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/**
* Copyright (C) 2022-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* 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
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/db/query/analyze_regex.h"
#include <cstring>
#include "mongo/util/ctype.h"
#include "mongo/util/str.h"
namespace mongo::analyze_regex {
namespace {
/**
* Returns true if 'str' contains a non-escaped pipe character '|' on a best-effort basis. This
* function reports no false negatives, but will return false positives. For example, a pipe
* character inside of a character class or the \Q...\E escape sequence has no special meaning but
* may still be reported by this function as being non-escaped.
*/
bool stringMayHaveUnescapedPipe(StringData str) {
if (str.size() > 0 && str[0] == '|') {
return true;
}
if (str.size() > 1 && str[1] == '|' && str[0] != '\\') {
return true;
}
for (size_t i = 2U; i < str.size(); ++i) {
auto probe = str[i];
auto prev = str[i - 1];
auto tail = str[i - 2];
// We consider the pipe to have a special meaning if it is not preceded by a backslash, or
// preceded by a backslash that is itself escaped.
if (probe == '|' && (prev != '\\' || (prev == '\\' && tail == '\\'))) {
return true;
}
}
return false;
}
} // namespace
std::pair<std::string, bool> getRegexPrefixMatch(const char* regex, const char* flags) {
bool multilineOK;
if (regex[0] == '\\' && regex[1] == 'A') {
multilineOK = true;
regex += 2;
} else if (regex[0] == '^') {
multilineOK = false;
regex += 1;
} else {
return {"", false};
}
// A regex with an unescaped pipe character is not considered a simple regex.
if (stringMayHaveUnescapedPipe(StringData(regex))) {
return {"", false};
}
bool extended = false;
while (*flags) {
switch (*(flags++)) {
case 'm':
// Multiline mode.
if (multilineOK)
continue;
else
return {"", false};
case 's':
// Single-line mode specified. This just changes the behavior of the '.' character
// to match every character instead of every character except '\n'.
continue;
case 'x':
// Extended free-spacing mode.
extended = true;
break;
default:
// Cannot use the index.
return {"", false};
}
}
str::stream ss;
std::string r = "";
while (*regex) {
char c = *(regex++);
if (c == '*' || c == '?') {
// These are the only two symbols that make the last char optional.
r = ss;
r = r.substr(0, r.size() - 1);
// Patterns like /^a?/ and /^a*/ can be implemented by scanning all the strings
// beginning with the prefix "a", but the regex must be reapplied. We cannot convert
// such regexes into exact bounds.
return {r, false};
} else if (c == '\\') {
c = *(regex++);
if (c == 'Q') {
// \Q...\E quotes everything inside.
while (*regex) {
c = (*regex++);
if (c == '\\' && (*regex == 'E')) {
regex++; // skip the 'E'
break; // go back to start of outer loop
} else {
ss << c; // character should match itself
}
}
} else if ((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') ||
(c == '\0')) {
// Bail out on any of these escape sequences.
r = ss;
break;
} else {
// Slash followed by non-alphanumeric represents the following char.
ss << c;
}
} else if (strchr("^$.[()+{", c)) {
// List of "metacharacters" from man pcrepattern.
//
// For prefix patterns ending in '.*' (ex. /^abc.*/) we can build exact index bounds.
if (!multilineOK && (c == '.')) {
c = *(regex++);
if (c == '*' && *regex == 0) {
return {ss, true};
} else {
c = *(regex--);
}
}
r = ss;
break;
} else if (extended && c == '#') {
// Comment.
r = ss;
break;
} else if (extended && ctype::isSpace(c)) {
continue;
} else {
// Self-matching char.
ss << c;
}
}
bool isExactPrefixMatch = false;
if (r.empty() && *regex == 0) {
r = ss;
isExactPrefixMatch = !r.empty();
}
return {r, isExactPrefixMatch};
}
} // namespace mongo::analyze_regex
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