test: Add test for FIN mishandling in http agent

Refs: nodejs#47130

test/fixtures/child-process-run-tcp-server.js

@@ -0,0 +1,67 @@
+'use strict';
+
+// NOTE: This file was purposefully constructed to run as a child process
+// of test-http-agent-fin-handling.js and should be considered a partner
+// of this test
+
+const net = require('net');
+
+function plaintextHttpResponse(text) {
+  return "HTTP/1.1 200 OK\r\n" +
+    "Content-Type: text/plain\r\n" +
+    `Content-Length: ${text.length}\r\n` +
+    "\r\n" +
+    `${text}`
+}
+
+function sendToParent(message) {
+  process.send(message, undefined, { swallowErrors: true });
+}
+
+let socketCount = 0;
+
+// Creates a TCP server (from e.g. test-http-1.0.js)
+const server = net.createServer({
+  // allowHalfOpen setting seems irrelevant
+}, function(socket) {
+  let allReceivedClientData = '';
+  let finHasBeenSent = false;
+  let socketNumber = ++socketCount;
+  process.send(`SERVER_SOCKET_OPEN: ${socketNumber}`);
+
+  socket.setEncoding('utf8');
+  socket.on('data', function(chunk) {
+    allReceivedClientData += chunk;
+    if (finHasBeenSent) {
+      // This isn't actually necessary to trigger the issues
+      // But is likely behaviour of a server receiving traffic
+      // after it sent a FIN.
+      sendToParent(`SERVER_SEND_RESET: ${socketNumber}`);
+      socket.resetAndDestroy();
+      return;
+    }
+    // Assume it's a GET request...
+    // Therefore \r\n\r\n marks the end of the request
+    const isEndOfRequest = allReceivedClientData.endsWith("\r\n\r\n");
+    if (isEndOfRequest) {
+      sendToParent(`SERVER_SEND_FIN: ${socketNumber}`);
+      socket.write(plaintextHttpResponse('Hello, world!'));
+
+      // Even if the request comes with Connection: Keep-Alive,
+      // we ignore it and just end the connection/socket.
+      finHasBeenSent = true;
+      socket.end();
+    }
+  });
+  socket.on('end', function() {
+    sendToParent(`SERVER_SOCKET_CLOSE: ${socketNumber}`);
+  });
+  socket.on('error', function() {
+    sendToParent(`SERVER_SOCKET_ERROR: ${socketNumber}`);
+  })
+});
+server.listen(0, function() {
+  // When we start listening, send the port to the parent:
+  sendToParent("SERVER_PORT: " + this.address().port);
+});
+sendToParent("SERVER_LAUNCHED");

