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The modern Web

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Cowboy is a server for the modern Web. This chapter explains +what it means and details all the standards involved.

Cowboy supports all the standards listed in this document.

HTTP/2

HTTP/2 is the most efficient protocol for consuming Web +services. It enables clients to keep a connection open +for long periods of time; to send requests concurrently; +to reduce the size of requests through HTTP headers +compression; and more. The protocol is binary, greatly +reducing the resources needed to parse it.

HTTP/2 also enables the server to push messages to the +client. This can be used for various purposes, including +the sending of related resources before the client requests +them, in an effort to reduce latency. This can also be used +to enable bidirectional communication.

Cowboy provides transparent support for HTTP/2. Clients +that know it can use it; others fall back to HTTP/1.1 +automatically.

HTTP/2 is compatible with the HTTP/1.1 semantics.

HTTP/2 is defined by RFC 7540 and RFC 7541.

HTTP/1.1

HTTP/1.1 is the previous version of the HTTP protocol. +The protocol itself is text-based and suffers from numerous +issues and limitations. In particular it is not possible +to execute requests concurrently (though pipelining is +sometimes possible), and it’s also sometimes difficult +to detect that a client disconnected.

HTTP/1.1 does provide very good semantics for interacting +with Web services. It defines the standard methods, headers +and status codes used by HTTP/1.1 and HTTP/2 clients and +servers.

HTTP/1.1 also defines compatibility with an older version +of the protocol, HTTP/1.0, which was never really standardized +across implementations.

The core of HTTP/1.1 is defined by RFC 7230, RFC 7231, +RFC 7232, RFC 7233, RFC 7234 and RFC 7235. Numerous RFCs +and other specifications exist defining additional HTTP +methods, status codes, headers or semantics.

Websocket

Websocket is a protocol built on top of HTTP/1.1 +that provides a two-ways communication channel between the client and +the server. Communication is asynchronous and can occur concurrently.

It consists of a Javascript object allowing setting up a +Websocket connection to the server, and a binary based +protocol for sending data to the server or the client.

Websocket connections can transfer either UTF-8 encoded text +data or binary data. The protocol also includes support for +implementing a ping/pong mechanism, allowing the server and +the client to have more confidence that the connection is still +alive.

A Websocket connection can be used to transfer any kind of data, +small or big, text or binary. Because of this Websocket is +sometimes used for communication between systems.

Websocket messages have no semantics on their own. Websocket +is closer to TCP in that aspect, and requires you to design +and implement your own protocol on top of it; or adapt an +existing protocol to Websocket.

Cowboy provides an interface known as Websocket handlers +that gives complete control over a Websocket connection.

The Websocket protocol is defined by RFC 6455.

Long-lived requests

Cowboy provides an interface that can be used to support +long-polling or to stream large amounts of data reliably, +including using Server-Sent Events.

Long-polling is a mechanism in which the client performs +a request which may not be immediately answered by the +server. It allows clients to request resources that may +not currently exist, but are expected to be created soon, +and which will be returned as soon as they are.

Long-polling is essentially a hack, but it is widely used +to overcome limitations on older clients and servers.

Server-Sent Events is a small protocol defined as a media +type, text/event-stream, along with a new HTTP header, +Last-Event-ID. It is defined in the EventSource W3C +specification.

Cowboy provides an interface known as loop handlers +that facilitates the implementation of long-polling or stream +mechanisms. It works regardless of the underlying protocol.

REST

REST, or REpresentational State Transfer, +is a style of architecture for loosely connected distributed +systems. It can easily be implemented on top of HTTP.

REST is essentially a set of constraints to be followed. +Many of these constraints are purely architectural and +solved by simply using HTTP. Some constraints must be +explicitly followed by the developer.

Cowboy provides an interface known as REST handlers +that simplifies the implementation of a REST API on top of +the HTTP protocol.

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