xref: /openbsd/usr.bin/mandoc/html.c (revision cecf84d4) 
1 /*	$OpenBSD: html.c,v 1.56 2015/03/27 21:17:16 schwarze Exp $ */
2 /*
3  * Copyright (c) 2008-2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
4  * Copyright (c) 2011-2015 Ingo Schwarze <schwarze@openbsd.org>
5  *
6  * Permission to use, copy, modify, and distribute this software for any
7  * purpose with or without fee is hereby granted, provided that the above
8  * copyright notice and this permission notice appear in all copies.
9  *
10  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
11  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
13  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17  */
18 #include <sys/types.h>
19 
20 #include <assert.h>
21 #include <ctype.h>
22 #include <stdarg.h>
23 #include <stdio.h>
24 #include <stdint.h>
25 #include <stdlib.h>
26 #include <string.h>
27 #include <unistd.h>
28 
29 #include "mandoc.h"
30 #include "mandoc_aux.h"
31 #include "out.h"
32 #include "html.h"
33 #include "manconf.h"
34 #include "main.h"
35 
36 struct	htmldata {
37 	const char	 *name;
38 	int		  flags;
39 #define	HTML_CLRLINE	 (1 << 0)
40 #define	HTML_NOSTACK	 (1 << 1)
41 #define	HTML_AUTOCLOSE	 (1 << 2) /* Tag has auto-closure. */
42 };
43 
44 static	const struct htmldata htmltags[TAG_MAX] = {
45 	{"html",	HTML_CLRLINE}, /* TAG_HTML */
46 	{"head",	HTML_CLRLINE}, /* TAG_HEAD */
47 	{"body",	HTML_CLRLINE}, /* TAG_BODY */
48 	{"meta",	HTML_CLRLINE | HTML_NOSTACK | HTML_AUTOCLOSE}, /* TAG_META */
49 	{"title",	HTML_CLRLINE}, /* TAG_TITLE */
50 	{"div",		HTML_CLRLINE}, /* TAG_DIV */
51 	{"h1",		0}, /* TAG_H1 */
52 	{"h2",		0}, /* TAG_H2 */
53 	{"span",	0}, /* TAG_SPAN */
54 	{"link",	HTML_CLRLINE | HTML_NOSTACK | HTML_AUTOCLOSE}, /* TAG_LINK */
55 	{"br",		HTML_CLRLINE | HTML_NOSTACK | HTML_AUTOCLOSE}, /* TAG_BR */
56 	{"a",		0}, /* TAG_A */
57 	{"table",	HTML_CLRLINE}, /* TAG_TABLE */
58 	{"tbody",	HTML_CLRLINE}, /* TAG_TBODY */
59 	{"col",		HTML_CLRLINE | HTML_NOSTACK | HTML_AUTOCLOSE}, /* TAG_COL */
60 	{"tr",		HTML_CLRLINE}, /* TAG_TR */
61 	{"td",		HTML_CLRLINE}, /* TAG_TD */
62 	{"li",		HTML_CLRLINE}, /* TAG_LI */
63 	{"ul",		HTML_CLRLINE}, /* TAG_UL */
64 	{"ol",		HTML_CLRLINE}, /* TAG_OL */
65 	{"dl",		HTML_CLRLINE}, /* TAG_DL */
66 	{"dt",		HTML_CLRLINE}, /* TAG_DT */
67 	{"dd",		HTML_CLRLINE}, /* TAG_DD */
68 	{"blockquote",	HTML_CLRLINE}, /* TAG_BLOCKQUOTE */
69 	{"pre",		HTML_CLRLINE }, /* TAG_PRE */
70 	{"b",		0 }, /* TAG_B */
71 	{"i",		0 }, /* TAG_I */
72 	{"code",	0 }, /* TAG_CODE */
73 	{"small",	0 }, /* TAG_SMALL */
74 	{"style",	HTML_CLRLINE}, /* TAG_STYLE */
