fix: handle invalid json when Content-Type=application/json (#558)

src/gaxios.ts

@@ -372,7 +372,7 @@ export class Gaxios {
    * @param {FetchResponse} response the HTTP response.
    * @returns {Promise<any>} a promise that resolves to the response data.
    */
-  private getResponseDataFromContentType(
+  private async getResponseDataFromContentType(
     response: FetchResponse
   ): Promise<any> {
     let contentType = response.headers.get('Content-Type');
@@ -382,7 +382,13 @@ export class Gaxios {
     }
     contentType = contentType.toLowerCase();
     if (contentType.includes('application/json')) {
-      return response.json();
+      let data = await response.text();
+      try {
+        data = JSON.parse(data);
+      } catch {
+        // continue
+      }
+      return data as {};
     } else if (
       contentType.includes('text/plain') ||
       contentType.includes('text/html')

test/test.getch.ts

@@ -587,6 +587,17 @@ describe('🎏 data handling', () => {
     assert.deepStrictEqual(res.data, body);
   });
 
+  it('should return invalid JSON as text when response Content-Type=application/json', async () => {
+    const body = 'hello world';
+    const scope = nock(url)
+      .get('/')
+      .reply(200, body, {'Content-Type': 'application/json'});
+    const res = await request({url});
+    scope.done();
+    assert.ok(res.data);
+    assert.deepStrictEqual(res.data, body);
+  });
+
   it('should return text when response Content-Type=text/plain', async () => {
     const body = 'hello world';
     const scope = nock(url)