Downloading FIDO metadata fails

[fcorneli]

Did something change? We get the following error recently:

19:25:02,937 WARN  [com.yubico.fido.metadata.FidoMetadataDownloader] (default task-4) Failed to read or parse cached BLOB.: java.util.NoSuchElementException
	at java.base/java.util.Scanner.throwFor(Scanner.java:937)
	at java.base/java.util.Scanner.next(Scanner.java:1478)
	at deployment.isms-webapp-1.20.1-SNAPSHOT-production.war//com.yubico.fido.metadata.FidoMetadataDownloader.parseBlob(FidoMetadataDownloader.java:1150)
	at deployment.isms-webapp-1.20.1-SNAPSHOT-production.war//com.yubico.fido.metadata.FidoMetadataDownloader.parseAndMaybeVerifyBlob(FidoMetadataDownloader.java:1087)

[emlun]

The integration tests are still passing, so there seems to be no issue for the library to parse the MDS payload.

Failed to read or parse cached BLOB.: java.util.NoSuchElementException

Please check your cached BLOB; this error indicates it may be corrupted or empty.

[fcorneli]

OK, I think the problem comes from FidoMetadataDownloader.readCacheFile.
If the application starts the system with two empty temporarily files:

File trustRootCacheFile;
File blobCacheFile;
trustRootCacheFile = File.createTempFile("fido-mds-trust-root-", ".bin");
blobCacheFile = File.createTempFile("fido-mds-blob-", ".bin");

which I guess makes sense initially, then you get this error.

[emlun]

Yeah, the file should not exist if the cache is empty, as described in the JavaDoc: https://developers.yubico.com/java-webauthn-server/JavaDoc/webauthn-server-attestation/2.7.0/com/yubico/fido/metadata/FidoMetadataDownloader.FidoMetadataDownloaderBuilder.Step5.html#useBlobCacheFile(java.io.File)

[...]
If cacheFile exists, is a normal file, is readable, and is not out of date, then it will be used as the FIDO Metadata Service BLOB.
[...]

Parameters:
cacheFile - a File which may or may not exist. If it exists, it MUST contain the metadata BLOB in JWS compact serialization format [RFC7515].