Expand description
An asynchronous, HTTP/2 server and client implementation.
This library implements the HTTP/2 specification. The implementation is asynchronous, using futures as the basis for the API. The implementation is also decoupled from TCP or TLS details. The user must handle ALPN and HTTP/1.1 upgrades themselves.
Getting started
Add the following to your Cargo.toml file:
[dependencies]
h2 = "0.3"Layout
The crate is split into client and server modules. Types that are
common to both clients and servers are located at the root of the crate.
See module level documentation for more details on how to use h2.
Handshake
Both the client and the server require a connection to already be in a state ready to start the HTTP/2 handshake. This library does not provide facilities to do this.
There are three ways to reach an appropriate state to start the HTTP/2 handshake.
- Opening an HTTP/1.1 connection and performing an upgrade.
- Opening a connection with TLS and use ALPN to negotiate the protocol.
- Open a connection with prior knowledge, i.e. both the client and the server assume that the connection is immediately ready to start the HTTP/2 handshake once opened.
Once the connection is ready to start the HTTP/2 handshake, it can be
passed to server::handshake or client::handshake. At this point, the
library will start the handshake process, which consists of:
- The client sends the connection preface (a predefined sequence of 24 octets).
- Both the client and the server sending a SETTINGS frame.
See the Starting HTTP/2 in the specification for more details.
Flow control
Flow control is a fundamental feature of HTTP/2. The h2 library
exposes flow control to the user.
An HTTP/2 client or server may not send unlimited data to the peer. When a
stream is initiated, both the client and the server are provided with an
initial window size for that stream. A window size is the number of bytes
the endpoint can send to the peer. At any point in time, the peer may
increase this window size by sending a WINDOW_UPDATE frame. Once a client
or server has sent data filling the window for a stream, no further data may
be sent on that stream until the peer increases the window.
There is also a connection level window governing data sent across all streams.
Managing flow control for inbound data is done through FlowControl.
Managing flow control for outbound data is done through SendStream. See
the struct level documentation for those two types for more details.