75 	{"math",	HTML_CLRLINE}, /* TAG_MATH */
76 	{"mrow",	0}, /* TAG_MROW */
77 	{"mi",		0}, /* TAG_MI */
78 	{"mo",		0}, /* TAG_MO */
79 	{"msup",	0}, /* TAG_MSUP */
80 	{"msub",	0}, /* TAG_MSUB */
81 	{"msubsup",	0}, /* TAG_MSUBSUP */
82 	{"mfrac",	0}, /* TAG_MFRAC */
83 	{"msqrt",	0}, /* TAG_MSQRT */
84 	{"mfenced",	0}, /* TAG_MFENCED */
85 	{"mtable",	0}, /* TAG_MTABLE */
86 	{"mtr",		0}, /* TAG_MTR */
87 	{"mtd",		0}, /* TAG_MTD */
88 	{"munderover",	0}, /* TAG_MUNDEROVER */
89 	{"munder",	0}, /* TAG_MUNDER*/
90 	{"mover",	0}, /* TAG_MOVER*/
91 };
92 
93 static	const char	*const htmlattrs[ATTR_MAX] = {
94 	"name", /* ATTR_NAME */
95 	"rel", /* ATTR_REL */
96 	"href", /* ATTR_HREF */
97 	"type", /* ATTR_TYPE */
98 	"media", /* ATTR_MEDIA */
99 	"class", /* ATTR_CLASS */
100 	"style", /* ATTR_STYLE */
101 	"id", /* ATTR_ID */
102 	"colspan", /* ATTR_COLSPAN */
103 	"charset", /* ATTR_CHARSET */
104 	"open", /* ATTR_OPEN */
105 	"close", /* ATTR_CLOSE */
106 	"mathvariant", /* ATTR_MATHVARIANT */
107 };
108 
109 static	const char	*const roffscales[SCALE_MAX] = {
110 	"cm", /* SCALE_CM */
111 	"in", /* SCALE_IN */
112 	"pc", /* SCALE_PC */
113 	"pt", /* SCALE_PT */
114 	"em", /* SCALE_EM */
115 	"em", /* SCALE_MM */
116 	"ex", /* SCALE_EN */
117 	"ex", /* SCALE_BU */
118 	"em", /* SCALE_VS */
119 	"ex", /* SCALE_FS */
120 };
121 
122 static	void	 bufncat(struct html *, const char *, size_t);
123 static	void	 print_ctag(struct html *, struct tag *);
124 static	int	 print_escape(char);
125 static	int	 print_encode(struct html *, const char *, int);
126 static	void	 print_metaf(struct html *, enum mandoc_esc);
127 static	void	 print_attr(struct html *, const char *, const char *);
128 
129 
130 void *
131 html_alloc(const struct mchars *mchars, const struct manoutput *outopts)
132 {
133 	struct html	*h;
134 
135 	h = mandoc_calloc(1, sizeof(struct html));
136 
137 	h->tags.head = NULL;
138 	h->symtab = mchars;
139 
140 	h->style = outopts->style;
141 	h->base_man = outopts->man;
142 	h->base_includes = outopts->includes;
143 	if (outopts->fragment)
144 		h->oflags |= HTML_FRAGMENT;
145 
146 	return(h);
147 }
148 
149 void
150 html_free(void *p)
151 {
152 	struct tag	*tag;
153 	struct html	*h;
154 
155 	h = (struct html *)p;
156 
157 	while ((tag = h->tags.head) != NULL) {
158 		h->tags.head = tag->next;
159 		free(tag);
160 	}
161 
162 	free(h);
163 }
164 
165 void
166 print_gen_head(struct html *h)
167 {
168 	struct htmlpair	 tag[4];
169 	struct tag	*t;
170 
171 	tag[0].key = ATTR_CHARSET;
172 	tag[0].val = "utf-8";
173 	print_otag(h, TAG_META, 1, tag);
174 
175 	/*
176 	 * Print a default style-sheet.
