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<HEADER>
<TITLE>HTParse: URI parsing in the WWW Library</TITLE>
<NEXTID N="1">
</HEADER>
<BODY>
<H1>HTParse</H1>
This module is a part of the <A HREF="Overview.html">CERN Common WWW Library</A>. It contains code to parse URIs and various related things such as:
<UL>
<LI> Parse a URI relative to another URI
<LI> Get the URI relative to another URI
<LI> Remove redundant data from the URI (HTSimplify and HTCanon)
<LI> Expand a local host name into a full domain name (HTExpand)
<LI> Search a URI for illigal characters in order to prevent security holes
<LI> Escape and Unescape a URI for <A HREF="http://info.cern.ch/hypertext/WWW/Addressing/URL/4_URI_Recommentations.html">reserved characters in URLs</A>
</UL>
Implemented by <A NAME=z0 HREF="HTParse.c">HTParse.c</A>.
<PRE>
#ifndef HTPARSE_H
#define HTPARSE_H
#include "HTUtils.h"
</PRE>
<H2>HTParse: Parse a URI relative to another URI</H2>
This returns those parts of a name which are given (and requested) substituting
bits from the related name where necessary.
<H3>Control Flags for HTParse</H3>
The following are flag bits which may be ORed together to form a number
to give the 'wanted' argument to HTParse.
<PRE>
#define PARSE_ACCESS 16
#define PARSE_HOST 8
#define PARSE_PATH 4
#define PARSE_ANCHOR 2
#define PARSE_PUNCTUATION 1
#define PARSE_ALL 31
</PRE>
<H3>On entry</H3>
<DL>
<DT>aName
<DD> A filename given
<DT>relatedName
<DD> A name relative to which
aName is to be parsed
<DT>wanted
<DD> A mask for the bits which
are wanted.
</DL>
<H3>On exit,</H3>
<DL>
<DT>returns
<DD> A pointer to a malloc'd string
which MUST BE FREED
</DL>
<PRE>
PUBLIC char * HTParse PARAMS(( const char * aName,
const char * relatedName,
int wanted));
</PRE>
<H2>HTStrip: Strip white space off a string</H2>
<H3>On exit</H3>Return value points to first non-white
character, or to 0 if none.<P>
All trailing white space is OVERWRITTEN
with zero.
<PRE>#ifdef __STDC__
extern char * HTStrip(char * s);
#else
extern char * HTStrip();
#endif
</PRE>
<H2>HTSimplify: Simplify a UTL</H2>
A URI is allowed to contain the seqeunce xxx/../ which may be
replaced by "" , and the seqeunce "/./" which may be replaced by "/".
Simplification helps us recognize duplicate URIs. Thus, the following
transformations are done:
<UL>
<LI> /etc/junk/../fred becomes /etc/fred
<LI> /etc/junk/./fred becomes /etc/junk/fred
</UL>
but we should NOT change
<UL>
<LI> http://fred.xxx.edu/../.. or
<LI> ../../albert.html
</UL>
In the same manner, the following prefixed are preserved:
<UL>
<LI> ./<etc>
<LI> //<etc>
</UL>
In order to avoid empty URIs the following URIs become:
<UL>
<LI> /fred/.. becomes /fred/..
<LI> /fred/././.. becomes /fred/..
<LI> /fred/.././junk/.././ becomes /fred/..
</UL>
If more than one set of `://' is found (several proxies in cascade) then
only the part after the last `://' is simplified.
<PRE>
PUBLIC char *HTSimplify PARAMS((char *filename));
</PRE>
<H2>HTRelative: Make Relative (Partial)
URI</H2>This function creates and returns
a string which gives an expression
of one address as related to another.
Where there is no relation, an absolute
address is retured.
<H3>On entry,</H3>Both names must be absolute, fully
qualified names of nodes (no anchor
bits)
<H3>On exit,</H3>The return result points to a newly
allocated name which, if parsed by
HTParse relative to relatedName,
will yield aName. The caller is responsible
for freeing the resulting name later.
<PRE>#ifdef __STDC__
extern char * HTRelative(const char * aName, const char *relatedName);
#else
extern char * HTRelative();
#endif
</PRE>
<H2>HTExpand: Expand a Local Host Name Into a Full Domain Name</H2>
This function expands the host name of the URI from a local name to a
full domain name, converts the host name to lower case and takes away
`:80', `:70' and `:21'. The advantage by doing this is that we only have
one entry in the host case and one entry in the document cache.
<PRE>
PUBLIC char *HTCanon PARAMS (( char ** filename,
char * host));
</PRE>
<H2>HTEscape: Encode unacceptable characters in string</H2>
This funtion takes a string containing
any sequence of ASCII characters,
and returns a malloced string containing
the same infromation but with all
"unacceptable" characters represented
in the form %xy where X and Y are
two hex digits.
<PRE>
PUBLIC char * HTEscape PARAMS((CONST char * str, unsigned char mask));
</PRE>
The following are valid mask values. The terms are the BNF names in the
URI document.
<PRE>
#define URL_XALPHAS (unsigned char) 1
#define URL_XPALPHAS (unsigned char) 2
#define URL_PATH (unsigned char) 4
</PRE>
<H2>HTUnEscape: Decode %xx escaped characters</H2>
This function takes a pointer to a string in which character smay
have been encoded in %xy form, where xy is the acsii hex code for character
16x+y. The string is converted in place, as it will never grow.
<PRE>
extern char * HTUnEscape PARAMS(( char * str));
</PRE>
<H2>Prevent Security Holes</H2>
<CODE>HTCleanTelnetString()</CODE> makes sure that the given string
doesn't contain characters that could cause security holes, such as
newlines in ftp, gopher, news or telnet URLs; more specifically:
allows everything between hexadesimal ASCII 20-7E, and also A0-FE,
inclusive.
<DL>
<DT> <CODE>str</CODE>
<DD> the string that is *modified* if necessary. The string will be
truncated at the first illegal character that is encountered.
<DT>returns
<DD> YES, if the string was modified.
NO, otherwise.
</DL>
<PRE>
PUBLIC BOOL HTCleanTelnetString PARAMS((char * str));
</PRE>
<PRE>
#endif /* HTPARSE_H */
</PRE>
End of HTParse Module
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