{"record":{"id":"2862d4db1cdfb1f6","repo":"risingwavelabs/risingwave","slug":"metadata-snapshot-is-truncated-while-reading-u32","errorCode":null,"errorMessage":"metadata snapshot is truncated while reading u32","messagePattern":"metadata snapshot is truncated while reading u32","errorType":"exception","errorClass":"BackupError","httpStatus":null,"severity":"error","filePath":"src/storage/backup/src/meta_snapshot.rs","lineNumber":258,"sourceCode":"    }\n\n    fn verify_checksum(&self, checksum: &[u8]) -> BackupResult<()> {\n        Self::verify_checksum_with_hasher(&self.hasher, checksum)\n    }\n\n    fn verify_checksum_with_hasher(hasher: &XxHash64, checksum: &[u8]) -> BackupResult<()> {\n        let expected = u64::from_le_bytes(checksum.try_into().expect(\"u64 length\"));\n        let found = hasher.finish();\n        if expected != found {\n            return Err(BackupError::ChecksumMismatch { expected, found });\n        }\n        Ok(())\n    }\n}\n\npub(crate) fn read_u32_le(buf: &mut &[u8]) -> BackupResult<u32> {\n    if buf.remaining() < 4 {\n        return Err(BackupError::Other(anyhow::anyhow!(\n            \"metadata snapshot is truncated while reading u32\"\n        )));\n    }\n    Ok(buf.get_u32_le())\n}\n\nimpl<T: Metadata> Display for MetaSnapshot<T> {\n    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {\n        writeln!(f, \"format_version: {}\", self.format_version)?;\n        writeln!(f, \"id: {}\", self.id)?;\n        writeln!(f, \"{}\", self.metadata)?;\n        Ok(())\n    }\n}\n","sourceCodeStart":240,"sourceCodeEnd":273,"githubUrl":"https://github.com/risingwavelabs/risingwave/blob/6469eb736d691e8e9b8a419a57edd6429ca77417/src/storage/backup/src/meta_snapshot.rs#L240-L273","documentation":"read_u32_le is a cursor helper used when parsing metadata snapshot sections; it throws BackupError::Other when fewer than 4 bytes remain in the in-memory buffer, reporting \"metadata snapshot is truncated while reading u32\". It means a length/count field was expected but the section data ran out mid-parse.","triggerScenarios":"Calling decode functions (e.g. decode_prost_message, section list decoders in meta_snapshot_v2) with a buffer cut off before a u32 length prefix — truncated section payload, a hand-crafted or corrupted snapshot body, or reading a slice boundary incorrectly.","commonSituations":"Restoring a snapshot whose object storage read truncated the buffer; tests feeding partial section bytes; corrupted backup files; mixing snapshot versions where a section is shorter than the parser expects.","solutions":["Validate the snapshot object size against the backup manifest and restore from an intact backup.","Check that the parser's expected section layout matches the snapshot's format_version.","Re-run the restore and check object store read errors/short reads in logs before concluding corruption.","In tests, build payloads via the writer helpers so all u32 length prefixes are emitted."],"exampleFix":"// before: decoding a manually built buffer missing a length prefix\nlet m = decode_section(&mut &payload[10..])?; // short slice\n// after: guarantee the full section is buffered\nensure!(payload.len() >= section_len, \"section truncated\");\nlet m = decode_section(&mut &payload[10..])?;","handlingStrategy":"validation","validationCode":"// before calling section decoders, ensure the buffer holds the whole section\nif buf.len() < expected_section_len {\n    return Err(anyhow!(\"section buffer truncated: {} < {}\", buf.len(), expected_section_len));\n}","typeGuard":"fn has_u32(buf: &[u8]) -> bool { buf.len() >= 4 }","tryCatchPattern":"match read_u32_le(&mut buf) {\n    Ok(v) => v,\n    Err(e) if e.to_string().contains(\"truncated while reading u32\") => {\n        return Err(anyhow!(\"snapshot section truncated; restore from intact backup\"));\n    }\n    Err(e) => return Err(e.into()),\n}","preventionTips":["Buffer entire snapshot bytes before parsing sections; avoid partial reads.","Validate snapshot size against the backup manifest first.","Use writer helpers to generate test fixtures so every u32 prefix is present."],"tags":["rust","backup","snapshot-decoding","truncated-data"],"backgroundTag":"file-read-failed","analyzedSha":"6469eb736d691e8e9b8a419a57edd6429ca77417","analyzedAt":"2026-09-11T21:06:21.487Z","contentChangedAt":"2026-09-11T21:06:21.487Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}