177 	 */
178 	t = print_otag(h, TAG_STYLE, 0, NULL);
179 	print_text(h, "table.head, table.foot { width: 100%; }\n"
180 	      "td.head-rtitle, td.foot-os { text-align: right; }\n"
181 	      "td.head-vol { text-align: center; }\n"
182 	      "table.foot td { width: 50%; }\n"
183 	      "table.head td { width: 33%; }\n"
184 	      "div.spacer { margin: 1em 0; }\n");
185 	print_tagq(h, t);
186 
187 	if (h->style) {
188 		tag[0].key = ATTR_REL;
189 		tag[0].val = "stylesheet";
190 		tag[1].key = ATTR_HREF;
191 		tag[1].val = h->style;
192 		tag[2].key = ATTR_TYPE;
193 		tag[2].val = "text/css";
194 		tag[3].key = ATTR_MEDIA;
195 		tag[3].val = "all";
196 		print_otag(h, TAG_LINK, 4, tag);
197 	}
198 }
199 
200 static void
201 print_metaf(struct html *h, enum mandoc_esc deco)
202 {
203 	enum htmlfont	 font;
204 
205 	switch (deco) {
206 	case ESCAPE_FONTPREV:
207 		font = h->metal;
208 		break;
209 	case ESCAPE_FONTITALIC:
210 		font = HTMLFONT_ITALIC;
211 		break;
212 	case ESCAPE_FONTBOLD:
213 		font = HTMLFONT_BOLD;
214 		break;
215 	case ESCAPE_FONTBI:
216 		font = HTMLFONT_BI;
217 		break;
218 	case ESCAPE_FONT:
219 		/* FALLTHROUGH */
220 	case ESCAPE_FONTROMAN:
221 		font = HTMLFONT_NONE;
222 		break;
223 	default:
224 		abort();
225 		/* NOTREACHED */
226 	}
227 
228 	if (h->metaf) {
229 		print_tagq(h, h->metaf);
230 		h->metaf = NULL;
231 	}
232 
233 	h->metal = h->metac;
234 	h->metac = font;
235 
236 	switch (font) {
237 	case HTMLFONT_ITALIC:
238 		h->metaf = print_otag(h, TAG_I, 0, NULL);
239 		break;
240 	case HTMLFONT_BOLD:
241 		h->metaf = print_otag(h, TAG_B, 0, NULL);
242 		break;
243 	case HTMLFONT_BI:
244 		h->metaf = print_otag(h, TAG_B, 0, NULL);
245 		print_otag(h, TAG_I, 0, NULL);
246 		break;
247 	default:
248 		break;
249 	}
250 }
251 
252 int
253 html_strlen(const char *cp)
254 {
255 	size_t		 rsz;
256 	int		 skip, sz;
257 
258 	/*
259 	 * Account for escaped sequences within string length
260 	 * calculations.  This follows the logic in term_strlen() as we
261 	 * must calculate the width of produced strings.
262 	 * Assume that characters are always width of "1".  This is
263 	 * hacky, but it gets the job done for approximation of widths.
264 	 */
265 
266 	sz = 0;
267 	skip = 0;
268 	while (1) {
269 		rsz = strcspn(cp, "\\");
270 		if (rsz) {
271 			cp += rsz;
272 			if (skip) {
273 				skip = 0;
274 				rsz--;
275 			}
276 			sz += rsz;
277 		}
278 		if ('\0' == *cp)
279 			break;
280 		cp++;
281 		switch (mandoc_escape(&cp, NULL, NULL)) {
282 		case ESCAPE_ERROR:
283 			return(sz);
284 		case ESCAPE_UNICODE:
285 			/* FALLTHROUGH */
286 		case ESCAPE_NUMBERED:
287 			/* FALLTHROUGH */
288 		case ESCAPE_SPECIAL:
289 			/* FALLTHROUGH */
290 		case ESCAPE_OVERSTRIKE:
291 			if (skip)
292 				skip = 0;
293 			else
294 				sz++;
295 			break;
296 		case ESCAPE_SKIPCHAR:
297 			skip = 1;
298 			break;
299 		default:
300 			break;
301 		}
302 	}
303 	return(sz);
304 }
305 
306 static int
307 print_escape(char c)
308 {
309 
310 	switch (c) {
311 	case '<':
312 		printf("&lt;");
313 		break;
314 	case '>':
315 		printf("&gt;");
316 		break;
317 	case '&':
318 		printf("&amp;");
319 		break;
320 	case '"':
321 		printf("&quot;");
322 		break;
323 	case ASCII_NBRSP:
324 		putchar('-');
325 		break;
326 	case ASCII_HYPH:
327 		putchar('-');
