usr.bin/mandoc/html.c

root/usr.bin/mandoc/html.c
/* $OpenBSD: html.c,v 1.150 2022/08/09 11:21:50 schwarze Exp $ */
/*
 * Copyright (c) 2008-2011, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
 * Copyright (c) 2011-2015, 2017-2021 Ingo Schwarze <schwarze@openbsd.org>
 * Copyright (c) 2022 Anna Vyalkova <cyber@sysrq.in>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 * Common functions for mandoc(1) HTML formatters.
 * For use by individual formatters and by the main program.
 */
#include <sys/types.h>
#include <sys/stat.h>

#include <assert.h>
#include <ctype.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "mandoc_aux.h"
#include "mandoc_ohash.h"
#include "mandoc.h"
#include "roff.h"
#include "out.h"
#include "html.h"
#include "manconf.h"
#include "main.h"

struct  htmldata {
        const char       *name;
        int               flags;
#define HTML_INPHRASE    (1 << 0)  /* Can appear in phrasing context. */
#define HTML_TOPHRASE    (1 << 1)  /* Establishes phrasing context. */
#define HTML_NOSTACK     (1 << 2)  /* Does not have an end tag. */
#define HTML_NLBEFORE    (1 << 3)  /* Output line break before opening. */
#define HTML_NLBEGIN     (1 << 4)  /* Output line break after opening. */
#define HTML_NLEND       (1 << 5)  /* Output line break before closing. */
#define HTML_NLAFTER     (1 << 6)  /* Output line break after closing. */
#define HTML_NLAROUND    (HTML_NLBEFORE | HTML_NLAFTER)
#define HTML_NLINSIDE    (HTML_NLBEGIN | HTML_NLEND)
#define HTML_NLALL       (HTML_NLAROUND | HTML_NLINSIDE)
#define HTML_INDENT      (1 << 7)  /* Indent content by two spaces. */
#define HTML_NOINDENT    (1 << 8)  /* Exception: never indent content. */
};

static  const struct htmldata htmltags[TAG_MAX] = {
        {"html",        HTML_NLALL},
        {"head",        HTML_NLALL | HTML_INDENT},
        {"meta",        HTML_NOSTACK | HTML_NLALL},
        {"link",        HTML_NOSTACK | HTML_NLALL},
        {"style",       HTML_NLALL | HTML_INDENT},
        {"title",       HTML_NLAROUND},
        {"body",        HTML_NLALL},
        {"main",        HTML_NLALL},
        {"div",         HTML_NLAROUND},
        {"section",     HTML_NLALL},
        {"nav",         HTML_NLALL},
        {"table",       HTML_NLALL | HTML_INDENT},
        {"tr",          HTML_NLALL | HTML_INDENT},
        {"td",          HTML_NLAROUND},
        {"li",          HTML_NLAROUND | HTML_INDENT},
        {"ul",          HTML_NLALL | HTML_INDENT},
        {"ol",          HTML_NLALL | HTML_INDENT},
        {"dl",          HTML_NLALL | HTML_INDENT},
        {"dt",          HTML_NLAROUND},
        {"dd",          HTML_NLAROUND | HTML_INDENT},
        {"h2",          HTML_TOPHRASE | HTML_NLAROUND},
        {"h3",          HTML_TOPHRASE | HTML_NLAROUND},
        {"p",           HTML_TOPHRASE | HTML_NLAROUND | HTML_INDENT},
        {"pre",         HTML_TOPHRASE | HTML_NLAROUND | HTML_NOINDENT},
        {"a",           HTML_INPHRASE | HTML_TOPHRASE},
        {"b",           HTML_INPHRASE | HTML_TOPHRASE},
        {"cite",        HTML_INPHRASE | HTML_TOPHRASE},
        {"code",        HTML_INPHRASE | HTML_TOPHRASE},
        {"i",           HTML_INPHRASE | HTML_TOPHRASE},
        {"small",       HTML_INPHRASE | HTML_TOPHRASE},
        {"span",        HTML_INPHRASE | HTML_TOPHRASE},
        {"var",         HTML_INPHRASE | HTML_TOPHRASE},
        {"br",          HTML_INPHRASE | HTML_NOSTACK | HTML_NLALL},
        {"hr",          HTML_INPHRASE | HTML_NOSTACK},
        {"mark",        HTML_INPHRASE },
        {"math",        HTML_INPHRASE | HTML_NLALL | HTML_INDENT},
        {"mrow",        0},
        {"mi",          0},
        {"mn",          0},
        {"mo",          0},
        {"msup",        0},
        {"msub",        0},
        {"msubsup",     0},
        {"mfrac",       0},
        {"msqrt",       0},
        {"mfenced",     0},
        {"mtable",      0},
        {"mtr",         0},
        {"mtd",         0},
        {"munderover",  0},
        {"munder",      0},
        {"mover",       0},
};

