fix(server): accept empty requests with unsupported media types

Inject an empty JSON object for requests that have an unsupported content type but zero content length. Fastify defaults to rejecting these with a 415 error.

Closes #348

server/src/common/utils/bootstrap.utils.ts

@@ -1,4 +1,11 @@
+import { UnsupportedMediaTypeException } from '@nestjs/common';
+import type { FastifyInstance } from 'fastify';
+import type { IncomingHttpHeaders } from 'http';
+import { Readable } from 'stream';
+
 const DEFAULT_TRUST_PROXY = 'loopback,linklocal,uniquelocal';
+const EMPTY_JSON_BODY = '{}';
+const BODY_METHODS = new Set(['DELETE', 'PATCH', 'POST', 'PUT']);
 
 export function parseTrustProxy(value: string | undefined): string | boolean | number {
   const raw = value?.trim();
@@ -52,3 +59,33 @@ export function buildCspDirectives(options: CspOptions = {}) {
     upgradeInsecureRequests: null,
   };
 }
+
+export function shouldInjectEmptyJsonBody(method: string, headers: IncomingHttpHeaders): boolean {
+  const contentType = getHeaderValue(headers['content-type'])?.toLowerCase();
+  if (!BODY_METHODS.has(method.toUpperCase()) || !contentType?.startsWith('application/json')) {
+    return false;
+  }
+
+  const contentLength = getHeaderValue(headers['content-length'])?.trim();
+  return contentLength === undefined || contentLength === '0';
+}
+
+export function buildEmptyJsonBodyStream(headers: IncomingHttpHeaders): Readable {
+  headers['content-length'] = String(Buffer.byteLength(EMPTY_JSON_BODY));
+  return Readable.from([EMPTY_JSON_BODY]);
+}
+
+export function registerEmptyBodyContentTypeParser(fastify: FastifyInstance): void {
+  fastify.addContentTypeParser<string>('*', { parseAs: 'string' }, (request, body, done) => {
+    if (BODY_METHODS.has(request.method.toUpperCase()) && body.length === 0) {
+      done(null, {});
+      return;
+    }
+
+    done(new UnsupportedMediaTypeException('Unsupported Media Type'));
+  });
+}
+
+function getHeaderValue(value: string | string[] | undefined): string | undefined {
+  return Array.isArray(value) ? value[0] : value;
+}