fix: bodyless posts no longer send json content-type (fastify 400 on empty body)

web/src/api.ts

@@ -48,8 +48,9 @@ async function request<T>(path: string, init?: RequestInit): Promise<T> {
 function post<T>(path: string, payload?: unknown): Promise<T> {
   return request<T>(path, {
     method: 'POST',
-    headers: { 'Content-Type': 'application/json' },
-    body: payload === undefined ? undefined : JSON.stringify(payload),
+    ...(payload !== undefined
+      ? { headers: { 'Content-Type': 'application/json' }, body: JSON.stringify(payload) }
+      : {}),
   })
 }
 

web/test/api.test.ts

@@ -40,4 +40,19 @@ describe('api additions', () => {
     expect(err).toBeInstanceOf(ApiError)
     expect((err as ApiError).code).toBe('no_subsonic_config')
   })
+
+  it('bodyless posts do not send a json content-type (Fastify 400s on empty json bodies)', async () => {
+    fetchMock.mockClear()
+    fetchMock.mockImplementation(() => jsonOk({ ok: true }))
+    await api.returnLoan(7)
+    await api.markPlayed('a1')
+    await api.logout()
+    await api.triggerBackup()
+    for (const call of fetchMock.mock.calls) {
+      const init = call[1] as RequestInit | undefined
+      const headers = (init?.headers ?? {}) as Record<string, string>
+      expect(headers['Content-Type']).toBeUndefined()
+      expect(init?.body).toBeUndefined()
+    }
+  })
 })