/* Avoid duplicate HTML id= attributes. */

struct  id_entry {
        int      ord;   /* Ordinal number of the latest occurrence. */
        char     id[];  /* The id= attribute without any ordinal suffix. */
};
static  struct ohash     id_unique;

static  void     html_reset_internal(struct html *);
static  void     print_byte(struct html *, char);
static  void     print_endword(struct html *);
static  void     print_indent(struct html *);
static  void     print_word(struct html *, const char *);

static  void     print_ctag(struct html *, struct tag *);
static  int      print_escape(struct html *, char);
static  int      print_encode(struct html *, const char *, const char *, int);
static  void     print_href(struct html *, const char *, const char *, int);
static  void     print_metaf(struct html *);


void *
html_alloc(const struct manoutput *outopts)
{
        struct html     *h;

        h = mandoc_calloc(1, sizeof(struct html));

        h->tag = NULL;
        h->metac = h->metal = ESCAPE_FONTROMAN;
        h->style = outopts->style;
        if ((h->base_man1 = outopts->man) == NULL)
                h->base_man2 = NULL;
        else if ((h->base_man2 = strchr(h->base_man1, ';')) != NULL)
                *h->base_man2++ = '\0';
        h->base_includes = outopts->includes;
        if (outopts->fragment)
                h->oflags |= HTML_FRAGMENT;
        if (outopts->toc)
                h->oflags |= HTML_TOC;

        mandoc_ohash_init(&id_unique, 4, offsetof(struct id_entry, id));

        return h;
}

static void
html_reset_internal(struct html *h)
{
        struct tag      *tag;
        struct id_entry *entry;
        unsigned int     slot;

        while ((tag = h->tag) != NULL) {
                h->tag = tag->next;
                free(tag);
        }
        entry = ohash_first(&id_unique, &slot);
        while (entry != NULL) {
                free(entry);
                entry = ohash_next(&id_unique, &slot);
        }
        ohash_delete(&id_unique);
}

void
html_reset(void *p)
{
        html_reset_internal(p);
        mandoc_ohash_init(&id_unique, 4, offsetof(struct id_entry, id));
}

void
html_free(void *p)
{
        html_reset_internal(p);
        free(p);
}

void
print_gen_head(struct html *h)
{
        struct tag      *t;

        print_otag(h, TAG_META, "?", "charset", "utf-8");
        print_otag(h, TAG_META, "??", "name", "viewport",
            "content", "width=device-width, initial-scale=1.0");
        if (h->style != NULL) {
                print_otag(h, TAG_LINK, "?h??", "rel", "stylesheet",
                    h->style, "type", "text/css", "media", "all");
                return;
        }

