feat: integrate Pi backend and Pi Web

pi-web/lib/bounded-form-data.ts

@@ -0,0 +1,49 @@
+export class RequestBodyTooLargeError extends Error {
+  constructor() {
+    super("Request body exceeds the allowed size");
+  }
+}
+
+function declaredContentLength(request: Request): number | null {
+  const value = request.headers.get("content-length");
+  if (!value || !/^\d+$/.test(value)) return null;
+  const length = Number(value);
+  return Number.isSafeInteger(length) ? length : null;
+}
+
+/**
+ * Parse multipart data only after constraining the complete wire body. This
+ * bounds chunked requests too, where Content-Length is unavailable or false.
+ */
+export async function parseFormDataWithinLimit(request: Request, maxBytes: number): Promise<FormData> {
+  const declared = declaredContentLength(request);
+  if (declared !== null && declared > maxBytes) {
+    throw new RequestBodyTooLargeError();
+  }
+
+  const reader = request.body?.getReader();
+  if (!reader) return request.formData();
+
+  const chunks: BlobPart[] = [];
+  let size = 0;
+  try {
+    while (true) {
+      const { done, value } = await reader.read();
+      if (done) break;
+      if (size + value.byteLength > maxBytes) {
+        await reader.cancel().catch(() => {});
+        throw new RequestBodyTooLargeError();
+      }
+      size += value.byteLength;
+      const chunk = new Uint8Array(value.byteLength);
+      chunk.set(value);
+      chunks.push(chunk);
+    }
+  } finally {
+    reader.releaseLock();
+  }
+
+  const contentType = request.headers.get("content-type");
+  const headers = contentType ? { "content-type": contentType } : undefined;
+  return new Response(new Blob(chunks), { headers }).formData();
+}