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htmlparse.cc

/* htmlparse.cc: simple HTML parser for omega indexer
 *
 * Copyright 1999,2000,2001 BrightStation PLC
 * Copyright 2001 Ananova Ltd
 * Copyright 2002,2006,2007,2008 Olly Betts
 *
 * 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., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
 * USA
 */

#include <config.h>

#include "htmlparse.h"

#include <xapian.h>

#include "utf8convert.h"

#include <algorithm>

#include <ctype.h>
#include <cstring>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

inline void
lowercase_string(string &str)
{
    for (string::iterator i = str.begin(); i != str.end(); ++i) {
      *i = tolower(static_cast<unsigned char>(*i));
    }
}

map<string, unsigned int> HtmlParser::named_ents;

inline static bool
p_notdigit(char c)
{
    return !isdigit(static_cast<unsigned char>(c));
}

inline static bool
p_notxdigit(char c)
{
    return !isxdigit(static_cast<unsigned char>(c));
}

inline static bool
p_notalnum(char c)
{
    return !isalnum(static_cast<unsigned char>(c));
}

inline static bool
p_notwhitespace(char c)
{
    return !isspace(static_cast<unsigned char>(c));
}

inline static bool
p_nottag(char c)
{
    return !isalnum(static_cast<unsigned char>(c)) &&
      c != '.' && c != '-' && c != ':'; // ':' for XML namespaces.
}

inline static bool
p_whitespacegt(char c)
{
    return isspace(static_cast<unsigned char>(c)) || c == '>';
}

inline static bool
p_whitespaceeqgt(char c)
{
    return isspace(static_cast<unsigned char>(c)) || c == '=' || c == '>';
}

bool
HtmlParser::get_parameter(const string & param, string & value)
{
    map<string, string>::const_iterator i = parameters.find(param);
    if (i == parameters.end()) return false;
    value = i->second;
    return true;
}

HtmlParser::HtmlParser()
{
    static const struct ent { const char *n; unsigned int v; } ents[] = {
#include "namedentities.h"
      { NULL, 0 }
    };
    if (named_ents.empty()) {
      const struct ent *i = ents;
      while (i->n) {
          named_ents[string(i->n)] = i->v;
          ++i;
      }
    }
}

void
HtmlParser::decode_entities(string &s)
{
    // We need a const_iterator version of s.end() - otherwise the
    // find() and find_if() templates don't work...
    string::const_iterator amp = s.begin(), s_end = s.end();
    while ((amp = find(amp, s_end, '&')) != s_end) {
      unsigned int val = 0;
      string::const_iterator end, p = amp + 1;
      if (p != s_end && *p == '#') {
          p++;
          if (p != s_end && (*p == 'x' || *p == 'X')) {
            // hex
            p++;
            end = find_if(p, s_end, p_notxdigit);
            sscanf(s.substr(p - s.begin(), end - p).c_str(), "%x", &val);
          } else {
            // number
            end = find_if(p, s_end, p_notdigit);
            val = atoi(s.substr(p - s.begin(), end - p).c_str());
          }
      } else {
          end = find_if(p, s_end, p_notalnum);
          string code = s.substr(p - s.begin(), end - p);
          map<string, unsigned int>::const_iterator i;
          i = named_ents.find(code);
          if (i != named_ents.end()) val = i->second;
      }
      if (end < s_end && *end == ';') end++;
      if (val) {
          string::size_type amp_pos = amp - s.begin();
          if (val < 0x80) {
            s.replace(amp_pos, end - amp, 1u, char(val));
          } else {
            // Convert unicode value val to UTF-8.
            char seq[4];
            unsigned len = Xapian::Unicode::nonascii_to_utf8(val, seq);
            s.replace(amp_pos, end - amp, seq, len);
          }
          s_end = s.end();
          // We've modified the string, so the iterators are no longer
          // valid...
          amp = s.begin() + amp_pos + 1;
      } else {
          amp = end;
      }
    }
}

void
HtmlParser::parse_html(const string &body)
{
    in_script = false;

    parameters.clear();
    string::const_iterator start = body.begin();

    while (true) {
      // Skip through until we find an HTML tag, a comment, or the end of
      // document.  Ignore isolated occurrences of `<' which don't start
      // a tag or comment.
      string::const_iterator p = start;
      while (true) {
          p = find(p, body.end(), '<');
          if (p == body.end()) break;
          unsigned char ch = *(p + 1);

          // Tag, closing tag, or comment (or SGML declaration).
          if ((!in_script && isalpha(ch)) || ch == '/' || ch == '!') break;

          if (ch == '?') {
            // PHP code or XML declaration.
            // XML declaration is only valid at the start of the first line.
            // FIXME: need to deal with BOMs...
            if (p != body.begin() || body.size() < 20) break;

            // XML declaration looks something like this:
            // <?xml version="1.0" encoding="UTF-8"?>
            if (p[2] != 'x' || p[3] != 'm' || p[4] != 'l') break;
            if (strchr(" \t\r\n", p[5]) == NULL) break;

            string::const_iterator decl_end = find(p + 6, body.end(), '?');
            if (decl_end == body.end()) break;