        /*
         * Print a minimal embedded style sheet.
         */

        t = print_otag(h, TAG_STYLE, "");
        print_text(h, "table.head, table.foot { width: 100%; }");
        print_endline(h);
        print_text(h, "td.head-rtitle, td.foot-os { text-align: right; }");
        print_endline(h);
        print_text(h, "td.head-vol { text-align: center; }");
        print_endline(h);
        print_text(h, ".Nd, .Bf, .Op { display: inline; }");
        print_endline(h);
        print_text(h, ".Pa, .Ad { font-style: italic; }");
        print_endline(h);
        print_text(h, ".Ms { font-weight: bold; }");
        print_endline(h);
        print_text(h, ".Bl-diag ");
        print_byte(h, '>');
        print_text(h, " dt { font-weight: bold; }");
        print_endline(h);
        print_text(h, "code.Nm, .Fl, .Cm, .Ic, code.In, .Fd, .Fn, .Cd "
            "{ font-weight: bold; font-family: inherit; }");
        print_tagq(h, t);
}

int
html_setfont(struct html *h, enum mandoc_esc font)
{
        switch (font) {
        case ESCAPE_FONTPREV:
                font = h->metal;
                break;
        case ESCAPE_FONTITALIC:
        case ESCAPE_FONTBOLD:
        case ESCAPE_FONTBI:
        case ESCAPE_FONTROMAN:
        case ESCAPE_FONTCR:
        case ESCAPE_FONTCB:
        case ESCAPE_FONTCI:
                break;
        case ESCAPE_FONT:
                font = ESCAPE_FONTROMAN;
                break;
        default:
                return 0;
        }
        h->metal = h->metac;
        h->metac = font;
        return 1;
}

static void
print_metaf(struct html *h)
{
        if (h->metaf) {
                print_tagq(h, h->metaf);
                h->metaf = NULL;
        }
        switch (h->metac) {
        case ESCAPE_FONTITALIC:
                h->metaf = print_otag(h, TAG_I, "");
                break;
        case ESCAPE_FONTBOLD:
                h->metaf = print_otag(h, TAG_B, "");
                break;
        case ESCAPE_FONTBI:
                h->metaf = print_otag(h, TAG_B, "");
                print_otag(h, TAG_I, "");
                break;
        case ESCAPE_FONTCR:
                h->metaf = print_otag(h, TAG_SPAN, "c", "Li");
                break;
        case ESCAPE_FONTCB:
                h->metaf = print_otag(h, TAG_SPAN, "c", "Li");
                print_otag(h, TAG_B, "");
                break;
        case ESCAPE_FONTCI:
                h->metaf = print_otag(h, TAG_SPAN, "c", "Li");
                print_otag(h, TAG_I, "");
                break;
        default:
                break;
        }
}

void
html_close_paragraph(struct html *h)
{
        struct tag      *this, *next;
        int              flags;

        this = h->tag;
        for (;;) {
                next = this->next;
                flags = htmltags[this->tag].flags;
                if (flags & (HTML_INPHRASE | HTML_TOPHRASE))
                        print_ctag(h, this);
                if ((flags & HTML_INPHRASE) == 0)
                        break;
                this = next;
        }
}

/*
 * ROFF_nf switches to no-fill mode, ROFF_fi to fill mode.
 * TOKEN_NONE does not switch.  The old mode is returned.
 */
enum roff_tok
html_fillmode(struct html *h, enum roff_tok want)
{
        struct tag      *t;
        enum roff_tok    had;

        for (t = h->tag; t != NULL; t = t->next)
                if (t->tag == TAG_PRE)
                        break;

        had = t == NULL ? ROFF_fi : ROFF_nf;

        if (want != had) {
                switch (want) {
                case ROFF_fi:
                        print_tagq(h, t);
                        break;
                case ROFF_nf:
                        html_close_paragraph(h);
                        print_otag(h, TAG_PRE, "");
                        break;
                case TOKEN_NONE:
                        break;
                default:
                        abort();
                }
        }
        return had;
}

/*
 * Allocate a string to be used for the "id=" attribute of an HTML
 * element and/or as a segment identifier for a URI in an <a> element.
 * The function may fail and return NULL if the node lacks text data
 * to create the attribute from.
 * The caller is responsible for free(3)ing the returned string.
 *
 * If the "unique" argument is non-zero, the "id_unique" ohash table
 * is used for de-duplication.  If the "unique" argument is 1,
 * it is the first time the function is called for this tag and
 * location, so if an ordinal suffix is needed, it is incremented.
 * If the "unique" argument is 2, it is the second time the function
 * is called for this tag and location, so the ordinal suffix
 * remains unchanged.
 */
char *
html_make_id(const struct roff_node *n, int unique)
{
        const struct roff_node  *nch;
        struct id_entry         *entry;
        char                    *buf, *cp;
        size_t                   len;
        unsigned int             slot;

