When using a web-browser to visit a website your browser uses HTTP headers to request information from a server by using http REQUEST headers.
Upon REQUEST a server responds to the request with a http RESPONSE.
The definition of HTTP header fields is: HTTP header fields are components of the header section of request and response messages in the Hypertext Transfer Protocol (HTTP). They define the operating parameters of an HTTP transaction. This basically means that a browser requests information from a server (Request headers) and gets a response upon that request (Response headers).
Your browser can make a wide variety of requests to a server. As you are able to see on this Wikipedia page about HTTP header fields. There are a lot of REQUESTS a browser can make from a server, it is important (in order to know the internet) to memorise all possible requests a browser can make. (nah.. just take a look at them once and you will be ok.)
Server RESPONSES on the other hand, can tell you much more about what is going on in the background when you open up a page. There are only 5 types of server responses and they are easily remembered. The server responses use values in the 100, 200, 300, 400 and 500 range as follows:
- 1xx Informational
- 2xx Successful
- 3xx Redirection
- 4xx Client Error
- 5xx Server Error
The response header 301 Moved Permanently is pretty powerful. I will show you one basic – yet powerful – application of it.
Sending targeted e-mails to your site users containing third party tracking links
Email servers do not like it when you add links to your emails that are referring to third party sites or affiliate marketing tracking system in order for you to measure the effectiveness and reach of your outgoing e-mails. In order to avoid your emails to get rejected by the recipients mail-server you are able to host a click-out file on your server. This allows you to add third-party measurement logic to the file and link to that location, instead of linking directly to a statistics system (with the risk of your emails not being received).