            // Default charset for XML is UTF-8.
            charset = "UTF-8";

            string decl(p + 6, decl_end);
            size_t enc = decl.find("encoding");
            if (enc == string::npos) break;

            enc = decl.find_first_not_of(" \t\r\n", enc + 8);
            if (enc == string::npos || enc == decl.size()) break;

            if (decl[enc] != '=') break;
            
            enc = decl.find_first_not_of(" \t\r\n", enc + 1);
            if (enc == string::npos || enc == decl.size()) break;

            if (decl[enc] != '"' && decl[enc] != '\'') break;

            char quote = decl[enc++];
            size_t enc_end = decl.find(quote, enc);

            if (enc != string::npos)
                charset = decl.substr(enc, enc_end - enc);

            break;
          }
          p++;
      }

      // Process text up to start of tag.
      if (p > start) {
          string text = body.substr(start - body.begin(), p - start);
          convert_to_utf8(text, charset);
          decode_entities(text);
          process_text(text);
      }

      if (p == body.end()) break;

      start = p + 1;

      if (start == body.end()) break;

      if (*start == '!') {
          if (++start == body.end()) break;
          if (++start == body.end()) break;
          // comment or SGML declaration
          if (*(start - 1) == '-' && *start == '-') {
            ++start;
            string::const_iterator close = find(start, body.end(), '>');
            // An unterminated comment swallows rest of document
            // (like Netscape, but unlike MSIE IIRC)
            if (close == body.end()) break;

            p = close;
            // look for -->
            while (p != body.end() && (*(p - 1) != '-' || *(p - 2) != '-'))
                p = find(p + 1, body.end(), '>');

            if (p != body.end()) {
                // Check for htdig's "ignore this bit" comments.
                if (p - start == 15 && string(start, p - 2) == "htdig_noindex") {
                  string::size_type i;
                  i = body.find("<!--/htdig_noindex-->", p + 1 - body.begin());
                  if (i == string::npos) break;
                  start = body.begin() + i + 21;
                  continue;
                }
                // If we found --> skip to there.
                start = p;
            } else {
                // Otherwise skip to the first > we found (as Netscape does).
                start = close;
            }
          } else {
            // just an SGML declaration, perhaps giving the DTD - ignore it
            start = find(start - 1, body.end(), '>');
            if (start == body.end()) break;
          }
          ++start;
      } else if (*start == '?') {
          if (++start == body.end()) break;
          // PHP - swallow until ?> or EOF
          start = find(start + 1, body.end(), '>');

          // look for ?>
          while (start != body.end() && *(start - 1) != '?')
            start = find(start + 1, body.end(), '>');

          // unterminated PHP swallows rest of document (rather arbitrarily
          // but it avoids polluting the database when things go wrong)
          if (start != body.end()) ++start;
      } else {
          // opening or closing tag
          int closing = 0;

          if (*start == '/') {
            closing = 1;
            start = find_if(start + 1, body.end(), p_notwhitespace);
          }

          p = start;
          start = find_if(start, body.end(), p_nottag);
          string tag = body.substr(p - body.begin(), start - p);
          // convert tagname to lowercase
          lowercase_string(tag);

          if (closing) {
            closing_tag(tag);
            if (in_script && tag == "script") in_script = false;

            /* ignore any bogus parameters on closing tags */
            p = find(start, body.end(), '>');
            if (p == body.end()) break;
            start = p + 1;
          } else {
            // FIXME: parse parameters lazily.
            while (start < body.end() && *start != '>') {
                string name, value;

                p = find_if(start, body.end(), p_whitespaceeqgt);

                name.assign(body, start - body.begin(), p - start);

                p = find_if(p, body.end(), p_notwhitespace);

                start = p;
                if (start != body.end() && *start == '=') {
                  start = find_if(start + 1, body.end(), p_notwhitespace);

                  p = body.end();

                  int quote = *start;
                  if (quote == '"' || quote == '\'') {
                      start++;
                      p = find(start, body.end(), quote);
                  }

                  if (p == body.end()) {
                      // unquoted or no closing quote
                      p = find_if(start, body.end(), p_whitespacegt);
                  }
                  value.assign(body, start - body.begin(), p - start);
                  start = find_if(p, body.end(), p_notwhitespace);

                  if (!name.empty()) {
                      // convert parameter name to lowercase
                      lowercase_string(name);
                      // in case of multiple entries, use the first
                      // (as Netscape does)
                      parameters.insert(make_pair(name, value));
                  }
                }
            }
#if 0
            cout << "<" << tag;
            map<string, string>::const_iterator x;
            for (x = parameters.begin(); x != parameters.end(); x++) {
                cout << " " << x->first << "=\"" << x->second << "\"";
            }
            cout << ">\n";
#endif
            opening_tag(tag);
            parameters.clear();

            // In <script> tags we ignore opening tags to avoid problems
            // with "a<b".
            if (tag == "script") in_script = true;

            if (start != body.end() && *start == '>') ++start;
          }
      }
    }
}

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