Copy strings URL-escaped

	The function [[strcpy_escaped]] copies [[s2]] to [[s1]] and
	escapes the result, according to the rules for URLs:
	characters [[/?=#%]] and space are coded as [%XX]], where
	[[XX]] is the hexadeciaml code for the character.

	[[s1]] must have enough room; no check is made. The function
	returns a pointer to [[s1]].

<<*>>=
#include <config.h>

#define hex(n) ((n) < 10 ? (n) + '0' : (n) + 'A' - 10)

EXPORT int URL_strcpy_escaped(char *s1, const char *s2)
{
    char *t = s1;

    for (; *s2; s2++)
	if (*s2 == '/' || *s2 == '+' || *s2 == '?' || *s2 == '#' ||
	    *s2 == '%' || *s2 <= ' ' || *s2 == '\177' || *s2 == ':' ||
	    *s2 == '@') {
	    *t++ = '%'; *t++ = hex(*s2/16); *t++ = hex(*s2 % 16);
	} else
	    *t++ = *s2;
    *t = '\0';
    return t - s1;
}