Handle invalid JSON request bodies (#7)

apps/commandboard-api/src/contract.test.ts

@@ -181,4 +181,16 @@ describe("CommandBoard API contracts", () => {
     expect(response.status).toBe(422);
     expect(Array.isArray(body.errors)).toBe(true);
   });
+
+  it("rejects malformed JSON request bodies as client errors", async () => {
+    const response = await fetch(`${baseUrl}/api/tasks`, {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: "{bad"
+    });
+    const body = await response.json() as { error: string };
+
+    expect(response.status).toBe(400);
+    expect(body).toEqual({ error: "Invalid JSON body" });
+  });
 });

apps/commandboard-api/src/index.ts

@@ -55,11 +55,22 @@ const c0mputeWorkers = [
   { id: "worker_pool_1", region: "us-west", status: "preview", capacity: "wip" }
 ];
 
+class InvalidJsonBodyError extends Error {
+  constructor() {
+    super("Invalid JSON body");
+    this.name = "InvalidJsonBodyError";
+  }
+}
+
 export function createCommandBoardServer() {
   return createServer(async (request, response) => {
     try {
       await route(request, response);
     } catch (error) {
+      if (error instanceof InvalidJsonBodyError) {
+        json(response, 400, { error: error.message });
+        return;
+      }
       json(response, 500, { error: error instanceof Error ? error.message : String(error) });
     }
   });
@@ -287,7 +298,14 @@ async function readJson(request: IncomingMessage) {
     chunks.push(Buffer.from(chunk));
   }
 
-  return JSON.parse(Buffer.concat(chunks).toString("utf8")) as unknown;
+  try {
+    return JSON.parse(Buffer.concat(chunks).toString("utf8")) as unknown;
+  } catch (error) {
+    if (error instanceof SyntaxError) {
+      throw new InvalidJsonBodyError();
+    }
+    throw error;
+  }
 }
 
 function isRecord(value: unknown): value is Record<string, unknown> {