        if (n->tag != NULL)
                buf = mandoc_strdup(n->tag);
        else {
                switch (n->tok) {
                case MDOC_Sh:
                case MDOC_Ss:
                case MDOC_Sx:
                case MAN_SH:
                case MAN_SS:
                        for (nch = n->child; nch != NULL; nch = nch->next)
                                if (nch->type != ROFFT_TEXT)
                                        return NULL;
                        buf = NULL;
                        deroff(&buf, n);
                        if (buf == NULL)
                                return NULL;
                        break;
                default:
                        if (n->child == NULL || n->child->type != ROFFT_TEXT)
                                return NULL;
                        buf = mandoc_strdup(n->child->string);
                        break;
                }
        }

        /*
         * In ID attributes, only use ASCII characters that are
         * permitted in URL-fragment strings according to the
         * explicit list at:
         * https://url.spec.whatwg.org/#url-fragment-string
         * In addition, reserve '~' for ordinal suffixes.
         */

        for (cp = buf; *cp != '\0'; cp++) {
                if (*cp == ASCII_HYPH)
                        *cp = '-';
                else if (isalnum((unsigned char)*cp) == 0 &&
                    strchr("!$&'()*+,-./:;=?@_", *cp) == NULL)
                        *cp = '_';
        }

        if (unique == 0)
                return buf;

        /* Avoid duplicate HTML id= attributes. */

        slot = ohash_qlookup(&id_unique, buf);
        if ((entry = ohash_find(&id_unique, slot)) == NULL) {
                len = strlen(buf) + 1;
                entry = mandoc_malloc(sizeof(*entry) + len);
                entry->ord = 1;
                memcpy(entry->id, buf, len);
                ohash_insert(&id_unique, slot, entry);
        } else if (unique == 1)
                entry->ord++;

        if (entry->ord > 1) {
                cp = buf;
                mandoc_asprintf(&buf, "%s~%d", cp, entry->ord);
                free(cp);
        }
        return buf;
}

static int
print_escape(struct html *h, char c)
{

        switch (c) {
        case '<':
                print_word(h, "&lt;");
                break;
        case '>':
                print_word(h, "&gt;");
                break;
        case '&':
                print_word(h, "&amp;");
                break;
        case '"':
                print_word(h, "&quot;");
                break;
        case ASCII_NBRSP:
                print_word(h, "&nbsp;");
                break;
        case ASCII_HYPH:
                print_byte(h, '-');
                break;
        case ASCII_BREAK:
                break;
        default:
                return 0;
        }
        return 1;
}

static int
print_encode(struct html *h, const char *p, const char *pend, int norecurse)
{
        char             numbuf[16];
        const char      *seq;
        size_t           sz;
        int              c, len, breakline, nospace;
        enum mandoc_esc  esc;
        static const char rejs[10] = { ' ', '\\', '<', '>', '&', '"',
                ASCII_NBRSP, ASCII_HYPH, ASCII_BREAK, '\0' };

        if (pend == NULL)
                pend = strchr(p, '\0');

        breakline = 0;
        nospace = 0;

        while (p < pend) {
                if (HTML_SKIPCHAR & h->flags && '\\' != *p) {
                        h->flags &= ~HTML_SKIPCHAR;
                        p++;
                        continue;
                }

                for (sz = strcspn(p, rejs); sz-- && p < pend; p++)
                        print_byte(h, *p);

                if (breakline &&
                    (p >= pend || *p == ' ' || *p == ASCII_NBRSP)) {
                        print_otag(h, TAG_BR, "");
                        breakline = 0;
                        while (p < pend && (*p == ' ' || *p == ASCII_NBRSP))
                                p++;
                        continue;
                }

                if (p >= pend)
                        break;

                if (*p == ' ') {
                        print_endword(h);
                        p++;
                        continue;
                }

