fix: only "swallow" the json() parsing error if the response is empty (#47493)

public/app/core/utils/fetch.test.ts

@@ -135,7 +135,12 @@ describe('parseCredentials', () => {
 });
 
 describe('parseResponseBody', () => {
-  const rsp = {} as unknown as Response;
+  let rsp: Response;
+
+  beforeEach(() => {
+    rsp = new Response();
+  });
+
   it('parses json', async () => {
     const value = { hello: 'world' };
     const body = await parseResponseBody(
@@ -148,6 +153,24 @@ describe('parseResponseBody', () => {
     expect(body).toEqual(value);
   });
 
+  it('returns an empty object {} when the response is empty but is declared as JSON type', async () => {
+    rsp.headers.set('Content-Length', '0');
+    jest.spyOn(console, 'warn').mockImplementation();
+
+    const json = jest.fn();
+    const body = await parseResponseBody(
+      {
+        ...rsp,
+        json,
+      },
+      'json'
+    );
+
+    expect(body).toEqual({});
+    expect(json).not.toHaveBeenCalled();
+    expect(console.warn).toHaveBeenCalledTimes(1);
+  });
+
   it('parses text', async () => {
     const value = 'RAW TEXT';
     const body = await parseResponseBody(

public/app/core/utils/fetch.ts

@@ -106,13 +106,15 @@ export async function parseResponseBody<T>(
         return response.blob() as any;
 
       case 'json':
-        try {
+        // An empty string is not a valid JSON.
-          return await response.json();
+        // Sometimes (unfortunately) our APIs declare their Content-Type as JSON, however they return an empty body.
-        } catch (err) {
+        if (response.headers.get('Content-Length') === '0') {
-          console.warn(`${response.url} returned an invalid JSON -`, err);
+          console.warn(`${response.url} returned an invalid JSON`);
           return {} as unknown as T;
         }
 
+        return await response.json();
+
       case 'text':
         return response.text() as any;
     }