cayleygraph/cayley · error

decoding of %q is not supported

Error message

decoding of %q is not supported

What it means

This error means the quad format was recognized by quad.FormatByName, but the registered Format has a nil Reader, i.e. the format can only be written (serialized), not decoded. Cayley refuses to load data in a write-only format such as pquads (its custom binary format) when used as an input. It exists to distinguish 'unknown format' from 'known but not decodable'.

Source

Thrown at internal/load.go:104

		qr = nquads.NewReader(r, false)
	default:
		var format *quad.Format
		if typ == "" {
			name := filepath.Base(path)
			name = strings.TrimSuffix(name, ".gz")
			name = strings.TrimSuffix(name, ".bz2")
			format = quad.FormatByExt(filepath.Ext(name))
			if format == nil {
				typ = "nquads"
			}
		}
		if format == nil {
			format = quad.FormatByName(typ)
		}
		if format == nil {
			err = fmt.Errorf("unknown quad format %q", typ)
		} else if format.Reader == nil {
			err = fmt.Errorf("decoding of %q is not supported", typ)
		}
		if err != nil {
			if c != nil {
				c.Close()
			}
			return nil, err
		}
		qr = format.Reader(r)
	}
	if c != nil {
		return readCloser{ReadCloser: qr, close: c.Close}, nil
	}
	return qr, nil
}

// DecompressAndLoad will load or fetch a graph from the given path, decompress
// it, and then call the given load function to process the decompressed graph.
// If no loadFn is provided, db.Load is called.

View on GitHub (pinned to 81dcd7d73e)

Solutions

1. Pick a decodable input format: dump to nquads (or jsonld) and load that instead of pquads.
2. Check format.Reader (or format.Writer) is non-nil programmatically before calling QuadReaderFor.
3. If you need round-tripping, use nquads: `cayley dump --format nquads` then `cayley load --format nquads`.

Example fix

// before
cayley load --format pquads backup.pquads
// after
cayley load --format nquads backup.nq

if f := quad.FormatByName(formatName); f == nil || f.Reader == nil {
	return fmt.Errorf("format %q cannot be used as input; dump to nquads instead", formatName)
}

When it happens

Trigger: Calling internal.QuadReaderFor (or internal.DecompressAndLoad / `cayley load`) with a type string that resolves to a format whose Format.Reader is nil — for example asking to load from the pquads binary format, which is write-only.

Common situations: Pointing `cayley load` at a database dump produced by cayley dump in pquads format and expecting it to be re-loadable; copying a dump command's format flag into a load command without checking decodability.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

• unknown quad format %q
• db: failed to load data: %v
• cannot count iterator without a valid context
• node tokens not valid
• varint: overflow

AI-assisted analysis of cayleygraph/cayley@81dcd7d73e (2026-09-06). Data as JSON: /api/errors/70ab67edc49fbe5f. Report an issue: GitHub.