                if (print_escape(h, *p++))
                        continue;

                esc = mandoc_escape(&p, &seq, &len);
                switch (esc) {
                case ESCAPE_FONT:
                case ESCAPE_FONTPREV:
                case ESCAPE_FONTBOLD:
                case ESCAPE_FONTITALIC:
                case ESCAPE_FONTBI:
                case ESCAPE_FONTROMAN:
                case ESCAPE_FONTCR:
                case ESCAPE_FONTCB:
                case ESCAPE_FONTCI:
                        if (0 == norecurse) {
                                h->flags |= HTML_NOSPACE;
                                if (html_setfont(h, esc))
                                        print_metaf(h);
                                h->flags &= ~HTML_NOSPACE;
                        }
                        continue;
                case ESCAPE_SKIPCHAR:
                        h->flags |= HTML_SKIPCHAR;
                        continue;
                case ESCAPE_ERROR:
                        continue;
                default:
                        break;
                }

                if (h->flags & HTML_SKIPCHAR) {
                        h->flags &= ~HTML_SKIPCHAR;
                        continue;
                }

                switch (esc) {
                case ESCAPE_UNICODE:
                        /* Skip past "u" header. */
                        c = mchars_num2uc(seq + 1, len - 1);
                        break;
                case ESCAPE_NUMBERED:
                        c = mchars_num2char(seq, len);
                        if (c < 0)
                                continue;
                        break;
                case ESCAPE_SPECIAL:
                        c = mchars_spec2cp(seq, len);
                        if (c <= 0)
                                continue;
                        break;
                case ESCAPE_UNDEF:
                        c = *seq;
                        break;
                case ESCAPE_DEVICE:
                        print_word(h, "html");
                        continue;
                case ESCAPE_BREAK:
                        breakline = 1;
                        continue;
                case ESCAPE_NOSPACE:
                        if ('\0' == *p)
                                nospace = 1;
                        continue;
                case ESCAPE_OVERSTRIKE:
                        if (len == 0)
                                continue;
                        c = seq[len - 1];
                        break;
                default:
                        continue;
                }
                if ((c < 0x20 && c != 0x09) ||
                    (c > 0x7E && c < 0xA0))
                        c = 0xFFFD;
                if (c > 0x7E) {
                        (void)snprintf(numbuf, sizeof(numbuf), "&#x%.4X;", c);
                        print_word(h, numbuf);
                } else if (print_escape(h, c) == 0)
                        print_byte(h, c);
        }

        return nospace;
}

static void
print_href(struct html *h, const char *name, const char *sec, int man)
{
        struct stat      sb;
        const char      *p, *pp;
        char            *filename;

        if (man) {
                pp = h->base_man1;
                if (h->base_man2 != NULL) {
                        mandoc_asprintf(&filename, "%s.%s", name, sec);
                        if (stat(filename, &sb) == -1)
                                pp = h->base_man2;
                        free(filename);
                }
        } else
                pp = h->base_includes;

        while ((p = strchr(pp, '%')) != NULL) {
                print_encode(h, pp, p, 1);
                if (man && p[1] == 'S') {
                        if (sec == NULL)
                                print_byte(h, '1');
                        else
                                print_encode(h, sec, NULL, 1);
                } else if ((man && p[1] == 'N') ||
                    (man == 0 && p[1] == 'I'))
                        print_encode(h, name, NULL, 1);
                else
                        print_encode(h, p, p + 2, 1);
                pp = p + 2;
        }
        if (*pp != '\0')
                print_encode(h, pp, NULL, 1);
}

struct tag *
print_otag(struct html *h, enum htmltag tag, const char *fmt, ...)
{
        va_list          ap;
        struct tag      *t;
        const char      *attr;
        char            *arg1, *arg2;
        int              style_written, tflags;

        tflags = htmltags[tag].flags;

        /* Flow content is not allowed in phrasing context. */

        if ((tflags & HTML_INPHRASE) == 0) {
                for (t = h->tag; t != NULL; t = t->next) {
                        if (t->closed)
                                continue;
                        assert((htmltags[t->tag].flags & HTML_TOPHRASE) == 0);
                        break;
                }

