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KAFKA-20617: add validation for cluster-id in Formatter #22384

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KAFKA-20617: add validation for cluster-id in Formatter #22384

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KAFKA-20617: add validation for cluster-id in Formatter
gaurav-narula May 27, 2026
2a70079
Address review comments
gaurav-narula May 29, 2026
55d3e00
Stress that validating `-` would break compatibility with old cids
gaurav-narula May 29, 2026
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11 changes: 11 additions & 0 deletions metadata/src/main/java/org/apache/kafka/metadata/storage/Formatter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -236,6 +236,17 @@ public void run() throws Exception {
if (clusterId == null) {
throw new FormatterException("You must specify the cluster id.");
}
try {
if (clusterId.contains("=")) {
throw new FormatterException("The specified cluster id, " + clusterId + " contains padding and is invalid");
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@showuon showuon May 29, 2026

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Our randomUuid method is possible to output the uuid contains = sign:

This will not generate a UUID equal to 0, 1, or one whose string representation starts with a dash ("-")

So is this the expected validation?

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@gaurav-narula gaurav-narula May 29, 2026

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I don't think it is possible because Uuid#toString does not use padding and = sign can only be present when padding is enabled

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@fvaleri fvaleri May 29, 2026

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I think this actually covers a real gap. The one in which a CID like igNUVIdeSPO5JCZYFhOh7Q== would pass the validation, but would be returned as igNUVIdeSPO5JCZYFhOh7Q by Uuid.toString(). I would just move it outside the try-catch block as it throws FormatterException directly and would bypass the catch anyway.

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@fvaleri fvaleri May 29, 2026

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Suggested change
throw new FormatterException("The specified cluster id, " + clusterId + " contains padding and is invalid");
throw new FormatterException("The specified cluster id, " + clusterId + " is invalid: contains padding");

}
Uuid uuid = Uuid.fromString(clusterId);
if (Uuid.RESERVED.contains(uuid)) {
throw new FormatterException("The specified cluster id, " + clusterId + " is reserved");
}
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@showuon showuon May 29, 2026

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Let's also validate the starting - sign.

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@gaurav-narula gaurav-narula May 29, 2026 •
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I think these are cosmetic improvemenst that've been added over time but have no bearing on correctness. Failing validation on them would hinder migration from older clusters where - was allowed.

The motivation for avoiding - in the beginning was to avoid shell escaping issues when passing cluster id in CLI tools. https://issues.apache.org/jira/browse/KAFKA-13741

Lately, https://issues.apache.org/jira/browse/KAFKA-20072 avoided - altogether to allow easier copy-pasting.

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@fvaleri fvaleri May 29, 2026 •
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Good point. Let's add a comment about this for future reference.

} catch (IllegalArgumentException e) {
throw new FormatterException("The specified cluster id, " + clusterId + " is invalid", e);
}
if (directories.isEmpty()) {
throw new FormatterException("You must specify at least one directory to format");
}
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14 changes: 14 additions & 0 deletions metadata/src/test/java/org/apache/kafka/metadata/storage/FormatterTest.java
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Expand Up @@ -587,4 +587,18 @@ public void testFormatWithNoInitialControllers() throws Exception {
assertNotNull(logDirProps1);
}
}

@ParameterizedTest
@ValueSource(strings = {"unrvTtQISjar0JUWGU/8Pg", "igNUVIdeSPO5JCZYFhOh7Q==", "AAAAAAAAAAAAAAAAAAAAAA", "AAAAAAAAAAAAAAAAAAAAAQ"})
public void testFormatWithInvalidClusterId(String clusterId) throws Exception {
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@fvaleri fvaleri May 29, 2026

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There's no corresponding positive test showing that a valid CID passes validation. This would guard against the validation being too aggressive.

try (TestEnv testEnv = new TestEnv(2)) {
FormatterContext formatter1 = testEnv.newFormatter();
formatter1.formatter.setClusterId(clusterId);
String expectedPrefix = "The specified cluster id, " + clusterId;
assertEquals(expectedPrefix,
assertThrows(FormatterException.class,
formatter1.formatter::run).
getMessage().substring(0, expectedPrefix.length()));
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@fvaleri fvaleri May 29, 2026

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Wouldn't be easier to rewrite like:

assertTrue(message.startsWith(expectedPrefix))

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@gaurav-narula gaurav-narula May 29, 2026

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I'm indifferent here - I followed the convention used in another test in the same class

}
}
}