Distribution Probe

Probes a DCAT Distribution to check availability and gather metadata. Returns SparqlProbeResult, DataDumpProbeResult, or NetworkError – the probe never throws.

import { Distribution } from '@lde/dataset';
import { probe } from '@lde/distribution-probe';

const distribution = new Distribution(
  new URL('https://example.org/data.ttl'),
  'text/turtle',
);
const result = await probe(distribution);

Behaviour

SPARQL endpoints

Sends POST with SELECT * { ?s ?p ?o } LIMIT 1 and Accept: application/sparql-results+json, then:

• Content-Type is enforced. The response Content-Type must start with application/sparql-results+json; anything else fails the probe (isSuccess() === false). This rules out HTML error pages served with 200 OK.
• The JSON body must parse and contain a results object. Empty bodies, invalid JSON, and missing results all fail the probe with a failureReason.

Data dumps

Sends HEAD with Accept: <distribution.mimeType> and Accept-Encoding: identity. If Content-Length is missing or ≤ 10 KB, retries with GET to validate the body – this also catches servers that return 0 from HEAD.

• Content-Type is checked as a soft warning, not a hard failure. If the server’s Content-Type disagrees with the distribution’s declared mimeType, a message is appended to result.warnings but isSuccess() stays true. Compression wrappers (application/gzip, application/x-gzip, application/octet-stream) are skipped so a gzipped Turtle file doesn’t trigger a warning.
• Body is parse-validated only for Turtle, N-Triples, and N-Quads (Content-Type starting with text/turtle, application/n-triples, or application/n-quads). Empty bodies and parse errors fail the probe. Other RDF serializations (RDF/XML, JSON-LD, TriG, …) are not parse-validated – only HTTP status and headers are checked.
• Bodies larger than 10 KB are not fetched; only HEAD metadata is inspected.

Network errors

Any thrown exception from fetch (DNS, connection refused, TLS, timeout after the configured timeout – default 5 000 ms) is caught and returned as a NetworkError with the original message.