honey_synonym.cc

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/* Copyright (C) 2004,2005,2006,2007,2008,2009,2011,2017,2024 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, see
 * <https://www.gnu.org/licenses/>.
 */
 
#include <config.h>
#include "honey_synonym.h"
 
#include "xapian/error.h"
 
#include "honey_cursor.h"
#include "honey_database.h"
#include "debuglog.h"
#include "stringutils.h"
#include "api/vectortermlist.h"
 
#include <set>
#include <string>
#include <string_view>
#include <vector>
 
using namespace std;
 
// We XOR the length values with this so that they are more likely to coincide
// with lower case ASCII letters, which are likely to be common.  This means
// that zlib should do a better job of compressing tag values.
#define MAGIC_XOR_VALUE 96
 
void
HoneySynonymTable::merge_changes()
{
    if (last_term.empty()) return;
 
    if (last_synonyms.empty()) {
        del(last_term);
    } else {
        string tag;
 
        for (auto&& synonym : last_synonyms) {
            tag += uint8_t(synonym.size() ^ MAGIC_XOR_VALUE);
            tag += synonym;
        }
 
        add(last_term, tag);
        last_synonyms.clear();
    }
    last_term.resize(0);
}
 
void
HoneySynonymTable::add_synonym(string_view term, string_view synonym)
{
    if (last_term != term) {
        merge_changes();
        last_term = term;
 
        string tag;
        if (get_exact_entry(term, tag)) {
            const char* p = tag.data();
            const char* end = p + tag.size();
            while (p != end) {
                size_t len;
                if (p == end ||
                    (len = uint8_t(*p) ^ MAGIC_XOR_VALUE) >= size_t(end - p))
                    throw Xapian::DatabaseCorruptError("Bad synonym data");
                ++p;
                last_synonyms.insert(string(p, len));
                p += len;
            }
        }
    }
 
    last_synonyms.emplace(synonym);
}
 
void
HoneySynonymTable::remove_synonym(string_view term, string_view synonym)
{
    if (last_term != term) {
        merge_changes();
        last_term = term;
 
        string tag;
        if (get_exact_entry(term, tag)) {
            const char* p = tag.data();
            const char* end = p + tag.size();
            while (p != end) {
                size_t len;
                if (p == end ||
                    (len = uint8_t(*p) ^ MAGIC_XOR_VALUE) >= size_t(end - p))
                    throw Xapian::DatabaseCorruptError("Bad synonym data");
                ++p;
                last_synonyms.emplace(p, len);
                p += len;
            }
        }
    }
 
#ifdef __cpp_lib_associative_heterogeneous_erasure // C++23
    last_synonyms.erase(synonym);
#else
    last_synonyms.erase(string(synonym));
#endif
}
 
void
HoneySynonymTable::clear_synonyms(string_view term)
{
    // We don't actually ever need to merge_changes() here, but it's quite
    // likely that someone might clear_synonyms() and then add_synonym() for
    // the same term.  The alternative we could otherwise optimise for (modify
    // synonyms for a term, then clear those for another, then modify those for
    // the first term again) seems much less likely.
    if (last_term == term) {
        last_synonyms.clear();
    } else {
        merge_changes();
        last_term = term;
    }
}
 
TermList*
HoneySynonymTable::open_termlist(string_view term) const
{
    vector<string> synonyms;
 
    if (last_term == term) {
        if (last_synonyms.empty()) return NULL;
 
        synonyms.reserve(last_synonyms.size());
        for (auto&& i : last_synonyms) {
            synonyms.push_back(i);
        }
    } else {
        string tag;
        if (!get_exact_entry(term, tag)) return NULL;
 
        const char* p = tag.data();
        const char* end = p + tag.size();
        while (p != end) {
            size_t len;
            if (p == end ||
                (len = uint8_t(*p) ^ MAGIC_XOR_VALUE) >= size_t(end - p))
                throw Xapian::DatabaseCorruptError("Bad synonym data");
            ++p;
            synonyms.push_back(string(p, len));
            p += len;
        }
    }
 
    return new VectorTermList(synonyms.begin(), synonyms.end());
}
 
 
HoneySynonymTermList::~HoneySynonymTermList()
{
    LOGCALL_DTOR(DB, "HoneySynonymTermList");
    delete cursor;
}
 
Xapian::termcount
HoneySynonymTermList::get_approx_size() const
{
    // This is an over-estimate, but we only use this value to build a balanced
    // or-tree, and it'll do a decent enough job for that.
    return database->synonym_table.get_approx_entry_count();
}
 
Xapian::doccount
HoneySynonymTermList::get_termfreq() const
{
    throw Xapian::InvalidOperationError("HoneySynonymTermList::get_termfreq() "
                                        "not meaningful");
}
 
TermList*
HoneySynonymTermList::next()
{
    LOGCALL(DB, TermList*, "HoneySynonymTermList::next", NO_ARGS);
    if (cursor->after_end()) {
        // This is the first action on a new HoneySynonymTermList.
        if (cursor->find_entry_ge(prefix))
            RETURN(NULL);
    } else {
        cursor->next();
    }
    if (cursor->after_end() || !startswith(cursor->current_key, prefix)) {
        // We've reached the end of the prefixed terms.
        RETURN(this);
    }
    current_term = cursor->current_key;
 
    RETURN(NULL);
}
 
TermList*
HoneySynonymTermList::skip_to(string_view term)
{
    LOGCALL(DB, TermList*, "HoneySynonymTermList::skip_to", term);
    if (cursor->after_end() && prefix > term) {
        // This is the first action on a new HoneySynonymTermList and we were
        // asked to skip to a term before the prefix - this ought to leave us
        // on the first term with the specified prefix.
        RETURN(skip_to(prefix));
    }
 
    if (cursor->find_entry_ge(term)) {
        // Exact match.
        current_term = term;
    } else {
        // The exact term we asked for isn't there, so check if the next
        // term after it also has the right prefix.
        if (cursor->after_end() || !startswith(cursor->current_key, prefix)) {
            // We've reached the end of the prefixed terms.
            RETURN(this);
        }
        current_term = cursor->current_key;
    }
    RETURN(NULL);
}