        /*
         * Always wrap phrasing elements in a paragraph
         * unless already contained in some flow container;
         * never put them directly into a section.
         */

        } else if (tflags & HTML_TOPHRASE && h->tag->tag == TAG_SECTION)
                print_otag(h, TAG_P, "c", "Pp");

        /* Push this tag onto the stack of open scopes. */

        if ((tflags & HTML_NOSTACK) == 0) {
                t = mandoc_malloc(sizeof(struct tag));
                t->tag = tag;
                t->next = h->tag;
                t->refcnt = 0;
                t->closed = 0;
                h->tag = t;
        } else
                t = NULL;

        if (tflags & HTML_NLBEFORE)
                print_endline(h);
        if (h->col == 0)
                print_indent(h);
        else if ((h->flags & HTML_NOSPACE) == 0) {
                if (h->flags & HTML_KEEP)
                        print_word(h, "&#x00A0;");
                else {
                        if (h->flags & HTML_PREKEEP)
                                h->flags |= HTML_KEEP;
                        print_endword(h);
                }
        }

        if ( ! (h->flags & HTML_NONOSPACE))
                h->flags &= ~HTML_NOSPACE;
        else
                h->flags |= HTML_NOSPACE;

        /* Print out the tag name and attributes. */

        print_byte(h, '<');
        print_word(h, htmltags[tag].name);

        va_start(ap, fmt);

        while (*fmt != '\0' && *fmt != 's') {

                /* Parse attributes and arguments. */

                arg1 = va_arg(ap, char *);
                arg2 = NULL;
                switch (*fmt++) {
                case 'c':
                        attr = "class";
                        break;
                case 'h':
                        attr = "href";
                        break;
                case 'i':
                        attr = "id";
                        break;
                case 'r':
                        attr = "role";
                        break;
                case '?':
                        attr = arg1;
                        arg1 = va_arg(ap, char *);
                        break;
                default:
                        abort();
                }
                if (*fmt == 'M')
                        arg2 = va_arg(ap, char *);
                if (arg1 == NULL)
                        continue;

                /* Print the attributes. */

                print_byte(h, ' ');
                print_word(h, attr);
                print_byte(h, '=');
                print_byte(h, '"');
                switch (*fmt) {
                case 'I':
                        print_href(h, arg1, NULL, 0);
                        fmt++;
                        break;
                case 'M':
                        print_href(h, arg1, arg2, 1);
                        fmt++;
                        break;
                case 'R':
                        print_byte(h, '#');
                        print_encode(h, arg1, NULL, 1);
                        fmt++;
                        break;
                default:
                        print_encode(h, arg1, NULL, 1);
                        break;
                }
                print_byte(h, '"');
        }

        style_written = 0;
        while (*fmt++ == 's') {
                arg1 = va_arg(ap, char *);
                arg2 = va_arg(ap, char *);
                if (arg2 == NULL)
                        continue;
                print_byte(h, ' ');
                if (style_written == 0) {
                        print_word(h, "style=\"");
                        style_written = 1;
                }
                print_word(h, arg1);
                print_byte(h, ':');
                print_byte(h, ' ');
                print_word(h, arg2);
                print_byte(h, ';');
        }
        if (style_written)
                print_byte(h, '"');

        va_end(ap);

        /* Accommodate for "well-formed" singleton escaping. */

        if (htmltags[tag].flags & HTML_NOSTACK)
                print_byte(h, '/');

        print_byte(h, '>');

        if (tflags & HTML_NLBEGIN)
                print_endline(h);
        else
                h->flags |= HTML_NOSPACE;

        if (tflags & HTML_INDENT)
                h->indent++;
        if (tflags & HTML_NOINDENT)
                h->noindent++;

        return t;
}

/*
 * Print an element with an optional "id=" attribute.
 * If the element has phrasing content and an "id=" attribute,
 * also add a permalink: outside if it can be in phrasing context,
 * inside otherwise.
 */
struct tag *
print_otag_id(struct html *h, enum htmltag elemtype, const char *cattr,
    struct roff_node *n)
{
        struct roff_node *nch;
        struct tag      *ret, *t;
        char            *id, *href;

