Omit Content-Type header for files of unknown extension in Workers Assets (#8248)

* Omit Content-Type header for files of unknown extension in Workers Assets

* Omit Content-Type header for files of unknown extension in Workers Assets

Author: GregBrimble

.changeset/quick-singers-stand.md

@@ -0,0 +1,5 @@
+---
+"wrangler": minor
+---
+
+feat: Omits Content-Type header for files of an unknown extension in Workers Assets

packages/wrangler/src/__tests__/deploy.test.ts

@@ -5038,6 +5038,59 @@ addEventListener('fetch', event => {});`
 			`);
 		});
 
+		it("should attach an 'application/null' content-type header when uploading files with an unknown extension", async () => {
+			const assets = [{ filePath: "foobar.greg", content: "something-binary" }];
+			writeAssets(assets);
+			writeWranglerConfig({
+				assets: { directory: "assets" },
+			});
+
+			const manifestBodies: AssetManifest[] = [];
+			const mockBuckets = [["80e40c1f2422528cb2fba3f9389ce315"]];
+			await mockAUSRequest(manifestBodies, mockBuckets, "<<aus-token>>");
+			const uploadBodies: FormData[] = [];
+			const uploadAuthHeaders: (string | null)[] = [];
+			const uploadContentTypeHeaders: (string | null)[] = [];
+			await mockAssetUploadRequest(
+				mockBuckets.length,
+				uploadBodies,
+				uploadAuthHeaders,
+				uploadContentTypeHeaders
+			);
+			mockSubDomainRequest();
+			mockUploadWorkerRequest({
+				expectedAssets: {
+					jwt: "<<aus-completion-token>>",
+					config: {},
+				},
+				expectedType: "none",
+			});
+			await runWrangler("deploy");
+			expect(manifestBodies.length).toBe(1);
+			expect(manifestBodies[0]).toEqual({
+				manifest: {
+					"/foobar.greg": {
+						hash: "80e40c1f2422528cb2fba3f9389ce315",
+						size: 16,
+					},
+				},
+			});
+			const flatBodies = Object.fromEntries(
+				uploadBodies.flatMap((b) => [...b.entries()])
+			);
+			await expect(
+				flatBodies["80e40c1f2422528cb2fba3f9389ce315"]
+			).toBeAFileWhichMatches(
+				new File(
+					["c29tZXRoaW5nLWJpbmFyeQ=="],
+					"80e40c1f2422528cb2fba3f9389ce315",
+					{
+						type: "application/null",
+					}
+				)
+			);
+		});
+
 		it("should be able to upload files with special characters in filepaths", async () => {
 			// NB windows will disallow these characters in file paths anyway < > : " / \ | ? *
 			const assets = [

packages/wrangler/src/assets.ts

@@ -138,7 +138,11 @@ export const syncAssets = async (
 						[(await readFile(absFilePath)).toString("base64")],
 						manifestEntry[1].hash,
 						{
-							type: getContentType(absFilePath) || "application/octet-stream",
+							// Most formdata body encoders (incl. undici's) will override with "application/octet-stream" if you use a falsy value here
+							// Additionally, it appears that undici doesn't support non-standard main types (e.g. "null")
+							// So, to make it easier for any other clients, we'll just parse "application/null" on the API
+							// to mean actually null (signal to not send a Content-Type header with the response)
+							type: getContentType(absFilePath) ?? "application/null",
 						}
 					),
 					manifestEntry[1].hash