Clean up HTTP async iterator code (denoland/deno_std#411)

Original: https://github.com/denoland/deno_std/commit/68faf32f721d2a95c7b1c75661713c8118c077c7

3 files changed, 86 insertions, 182 deletions

diff --git a/http/http_bench.ts b/http/http_bench.ts
index 6d72d4be6..06043f9e4 100644
--- a/http/http_bench.ts
+++ b/http/http_bench.ts
@@ -3,13 +3,12 @@ import { serve } from "./server.ts";
 
 const addr = Deno.args[1] || "127.0.0.1:4500";
 const server = serve(addr);
-
 const body = new TextEncoder().encode("Hello World");
 
 async function main(): Promise<void> {
   console.log(`http://${addr}/`);
-  for await (const request of server) {
-    request.respond({ status: 200, body });
+  for await (const req of server) {
+    req.respond({ body });
   }
 }
 
diff --git a/http/server.ts b/http/server.ts
index 484ecf808..281f8d302 100644
--- a/http/server.ts
+++ b/http/server.ts
@@ -1,55 +1,14 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 const { listen, copy, toAsyncIterator } = Deno;
+type Listener = Deno.Listener;
 type Conn = Deno.Conn;
 type Reader = Deno.Reader;
 type Writer = Deno.Writer;
 import { BufReader, BufState, BufWriter } from "../io/bufio.ts";
 import { TextProtoReader } from "../textproto/mod.ts";
 import { STATUS_TEXT } from "./http_status.ts";
-import { assert } from "../testing/asserts.ts";
-
-interface Deferred {
-  promise: Promise<{}>;
-  resolve: () => void;
-  reject: () => void;
-}
-
-function deferred(isResolved = false): Deferred {
-  let resolve, reject;
-  const promise = new Promise(
-    (res, rej): void => {
-      resolve = res;
-      reject = rej;
-    }
-  );
-  if (isResolved) {
-    resolve();
-  }
-  return {
-    promise,
-    resolve,
-    reject
-  };
-}
-
-interface HttpConn extends Conn {
-  // When read by a newly created request B, lastId is the id pointing to a previous
-  // request A, such that we must wait for responses to A to complete before
-  // writing B's response.
-  lastPipelineId: number;
-  pendingDeferredMap: Map<number, Deferred>;
-}
-
-function createHttpConn(c: Conn): HttpConn {
-  const httpConn = Object.assign(c, {
-    lastPipelineId: 0,
-    pendingDeferredMap: new Map()
-  });
-
-  const resolvedDeferred = deferred(true);
-  httpConn.pendingDeferredMap.set(0, resolvedDeferred);
-  return httpConn;
-}
+import { assert, fail } from "../testing/asserts.ts";
+import { deferred, Deferred, MuxAsyncIterator } from "../util/async.ts";
 
 function bufWriter(w: Writer): BufWriter {
   if (w instanceof BufWriter) {
@@ -58,6 +17,7 @@ function bufWriter(w: Writer): BufWriter {
     return new BufWriter(w);
   }
 }
+
 export function setContentLength(r: Response): void {
   if (!r.headers) {
     r.headers = new Headers();
@@ -74,6 +34,7 @@ export function setContentLength(r: Response): void {
     }
   }
 }
+
 async function writeChunkedBody(w: Writer, r: Reader): Promise<void> {
   const writer = bufWriter(w);
   const encoder = new TextEncoder();
@@ -90,6 +51,7 @@ async function writeChunkedBody(w: Writer, r: Reader): Promise<void> {
   const endChunk = encoder.encode("0\r\n\r\n");
   await writer.write(endChunk);
 }
+
 export async function writeResponse(w: Writer, r: Response): Promise<void> {
   const protoMajor = 1;
   const protoMinor = 1;
@@ -131,6 +93,7 @@ export async function writeResponse(w: Writer, r: Response): Promise<void> {
   }
   await writer.flush();
 }
+
 async function readAllIterator(
   it: AsyncIterableIterator<Uint8Array>
 ): Promise<Uint8Array> {
@@ -154,14 +117,14 @@ async function readAllIterator(
 }
 
 export class ServerRequest {
-  pipelineId: number;
   url: string;
   method: string;
   proto: string;
   headers: Headers;
-  conn: HttpConn;
+  conn: Conn;
   r: BufReader;
   w: BufWriter;
+  done: Deferred<void> = deferred();
 