        ret = NULL;
        id = href = NULL;
        if (n->flags & NODE_ID)
                id = html_make_id(n, 1);
        if (n->flags & NODE_HREF)
                href = id == NULL ? html_make_id(n, 2) : id;
        if (href != NULL && htmltags[elemtype].flags & HTML_INPHRASE)
                ret = print_otag(h, TAG_A, "chR", "permalink", href);
        t = print_otag(h, elemtype, "ci", cattr, id);
        if (ret == NULL) {
                ret = t;
                if (href != NULL && (nch = n->child) != NULL) {
                        /* man(7) is safe, it tags phrasing content only. */
                        if (n->tok > MDOC_MAX ||
                            htmltags[elemtype].flags & HTML_TOPHRASE)
                                nch = NULL;
                        else  /* For mdoc(7), beware of nested blocks. */
                                while (nch != NULL && nch->type == ROFFT_TEXT)
                                        nch = nch->next;
                        if (nch == NULL)
                                print_otag(h, TAG_A, "chR", "permalink", href);
                }
        }
        free(id);
        if (id == NULL)
                free(href);
        return ret;
}

static void
print_ctag(struct html *h, struct tag *tag)
{
        int      tflags;

        if (tag->closed == 0) {
                tag->closed = 1;
                if (tag == h->metaf)
                        h->metaf = NULL;
                if (tag == h->tblt)
                        h->tblt = NULL;

                tflags = htmltags[tag->tag].flags;
                if (tflags & HTML_INDENT)
                        h->indent--;
                if (tflags & HTML_NOINDENT)
                        h->noindent--;
                if (tflags & HTML_NLEND)
                        print_endline(h);
                print_indent(h);
                print_byte(h, '<');
                print_byte(h, '/');
                print_word(h, htmltags[tag->tag].name);
                print_byte(h, '>');
                if (tflags & HTML_NLAFTER)
                        print_endline(h);
        }
        if (tag->refcnt == 0) {
                h->tag = tag->next;
                free(tag);
        }
}

void
print_gen_decls(struct html *h)
{
        print_word(h, "<!DOCTYPE html>");
        print_endline(h);
}

void
print_gen_comment(struct html *h, struct roff_node *n)
{
        int      wantblank;

        print_word(h, "<!-- This is an automatically generated file."
            "  Do not edit.");
        h->indent = 1;
        wantblank = 0;
        while (n != NULL && n->type == ROFFT_COMMENT) {
                if (strstr(n->string, "-->") == NULL &&
                    (wantblank || *n->string != '\0')) {
                        print_endline(h);
                        print_indent(h);
                        print_word(h, n->string);
                        wantblank = *n->string != '\0';
                }
                n = n->next;
        }
        if (wantblank)
                print_endline(h);
        print_word(h, " -->");
        print_endline(h);
        h->indent = 0;
}

void
print_text(struct html *h, const char *word)
{
        print_tagged_text(h, word, NULL);
}

void
print_tagged_text(struct html *h, const char *word, struct roff_node *n)
{
        struct tag      *t;
        char            *href;

        /*
         * Always wrap text in a paragraph unless already contained in
         * some flow container; never put it directly into a section.
         */

        if (h->tag->tag == TAG_SECTION)
                print_otag(h, TAG_P, "c", "Pp");

        /* Output whitespace before this text? */

        if (h->col && (h->flags & HTML_NOSPACE) == 0) {
                if ( ! (HTML_KEEP & h->flags)) {
                        if (HTML_PREKEEP & h->flags)
                                h->flags |= HTML_KEEP;
                        print_endword(h);
                } else
                        print_word(h, "&#x00A0;");
        }

