refactor(bluebubbles): share multipart helpers

extensions/bluebubbles/src/multipart.ts

@@ -0,0 +1,32 @@
+import { blueBubblesFetchWithTimeout } from "./types.js";
+
+export function concatUint8Arrays(parts: Uint8Array[]): Uint8Array {
+  const totalLength = parts.reduce((acc, part) => acc + part.length, 0);
+  const body = new Uint8Array(totalLength);
+  let offset = 0;
+  for (const part of parts) {
+    body.set(part, offset);
+    offset += part.length;
+  }
+  return body;
+}
+
+export async function postMultipartFormData(params: {
+  url: string;
+  boundary: string;
+  parts: Uint8Array[];
+  timeoutMs: number;
+}): Promise<Response> {
+  const body = concatUint8Arrays(params.parts);
+  return await blueBubblesFetchWithTimeout(
+    params.url,
+    {
+      method: "POST",
+      headers: {
+        "Content-Type": `multipart/form-data; boundary=${params.boundary}`,
+      },
+      body,
+    },
+    params.timeoutMs,
+  );
+}