Cannot get data catalog name for malformed topic path

Error message

Cannot get data catalog name for malformed topic path {}. Expected format: projects/<project>/topics/<topic>

What it means

PubsubClient.getDataCatalogSegments parses a topic path to extract project and topic name segments for Data Catalog lineage. When the path does not have the well-formed projects/<project>/topics/<topic> shape (path split does not yield 4 segments), it logs a warning and returns an empty list instead of throwing, since the malformed path will fail later at publish time anyway.

Solutions

Pass a fully-qualified topic path: projects/<project>/topics/<topic>.
Use PubsubClient.topicPathFromName(project, topic) to construct a valid path from components.
If this is a test fixture, either ignore the warning or supply a well-formed fake path to keep lineage parsing quiet.
Check the path value at the call site (apply/topicPathFromNameWellFormed) for typos or truncated project IDs.

Example fix

// before
String badPath = "my-topic";
client.getDataCatalogSegments(badPath);
// after
String goodPath = PubsubClient.topicPathFromName("my-project", "my-topic");
// -> projects/my-project/topics/my-topic

Defensive patterns

Strategy: validation

Validate before calling

static boolean isWellFormedTopicPath(String p) {
  return p != null && p.matches("projects/[^/]+/topics/[^/]+");
}

Type guard

String requireTopicPath(String p) {
  if (p == null || !p.matches("projects/[^/]+/topics/[^/]+"))
    throw new IllegalArgumentException("topic path must be projects/<project>/topics/<topic>: " + p);
  return p;
}

Try / catch

// No exception thrown; check the returned list before use:
List<String> segs = client.getDataCatalogSegments(path);
if (segs.isEmpty()) { throw new IllegalArgumentException("malformed topic path: " + path); }

Prevention

Build paths via topicPathFromName(project, topic) instead of string concatenation.
Validate user-supplied topic strings against projects/<project>/topics/<topic> at config load.
Never pass subscription paths or short topic names to topic-path APIs.
Avoid short fake names in tests; use well-formed fixture paths.

When it happens

Trigger: Calling getDataCatalogSegments (directly or via topicPathFromPath / apply) with a topic path like 'my-topic', 'projects/p/topics/' (trailing empty segment), or a test fixture path that lacks the full 4-segment structure.

Common situations: Unit tests using short fake topic names; user-supplied topic strings missing the full resource path; accidentally passing a subscription path or topic short-name where a fully-qualified topic path is expected.

Understand the failure class

Background: "Invalid URL" errors: why new URL(), URI.parse, and reqwest::Url reject your string — missing scheme, whitespace, and bad path format — this error's family across 39 libraries.

Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/c5287f231c0d703b. Report an issue: GitHub.

Appendix: source

Thrown at sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubClient.java:329

      List<String> splits = Splitter.on('/').splitToList(path);

      checkState(splits.size() == 4, "Malformed topic path %s", path);
      return splits.get(3);
    }

    /**
     * Returns the data catalog segments. This method is fail-safe. If topic path is malformed, it
     * returns an empty string.
     */
    public List<String> getDataCatalogSegments() {
      List<String> splits = Splitter.on('/').splitToList(path);
      if (splits.size() == 4) {
        // well-formed path
        return ImmutableList.of(splits.get(1), splits.get(3));
      } else {
        // Mal-formed path. It is either a test fixture or user error and will fail on publish.
        // We do not throw exception instead return empty string here.
        LOG.warn(
            "Cannot get data catalog name for malformed topic path {}. Expected format: "
                + "projects/<project>/topics/<topic>",
            path);
        return ImmutableList.of();
      }
    }

    public String getFullPath() {
      List<String> splits = Splitter.on('/').splitToList(path);
      checkState(splits.size() == 4, "Malformed topic path %s", path);
      return String.format("/topics/%s/%s", splits.get(1), splits.get(3));
    }

    @Override
    public boolean equals(@Nullable Object o) {
      if (this == o) {
        return true;
      }

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