04 Protocol 1: HTTP - LIttleAncientForestKami/shiny-octo-doodle GitHub Wiki

Language of the Web or on HTTP

ℹ️	History note sir Timothy Berners-Lee ENQUIRE Pascal, on NORD10 microcomputer Enquire Within Upon Everything, self-learning book used relations between cards (includes, describes, uses, made) close to Wiki WWW relations based upon Enquire HyperText + DNS + TCP HTTP, or HyperText Transfer Protocol Protocol Transfer HyperText - The Garden of Forking Paths standardized by World Wide Web Consortium and the Internet Engineering Task Force HTTP version 0.9 was the first documented version of HTTP

💡	allows to fork reading paths by linking documents.

🔥	allows the improvement of its request and response (via gateway, proxy, or a tunnel)

ℹ️	https://en.wikipedia.org/wiki/Hypertext - take a look at history

during interview at CERN

HyperText is a way to link and access information of various kinds as a web of nodes in which the user can browse at will. Potentially, HyperText provides a single user-interface to many large classes of stored information such as reports, notes, data-bases, computer documentation and on-line systems help. We propose the implementation of a simple scheme to incorporate several different servers of machine-stored information already available at CERN, including an analysis of the requirements for information access needs by experiments… A program which provides access to the hypertext world we call a browser.

— T. Berners-Lee & R. Cailliau on 12 November 1990

Basics

Stateless
Request - Response
1. client requests
2. server responds
application layer protocol
defaults:
1. port: 80
2. underlying protocol: TCP/IP
hostname in the request is case insensitive

Stateless protocol

after connection is broken, no information about it remains.

HTTP session

series of request and response in http is called as a session in HTTP

❗

About URLs

Whatever can be requested by using HTTP protocol is identified and reached via a type of URI(Uniform Resource Identifier) called URL(Uniform Resource Locator).

URI: Uniform Resource Identifier
URL: Uniform Resource Locator

🔥	URLs are often used synonymously with URIs, though there’s a difference!

Methods

GET: params passed in URI / address bar, can be conditional with If-Modified-Since header
HEAD: heads up resource! Info about you required. Similar to GET, but without the message body. It’s used to retrieve the server headers for a particular resource, generally to check if the resource has changed, via timestamps.
POST: all forms submit posts. Submitting data from client to server in a request body.
PUT: takes data from client to server, usually to create / update entities.
DELETE: requests resource removal, for privileged users
OPTIONS: options and requirements information in given comm channel. Used to retrieve the server capabilities. On the client-side, it can be used to modify the request based on what the server can support.
TRACE: diagnostic for comm channel. Used to retrieve the hops that a request takes to round trip from the server. Each intermediate proxy or gateway would inject its IP or DNS name into the Via header field.
CONNECT: connect me up, proxy!

🔥	CONNECT is implemented based on expired protocol draft from 1999… :-/

PATCH: update part of data with patch client sends

ℹ️	Four important HTTP methods are `GET`, `POST`, `PUT` and `DELETE`. For some time only first two were commonly handled.

Headers

Wikipedia is good enough source for this: has headers, their fields, examples and limitations.

Codes

ℹ️	Information codes, 1xx

Code	In words	Meaning or resource returned
100	Continue	Please continue sending the query
101	Switching Protocols	Change of protocols
110	Connection Timed Out	Server did not answer for too long
111	Connection refused	Server refused connecting

💡	Success codes, 2xx

Code	In words	Meaning or resource returned
200	OK	Most often answer, returns requested resource
201	Created	Sent document was saved on server
202	Accepted	Query is being served
203	Non-Authoritative Information	Information created from local or external copies, not exact answer from the server
204	No Content	Nothing to return, server did what was asked of it
205	Reset Content	Server did it’s job, client should refresh now
206	Partial Content	Server did part of the query, returned `Range` header telling which part