test/parallel/test-http-agent-fin-handling.js

@@ -0,0 +1,143 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const fork = require('child_process').fork;
+const fixtures = require('../common/fixtures');
+const http = require('http');
+
+// Note to self: Normal debug has stopped printing debug messages...
+// Not sure why. Instead let's implement our own:
+// const debug = require('util').debuglog('test');
+function debug(message) {
+  console.log(message);
+}
+
+// NOTE:
+// Putting the server in a separate process ensures that its
+// responses are in a different event loop.
+// This enables certain edge cases to happen which wouldn't otherwise be caught.
+// I'm not actually 100% sure this is needed, but for now it makes sense
+// to get the reproduction.
+function runServerInChildProcessWithFreePort(listeningCallback, maxLifetimeMs) {
+  const cp = fork(fixtures.path('child-process-run-tcp-server.js'));
+
+  let messageIndex = 0;
+
+  cp.on('message', function messageHandler(message) {
+    switch (messageIndex++) {
+      case 0:
+        assert.strictEqual(message, "SERVER_LAUNCHED");
+        break;
+      case 1:
+        assert.match(message, /SERVER_PORT: \d+/);
+        const port = +message.split(" ")[1];
+        listeningCallback(port);
+        break;
+      default:
+        debug(message);
+        break;
+    }
+  });
+  setTimeout(() => {
+    cp.kill();
+  }, maxLifetimeMs);
+}
+
+const agent = new http.Agent({
+  keepAlive: true,
+  // NOTE:
+  // > If maxSockets = 1 - second request gets "Error: socket hang up" immediately
+  // > If maxSockets = 2, we also get this issue always
+  // > But maxSockets isn't necessary to trigger this bug, so leaving it out
+  // maxSockets: 1,
+});
+
+function formatError(e) {
+  let out = '';
+  if (e instanceof AggregateError) {
+    out += `AggregateError [${e.errors.length} SubError/s]`;
+    if (e.message) {
+      out += `- ${e.message}`;
+    }
+    for (let i = 0; i < e.errors.length; i++) {
+      out += `\n> SubError ${i+1} of ${e.errors.length}:\n`
+      out += formatError(e.errors[i]) 
+    }
+  }
+  else {
+    out += e;
+    if (e.code) {
+      out += ` (e.code: ${e.code})`;
+    }
+  }
+  return out;
+}
+
+let socketCount = 0;
+
+function getRequireSuccess(port, attemptMessage, onReceiveResponse) {
+  return http.get({
+    host: 'localhost',
+    port: port,
+    agent: agent,
+    path: "/"
+  }, function(res) {
+    res.setEncoding('utf8');
+    // According to ClientRequest, a data handler is mandatory
+    res.on('data', common.mustCall((chunk) => {
+      assert.strictEqual(chunk, "Hello, world!")
+    }), 1);
+    res.on('error', () => {
+      assert.fail(`Response error ${attemptMessage}: ${formatError(e)}`);
+    });
+    res.on('end', () => {
+      debug(`CLIENT_FULL_RESPONSE_RECEIVED: for ${attemptMessage}`)
+      onReceiveResponse && onReceiveResponse();
+    });
+  })
+  .on('socket', (socket) => {
+    if (socket.DEBUG_ATTEMPT) {
+      debug(`CLIENT_SOCKET_REUSED: Socket from ${socket.DEBUG_ATTEMPT} reused for ${attemptMessage}`)
+    } else {
+      socket.DEBUG_ATTEMPT = attemptMessage;
+      socket.on("error", (e) => {
+        assert.fail(`Socket error at ${attemptMessage}: ${formatError(e)}`);
+      });
+    }
+  })
+  .on('error', (e) => {
+    assert.fail(`Request error at ${attemptMessage}: ${formatError(e)}`);
+  });
+}
+
+// If the server lasts less long (e.g. 100ms) we get some
+// ECONNRESET from the server being killed too early.
+const MAX_SERVER_LIFETIME_MS = 500;
+
+runServerInChildProcessWithFreePort(common.mustCall(function(port) {
+  debug("CLIENT_PORT_RECEIVED_FROM_SERVER: " + port);
+
+  // Any one of these can cause the error (randomly)
+  // But the probability increases from ~50% to >90% by adding
+  // a few more. We do this to ensure the test is repeatable.
+
+  // This gives an error, with either:
+  // * Request 1.1 reusing the socket from Request 2
+  // * Request 2.1 reusing the socket from Request 1
+  // Either of these appears to cause Error: socket hang up (e.code: ECONNRESET)
+  // BECAUSE the server has already sent a FIN, which the client recognises, but
+  // for some reason, still attempts to re-use the socket.
+
+  getRequireSuccess(port, "Request 1", () => {
+    getRequireSuccess(port, "Request 1.1");
+  });
+  getRequireSuccess(port, "Request 2", () => {
+    getRequireSuccess(port, "Request 2.1");
+  });
+
+  // For debugging - uncomment this to force debug messages
+  // to print even if the test succeeds.
+  // setTimeout(() => {
+  //   assert.fail("SUCCESS - TRIGGERING DEBUG MESSAGES");
+  // }, 500);
+}), MAX_SERVER_LIFETIME_MS);