4. HTTP

Question 1

What are the 2 general types of HTTP messages?

Answer 1

Request and response. Client’s browser (aka user agent) requests, receives and renders Web objects. Server sends objects in reponse to the requests.

Question 2

What are the 4 common HTTP methods? Describe them.

Answer 2

GET: typically a request for a file.
HEAD: returns header information e.g last-modified date, size, content-type. Should be indentical to the header part of a GET response.
POST: submits user input usually from a form.
Conditional GET: Conditional fields include: If-Modified-Since, If-Match, If-Range. Requests that the entity be transferred ony under the circumstances described. Reduces unnecessary network usage by allowing cached entities to be refreshed without mutliple requests.

Question 3

How does the conditional-GET request reduce network usage?

Answer 3

Reduces unnecessary network usage by allowing cached entities to be refreshed without mutliple requests

Question 4

Describe both methods of uploading form input.

Answer 4

POST method - web page includes a form input, input is uploaded to server in entity body

URL method - uses GET method, input is uploaded in URL field of request line:
www.somesite.com/animalsearch?monkeys&banana

Question 5

HTTP is stateless. What does this mean, and why is this an advantage?

Answer 5

This means that the server maintains no information about past client requests.
Protocols that maintain state are potentially complex:
- past history must be maintained
- if client/server crashes their views of state may be incosistent with the other and must be reconciled

Question 6

What is the relationship between HTTP 1.0 and TCP?

Answer 6

HTTP 1.0 used a single TCP connection for each request/response transaction, so multiple transactions between the same client and server needed multiple TCP connections. HTTP 1.1 introduced means to keep the TCP connection open, reducing congestion. e.g keep-alive: 115/r/n

Question 7

What are the 5 types of HTTP response codes?

Answer 7

1xx - Informational
2xx - Successful
3xx - Redirection
4xx - Client Error
5xx - Server Error

Question 8

What can cookies be used for?

Answer 8

• authorization
• shopping carts
• recommendations
• user session state (http messages can carry state)