   public async *bodyStream(): AsyncIterableIterator<Uint8Array> {
     if (this.headers.has("content-length")) {
@@ -244,134 +207,102 @@ export class ServerRequest {
   }
 
   async respond(r: Response): Promise<void> {
-    // Check and wait if the previous request is done responding.
-    const lastPipelineId = this.pipelineId - 1;
-    const lastPipelineDeferred = this.conn.pendingDeferredMap.get(
-      lastPipelineId
-    );
-    assert(!!lastPipelineDeferred);
-    await lastPipelineDeferred.promise;
-    // If yes, delete old deferred and proceed with writing.
-    this.conn.pendingDeferredMap.delete(lastPipelineId);
     // Write our response!
     await writeResponse(this.w, r);
-    // Signal the next pending request that it can start writing.
-    const currPipelineDeferred = this.conn.pendingDeferredMap.get(
-      this.pipelineId
-    );
-    assert(!!currPipelineDeferred);
-    currPipelineDeferred.resolve();
+    // Signal that this request has been processed and the next pipelined
+    // request on the same connection can be accepted.
+    this.done.resolve();
   }
 }
 
-interface ServeEnv {
-  reqQueue: ServerRequest[];
-  serveDeferred: Deferred;
-}
-
-/** Continuously read more requests from conn until EOF
- * Calls maybeHandleReq.
- * bufr is empty on a fresh TCP connection.
- * Would be passed around and reused for later request on same conn
- * TODO: make them async function after this change is done
- * https://github.com/tc39/ecma262/pull/1250
- * See https://v8.dev/blog/fast-async
- */
 async function readRequest(
-  c: HttpConn,
-  bufr?: BufReader
+  conn: Conn,
+  bufr: BufReader
 ): Promise<[ServerRequest, BufState]> {
-  if (!bufr) {
-    bufr = new BufReader(c);
-  }
-  const bufw = new BufWriter(c);
   const req = new ServerRequest();
-
-  // Set and incr pipeline id;
-  req.pipelineId = ++c.lastPipelineId;
-  // Set a new pipeline deferred associated with this request
-  // for future requests to wait for.
-  c.pendingDeferredMap.set(req.pipelineId, deferred());
-
-  req.conn = c;
-  req.r = bufr!;
-  req.w = bufw;
-  const tp = new TextProtoReader(bufr!);
-
-  let s: string;
+  req.conn = conn;
+  req.r = bufr;
+  req.w = new BufWriter(conn);
+  const tp = new TextProtoReader(bufr);
   let err: BufState;
-
   // First line: GET /index.html HTTP/1.0
-  [s, err] = await tp.readLine();
+  let firstLine: string;
+  [firstLine, err] = await tp.readLine();
   if (err) {
     return [null, err];
   }
-  [req.method, req.url, req.proto] = s.split(" ", 3);
-
+  [req.method, req.url, req.proto] = firstLine.split(" ", 3);
   [req.headers, err] = await tp.readMIMEHeader();
-
   return [req, err];
 }
 
-function maybeHandleReq(
-  env: ServeEnv,
-  conn: Conn,
-  maybeReq: [ServerRequest, BufState]
-): void {
-  const [req, _err] = maybeReq;
-  if (_err) {
-    conn.close(); // assume EOF for now...
-    return;
-  }
-  env.reqQueue.push(req); // push req to queue
-  env.serveDeferred.resolve(); // signal while loop to process it
-}
+export class Server implements AsyncIterable<ServerRequest> {
+  private closing = false;
 
-function serveConn(env: ServeEnv, conn: HttpConn, bufr?: BufReader): void {
-  readRequest(conn, bufr).then(maybeHandleReq.bind(null, env, conn));
-}
+  constructor(public listener: Listener) {}
 
-export async function* serve(
-  addr: string
-): AsyncIterableIterator<ServerRequest> {
-  const listener = listen("tcp", addr);
-  const env: ServeEnv = {
-    reqQueue: [], // in case multiple promises are ready
-    serveDeferred: deferred()
-  };
+  close(): void {
+    this.closing = true;
+    this.listener.close();
+  }
 
