thanos-io/thanos · error

hash function is not supported

Error message

hash function %v is not supported

What it means

CalculateHash in pkg/block/metadata only implements a fixed set of object hash functions (currently SHA-256 via SHA256Func). When the caller passes a hash function identifier (hf) that is not one of the supported ones, the function returns this error instead of computing a hash. It is a guard against unsupported enum values for the hash algorithm.

Solutions

1. Change the hash function configuration/value to SHA256Func, the only currently supported algorithm.
2. Check the Thanos version: metadata written by a newer version with a different hash function needs that version (or later) to be read.
3. If you believe the algorithm should be supported, add a case for it in CalculateHash and upstream it; otherwise do not pass arbitrary hash func identifiers.

Example fix

// before
hf := metadata.HashFunc("sha512")
h, err := metadata.CalculateHash(ctx, bkt, hf, id)
// after
hf := metadata.SHA256Func
h, err := metadata.CalculateHash(ctx, bkt, hf, id)

if hf != metadata.SHA256Func {
	return fmt.Errorf("unsupported hash function %v; only %v is supported", hf, metadata.SHA256Func)
}
// proceed with metadata.CalculateHash(ctx, bkt, hf, id)

func isSupportedHashFunc(hf metadata.HashFunc) bool { return hf == metadata.SHA256Func }

When it happens

Trigger: Calling metadata.CalculateHash (directly or via Download, GatherFileStats, or block creation in createBlock) with an ObjectHash.Func / HashFunc value other than the supported SHA256Func, e.g. SHA1, SHA512, or a zero value.

Common situations: Config files or metadata JSON produced by newer/older Thanos versions that use a hash algorithm this build does not know; custom tooling writing block meta with a hand-picked hash function; copy-pasted code that hardcodes a different constant than SHA256Func.

Related errors

• could not sync metas
• meta.json bkt get for
• read meta from
• fetch overlaps
• create meta fetcher

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/74730d5799af0fd6. Report an issue: GitHub.

Appendix: source

Thrown at pkg/block/metadata/hash.go:62

	case SHA256Func:
		f, err := os.Open(filepath.Clean(p))
		if err != nil {
			return ObjectHash{}, errors.Wrap(err, "opening file")
		}
		defer runutil.CloseWithLogOnErr(logger, f, "closing %s", p)

		h := sha256.New()

		if _, err := io.Copy(h, f); err != nil {
			return ObjectHash{}, errors.Wrap(err, "copying")
		}

		return ObjectHash{
			Func:  SHA256Func,
			Value: hex.EncodeToString(h.Sum(nil)),
		}, nil
	}
	return ObjectHash{}, fmt.Errorf("hash function %v is not supported", hf)

}

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