SERVER-86326 Increase regex max pattern length to 32764 characters (#44449)

GitOrigin-RevId: 19e9132f7fe3624a918277af071bbcf616801244

etc/backports_required_for_multiversion_tests.yml

@@ -97,6 +97,8 @@ last-continuous:
       ticket: SERVER-109322
     - test_file: jstests/sharding/reshard_collection_with_zones_stale_mongos.js
       ticket: SERVER-109322
+    - test_file: jstests/core/query/regex/regex_max_pattern_length.js
+      ticket: SERVER-86326
   suites: null
 last-lts:
   all:
@@ -696,4 +698,6 @@ last-lts:
       ticket: SERVER-109322
     - test_file: jstests/sharding/reshard_collection_with_zones_stale_mongos.js
       ticket: SERVER-109322
+    - test_file: jstests/core/query/regex/regex_max_pattern_length.js
+      ticket: SERVER-86326
   suites: null

jstests/aggregation/expressions/regex_limits.js

@@ -36,15 +36,18 @@ function testRegexAggException(inputObj, exceptionCode, expression) {
 }
 
 (function testLongRegex() {
-    // Our limit on regex pattern length is 2^14.
+    // The maximum allowed pattern length is 16384 before SERVER-86326, and 32764 with it.
+    // Using a limit of 16384 should work across all versions in multiversion tests.
     const kMaxRegexPatternLen = 16384;
-    const patternMaxLen = "c".repeat(kMaxRegexPatternLen);
+    const patternMaxLen = "c".repeat(kMaxRegexPatternLen - 1);
+    const anchoredPatternMaxLen = "^" + patternMaxLen;
 
     // Test that a regex with maximum allowable pattern length can find a document.
-    testRegexAgg({input: "$z", regex: patternMaxLen}, [{match: patternMaxLen, "idx": 0, "captures": []}]);
+    testRegexAgg({input: "$z", regex: anchoredPatternMaxLen}, [{match: patternMaxLen, "idx": 0, "captures": []}]);
 
-    // Test that a regex pattern exceeding the limit fails.
-    const patternTooLong = patternMaxLen + "c";
+    // Test that a regex pattern exceeding the limit fails. A pattern length of 32765 is
+    // disallowed in all versions in multiversion tests.
+    const patternTooLong = "c".repeat(32765);
     testRegexAggException({input: "$z", regex: patternTooLong}, 51111);
 })();
 

jstests/core/query/regex/regex_max_pattern_length.js

@@ -0,0 +1,30 @@
+/**
+ * @tags: [
+ *   assumes_read_concern_local,
+ *   # Retryable writes are required for the remove() command in the test.
+ *   requires_non_retryable_writes,
+ * ]
+ */
+const kCollName = jsTestName();
+const kMaxOldRegexPatternLength = 16384;
+
+const buildAnchoredPattern = (length) => "^" + "y".repeat(length - 1);
+
+const coll = db[kCollName];
+coll.drop();
+
+// Assume that the following queries succeed, despite long patterns being used.
+[0, 1, 100, 1000, 10000].forEach((length) => {
+    coll.remove({});
+    assert.commandWorked(coll.insert({a: "y".repeat(kMaxOldRegexPatternLength + length)}));
+    assert.eq(1, coll.find({a: {$regex: buildAnchoredPattern(kMaxOldRegexPatternLength + length)}}).itcount());
+});
+
+// Using a too long pattern will always fail.
+let error = assert.throws(() => coll.find({a: {$regex: buildAnchoredPattern(32767)}}).itcount());
+assert.commandFailedWithCode(error, 51091);
+assert(
+    error.message.includes(
+        "Regular expression is invalid: pattern string is longer than the limit set by the application",
+    ),
+);

src/mongo/util/pcre.cpp

@@ -125,8 +125,9 @@ const std::error_category& pcreCategory() noexcept {
 namespace detail {
 
 
-// Global.
-inline constexpr size_t kMaxPatternLength = 16384;
+// Maximum length of the pattern accepted by PCRE2, in bytes. The effectively usable pattern length
+// may be less than this value.
+constexpr size_t kMaxPatternLength = 32764;
 
 /** Wrapper around a pcre2_compile_context. */
 class CompileContext {

src/mongo/util/pcre_test.cpp

@@ -443,5 +443,32 @@ TEST(PcreTest, HeapLimit) {
     }
 }
 
+TEST(PcreTest, MaxPatternLength) {
+    const std::string s(1024, 'y');
+
+    // Test patterns of various lengths
+    for (uint32_t patternLength : {2, 5, 10, 100, 1000, 10000, 16384, 20000, 30000, 32764}) {
+        std::string pattern = fmt::format("^{}", std::string(patternLength - 1, 'x'));
+
+        // We use an anchored pattern here in order to reduce internal memory usage during regex
+        // execution.
+        Regex customLimitRegex(pattern, CompileOptions{});
+        ASSERT_FALSE(customLimitRegex.error());
+        auto match = customLimitRegex.match(s);
+        ASSERT_TRUE(match.error());
+        ASSERT_EQ(match.error().message(), "no match");
+    }
+
+    // Test a pattern that is above the maximum allowed pattern length.
+    {
+        const std::string kTooLongErrorMessage =
+            "pattern string is longer than the limit set by the application";
+        const std::string pattern = fmt::format("^{}", std::string(32764, 'x'));
+        Regex defaultLimitRegex(pattern, CompileOptions{});
+        ASSERT_TRUE(defaultLimitRegex.error());
+        ASSERT_EQ(defaultLimitRegex.error().message(), kTooLongErrorMessage);
+    }
+}
+
 }  // namespace
 }  // namespace mongo::pcre