fix(http): Use the response content-type to set the blob type. (#52840)

When downloading a PDF with the fetch client, the blob had no content. It couldn't be displayed in an iframe. This commit fixes this.

Relate to: https://stackoverflow.com/questions/77470626/possible-bug-in-httpclient-when-using-the-blob-data-type

PR Close #52840

packages/common/http/src/fetch.ts

@@ -145,7 +145,8 @@ export class FetchBackend implements HttpBackend {
       // Combine all chunks.
       const chunksAll = this.concatChunks(chunks, receivedLength);
       try {
-        body = this.parseBody(request, chunksAll);
+        const contentType = response.headers.get('Content-Type') ?? '';
+        body = this.parseBody(request, chunksAll, contentType);
       } catch (error) {
         // Body loading or parsing failed
         observer.error(new HttpErrorResponse({
@@ -193,8 +194,8 @@ export class FetchBackend implements HttpBackend {
     }
   }
 
-  private parseBody(request: HttpRequest<any>, binContent: Uint8Array): string|ArrayBuffer|Blob
-      |object|null {
+  private parseBody(request: HttpRequest<any>, binContent: Uint8Array, contentType: string): string
+      |ArrayBuffer|Blob|object|null {
     switch (request.responseType) {
       case 'json':
         // stripping the XSSI when present
@@ -203,7 +204,7 @@ export class FetchBackend implements HttpBackend {
       case 'text':
         return new TextDecoder().decode(binContent);
       case 'blob':
-        return new Blob([binContent]);
+        return new Blob([binContent], {type: contentType});
       case 'arraybuffer':
         return binContent.buffer;
     }

packages/common/http/test/fetch_spec.ts

@@ -217,6 +217,16 @@ describe('FetchBackend', async () => {
     expect(res.body!.data).toBe('some data');
   });
 
+  it('handles a blob with a mime type', async () => {
+    const promise = trackEvents(backend.handle(TEST_POST.clone({responseType: 'blob'})));
+    const type = 'aplication/pdf';
+    fetchMock.mockFlush(HttpStatusCode.Ok, 'OK', new Blob(), {'Content-Type': type});
+    const events = await promise;
+    expect(events.length).toBe(2);
+    const res = events[1] as HttpResponse<Blob>;
+    expect(res.body?.type).toBe(type);
+  });
+
   it('emits unsuccessful responses via the error path', done => {
     backend.handle(TEST_POST).subscribe({
       error: (err: HttpErrorResponse) => {
@@ -400,12 +410,18 @@ export class MockFetchFactory extends FetchFactory {
         return this.promise;
       }
 
-  mockFlush(status: number, statusText: string, body?: string): void {
+  mockFlush(
+      status: number, statusText: string, body?: string|Blob, headers?: Record<string, string>):
+      void {
     this.clearWarningTimeout?.();
-    this.response.setupBodyStream(body);
-
-    const response =
-        new Response(this.response.stream, {statusText, headers: this.response.headers});
+    if (typeof body === 'string') {
+      this.response.setupBodyStream(body);
+    } else {
+      this.response.setBody(body);
+    }
+    const response = new Response(
+        this.response.stream,
+        {statusText, headers: {...this.response.headers, ...(headers ?? {})}});
 
     // Have to be set outside the constructor because it might throw
     // RangeError: init["status"] must be in the range of 200 to 599, inclusive
@@ -470,6 +486,11 @@ class MockFetchResponse {
     },
   });
 
+  public setBody(body: any) {
+    this.sub$.next(body);
+    this.sub$.complete();
+  }
+
   public setupBodyStream(body?: string) {
     if (body && this.progress.length) {
       this.headers['content-length'] = `${body.length}`;