HTTP: The Definitive Guide

URL Syntax

URLs provide a means of locating any resource on the Internet, but these resources can be accessed by different schemes (e.g., HTTP, FTP, SMTP), and URL syntax varies from scheme to scheme.

Does this mean that each different URL scheme has a radically different syntax? In practice, no. Most URLs adhere to a general URL syntax, and there is significant overlap in the style and syntax between different URL schemes.

Most URL schemes base their URL syntax on this nine-part general format:

<scheme>://<user>:<password>@<host>:<port>/<path>;<params>?<query>#<frag>

Almost no URLs contain all these components. The three most important parts of a URL are the scheme, the host, and the path. Table 2-1 summarizes the various components.

Table 2-1. General URL components

Component	Description	Default value
scheme	Which protocol to use when accessing a server to get a resource.	None
user	The username some schemes require to access a resource.	anonymous
password	The password that may be included after the username, separated by a colon (:).	<Email address>
host	The hostname or dotted IP address of the server hosting the resource.	None
port	The port number on which the server hosting the resource is listening. Many schemes have default port numbers (the default port number for HTTP is 80).	Scheme-specific
path	The local name for the resource on the server, separated from the previous URL components by a slash (/). The syntax of the path component is server- and ...