fix: empty filename should not be treated as string (#28)

Co-authored-by: Jacob Ebey <jacob.ebey@live.com>
Co-authored-by: Matt Brophy <matt@brophy.org>

.changeset/light-snails-leave.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/web-fetch": patch
+---
+
+If you create a FormData object on the browser with empty file input, a default empty file entry (i.e. new File([], '')) would be generated. However, this is currently presented as an empty string instead when you read it on the server. This should fix the discrepancy.

packages/fetch/src/utils/form-data.js

@@ -104,8 +104,10 @@ export const toFormData = async (source) => {
     const form = new FormData()
     const parts = iterateMultipart(body, boundary)
     for await (const { name, data, filename, contentType } of parts) {
-      if (filename) {
+      if (typeof filename === 'string') {
         form.append(name, new File([data], filename, { type: contentType }))
+      } else if (typeof filename !== 'undefined') {
+        form.append(name, new File([], '', { type: contentType }))
       } else {
         form.append(name, new TextDecoder().decode(data), filename)
       }

packages/fetch/test/request.js

@@ -439,4 +439,52 @@ describe('Request', () => {
 			expect(file.lastModified).to.be.a('number');
 		});
 	});
+
+	it('should decode empty file inputs into File instances (web FormData)', async () => {
+		const ogFormData = new WebFormData();
+		ogFormData.append('a', 1);
+		// This is what happens when you construct the form data set with an empty file input:
+		// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#constructing-the-form-data-set
+		ogFormData.append('file', new File([], '', { type: 'application/octet-stream' }));
+		const request = new Request(base, {
+			method: 'POST',
+			body: ogFormData,
+		});
+		const clonedRequest = request.clone();
+		return clonedRequest.formData().then(async clonedFormData => {
+			expect(clonedFormData.get('a')).to.equal("1");
+			const file = clonedFormData.get('file');
+			expect(file.name).to.equal("");
+			expect(file.type).to.equal("application/octet-stream");
+			expect(file.size).to.equal(0);
+		});
+	});
+
+	it.skip('should decode empty file inputs into File instances (node FormData)', async () => {
+		const ogFormData = new FormData();
+		ogFormData.append('a', 1);
+		// This is what happens when you construct the form data set with an empty file input:
+		// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#constructing-the-form-data-set
+		ogFormData.append('file', Buffer.from(''), {
+			// Note: This doesn't work at the moment due to https://github.com/form-data/form-data/issues/412.
+			// There is a v4 released which has a fix that might handle this but I
+			// wasn't positive if it had breaking changes that would impact us so we
+			// can handle an upgrade separately.
+			filename: '',
+			contentType: 'application/octet-stream',
+		});
+		const request = new Request(base, {
+			method: 'POST',
+			body: ogFormData,
+		});
+		const clonedRequest = request.clone();
+		return clonedRequest.formData().then(async clonedFormData => {
+			expect(clonedFormData.get('a')).to.equal("1");
+			const file = clonedFormData.get('file');
+			expect(file.name).to.equal("");
+			expect(file.type).to.equal("application/octet-stream");
+			expect(file.size).to.equal(0);
+		});
+
+	});
 });