Add docs navigation and tighten API request security

lib/json-body.ts

@@ -0,0 +1,21 @@
+import { ServiceError } from "./service-error";
+
+export const jsonBodyLimit = 2 * 1024 * 1024;
+
+export async function jsonBody(request: Pick<Request, "body">) {
+  const reader = request.body?.getReader();
+  if (!reader) throw new ServiceError("JSON request required", 400);
+  const chunks: Uint8Array[] = [];
+  let size = 0;
+  while (true) {
+    const { done, value } = await reader.read();
+    if (done) break;
+    size += value.byteLength;
+    if (size > jsonBodyLimit) {
+      await reader.cancel();
+      throw new ServiceError("Request too large", 413);
+    }
+    chunks.push(value);
+  }
+  return JSON.parse(Buffer.concat(chunks).toString("utf8"));
+}