HTTP - Hypertext Transfer Protocol

HTTP is a network protocol

• Mental model: calling a function across a network
  • Client is the caller
  • Server is where the function exists
  • Client receives the result

Let’s use telnet to make such a ‘call’

$ telnet example.com 80
$ GET / HTTP/1.1
$ Host: example.com

Deconstructing the call

• “Call” includes:
  • target host (example.com)
  • target port on the host (80)
  • HTTP verb: “GET” (a.k.a. method) (ref: HTTP Method Definitions)
  • address: (the path or “/”)
  • Version of HTTP protocol (1.1)
  • Datatype of required response (aka mime-type)
• There are lots of other “parameters” that are allowed in this call

Deconstructing the returned data from that call

• (Reference: HTTP Response Fields)
• “Response” includes:
  • Status code: 200 (see [HTTP Status Codes(http://httpstatus.es)])
  • Accept-Ranges: bytes (lets the server tell the caller that it has that capability)
  • Cache-Control: max-age=604800, how long this response may be cached)
  • Content-Type: text/html Tells recipient how to parse the result)
  • Date: Thu, 27 Feb 2014 00:33:26 GMT The current date time on the server)
  • Etag: “359670651” kind of a unique-id for caching purposes)
  • Expires: Thu, 06 Mar 2014 00:33:26 GMT (says when the page is required to expire)
  • Last-Modified: Fri, 09 Aug 2013 23:54:35 GMT (When this page was edited)
  • Server: ECS (ewr/1584) (Software running the server)
  • X-Cache: HIT (Page came out of a cache)
  • x-ec-custom-error: 1 (There was no error in the cache)
  • Content-Length: 1270 (Content following this is 1270 bytes)
• All this is followed by text that we know should be interpretted as text/html

What are the HTTP Methods

• GET, PUT, POST, DELETE
• Think of them like a reguired first argument to the call
• The interpretation of the

Simplified view of the world

• Think of the relationship between the client (the user in a browser) and the server (the rails server) as a program calling a function!
  • Call: CallUsingHTTP(“GET”, “www.brandeis.edu”, “/index.html”)
  • Returns: Status code, Content type, Content, and potentially more