[[introduction]]
== Introduction

Gun is an HTTP client for Erlang/OTP.

Gun supports the HTTP/2, HTTP/1.1 and Websocket protocols.

=== Prerequisites

Knowledge of Erlang, but also of the HTTP/1.1, HTTP/2 and Websocket
protocols is required in order to read this guide.

=== Supported platforms

Gun is tested and supported on Linux, FreeBSD, Windows and OSX.

Gun is developed for Erlang/OTP 20.0 and newer.

Note that Gun will not work on the Windows build of Erlang/OTP 20.3
due to a bug in Erlang/OTP's stdlib application. The ticket number
for this bug is OTP-13995 and it was fixed in the patch release
OTP-20.3.2. Replacing the `gen_statem.beam` file on an 20.3
installation is enough to fix the issue.

=== License

Gun uses the ISC License.

----
Copyright (c) 2013-2019, Loïc Hoguin <essen@ninenines.eu>

Permission to use, copy, modify, and/or distribute this software for any
purpose with or without fee is hereby granted, provided that the above
copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
----

=== Versioning

Gun uses http://semver.org/[Semantic Versioning 2.0.0].

=== Conventions

In the HTTP protocol, the method name is case sensitive. All standard
method names are uppercase.

Header names are case insensitive. Gun converts all the header names
to lowercase, including request headers provided by your application.