        /*
         * Optionally switch fonts, optionally write a permalink, then
         * print the text, optionally surrounded by HTML whitespace.
         */

        assert(h->metaf == NULL);
        print_metaf(h);
        print_indent(h);

        if (n != NULL && (href = html_make_id(n, 2)) != NULL) {
                t = print_otag(h, TAG_A, "chR", "permalink", href);
                free(href);
        } else
                t = NULL;

        if ( ! print_encode(h, word, NULL, 0)) {
                if ( ! (h->flags & HTML_NONOSPACE))
                        h->flags &= ~HTML_NOSPACE;
                h->flags &= ~HTML_NONEWLINE;
        } else
                h->flags |= HTML_NOSPACE | HTML_NONEWLINE;

        if (h->metaf != NULL) {
                print_tagq(h, h->metaf);
                h->metaf = NULL;
        } else if (t != NULL)
                print_tagq(h, t);

        h->flags &= ~HTML_IGNDELIM;
}

void
print_tagq(struct html *h, const struct tag *until)
{
        struct tag      *this, *next;

        for (this = h->tag; this != NULL; this = next) {
                next = this == until ? NULL : this->next;
                print_ctag(h, this);
        }
}

/*
 * Close out all open elements up to but excluding suntil.
 * Note that a paragraph just inside stays open together with it
 * because paragraphs include subsequent phrasing content.
 */
void
print_stagq(struct html *h, const struct tag *suntil)
{
        struct tag      *this, *next;

        for (this = h->tag; this != NULL; this = next) {
                next = this->next;
                if (this == suntil || (next == suntil &&
                    (this->tag == TAG_P || this->tag == TAG_PRE)))
                        break;
                print_ctag(h, this);
        }
}


/***********************************************************************
 * Low level output functions.
 * They implement line breaking using a short static buffer.
 ***********************************************************************/

/*
 * Buffer one HTML output byte.
 * If the buffer is full, flush and deactivate it and start a new line.
 * If the buffer is inactive, print directly.
 */
static void
print_byte(struct html *h, char c)
{
        if ((h->flags & HTML_BUFFER) == 0) {
                putchar(c);
                h->col++;
                return;
        }

        if (h->col + h->bufcol < sizeof(h->buf)) {
                h->buf[h->bufcol++] = c;
                return;
        }

        putchar('\n');
        h->col = 0;
        print_indent(h);
        putchar(' ');
        putchar(' ');
        fwrite(h->buf, h->bufcol, 1, stdout);
        putchar(c);
        h->col = (h->indent + 1) * 2 + h->bufcol + 1;
        h->bufcol = 0;
        h->flags &= ~HTML_BUFFER;
}

/*
 * If something was printed on the current output line, end it.
 * Not to be called right after print_indent().
 */
void
print_endline(struct html *h)
{
        if (h->col == 0)
                return;

        if (h->bufcol) {
                putchar(' ');
                fwrite(h->buf, h->bufcol, 1, stdout);
                h->bufcol = 0;
        }
        putchar('\n');
        h->col = 0;
        h->flags |= HTML_NOSPACE;
        h->flags &= ~HTML_BUFFER;
}

/*
 * Flush the HTML output buffer.
 * If it is inactive, activate it.
 */
static void
print_endword(struct html *h)
{
        if (h->noindent) {
                print_byte(h, ' ');
                return;
        }

        if ((h->flags & HTML_BUFFER) == 0) {
                h->col++;
                h->flags |= HTML_BUFFER;
        } else if (h->bufcol) {
                putchar(' ');
                fwrite(h->buf, h->bufcol, 1, stdout);
                h->col += h->bufcol + 1;
        }
        h->bufcol = 0;
}

/*
 * If at the beginning of a new output line,
 * perform indentation and mark the line as containing output.
 * Make sure to really produce some output right afterwards,
 * but do not use print_otag() for producing it.
 */
static void
print_indent(struct html *h)
{
        size_t   i;

        if (h->col || h->noindent)
                return;

        h->col = h->indent * 2;
        for (i = 0; i < h->col; i++)
                putchar(' ');
}

/*
 * Print or buffer some characters
 * depending on the current HTML output buffer state.
 */
static void
print_word(struct html *h, const char *cp)
{
        while (*cp != '\0')
                print_byte(h, *cp++);
}