328 		/* FALLTHROUGH */
329 	case ASCII_BREAK:
330 		break;
331 	default:
332 		return(0);
333 	}
334 	return(1);
335 }
336 
337 static int
338 print_encode(struct html *h, const char *p, int norecurse)
339 {
340 	size_t		 sz;
341 	int		 c, len, nospace;
342 	const char	*seq;
343 	enum mandoc_esc	 esc;
344 	static const char rejs[9] = { '\\', '<', '>', '&', '"',
345 		ASCII_NBRSP, ASCII_HYPH, ASCII_BREAK, '\0' };
346 
347 	nospace = 0;
348 
349 	while ('\0' != *p) {
350 		if (HTML_SKIPCHAR & h->flags && '\\' != *p) {
351 			h->flags &= ~HTML_SKIPCHAR;
352 			p++;
353 			continue;
354 		}
355 
356 		sz = strcspn(p, rejs);
357 
358 		fwrite(p, 1, sz, stdout);
359 		p += (int)sz;
360 
361 		if ('\0' == *p)
362 			break;
363 
364 		if (print_escape(*p++))
365 			continue;
366 
367 		esc = mandoc_escape(&p, &seq, &len);
368 		if (ESCAPE_ERROR == esc)
369 			break;
370 
371 		switch (esc) {
372 		case ESCAPE_FONT:
373 			/* FALLTHROUGH */
374 		case ESCAPE_FONTPREV:
375 			/* FALLTHROUGH */
376 		case ESCAPE_FONTBOLD:
377 			/* FALLTHROUGH */
378 		case ESCAPE_FONTITALIC:
379 			/* FALLTHROUGH */
380 		case ESCAPE_FONTBI:
381 			/* FALLTHROUGH */
382 		case ESCAPE_FONTROMAN:
383 			if (0 == norecurse)
384 				print_metaf(h, esc);
385 			continue;
386 		case ESCAPE_SKIPCHAR:
387 			h->flags |= HTML_SKIPCHAR;
388 			continue;
389 		default:
390 			break;
391 		}
392 
393 		if (h->flags & HTML_SKIPCHAR) {
394 			h->flags &= ~HTML_SKIPCHAR;
395 			continue;
396 		}
397 
398 		switch (esc) {
399 		case ESCAPE_UNICODE:
400 			/* Skip past "u" header. */
401 			c = mchars_num2uc(seq + 1, len - 1);
402 			break;
403 		case ESCAPE_NUMBERED:
404 			c = mchars_num2char(seq, len);
405 			if (c < 0)
406 				continue;
407 			break;
408 		case ESCAPE_SPECIAL:
409 			c = mchars_spec2cp(h->symtab, seq, len);
410 			if (c <= 0)
411 				continue;
412 			break;
413 		case ESCAPE_NOSPACE:
414 			if ('\0' == *p)
415 				nospace = 1;
416 			continue;
417 		case ESCAPE_OVERSTRIKE:
418 			if (len == 0)
419 				continue;
420 			c = seq[len - 1];
421 			break;
422 		default:
423 			continue;
424 		}
425 		if ((c < 0x20 && c != 0x09) ||
426 		    (c > 0x7E && c < 0xA0))
427 			c = 0xFFFD;
428 		if (c > 0x7E)
429 			printf("&#%d;", c);
430 		else if ( ! print_escape(c))
431 			putchar(c);
432 	}
433 
434 	return(nospace);
435 }
436 
437 static void
438 print_attr(struct html *h, const char *key, const char *val)
439 {
440 	printf(" %s=\"", key);
441 	(void)print_encode(h, val, 1);
442 	putchar('\"');
443 }
444 
445 struct tag *
446 print_otag(struct html *h, enum htmltag tag,
447 		int sz, const struct htmlpair *p)
448 {
449 	int		 i;
450 	struct tag	*t;
451 
452 	/* Push this tags onto the stack of open scopes. */
453 
454 	if ( ! (HTML_NOSTACK & htmltags[tag].flags)) {
455 		t = mandoc_malloc(sizeof(struct tag));
456 		t->tag = tag;
457 		t->next = h->tags.head;
458 		h->tags.head = t;
459 	} else
460 		t = NULL;
461 
462 	if ( ! (HTML_NOSPACE & h->flags))
463 		if ( ! (HTML_CLRLINE & htmltags[tag].flags)) {
464 			/* Manage keeps! */
465 			if ( ! (HTML_KEEP & h->flags)) {
466 				if (HTML_PREKEEP & h->flags)
467 					h->flags |= HTML_KEEP;
468 				putchar(' ');
469 			} else
470 				printf("&#160;");
471 		}
472 
473 	if ( ! (h->flags & HTML_NONOSPACE))
474 		h->flags &= ~HTML_NOSPACE;