-  // Routine that keeps calling accept
-  let handleConn = (_conn: Conn): void => {};
-  let scheduleAccept = (): void => {};
-  const acceptRoutine = (): void => {
-    scheduleAccept = (): void => {
-      listener.accept().then(handleConn);
-    };
-    handleConn = (conn: Conn): void => {
-      const httpConn = createHttpConn(conn);
-      serveConn(env, httpConn); // don't block
-      scheduleAccept(); // schedule next accept
-    };
+  // Yields all HTTP requests on a single TCP connection.
+  private async *iterateHttpRequests(
+    conn: Conn
+  ): AsyncIterableIterator<ServerRequest> {
+    const bufr = new BufReader(conn);
+    let bufStateErr: BufState;
+    let req: ServerRequest;
+
+    while (!this.closing) {
+      [req, bufStateErr] = await readRequest(conn, bufr);
+      if (bufStateErr) break;
+      yield req;
+      // Wait for the request to be processed before we accept a new request on
+      // this connection.
+      await req.done;
+    }
 
-    scheduleAccept();
-  };
+    if (bufStateErr === "EOF") {
+      // The connection was gracefully closed.
+    } else if (bufStateErr instanceof Error) {
+      // TODO(ry): send something back like a HTTP 500 status.
+    } 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.
+    } else {
+      fail(`unexpected BufState: ${bufStateErr}`);
+    }
 
-  acceptRoutine();
+    conn.close();
+  }
 
-  // Loop hack to allow yield (yield won't work in callbacks)
-  while (true) {
-    await env.serveDeferred.promise;
-    env.serveDeferred = deferred(); // use a new deferred
-    let queueToProcess = env.reqQueue;
-    env.reqQueue = [];
-    for (const result of queueToProcess) {
-      yield result;
-      // Continue read more from conn when user is done with the current req
-      // Moving this here makes it easier to manage
-      serveConn(env, result.conn, result.r);
-    }
+  // Accepts a new TCP connection and yields all HTTP requests that arrive on
+  // it. When a connection is accepted, it also creates a new iterator of the
+  // same kind and adds it to the request multiplexer so that another TCP
+  // connection can be accepted.
+  private async *acceptConnAndIterateHttpRequests(
+    mux: MuxAsyncIterator<ServerRequest>
+  ): AsyncIterableIterator<ServerRequest> {
+    if (this.closing) return;
+    // Wait for a new connection.
+    const conn = await this.listener.accept();
+    // Try to accept another connection and add it to the multiplexer.
+    mux.add(this.acceptConnAndIterateHttpRequests(mux));
+    // Yield the requests that arrive on the just-accepted connection.
+    yield* this.iterateHttpRequests(conn);
   }
-  listener.close();
+
+  [Symbol.asyncIterator](): AsyncIterableIterator<ServerRequest> {
+    const mux: MuxAsyncIterator<ServerRequest> = new MuxAsyncIterator();
+    mux.add(this.acceptConnAndIterateHttpRequests(mux));
+    return mux.iterate();
+  }
+}
+
+export function serve(addr: string): Server {
+  const listener = listen("tcp", addr);
+  return new Server(listener);
 }
 
 export async function listenAndServe(
diff --git a/http/server_test.ts b/http/server_test.ts
index 82a368395..396a0321a 100644
--- a/http/server_test.ts
+++ b/http/server_test.ts
@@ -22,31 +22,6 @@ const dec = new TextDecoder();
 
 type Handler = () => void;
 
-interface Deferred {
-  promise: Promise<{}>;
-  resolve: Handler;
-  reject: Handler;
-}
-
-function deferred(isResolved = false): Deferred {
-  let resolve: Handler = (): void => void 0;
-  let reject: Handler = (): void => void 0;
-  const promise = new Promise(
-    (res, rej): void => {
-      resolve = res;
-      reject = rej;
-    }
-  );
-  if (isResolved) {
-    resolve();
-  }
-  return {
-    promise,
-    resolve,
-    reject
-  };
-}
-
 const responseTests: ResponseTest[] = [
   // Default response
   {
@@ -72,8 +47,8 @@ test(async function responseWrite(): Promise<void> {
     const buf = new Buffer();
     const bufw = new BufWriter(buf);
     const request = new ServerRequest();
-    request.pipelineId = 1;
     request.w = bufw;
+
     request.conn = {
       localAddr: "",
       remoteAddr: "",
@@ -86,13 +61,12 @@ test(async function responseWrite(): Promise<void> {
       write: async (): Promise<number> => {
         return -1;
       },
-      close: (): void => {},
-      lastPipelineId: 0,
-      pendingDeferredMap: new Map([[0, deferred(true)], [1, deferred()]])
+      close: (): void => {}
     };
 
     await request.respond(testCase.response);
     assertEquals(buf.toString(), testCase.raw);
+    await request.done;
   }
 });