fix: don't throw when the connection is destroyed

http/racing_server.ts

@@ -1,16 +1,13 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { serve, ServerRequest } from "./server.ts";
+import { sleep } from "./util.ts";
 
 const addr = Deno.args[1] || "127.0.0.1:4501";
 const server = serve(addr);
 
 const body = new TextEncoder().encode("Hello 1\n");
 const body4 = new TextEncoder().encode("World 4\n");
 
-function sleep(ms: number): Promise<void> {
-  return new Promise((res): number => setTimeout(res, ms));
-}
-
 async function delayedRespond(request: ServerRequest): Promise<void> {
   await sleep(3000);
   await request.respond({ status: 200, body });

http/racing_server_test.ts

@@ -11,7 +11,7 @@ async function startServer(): Promise<void> {
     args: ["deno", "run", "-A", "http/racing_server.ts"],
     stdout: "piped"
   });
-  // Once fileServer is ready it will write to its stdout.
+  // Once racing server is ready it will write to its stdout.
   const r = new TextProtoReader(new BufReader(server.stdout!));
   const s = await r.readLine();
   assert(s !== Deno.EOF && s.includes("Racing server listening..."));

http/server.ts

@@ -342,10 +342,15 @@ export class Server implements AsyncIterable<ServerRequest> {
       // The connection was gracefully closed.
     } else if (err) {
       // An error was thrown while parsing request headers.
-      await writeResponse(req!.w, {
-        status: 400,
-        body: new TextEncoder().encode(`${err.message}\r\n\r\n`)
-      });
+      try {
+        await writeResponse(req!.w, {
+          status: 400,
+          body: new TextEncoder().encode(`${err.message}\r\n\r\n`)
+        });
+      } catch (_) {
+        // The connection is destroyed.
+        // Ignores the error.
+      }
     } else if (this.closing) {
       // There are more requests incoming but the server is closing.
       // TODO(ry): send a back a HTTP 503 Service Unavailable status.

http/server_test.ts

@@ -6,6 +6,7 @@
 // https://github.com/golang/go/blob/master/src/net/http/responsewrite_test.go
 
 const { Buffer } = Deno;
+import { TextProtoReader } from "../textproto/mod.ts";
 import { test, runIfMain } from "../testing/mod.ts";
 import { assert, assertEquals, assertNotEquals } from "../testing/asserts.ts";
 import {
@@ -15,6 +16,7 @@ import {
   readRequest,
   parseHTTPVersion
 } from "./server.ts";
+import { sleep } from "./util.ts";
 import {
   BufReader,
   BufWriter,
@@ -456,4 +458,45 @@ test({
   }
 });
 
+test({
+  name: "[http] destroyed connection",
+  async fn(): Promise<void> {
+    // Runs a simple server as another process
+    const p = Deno.run({
+      args: [Deno.execPath, "http/testdata/simple_server.ts", "--allow-net"],
+      stdout: "piped"
+    });
+
+    try {
+      const r = new TextProtoReader(new BufReader(p.stdout!));
+      const s = await r.readLine();
+      assert(s !== Deno.EOF && s.includes("server listening"));
+
+      let serverIsRunning = true;
+      p.status().then(
+        (): void => {
+          serverIsRunning = false;
+        }
+      );
+
+      await sleep(100);
+
+      // Reqeusts to the server and immediately closes the connection
+      const conn = await Deno.dial("tcp", "127.0.0.1:4502");
+      await conn.write(new TextEncoder().encode("GET / HTTP/1.0\n\n"));
+      conn.close();
+
+      // Waits for the server to handle the above (broken) request
+      await sleep(100);
+
+      assert(serverIsRunning);
+
+    } finally {
+      // Stops the sever.
+      p.close();
+      p.stdout!.close();
+    }
+  }
+});
+
 runIfMain(import.meta);

http/testdata/simple_server.ts

@@ -0,0 +1,9 @@
+import { serve } from "../server.ts";
+
+window.onload = async function main() {
+  const addr = "0.0.0.0:4502";
+  console.log(`Simple server listening on ${addr}`);
+  for await (let req of serve(addr)) {
+    req.respond({});
+  }
+}

http/util.ts

@@ -0,0 +1,9 @@
+// Sleeps the given milliseconds and resolves.
+export function sleep(ms: number): Promise<void> {
+  return new Promise(
+    (res): number =>
+      setTimeout((): void => {
+        res();
+      }, ms)
+  );
+}