HTTP (RubyMonsters Edition)

HTTP { Hypertext Transfer Protocol }

HTML HTTP

https://speakerinnen.org/de/sign_up is translated to https://54.255.158.2:443/de/sign_up using the DNS protocol

4 Connect to the computer reachable under IP address 54.255.158.2
4 Use an SSL/TLS encrypted TCP socket on port 443 4 Speak HTTP 4 Tell the server we know it as speakerinnen.org 4 Access resource /de/sign_up

Server listens on TCP port

TCP socket 4 Is opened when client connects to port
4 Client and server can send each other messages

Client starts speaking GET /de/sign_up HTTP/1.1 Host: speakerinnen.org

Server replies HTTP/1.1 200 OK Content-Type: text/html <html> <head> <title>Speakerinnen*-Liste</title>
</head> </html>

request vs response VERB path HTTP/1.1 HTTP/1.1 code description Header:
Value Header: Value ... ... Body (if there is one) Body (if there is one)

Resources 4 identified by host and path 4 allow multiple
operations 4 can have multiple representations speakerinnen.org/de/sign_up

HTTP methods

GET 4 Request a resource in its current state. 4
The standard operation. 4 Request does not include a body. 4 Request is safe (and idempotent).

Safe? Idempotent? Resource state? What??

Resource state 4 Representations, headers and availability associated with a
resource. 4 /de/sign_up exists, is accessible, and has an HTML page with a form as its representation.

Safe requests 4 Safe requests do not change the state
of a resource. 4 HTTP client does not need to ask the user for permission to perform request.

Idempotent requests 4 The resource state will be the same
after performing the request once or multiple times. 4 HTTP client does not need to ask the user for permission to repeat the request.

Non-idempotent requests 4 Can't be sure about the resource state
after multiple requests. 4 HTTP client should always ask the user for confirmation.

GET 4 Request a resource in its current state. 4
The standard operation. 4 Request does not include a body. 4 Request is safe (and idempotent).

HEAD 4 Same as GET, but there wont be a
response body. 4 Useful if you only care about the headers. 4 Request is safe (and idempotent).

POST 4 "Do something dangerous." 4 Default for requests that
change something. 4 Used for creating a new speakerinnen. 4 Unsafe and non-idempotent.

<form action="/de/profiles" method="post">
<input name="profile[email]" /> <input name="profile[password]" type="password" /> <input type="submit" value="Registrieren" /> </form>

POST /de/profiles HTTP/1.1 Content-Type: application/x-www-form-urlencoded Content-Length: 49 profile[email]=me@rkh.im&profile[password]=abc123

PUT 4 Writing a resource to a given path. 4
Often used for uploads. 4 Unsafe, but idempotent (yay).

Other HTTP methods 4 DELETE: Remove a resource, idempotent. 4
OPTIONS: Learn about available methods and representations for a resource, safe. 4 PATCH: Update a resource from a partial representation, non-idempotent. 4 LINK and UNLINK: Create or destroy relations between resources, idempotent.

Response Status 4 1xx - informational 4 2xx - success
4 3xx - redirection 4 4xx - client error 4 5xx - server error

If you don't know status xyz, treat it like x00.

Examples 4 303 See Other 4 403 Forbidden 4 404
File Not Found 4 405 Method Not Allowed 4 418 I'm a Teapot 4 500 Internal Server Error

Headers

Common request headers 4 Host: Domain name in URI. 4
User-Agent: Client software used. 4 Referer[sic]: Page user was on before.

Safari on iPad User-Agent: Mozilla/5.0 (iPad; U; CPU OS 3_2_1
like Mac OS X; en-us) AppleWebKit/ 531.21.10 (KHTML, like Gecko) Mobile/ 7B405

Common response headers 4 Server: Server software used. 4 Last-Modified:
The last time the resource state has changed.

Representations

The "file type" of the response or request body.

We have seen two so far 4 text/html 4 application/x-www-form-urlencoded

Other examples 4 image/gif, image/png, image/jpeg 4 text/plain, text/css, text/x-script.ruby
4 application/javascript, application/ json

A resource can have multiple representations But we need to
tell it which one we want

We want a PNG image GET /resource HTTP/1.1 Host: example.org
Accept: image/png Server gives us PNG image HTTP/1.1 200 OK Content-Type: image/png [ png data ]

We want a PNG image GET /resource HTTP/1.1 Host: example.org
Accept: image/png Resource doesn't have a PNG representation HTTP/1.1 406 Not Acceptable Content-Type: text/plain No PNG, sorry.

We want any kind of image GET /resource HTTP/1.1 Host:
example.org Accept: image/* Server gives us PNG image HTTP/1.1 200 OK Content-Type: image/png [ png data ]

We want a PNG or GIF image (but prefer PNG)
GET /resource HTTP/1.1 Host: example.org Accept: image/png; q=1.0,image/gif; q=0.5 Server gives us PNG image HTTP/1.1 200 OK Content-Type: image/png [ png data ]

The same works for language. GET /resource HTTP/1.1 Host: example.org
Accept-Language: en, de

Cookies

HTTP is stateless. Cookies are a way to attach state.

HTTP/1.1 200 OK Set-Cookie: mycookie=foobar; HttpOnly Content-Type: text/plain Just gave
you a cookie!

GET /somepage HTTP/1.1 Host: example.org Cookie: mycookie=foobar

get '/' do name = session[:name] "Hello #{ name }!"
end

Thank You!

HTTP (RubyMonsters Edition)

HTTP (RubyMonsters Edition)

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