printh.c

/* 
 * $Id: printh.c,v 1.1.2.2 2004-11-14 18:05:55 tomcollins Exp $
 * Copyright (C) 2004 Tom Logic LLC 
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include "printh.h"
/* included from printh.h:
#include <stdlib.h>
#include <stdarg.h>
*/
#include <string.h>
#include <stdio.h>
#include <ctype.h>

/* vsnprinth - Custom version of sprintf for escaping strings for use on HTML
 *             pages and in cgi script parameters.
 *
 * (based on qnprintf from vpopmail)
 *
 * int vsnprinth (char *buffer, size_t size, const char *format, va_list ap)
 * int snprinth (char *buffer, size_t size, const char *format, ...);
 * int printh (const char *format, ...);
 *
 *   buffer - buffer to print string to
 *   size   - size of buffer
 *   format - a printf-style format string*
 *   ...    - variable arguments for the format string
 *
 *  NOTE: Currently supported formats: %%, %c, %s, %d/%i, %u, %ld/%li, %lu
 *  Since this function was designed to escape strings for use on HTML pages,
 *  the formats don't support any extended options.
 *
 *  Extra formats: %C (like %s, but converts string to cgi-parameter safe
 *                 version) and %H (like %s, but converts to HTML-safe version)
 *
 * Returns the number of characters that would have been printed to buffer
 * if it was big enough.  (i.e., if return value is larger than (size-1),
 * buffer received an incomplete copy of the formatted string).
 *
 * It is possible to call snprinth with a NULL buffer of 0 bytes to determine
 * how large the buffer needs to be.  This is inefficient, as snprinth has
 * to run twice.
 *
 * snprinth written November 2004 by Tom Collins <tom@tomlogic.com>
 * qnprintf written February 2004 by Tom Collins <tom@tomlogic.com>
 */
int vsnprinth (char *buffer, size_t size, const char *format, va_list ap)
{
	const char hex[] = "0123456789abcdef";

	int printed;   /* number of characters that would have been printed */
	const char *f; /* current position in format string */
	char *b;       /* current position in output buffer */
	char n[20];    /* buffer to hold string representation of number */
	
	char *s;       /* pointer to string to insert */
	char *copy;    /* pointer to replacement string for special char */
	
	int stringtype;
	#define SPRINTH_NORMAL 0
	#define SPRINTH_HTML 1
	#define SPRINTH_CGI 2
	
	if (buffer == NULL && size > 0) return -1;

	printed = 0;
	b = buffer;
	for (f = format; *f != '\0'; f++) {
		if (*f != '%') {
			if (++printed < size) *b++ = *f;
		} else {
			f++;
			s = n;
			stringtype = SPRINTH_NORMAL;
			switch (*f) {
				case '%':
					strcpy (n, "%");
					break;
					
				case 'c':
					snprintf (n, sizeof(n), "%c", va_arg (ap, int));
					break;
					
				case 'd':
				case 'i':
					snprintf (n, sizeof(n), "%d", va_arg (ap, int));
					break;
					
				case 'u':
					snprintf (n, sizeof(n), "%u", va_arg (ap, unsigned int));
					break;
					
				case 'l':
					f++;
					switch (*f) {
						case 'd':
						case 'i':
							snprintf (n, sizeof(n), "%ld", va_arg (ap, long));
							break;
					
						case 'u':
							snprintf (n, sizeof(n), "%lu", va_arg (ap, unsigned long));
							break;

						default:
							strcpy (n, "*");
					}
					break;
										
				case 's':
					s = va_arg (ap, char *);
					break;
					
				case 'H':
					s = va_arg (ap, char *);
					stringtype = SPRINTH_HTML;
					break;
					
				case 'C':
					s = va_arg (ap, char *);
					stringtype = SPRINTH_CGI;
					break;
					
				default:
					strcpy (n, "*");
			}
			
			/* now copy the string parameter into the buffer */
			while (*s != '\0') {
				copy = NULL;	/* default to no special handling */
				if (stringtype == SPRINTH_HTML) {
					switch (*s) {
						case '"': copy = "&quot;";	break;
						case '<': copy = "&lt;";	break;
						case '>': copy = "&gt;";	break;
						case '&': copy = "&amp;";	break;
					}
				} else if (stringtype == SPRINTH_CGI) {
					if (*s == ' ')
						copy = strcpy (n, "+");
					else if (! isalnum(*s) && (strchr("._-", *s) == NULL)) {
						copy = n;
						sprintf (n, "%%%c%c", hex[*s >> 4 & 0x0F], hex[*s & 0x0F]);
					}
				}
				if (copy == NULL) {
					if (++printed < size) *b++ = *s;
				} else {
					/* replace *s with buffer pointed to by copy */
					while (*copy != '\0') {
						if (++printed < size) *b++ = *copy;
						copy++;
					}
				}
				s++;
			}
		}
	}

	*b = '\0';

	/* If the formatted string doesn't fit in the buffer, zero out the buffer. */
	if (printed >= size) {
		memset (buffer, '\0', size);
	}
	
	return printed;
}

int snprinth (char *buffer, size_t size, const char *format, ...)
{
	int ret;
	
	va_list argp;
	
	va_start (argp, format);
	ret = vsnprinth (buffer, size, format, argp);
	va_end (argp);
	
	return ret;
}

int printh (const char *format, ...)
{
	int ret;
	char buffer[1024];
	
	va_list argp;
	
	va_start (argp, format);
	ret = vsnprinth (buffer, sizeof(buffer), format, argp);
	va_end (argp);
	
	printf ("%s", buffer);
	
	return ret;
}