Return a HTTP 206 response as-is (#1721)

packages/workbox-range-requests/createPartialResponse.mjs

@@ -20,10 +20,13 @@ import './_version.mjs';
  * Given a `Request` and `Response` objects as input, this will return a
  * promise for a new `Response`.
  *
+ * If the original `Response` already contains partial content (i.e. it has
+ * a status of 206), then this assumes it already fulfills the `Range:`
+ * requirements, and will return it as-is.
+ *
  * @param {Request} request A request, which should contain a Range:
  * header.
- * @param {Response} originalResponse An original response containing the full
- * content.
+ * @param {Response} originalResponse A response.
  * @return {Promise<Response>} Either a `206 Partial Content` response, with
  * the response body set to the slice of content specified by the request's
  * `Range:` header, or a `416 Range Not Satisfiable` response if the
@@ -47,6 +50,12 @@ async function createPartialResponse(request, originalResponse) {
       });
     }
 
+    if (originalResponse.status === 206) {
+      // If we already have a 206, then just pass it through as-is;
+      // see https://github.com/GoogleChrome/workbox/issues/1720
+      return originalResponse;
+    }
+
     const rangeHeader = request.headers.get('range');
     if (!rangeHeader) {
       throw new WorkboxError('no-range-header');

test/workbox-range-requests/node/createPartialResponse.mjs

@@ -59,5 +59,13 @@ describe(`[workbox-range-requests] createPartialResponse`, function() {
       const expectedBlob = constructBlob(101);
       expect(responseBlob._text).to.eql(expectedBlob._text);
     });
+
+    it(`should handle being passed a Response with a status of 206 by returning it as-is`, async function() {
+      const originalPartialResponse = new Response('expected text', {status: 206});
+      const createdPartialResponse = await createPartialResponse(VALID_REQUEST, originalPartialResponse);
+
+      // We should get back the exact same response.
+      expect(createdPartialResponse).to.eql(originalPartialResponse);
+    });
   });
 });