132 lines
4.3 KiB
TeX
132 lines
4.3 KiB
TeX
\chapter{Parsing and Processing URIs}\label{cha:uri}
|
|
|
|
The \ex{uri} structure contains a library for dealing with URIs.
|
|
and is out-of-date by now---it is build up on RFC 1360 of 1994 which
|
|
was replaced by RFC 1738, RFC 1808, and finally RFC 2396 of 1998.
|
|
|
|
\section{Notes on URI Syntax}
|
|
|
|
A URI (Uniform Resource Identifier) is of following syntax:
|
|
%
|
|
\begin{inset}
|
|
[\var{scheme}] \verb|:| \var{path} [\verb|?| \var{search}] [\verb|#| \var{fragid}]
|
|
\end{inset}
|
|
%
|
|
Parts in brackets may be omitted.
|
|
|
|
The URI contains characters like \verb|:| to indicate its different
|
|
parts. Some special characters are \emph{escaped} if they are a
|
|
regular part of a name and not indicators for the structure of a URI.
|
|
Escape sequences are of following scheme: \verb|%|\var{h}\var{h} where \var{h}
|
|
is a hexadecimal digit. The hexadecimal number refers to the
|
|
ASCII of the escaped character, e.g.\ \verb|%20| is space (ASCII
|
|
32) and \verb|%61| is `a' (ASCII 97). This module
|
|
provides procedures to escape and unescape strings that are meant to
|
|
be used in a URI.
|
|
|
|
\section{Procedures}
|
|
|
|
\defun{unescape-uri}{string [start] [end]}{string}
|
|
\begin{desc}
|
|
\ex{Unescape-uri} unescapes a string. If \var{start} and/or \var{end} are
|
|
specified, they specify start and end positions within \var{string}
|
|
should be unescaped.
|
|
\end{desc}
|
|
%
|
|
This procedure should only be used \emph{after} the URI was parsed,
|
|
since unescaping may introduce characters that blow up the
|
|
parse---that's why escape sequences are used in URIs.
|
|
|
|
\defvar{uri-escaped-chars}{char-set}
|
|
\begin{desc}
|
|
This is a set of characters (in the sense of SRFI~14) which are
|
|
escaped in URIs. RFC 2396 defines this set as all characters which
|
|
are neither letters, nor digits, nor one of the following characters:
|
|
\verb|-|, \verb|_|, \verb|.|, \verb|!|, %$
|
|
\verb|~|, \verb|*|, \verb|'|, \verb|(|, \verb|)|.
|
|
\end{desc}
|
|
|
|
\defun{escape-uri} {string [escaped-chars]} {string}
|
|
\begin{desc}
|
|
This procedure escapes characters of \var{string} that are in
|
|
\var{escaped\=chars}. \var{Escaped\=chars} defaults to
|
|
\ex{uri\=escaped\=chars}.
|
|
\end{desc}
|
|
%
|
|
Be careful with using this procedure to chunks of text with
|
|
syntactically meaningful reserved characters (e.g., paths with URI
|
|
slashes or colons)---they'll be escaped, and lose their special
|
|
meaning. E.g.\ it would be a mistake to apply \ex{escape-uri} to
|
|
\begin{verbatim}
|
|
//lcs.mit.edu:8001/foo/bar.html
|
|
\end{verbatim}
|
|
%
|
|
because the sla\-shes and co\-lons would be escaped.
|
|
|
|
\defun{split-uri}{uri start end} {list}
|
|
\begin{desc}
|
|
This procedure splits \var{uri} at slashes. Only the substring given
|
|
with \var{start} (inclusive) and \var{end} (exclusive) as indices is
|
|
considered. \var{start} and $\var{end} - 1$ have to be within the
|
|
range of \var{uri}. Otherwise an \ex{index-out-of-range} exception
|
|
will be raised.
|
|
|
|
Example: \codex{(split-uri "foo/bar/colon" 4 11)} returns
|
|
\codex{("bar" "col")}
|
|
\end{desc}
|
|
|
|
\defun{uri-path->uri}{path}{string}
|
|
\begin{desc}
|
|
This procedure generates a path out of a URI path list by inserting
|
|
slashes between the elements of \var{plist}.
|
|
\end{desc}
|
|
%
|
|
If you want to use the resulting string for further operation, you
|
|
should escape the elements of \var{plist} in case they contain
|
|
slashes, like so:
|
|
%
|
|
\begin{verbatim}
|
|
(uri-path->uri (map escape-uri pathlist))
|
|
\end{verbatim}
|
|
|
|
\defun{simplify-uri-path}{path}{list}
|
|
\begin{desc}
|
|
This procedure simplifies a URI path. It removes \verb|"."| and
|
|
\verb|"/.."| entries from path, and removes parts before a root.
|
|
The result is a list, or \sharpf{} if the path tries to back up past
|
|
root.
|
|
\end{desc}
|
|
%
|
|
According to RFC~2396, relative paths are considered not to start with
|
|
\verb|/|. They are appended to a base URL path and then simplified.
|
|
So before you start to simplify a URL try to find out if it is a
|
|
relative path (i.e. it does not start with a \verb|/|).
|
|
|
|
Examples:
|
|
%
|
|
\begin{alltt}
|
|
(simplify-uri-path (split-uri "/foo/bar/baz/.." 0 15))
|
|
\(\Rightarrow\) ("" "foo" "bar")
|
|
|
|
(simplify-uri-path (split-uri "foo/bar/baz/../../.." 0 20))
|
|
\(\Rightarrow\) ()
|
|
|
|
(simplify-uri-path (split-uri "/foo/../.." 0 10))
|
|
\(\Rightarrow\) #f
|
|
|
|
(simplify-uri-path (split-uri "foo/bar//" 0 9))
|
|
\(\Rightarrow\) ("")
|
|
|
|
(simplify-uri-path (split-uri "foo/bar/" 0 8))
|
|
\(\Rightarrow\) ("")
|
|
|
|
(simplify-uri-path (split-uri "/foo/bar//baz/../.." 0 19))
|
|
\(\Rightarrow\) #f
|
|
\end{alltt}
|
|
|
|
|
|
%%% Local Variables:
|
|
%%% mode: latex
|
|
%%% TeX-master: "man"
|
|
%%% End:
|