HTTP/1.1 protocol Cheat Sheet

The HTTP protocol consist into a request message, sent from a client to a web server; and a response message, sent from the server to the origin­ating client.

Request message general format:
HTTP Request Line
HTTP Request Headers
(empty line)
HTTP Request Body

Response message general format:
HTTP Response Line
HTTP Response Headers
(empty line)
HTTP Response Body

Format: "METHOD PATH PROTOCOL"

METHOD: GET, HEAD, POST, PUT, DELETE, TRACE, OPTIONS, CONNECT, PATCH
PATH: the path of the resource
PROTOCOL: HTTP/1.1

"NAME: VALUE"*

NAME: [A-Za-­z0-­9][­A-Z­a-z­0-9-]+
VALUE: US-ASCII octets

Headers are extra inform­ation for the request. There are many standard headers and you can create your own.

See Common HTTP Request Headers

If the HTTP method used is POST or PUT, the request may be followed by a body. It can be a file or a specific form of data.

The Conten­t-Type header must be filled with a MIME type to indicate the type of content.

The body is separated from the header by two line feeds (\n).

Format: PROTOCOL STATUS REASON

PROTOCOL: HTTP/1.1
STATUS: Any HTTP Status Code
REASON: A reason message

The reason message is usually the label associated to the status code. Some APIs may use this text field to specify an error message.

"NAME: VALUE"*

NAME: [A-Za-­z0-­9][­A-Z­a-z­0-9-]+
VALUE: US-ASCII octets

Headers are extra inform­ation for the response. There are many standard headers and you can create your own.

See Common HTTP Response Headers

The is usually a response body after the response headers. It can be a file or a specific form of data.

The Conte­­nt-­­Type header must be filled with a MIME type to indicate the type of content.

The body is separated from the headers by two line feeds (\n).

GET: used to retrieve a resource. Has no request body.
POST: used to submit a new resource (path) or send data. Usually has a body.
HEAD: used to preview the result of a GEToperation. Has no request body and no respond body.
PUT: used to submit an update to an existing resource
DELETE: used to delete the specified resource
TRACE: echoes the received request for tracing purposes
OPTIONS: verify the server supports a specified request (see Preflight requests)
CONNECT: used by HTTPS
PATCH: allows partial modifi­cation of a resource

Cache-­Control: Indicates client caching conditions
Conten­t-L­ength: Length of the response body in bytes
Conten­t-Type: MIME type of the response body
Expires: Client is allowed to keep the resouce in cache
Location: Redire­ction URL
Server: name of the server software
Set-Cookie: new cookies that should be stored client­-side

When a message body is exchanged, the receiver must be able to determine when the message is complete (or how many bytes should be received to consider the body complete).

The main operating way is to use the Conten­t-L­ength header with the size (in bytes) of the body that is to come.

When a streaming method is desired, an altern­ative way is to use the Transf­er-­Enc­oding: chunked header and to follow the Chunked transfer encoding protocol.

All specif­ica­tions in this document have been simplified from the official HTTP standard. Always refer to the RFCs if necessary.

RFC-7230: Hypertext Transfer Protocol (HTTP/­1.1): Message Syntax and Routing

HTTP/0.9 and HTTP/1.0
History: RFC-1945 (actual)

HTTP/1.1
This is the most used HTTP version.

History: RFC-2068 (obsol­ete), RFC-2616 (obsol­ete), RFC-7230 (actual)

HTTP/2
According to W3Techs, as of March 2019, 33.9% of the top 10 million websites supported HTTP/2.

History: RFC-7540 (actual)

HTTP/3
Also called HTTP-o­ver­-QUIC, it is the upcoming major version of HTTP.

The Accept and Conten­t-Type headers use MIME types to specify the type of message content.

There are basic MIME types for simple files and web formats: text/plain, text/html, applic­ati­on/xml, applic­ati­on/json, applic­ati­on/­oct­et-­stream, text/css, text/j­ava­script...

There are MIME types for all known file formats: image/jpeg, image/png, audio/mpeg, applic­ati­on/pdf, applic­ati­on/zip, font/woff, video/mp4...

There are specific MIME types related to browsers and APIs: multip­art­/mixed, multip­art­/fo­rm-data, multip­art­/by­ter­anges, applic­ati­on/­x-w­ww-­for­m-u­rle­ncoded...

Sometimes, extra inform­ation are added to a type. Text format can have a charset specif­ica­tion: text/p­lai­n;c­har­set­=UTF-8

See: RFC-2045, RFC-2046, RFC-2047, RFC-4288, RFC-4289, RFC-2049; and MDN: MIME type

HTTP Proxy servers are act as an interm­ediary for client­-to­-server requests such as HTTP.

A forward proxy is a type of proxy server that receives and forwards requests in order to cache and facilitate access to a wide range of web servers.

A reverse proxy is a type of proxy server that receives and forwards requests in order to do load-b­ala­ncing for a group of web servers.