset |
| :priority | fires once for each received priority update (server only) |
Each HTTP/2 stream has a priority value that can be sent when the new stream is initialized, and optionally reprioritized later:
client = HTTP2::Client.new
default_priority_stream = client.new_stream
custom_priority_stream = client.new_stream(priority: 42)
# sometime later: change priority value
custom_priority_stream.reprioritize(32000) # emits PRIORITY frameOn the opposite side, the server can optimize its stream processing order or resource allocation by accessing the stream priority value (stream.priority).
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:
conn.buffered_amount # check amount of buffered data
conn.window # check current window size
conn.window_update(1024) # increment connection window by 1024 bytes
stream.buffered_amount # check amount of buffered data
stream.window # check current window size
stream.window_update(2048) # increment stream window by 2048 bytesAlternatively, flow control can be disabled by emitting an appropriate settings frame on the connection:
# limit number of concurrent streams to 100 and disable flow control
conn.settings(streams: 100, window: Float::INFINITY)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:
conn = HTTP2::Server.new
conn.on(:stream) do |stream|
stream.on(:headers) { |head| ... }
stream.on(:data) { |chunk| ... }
# fires when client terminates its request (i.e. request finished)
stream.on(:half_close) do
promise_header = { ':method' => 'GET',
':authority' => 'localhost',
':scheme' => 'https',
':path' => "/other_resource" }
# initiate server push stream
push_stream = nil
stream.promise(promise_header) do |push|
push.headers({...})
push_stream = push
end
# send response
stream.headers({
":status" => 200,
"content-type" => "text/plain"
})
# split response between multiple DATA frames
stream.data(response_chunk, end_stream: false)
stream.data(last_chunk)
# now send the previously promised data
push_stream.data(push_data)
end
endWhen a new push promise stream is sent by the server, the client is notified via the :promise event:
conn = HTTP2::Client.new
conn.on(:promise) do |push|
# process push stream
endThe client can cancel any given push stream (via .close), or disable server push entirely by sending the appropriate settings frame (note that below setting only impacts server > client direction):
client.settings(streams: 0) # setting max limit to 0 disables server pushTo run specs:
rake(MIT License) - Copyright (c) 2013 Ilya Grigorik
