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\libdoc{url}{Analysing and constructing URL}
This library deals with the analysis and construction of a URL,
\textbf{U}niversal \textbf{R}esource \textbf{L}ocator. URL is the
basis for communicating locations of resources (data) on the web.
A URL consists of a protocol identifier (e.g.\ \idx{HTTP}, \idx{FTP}),
and a protocol-specific syntax further defining the location. URLs
are standardized in \idx{RFC-1738}.
The implementation in this library covers only a small portion of the
defined protocols. Though the initial implementation followed RFC-1738
strictly, the current is more relaxed to deal with frequent violations
of the standard encountered in practical use.
This library contains code by Jan Wielemaker who wrote the initial
version and Lukas Faulstich who added various extensions.
\begin{description}
\predicate{parse_url}{2}{?URL, ?Parts}
Construct or analyse a \arg{URL}. \arg{URL} is an atom holding a
URL or a variable. \arg{Parts} is a list of components. Each
component is of the format \term{\arg{Name}}{Value}. Defined
components are:
\begin{description}
\termitem{protocol}{Protocol}
The used protocol. This is, after the optional \const{url:}, an
identifier separated from the remainder of the URL using \const{:}.
parse_url/2 assumes the \const{http} protocol if no protocol is
specified and the URL can be parsed as a valid HTTP url. In addition
to the RFC-1738 specified protocols, the \const{file:} protocol is
supported as well.
\termitem{host}{Host}
Host-name or IP-address on which the resource is located. Supported
by all network-based protocols.
\termitem{port}{Port}
Integer port-number to access on the \arg{Host}. This only appears
if the port is explicitly specified in the URL. Implicit default
ports (e.g.\ 80 for HTTP) do \emph{not} appear in the part-list.
\termitem{path}{Path}
(File-) path addressed by the URL. This is supported for the
\const{ftp}, \const{http} and \const{file} protocols. If no path
appears, the library generates the path \file{/}.
\termitem{search}{ListOfNameValue}
Search-specification of HTTP URL. This is the part after the \chr{?},
normally used to transfer data from HTML forms that use the
`\const{GET}' protocol. In the URL it consists of a www-form-encoded
list of \arg{Name}=\arg{Value} pairs. This is mapped to a list of
Prolog \arg{Name}=\arg{Value} terms with decoded names and values.
\termitem{fragment}{Fragment}
Fragment specification of HTTP URL. This is the part after the \verb$#$
character.
\end{description}
The example below illustrates the all this for an HTTP UTL.
\begin{code}
?- parse_url('http://swi.psy.uva.nl/message.cgi?msg=Hello+World%21#x',
P).
P = [ protocol(http),
host('swi.psy.uva.nl'),
fragment(x),
search([ msg = 'Hello World!'
]),
path('/message.cgi')
].
\end{code}
By instantiating the parts-list this predicate can be used to create
a URL.
\predicate{parse_url}{3}{?URL, +BaseURL, ?Parts}
Same as parse_url/2, but dealing a url that is relative to the given
\arg{BaseURL}. This is used to analyse or construct a URI found in
the document behind \arg{BaseURL}.
\predicate{global_url}{3}{+URL, +BaseURL, -AbsoluteUrl}
Transform a (possibly) relative URL into a global one.
\predicate{http_location}{2}{?Parts, ?Location}
Similar to parse_url/2, but only deals with the location part of
an HTTP URL. That is, the path, search and fragment specifiers.
In the HTTP protocol, the first line of a message is
\begin{quote}
\arg{Action} \arg{Location} [\const{HTTP/}\arg{HttpVersion}]
\end{quote}
\arg{Location} is either an atom or a code-list.
\predicate{www_form_encode}{2}{?Value, ?WwwFormEncoded}
Translate between a string-literal and the x-www-form-encoded
representation used in path and search specifications of the HTTP
protocol.
Encoding implies mapping space to +, preserving alpha-numercial
characters, map newlines to \%0D\%0A and anything else to \%XX.
When decoding, newlines appear as a single newline (10) character.
\end{description}
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