feat: add check for closed requests (#162)

## Checklist

- [x] I have ensured my pull request is not behind the main or master
branch of the original repository.
- [x] I have rebased all commits where necessary so that reviewing this
pull request can be done without having to merge it first.
- [x] I have written a commit message that passes commitlint linting.
- [x] I have ensured that my code changes pass linting tests.
- [x] I have ensured that my code changes pass unit tests.
- [x] I have described my pull request and the reasons for code changes
along with context if necessary.

## Changes

Added a check for `req.ctx.closed` to ensure that, when a request is
closed (canceled) before reaching the bodyparser middleware, the body of
the closed request is not attempted to be parsed (which would result in
an error). Instead, if the request is closed, then the middleware
returns a `499 Client Closed Request` status.

## Reason

Errors can occur when parsing bodies of closed requests - `stream not
readable`. This indicates the request was cancelled. This can happen
when body parser is not on the "synchronous path" of a request - e.g. if
Auth is verified asynchronously from headers before bothering to parse
the bodies. This allows time for users to occasionally close the
request, resulting in a `500 'stream not readable'` error.

src/body-parser.ts

@@ -95,6 +95,12 @@ export function bodyParserWrapper(opts: BodyParserOptions = {}) {
       return next();
     }
 
+    if (ctx.req.closed) {
+      ctx.status = 499;
+      ctx.body = 'Request already closed';
+      return;
+    }
+
     try {
       const response = await parseBody(ctx);
       // patch node

test/middleware.test.ts

@@ -558,4 +558,19 @@ describe("test/body-parser.test.ts", () => {
         .expect({ foo: "bar" });
     });
   });
+
+  describe("request closed", () => {
+    it("should return 499 on request closed", async () => {
+      const app = new Koa();
+
+      app.use(async (ctx, next) => {
+        Object.defineProperty(ctx.req, "closed", { value: true });
+        await next();
+      });
+      app.use(bodyParser());
+      server = app.listen();
+
+      await request(server).post("/").send({ foo: "bar" }).expect(499);
+    });
+  });
 });