fix(ext/http): Ensure cancelled requests don't crash Deno.serve (#19154)

Fixes for various `Attemped to access invalid request` bugs (#19058,
#15427, #17213).

We did not wait for both a drop event and a completion event before
removing items from the slab table. This ensures that we do so.

In addition, the slab methods are refactored out into `slab.rs` for
maintainability.

cli/tests/unit/serve_test.ts

@@ -15,7 +15,6 @@ import {
   deferred,
   fail,
 } from "./test_util.ts";
-import { consoleSize } from "../../../runtime/js/40_tty.js";
 
 const {
   upgradeHttpRaw,
@@ -665,6 +664,38 @@ Deno.test({ permissions: { net: true } }, async function httpServerClose() {
   await server;
 });
 
+// https://github.com/denoland/deno/issues/15427
+Deno.test({ permissions: { net: true } }, async function httpServerCloseGet() {
+  const ac = new AbortController();
+  const listeningPromise = deferred();
+  const requestPromise = deferred();
+  const responsePromise = deferred();
+  const server = Deno.serve({
+    handler: async () => {
+      requestPromise.resolve();
+      await new Promise((r) => setTimeout(r, 500));
+      responsePromise.resolve();
+      return new Response("ok");
+    },
+    port: 4501,
+    signal: ac.signal,
+    onListen: onListen(listeningPromise),
+    onError: createOnErrorCb(ac),
+  });
+  await listeningPromise;
+  const conn = await Deno.connect({ port: 4501 });
+  const encoder = new TextEncoder();
+  const body =
+    `GET / HTTP/1.1\r\nHost: example.domain\r\nConnection: close\r\n\r\n`;
+  const writeResult = await conn.write(encoder.encode(body));
+  assertEquals(body.length, writeResult);
+  await requestPromise;
+  conn.close();
+  await responsePromise;
+  ac.abort();
+  await server;
+});
+
 // FIXME:
 Deno.test(
   { permissions: { net: true } },

ext/http/00_serve.js

@@ -534,6 +534,8 @@ function mapToCallback(responseBodies, context, signal, callback, onError) {
 
     // Did everything shut down while we were waiting?
     if (context.closed) {
+      // We're shutting down, so this status shouldn't make it back to the client but "Service Unavailable" seems appropriate
+      op_http_set_promise_complete(req, 503);
       innerRequest?.close();
       return;
     }

ext/http/Cargo.toml

@@ -12,6 +12,7 @@ description = "HTTP server implementation for Deno"
 
 [features]
 "__zombie_http_tracking" = []
+"__http_tracing" = []
 
 [lib]
 path = "lib.rs"