upload current sources

worker/src/http/problem.ts

@@ -0,0 +1,37 @@
+/**
+ * RFC 9457 Problem Details for HTTP APIs — the governed contract
+ * (docs/api/worker.openapi.json) specifies `application/problem+json` for all
+ * error responses (400/401/404/502/503).
+ *
+ * We omit the `type` member: per RFC 9457 §3.1.1 an absent `type` is
+ * equivalent to "about:blank", in which case `title` mirrors the HTTP status
+ * phrase — which is exactly what we send.
+ */
+
+import type { FastifyReply } from 'fastify';
+
+export const PROBLEM_CONTENT_TYPE = 'application/problem+json';
+
+export interface ProblemDetails {
+  title: string;
+  status: number;
+  detail?: string;
+}
+
+export function sendProblem(
+  reply: FastifyReply,
+  status: number,
+  title: string,
+  detail?: string,
+  /** Extra response headers (e.g. `Retry-After` on 503). */
+  headers: Record<string, string> = {},
+): FastifyReply {
+  const body: ProblemDetails = detail === undefined ? { title, status } : { title, status, detail };
+  // Serialize explicitly: Fastify's default JSON serializer targets
+  // application/json, so send a pre-serialized string under the problem type.
+  reply.code(status).header('content-type', `${PROBLEM_CONTENT_TYPE}; charset=utf-8`);
+  for (const [name, value] of Object.entries(headers)) {
+    reply.header(name, value);
+  }
+  return reply.send(JSON.stringify(body));
+}