cayleygraph/cayley · error

format is not supported for reading quads

Error message

format is not supported for reading quads

What it means

The v2 HTTP DELETE data endpoint needs to parse a request body of quads. It picks a format from the Content-Type header via getFormat; if no format is negotiated or the format has no registered Reader, the endpoint rejects the request with 400. Only formats compiled in / registered (e.g. nquads) provide readers.

Source

Thrown at server/http/api_v2.go:277

		return
	}
	w.Header().Set(hdrContentType, contentTypeJSON)
	response := newWriteResponse(n)
	encoder := json.NewEncoder(w)
	encoder.Encode(response)
}

// ServeDelete deletes data received in the request body from the database.
// Responds with how many quads were deleted.
func (api *APIv2) ServeDelete(w http.ResponseWriter, r *http.Request) {
	defer r.Body.Close()
	if api.ro {
		jsonResponse(w, http.StatusForbidden, errors.New("database is read-only"))
		return
	}
	format := getFormat(r, "", hdrContentType)
	if format == nil || format.Reader == nil {
		jsonResponse(w, http.StatusBadRequest, fmt.Errorf("format is not supported for reading quads"))
		return
	}
	rd, err := readerFrom(r, hdrContentEncoding)
	if err != nil {
		jsonResponse(w, http.StatusBadRequest, err)
		return
	}
	defer rd.Close()
	qr := format.Reader(r.Body)
	defer qr.Close()
	h, err := api.handleForRequest(r)
	if err != nil {
		jsonResponse(w, http.StatusBadRequest, err)
		return
	}
	qw := graph.NewRemover(h.QuadWriter)
	defer qw.Close()
	n, err := quad.CopyBatch(qw, qr, api.batch)

View on GitHub (pinned to 81dcd7d73e)

Solutions

1. Set Content-Type to the supported quad MIME type (e.g. application/n-quads) on the DELETE request
2. Check which formats the server registered and use one with a Reader
3. Inspect the response body/format list (the formats endpoint) to find an acceptable Content-Type

Example fix

// before
curl -X DELETE -H 'Content-Type: application/json' --data-binary @quads.ndjson ...
// after
curl -X DELETE -H 'Content-Type: application/n-quads' --data-binary @quads.nq ...

const ct = "application/n-quads"
req.Header.Set("Content-Type", ct)
if !strings.HasPrefix(req.Header.Get("Content-Type"), "application/") {
    return errors.New("DELETE data requires a quad Content-Type")
}

resp, err := client.Do(req)
if err != nil { return err }
if resp.StatusCode == http.StatusBadRequest {
    b, _ := io.ReadAll(resp.Body)
    return fmt.Errorf("data delete rejected (check Content-Type): %s", b)
}

When it happens

Trigger: Sending a DELETE request to /api/v2/data with an unsupported or missing Content-Type (e.g. application/json, text/plain), or omitting the Content-Type header entirely.

Common situations: API clients defaulting to JSON when posting quad deletion batches; servers built without a quad format registered; typos like application/nquads vs supported MIME strings.

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

• format is not supported for reading nodes
• request data is too large
• cannot remove nil value
• no support for HTTP interface for this query language
• request is too large

AI-assisted analysis of cayleygraph/cayley@81dcd7d73e (2026-09-06). Data as JSON: /api/errors/18f34a87e6b0fafc. Report an issue: GitHub.