In order to fetch a web page for you,
your web browser must "talk" to a web server somewhere
else. When web browsers talk to web servers, they speak a
language known as HTTP, which stands for HyperText Transfer
Protocol. This language is actually very simple and understandable
and is not difficult for the human eye to follow.
The method by which World Wide Web pages
are transferred over the network.
A Simple HTTP Example
The browser says:
GET / HTTP/1.0
Host: www.boutell.com
And the server replies:
HTTP/1.0 200 OK
Content-Type: text/html
<head>
<title>Welcome to Boutell.Com, Inc.!</title>
</head>
<body>
The rest of Boutell.Com's home page appears here
</body>
The first line of the browser's request,
GET / HTTP/1.0, indicates that the browser wants to see the
home page of the site, and that the browser is using version
1.0 of the HTTP protocol. The second line, Host: www.boutell.com,
indicates the web site that the browser is asking for. This
is required because many web sites may share the same IP address
on the Internet and be hosted by a single computer. The Host:
line was added a few years after the original release of HTTP
1.0 in order to accommodate this.
The first line of the server's reply, HTTP/1.0
200 OK, indicates that the server is also speaking version
1.0 of the HTTP protocol, and that the request was successful.
If the page the browser asked for did not exist, the response
would read HTTP/1.0 404 Not Found. The second line of the
server's reply, Content-Type: text/html, tells the browser
that the object it is about to receive is a web page. This
is how the browser knows what to do with the response from
the server. If this line were Content-Type: image/png, the
browser would know to expect a PNG image file rather than
a web page, and would display it accordingly.
A modern web browser would say a bit more
using the HTTP 1.1 protocol, and a modern web server would
respond with a bit more information, but the differences are
not dramatic and the above transaction is still perfectly
valid; if a browser made a request exactly like the one above
today, it would still be accepted by any web server, and the
response above would still be accepted by any browser. This
simplicity is typical of most of the protocols that grew up
around the Internet.
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