An in depth overview of HTTP/2

link管理

链接快照平台

输入网页链接，自动生成快照
标签化管理网页链接

Introduction

HTTP/2 is a new protocol, intended as a higher performance alternative to HTTP/1.1. It introduces several new features, while remaining semantically compatible.

Key Features

HTTP/2 has the following key features compared to HTTP/1.1:

Binary Protocol: HTTP/2 is a binary protocol. This means that it is much more efficient on the wire, however as a result it is no longer human readable without using tools to decode the protocol.
Multiplexing: HTTP/2 supports multiplexing several streams over a single connection. This means that a client can send multiple requests on the same connection, and the server can respond in whatever order the responses become available.
Header Compression: HTTP requests and responses generally include a large number of redundant headers. HTTP/2 uses HPACK header compression to greatly compress headers.
Server Push: Server push allows a server to send additional cacheable resources to the client that the client has not explicitly asked for. The allows the server to anticipate the resources the client will request next and send them eagerly, which saves a round trip.

Connection Establishment

The first part of any usage of HTTP/2 is connection establishment. It would not be practical to allocate a new port just for HTTP/2 for various reasons, so instead the protocol defines 3 different methods of connection that allow the existing HTTP and HTTPS ports to be re-used.

ALPN based connection for https:// URIs
HTTP upgrade based connection http:// URIs
Connection via prior knowledge for hosts which are known to support HTTP/2

A detailed explanation of the three is given below. Once the initial connection has been established both the client and server send a connection preface, after which the connection is established.

HTTP/2 Connection methods

ALPN based connection for https:// URIs

ALPN stands for Application Layer Protocol Negotiation , and is a TLS extension that allows a client to negotiate the next protocol to use after the TLS handshake is complete. If either the client or the server does not support ALPN, then it will be ignored, and HTTP/1.1 will be used instead.

When the client connects to the server it sends a list of supported protocols. The server will then decide on the next
protocol to use and send this back in its response. If the server decides to use HTTP/2 it will send pack 'h2' as the