🔥	Redirect codes, 3xx

Code	In words	Meaning or resource returned
300	Multiple choices	Server may reply with location that can tell what to choose, more than one way to serve query
301	Moved permanently	Resource changed URI, adjust yours
302	Found	Usual redirect, requested resource is now available (temporarily) at different URI
303	See Other	Usual redirect for POST requests, but also can be used instead of 200. Why??
304	Not Modified	??
305	Use Proxy	Resource is available only via Proxy given in `Location` header
306	Switch Proxy	Unused but reserved for older protocol versions
307	Temporary Redirect	?? and how it differs from Found??
310	Too Many Redirects	as it says

⚠️	Client error codes, 4xx

Code	In words	Meaning or resource returned
400	Bad Request	Wrong request syntax, server won’t handle it
401	Unauthorized	Server demands authorization, none / wrong was given
402	Payment Required	Unused, reserved for future
403	Forbidden	Request understood yet configuration forbids handling it
404	Not Found	!302 - server found nothing under URL and nothing that indicates something was / should have been there
405	Method Not Allowed	We don’t want POSTs/GETs/others in this town (if kind, you’ll get allowed methods in response)
406	Not Acceptable	??
407	Proxy Authentication Required	401 for proxy
408	Request Timeout	Client did NOT send request to server in appropriate (for server? for whom?) time
409	Conflict	Request can’t be met as there’s conflict with current resource state. Returned when server suspects client may re-send corrected request. Response optionally (recommended) contains info helping the client with request correction
410	Gone	Removed or deleted resources should reply like that. New URI for this resource is not given, client should not ask for this
411	Length required	Header `Content-Length` required, but missing, client may repeat request with it
412	Precondition Failed	Some conditions (at least one) set in request cannot be met
413	Request Entity Too Large	Total request length too long due to it. Most likely POST form problem
414	Request-URI Too Long	GET with too many params? URI too long to process
415	Unsupported Media Type	Server won’t handle requests it cannot understand
416	Requested Range Not Satisfiable	Byte range in request cannot be applied to given resource
417	Expectation Failed	Header `Expect` cannot be met by server or proxy server knows it won’t be met by next server in line
418	I’m a teapot	as it says

Google implemented 418 response code: http://www.google.pl/teapot

❗	Server error codes, 5xx

Code	In words	Meaning or resource returned
500	Internal Server Error	Usual response when something unexpected happened on the server side and it failed handling our request
501	Not Implemented	Returned when unknown request type is received
502	Bad Gateway	Gateway got incorrect answer from server and can’t handle client’s request
503	Service Unavailable	Overloaded reserver can’t handle request
504	Gateway Timeout	Gateway did not get reply in given time (DNS waits include)
505	HTTP Version Not Supported	as it says
506	Variant Also Negotiates (RFC 2295)	irrelevant for our needs
507	Insufficient Storage (WebDAV; RFC 4918)	irrelevant for us
508	Loop Detected (WebDAV; RFC 5842)	irrelevant for us
510	Not Extended (RFC 2774)	as it says
511	Network Authentication Required (RFC 6585)	Intended for proxy gateways or accepting regs prior to surfing

Not every code is done by every server!

This is also incomplete list: http://httpstatus.es/ https://www.addedbytes.com/articles/for-beginners/http-status-codes/

Let’s play ourselves with requests and responses

Try viewing them. Choose for example http://datascienceretreat.com/ and try viewing the HTTP between your browser and the page’s server.

HTTP "inadequacies", or on Web evolution

Can you name any?

Why would you say these are inadequacies?

Do you know any mechanism for overcoming them?

Summary, Q&A, more… and break. :-)

Write down points you learned.

Questions?

💡	More on HTTP? http://code.tutsplus.com/tutorials/http-the-protocol-every-web-developer-must-know-part-1—net-31177 http://www.slashroot.in/httphypertext-transfer-protocol-request-and-response http://www.rexswain.com/httpview.html http://web-sniffer.net/