How does the communication between a browser and a

Question

Can anyone explain how the communication takes place between the browser and web server? I want to learn how

• GET, POST verbs (among others)
• cookies
• sessions
• query strings

work behind the scene.

Answer 1

The links for specifications of each aspect of the question is as follows:

• GET, POST verbs (among others) - The HTTP Specification exhaustively discusses all aspects of HTTP communication (the protocol for communication between the web server and the browser). It explains the Request message and Response message protocols.

• Cookies - are set by attaching a Set-Cookie HTTP Header to the HTTP response.

• QueryStrings - are the part of the URL in the HTTP request that follow the first occurrence of a "?" character. The linked specification is for section 3.4 of the URI specification.

• Sessions - HTTP is a synchronous, stateless protocol. Sessions, or the illusion of state, can be created by (1) using cookies to store state data as plain text on the client's computer, (2) passing data-values in the URL and querystring of the request, (3) submitting POST requests with a collection of values that may indicate state and, (4) storing state information by a server-side persistence mechanism that is retrieved by a session-key (the session key is resolved from either the cookie, URL/Querystring or POST value collection.

An explanation of HTTP can go on for days, but I have attempted to provide a concise yet conceptually complete answer, and include the appropriate links for further reading of official specifications.

Answer 2

Your browser first resolves the servername via DNS to an IP. Then it opens a TCP connection to the webserver and tries to communicate via HTTP. Usually that is on TCP-port 80 but you can specify a different one (http://server:portnumber).

HTTP looks like this:

Once it is connected, it sends the request, which looks like:

GET /site HTTP/1.0
Header1: bla
Header2: blub
{emptyline}

E.g., a header might be Authorization or Range. See here for more.

Then the server responds like this:

200 OK
Header3: foo
Header4: bar

content following here...

E.g., a header might be Date or Content-Type. See here for more.

Look at Wikipedia for HTTP for some more information about this protocol.