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Improve efficiency of Grok circular reference check #74814

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Jul 1, 2021
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Improve efficiency of Grok circular reference check #74814

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19 changes: 10 additions & 9 deletions libs/grok/src/main/java/org/elasticsearch/grok/Grok.java
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Original file line number Diff line number Diff line change
Expand Up @@ -79,11 +79,7 @@ private Grok(Map<String, String> patternBank, String grokPattern, boolean namedC
this.namedCaptures = namedCaptures;
this.matcherWatchdog = matcherWatchdog;

for (Map.Entry<String, String> entry : patternBank.entrySet()) {
String name = entry.getKey();
String pattern = entry.getValue();
forbidCircularReferences(name, new ArrayList<>(), pattern);
}
forbidCircularReferences();

String expression = toRegex(grokPattern);
byte[] expressionBytes = expression.getBytes(StandardCharsets.UTF_8);
Expand All @@ -104,7 +100,8 @@ private Grok(Map<String, String> patternBank, String grokPattern, boolean namedC
* a reference to another named pattern. This method will navigate to all these named patterns and
* check for a circular reference.
*/
private void forbidCircularReferences(String patternName, List<String> path, String pattern) {
private void forbidCircularReferences() {

// first ensure that the pattern bank contains no simple circular references (i.e., any pattern
// containing an immediate reference to itself) as those can cause the remainder of this algorithm
// to recurse infinitely
Expand All @@ -114,8 +111,12 @@ private void forbidCircularReferences(String patternName, List<String> path, Str
}
}

// next recursively check any other pattern names referenced in the pattern
innerForbidCircularReferences(patternName, path, pattern);
// next, recursively check any other pattern names referenced in each pattern
for (Map.Entry<String, String> entry : patternBank.entrySet()) {
String name = entry.getKey();
String pattern = entry.getValue();
innerForbidCircularReferences(name, new ArrayList<>(), pattern);
}
}

private void innerForbidCircularReferences(String patternName, List<String> path, String pattern) {
Expand Down Expand Up @@ -151,7 +152,7 @@ private void innerForbidCircularReferences(String patternName, List<String> path
}
String otherPatternName = pattern.substring(begin, end);
path.add(otherPatternName);
forbidCircularReferences(patternName, path, patternBank.get(otherPatternName));
innerForbidCircularReferences(patternName, path, patternBank.get(otherPatternName));
}
}

Expand Down