Fix malformed multipart body

packages/abstractions/src/multipartBody.ts

@@ -93,7 +93,7 @@ interface MultipartEntry {
 	serializationCallback?: ModelSerializerFunction<Parsable>;
 }
 
-export const serializeMultipartBody = (writer: SerializationWriter, multipartBody: Partial<MultipartBody> | undefined | null = new MultipartBody()): void => {
+export const serializeMultipartBody = (writer: SerializationWriter, multipartBody: Partial<MultipartBody> = new MultipartBody()): void => {
 	if (!writer) {
 		throw new Error("writer cannot be undefined");
 	}
@@ -117,13 +117,16 @@ export const serializeMultipartBody = (writer: SerializationWriter, multipartBod
 			if (first) {
 				first = false;
 			} else {
-				writer.writeStringValue(undefined, "");
+				writer.writeStringValue(undefined, "\r\n");
 			}
 			writer.writeStringValue(undefined, "--" + boundary);
+			writer.writeStringValue(undefined, "\r\n");
 			const part = parts[partName];
 			writer.writeStringValue("Content-Type", part.contentType);
+			writer.writeStringValue(undefined, "\r\n");
 			writer.writeStringValue("Content-Disposition", 'form-data; name="' + part.originalName + '"');
-			writer.writeStringValue(undefined, "");
+			writer.writeStringValue(undefined, "\r\n");
+			writer.writeStringValue(undefined, "\r\n");
 			if (typeof part.content === "string") {
 				writer.writeStringValue(undefined, part.content);
 			} else if (part.content instanceof ArrayBuffer) {
@@ -150,8 +153,9 @@ export const serializeMultipartBody = (writer: SerializationWriter, multipartBod
 			}
 		}
 	}
-	writer.writeStringValue(undefined, "");
+	writer.writeStringValue(undefined, "\r\n");
 	writer.writeStringValue(undefined, "--" + boundary + "--");
+	writer.writeStringValue(undefined, "\r\n");
 };
 
 export const deserializeIntoMultipartBody = (

packages/serialization/multipart/src/multipartSerializationWriter.ts

@@ -34,19 +34,16 @@ export class MultipartSerializationWriter implements SerializationWriter {
 		if (key) {
 			this.writeRawStringValue(key);
 		}
-		if (value !== undefined) {
+		if (value) {
 			if (key) {
 				this.writeRawStringValue(": ");
 			}
 			this.writeRawStringValue(value);
 		}
-		this.writeRawStringValue("\r\n");
 	};
 	private writeRawStringValue = (value?: string | null): void => {
-		if (value !== undefined) {
-			const isNullValue = value === null;
-
-			this.writeByteArrayValue(undefined, new TextEncoder().encode(isNullValue ? "null" : value).buffer);
+		if (value) {
+			this.writeByteArrayValue(undefined, new TextEncoder().encode(value).buffer);
 		}
 	};
 	// eslint-disable-next-line @typescript-eslint/no-unused-vars

packages/serialization/multipart/test/common/multipartSerializationWriter.ts

@@ -50,6 +50,21 @@ describe("MultipartSerializationWriter", () => {
 				.join(""),
 		);
 	});
+	it("serializes multipart body with correct CRLF delimiters", () => {
+		const multipartSerializationWriter = new MultipartSerializationWriter();
+		const mpBody = new MultipartBody();
+		mpBody.addOrReplacePart("testPart", "text/plain", "test content");
+		mpBody.requestAdapter = {
+			getSerializationWriterFactory: () => new JsonSerializationWriterFactory(),
+		} as RequestAdapter;
+
+		multipartSerializationWriter.writeObjectValue(undefined, mpBody, serializeMultipartBody);
+		const multipartContent = multipartSerializationWriter.getSerializedContent();
+		const result = new TextDecoder().decode(multipartContent);
+
+		const expectedString = `--${mpBody.getBoundary()}\r\nContent-Type: text/plain\r\nContent-Disposition: form-data; name="testPart"\r\n\r\ntest content\r\n--${mpBody.getBoundary()}--\r\n`;
+		assert.equal(result, expectedString);
+	});
 	it("writes a structured object", () => {
 		const testEntity = {} as TestEntity;
 		testEntity.id = "48d31887-5fad-4d73-a9f5-3c356e68a038";