475 	else
476 		h->flags |= HTML_NOSPACE;
477 
478 	/* Print out the tag name and attributes. */
479 
480 	printf("<%s", htmltags[tag].name);
481 	for (i = 0; i < sz; i++)
482 		print_attr(h, htmlattrs[p[i].key], p[i].val);
483 
484 	/* Accommodate for "well-formed" singleton escaping. */
485 
486 	if (HTML_AUTOCLOSE & htmltags[tag].flags)
487 		putchar('/');
488 
489 	putchar('>');
490 
491 	h->flags |= HTML_NOSPACE;
492 
493 	if ((HTML_AUTOCLOSE | HTML_CLRLINE) & htmltags[tag].flags)
494 		putchar('\n');
495 
496 	return(t);
497 }
498 
499 static void
500 print_ctag(struct html *h, struct tag *tag)
501 {
502 
503 	/*
504 	 * Remember to close out and nullify the current
505 	 * meta-font and table, if applicable.
506 	 */
507 	if (tag == h->metaf)
508 		h->metaf = NULL;
509 	if (tag == h->tblt)
510 		h->tblt = NULL;
511 
512 	printf("</%s>", htmltags[tag->tag].name);
513 	if (HTML_CLRLINE & htmltags[tag->tag].flags) {
514 		h->flags |= HTML_NOSPACE;
515 		putchar('\n');
516 	}
517 
518 	h->tags.head = tag->next;
519 	free(tag);
520 }
521 
522 void
523 print_gen_decls(struct html *h)
524 {
525 
526 	puts("<!DOCTYPE html>");
527 }
528 
529 void
530 print_text(struct html *h, const char *word)
531 {
532 
533 	if ( ! (HTML_NOSPACE & h->flags)) {
534 		/* Manage keeps! */
535 		if ( ! (HTML_KEEP & h->flags)) {
536 			if (HTML_PREKEEP & h->flags)
537 				h->flags |= HTML_KEEP;
538 			putchar(' ');
539 		} else
540 			printf("&#160;");
541 	}
542 
543 	assert(NULL == h->metaf);
544 	switch (h->metac) {
545 	case HTMLFONT_ITALIC:
546 		h->metaf = print_otag(h, TAG_I, 0, NULL);
547 		break;
548 	case HTMLFONT_BOLD:
549 		h->metaf = print_otag(h, TAG_B, 0, NULL);
550 		break;
551 	case HTMLFONT_BI:
552 		h->metaf = print_otag(h, TAG_B, 0, NULL);
553 		print_otag(h, TAG_I, 0, NULL);
554 		break;
555 	default:
556 		break;
557 	}
558 
559 	assert(word);
560 	if ( ! print_encode(h, word, 0)) {
561 		if ( ! (h->flags & HTML_NONOSPACE))
562 			h->flags &= ~HTML_NOSPACE;
563 		h->flags &= ~HTML_NONEWLINE;
564 	} else
565 		h->flags |= HTML_NOSPACE | HTML_NONEWLINE;
566 
567 	if (h->metaf) {
568 		print_tagq(h, h->metaf);
569 		h->metaf = NULL;
570 	}
571 
572 	h->flags &= ~HTML_IGNDELIM;
573 }
574 
575 void
576 print_tagq(struct html *h, const struct tag *until)
577 {
578 	struct tag	*tag;
579 
580 	while ((tag = h->tags.head) != NULL) {
581 		print_ctag(h, tag);
582 		if (until && tag == until)
583 			return;
584 	}
585 }
586 
587 void
588 print_stagq(struct html *h, const struct tag *suntil)
589 {
590 	struct tag	*tag;
591 
592 	while ((tag = h->tags.head) != NULL) {
593 		if (suntil && tag == suntil)
594 			return;
595 		print_ctag(h, tag);
596 	}
597 }
598 
599 void
600 print_paragraph(struct html *h)
601 {
602 	struct tag	*t;
603 	struct htmlpair	 tag;
604 
605 	PAIR_CLASS_INIT(&tag, "spacer");
606 	t = print_otag(h, TAG_DIV, 1, &tag);
607 	print_tagq(h, t);
608 }
609 
610 
611 void
612 bufinit(struct html *h)
613 {
614 
615 	h->buf[0] = '\0';
616 	h->buflen = 0;
617 }
618 
619 void
620 bufcat_style(struct html *h, const char *key, const char *val)
621 {
622 
623 	bufcat(h, key);
624 	bufcat(h, ":");
625 	bufcat(h, val);
626 	bufcat(h, ";");
627 }
628 
629 void
630 bufcat(struct html *h, const char *p)
631 {
632 
633 	/*
634 	 * XXX This is broken and not easy to fix.
