HTTP (RubyMonsters Edition)

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HTTP { Hypertext Transfer Protocol }

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HTML HTTP

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

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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

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Server listens on TCP port

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

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

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

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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)

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

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HTTP methods

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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).

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Safe? Idempotent? Resource state? What??

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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.

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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.

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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.

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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.

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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).

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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).

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

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

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

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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.

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

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

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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

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Headers

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

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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

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

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Representations

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

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

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

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

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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 ]

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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.

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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 ]

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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 ]

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

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

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