feat: download of Worker script

Added the --from-dash <worker-name>, getting the source code into an initialized project replacing the template script.

Resolves #1624
Discussion: #1623
notes: Workaround for handling multipart/form-data slicing off top and bottom boundaries.
multipart/formdata parsing not supported currently in Undici nodejs/undici#974

.changeset/six-needles-begin.md

@@ -0,0 +1,11 @@
+---
+"wrangler": patch
+---
+
+feat: download of Worker script
+Added the --from-dash <worker-name>, getting the source code into an initialized project replacing the template script.
+
+Resolves #1624
+Discussion: #1623
+notes: Workaround for handling multipart/form-data slicing off top and bottom boundaries.
+multipart/formdata parsing not supported currently in Undici https://github.com/nodejs/undici/issues/974

packages/wrangler/src/__tests__/helpers/mock-cfetch.ts

@@ -183,6 +183,7 @@ export function unsetAllMocks() {
 
 const kvGetMocks = new Map<string, string | Buffer>();
 const r2GetMocks = new Map<string, string | undefined>();
+const dashScriptMocks = new Map<string, string | undefined>();
 
 /**
  * @mocked typeof fetchKVGetValue
@@ -260,4 +261,52 @@ export function setMockFetchR2Objects({
 export function unsetSpecialMockFns() {
 	kvGetMocks.clear();
 	r2GetMocks.clear();
+	dashScriptMocks.clear();
+}
+
+/**
+ * @mocked typeof fetchDashScript
+ * multipart/form-data is the response for modules and raw text for the Script endpoint.
+ */
+export async function mockFetchDashScript(
+	resource: string,
+	bodyInit: {
+		body: BodyInit | Readable;
+		headers: HeadersInit | undefined;
+		method: "GET";
+	}
+): Promise<string> {
+	/**
+	 * Here we destroy & removeListeners to "drain" the stream, for testing purposes
+	 * mimicking the fetch request taking in the stream and draining it.
+	 */
+	if (bodyInit.body instanceof Readable) {
+		bodyInit.body.destroy();
+		bodyInit.body.removeAllListeners();
+	}
+
+	if (dashScriptMocks.has(resource)) {
+		const value = dashScriptMocks.get(resource) ?? "";
+
+		return value;
+	}
+	throw new Error(`no mock found for \`init from-dash\` - ${resource}`);
+}
+
+/**
+ * Mock setter for usage within test blocks, companion helper to `mockFetchDashScript`
+ */
+export function setMockFetchDashScript({
+	accountId,
+	fromDashScriptName,
+	mockResponse,
+}: {
+	accountId: string;
+	fromDashScriptName: string;
+	mockResponse?: string;
+}) {
+	dashScriptMocks.set(
+		`/accounts/${accountId}/workers/scripts/${fromDashScriptName}`,
+		mockResponse
+	);
 }