635 	 * When using the -Oincludes option, buffmt_includes()
636 	 * may pass in strings overrunning BUFSIZ, causing a crash.
637 	 */
638 
639 	h->buflen = strlcat(h->buf, p, BUFSIZ);
640 	assert(h->buflen < BUFSIZ);
641 }
642 
643 void
644 bufcat_fmt(struct html *h, const char *fmt, ...)
645 {
646 	va_list		 ap;
647 
648 	va_start(ap, fmt);
649 	(void)vsnprintf(h->buf + (int)h->buflen,
650 	    BUFSIZ - h->buflen - 1, fmt, ap);
651 	va_end(ap);
652 	h->buflen = strlen(h->buf);
653 }
654 
655 static void
656 bufncat(struct html *h, const char *p, size_t sz)
657 {
658 
659 	assert(h->buflen + sz + 1 < BUFSIZ);
660 	strncat(h->buf, p, sz);
661 	h->buflen += sz;
662 }
663 
664 void
665 buffmt_includes(struct html *h, const char *name)
666 {
667 	const char	*p, *pp;
668 
669 	pp = h->base_includes;
670 
671 	bufinit(h);
672 	while (NULL != (p = strchr(pp, '%'))) {
673 		bufncat(h, pp, (size_t)(p - pp));
674 		switch (*(p + 1)) {
675 		case'I':
676 			bufcat(h, name);
677 			break;
678 		default:
679 			bufncat(h, p, 2);
680 			break;
681 		}
682 		pp = p + 2;
683 	}
684 	if (pp)
685 		bufcat(h, pp);
686 }
687 
688 void
689 buffmt_man(struct html *h, const char *name, const char *sec)
690 {
691 	const char	*p, *pp;
692 
693 	pp = h->base_man;
694 
695 	bufinit(h);
696 	while (NULL != (p = strchr(pp, '%'))) {
697 		bufncat(h, pp, (size_t)(p - pp));
698 		switch (*(p + 1)) {
699 		case 'S':
700 			bufcat(h, sec ? sec : "1");
701 			break;
702 		case 'N':
703 			bufcat_fmt(h, "%s", name);
704 			break;
705 		default:
706 			bufncat(h, p, 2);
707 			break;
708 		}
709 		pp = p + 2;
710 	}
711 	if (pp)
712 		bufcat(h, pp);
713 }
714 
715 void
716 bufcat_su(struct html *h, const char *p, const struct roffsu *su)
717 {
718 	double		 v;
719 
720 	v = su->scale;
721 	if (SCALE_MM == su->unit && 0.0 == (v /= 100.0))
722 		v = 1.0;
723 	else if (SCALE_BU == su->unit)
724 		v /= 24.0;
725 
726 	bufcat_fmt(h, "%s: %.2f%s;", p, v, roffscales[su->unit]);
727 }
728 
729 void
730 bufcat_id(struct html *h, const char *src)
731 {
732 
733 	/* Cf. <http://www.w3.org/TR/html4/types.html#h-6.2>. */
734 
735 	while ('\0' != *src)
736 		bufcat_fmt(h, "%.2x", *src++);
737 }
738