http: fix socket re-use races

Whether and when a socket is destroyed or not after a timeout is up to
the user. This leaves an edge case where a socket that has emitted
'timeout' might be re-used from the free pool. Even if destroy is called
on the socket, it won't be removed from the freelist until 'close' which
can happen several ticks later.

Sockets are removed from the free list on the 'close' event.
However, there is a delay between calling destroy() and 'close'
being emitted. This means that it possible for a socket that has
been destroyed to be re-used from the free list, causing unexpected
failures.

lib/_http_agent.js

@@ -120,6 +120,12 @@ function Agent(options) {
           socket[async_id_symbol] = -1;
           socket._httpMessage = null;
           this.removeSocket(socket, options);
+
+          const agentTimeout = this.options.timeout || 0;
+          if (socket.timeout !== agentTimeout) {
+            socket.setTimeout(agentTimeout);
+          }
+
           freeSockets.push(socket);
         } else {
           // Implementation doesn't want to keep socket alive
@@ -202,12 +208,21 @@ Agent.prototype.addRequest = function addRequest(req, options, port/* legacy */,
     this.sockets[name] = [];
   }
 
-  const freeLen = this.freeSockets[name] ? this.freeSockets[name].length : 0;
+  const freeSockets = this.freeSockets[name];
+  let socket;
+  if (freeSockets) {
+    while (freeSockets.length && freeSockets[0].destroyed) {
+      freeSockets.shift();
+    }
+    socket = freeSockets.shift();
+    if (!freeSockets.length)
+      delete this.freeSockets[name];
+  }
+
+  const freeLen = freeSockets ? freeSockets.length : 0;
   const sockLen = freeLen + this.sockets[name].length;
 
-  if (freeLen) {
-    // We have a free socket, so use that.
-    const socket = this.freeSockets[name].shift();
+  if (socket) {
     // Guard against an uninitialized or user supplied Socket.
     const handle = socket._handle;
     if (handle && typeof handle.asyncReset === 'function') {
@@ -216,10 +231,6 @@ Agent.prototype.addRequest = function addRequest(req, options, port/* legacy */,
       socket[async_id_symbol] = handle.getAsyncId();
     }
 
-    // don't leak
-    if (!this.freeSockets[name].length)
-      delete this.freeSockets[name];
-
     this.reuseSocket(socket, req);
     setRequestSocket(this, req, socket);
     this.sockets[name].push(socket);
@@ -319,6 +330,20 @@ function installListeners(agent, s, options) {
   }
   s.on('close', onClose);
 
+  function onTimeout() {
+    debug('CLIENT socket onTimeout');
+
+    // Destroy if in free list.
+    // TODO(ronag): Always destroy, even if not in free list.
+    const sockets = agent.freeSockets;
+    for (const name of ObjectKeys(sockets)) {
+      if (sockets[name].includes(s)) {
+        return s.destroy();
+      }
+    }
+  }
+  s.on('timeout', onTimeout);
+
   function onRemove() {
     // We need this function for cases like HTTP 'upgrade'
     // (defined by WebSockets) where we need to remove a socket from the
@@ -327,6 +352,7 @@ function installListeners(agent, s, options) {
     agent.removeSocket(s, options);
     s.removeListener('close', onClose);
     s.removeListener('free', onFree);
+    s.removeListener('timeout', onTimeout);
     s.removeListener('agentRemove', onRemove);
   }
   s.on('agentRemove', onRemove);
@@ -409,14 +435,6 @@ function setRequestSocket(agent, req, socket) {
     return;
   }
   socket.setTimeout(req.timeout);
-  // Reset timeout after response end
-  req.once('response', (res) => {
-    res.once('end', () => {
-      if (socket.timeout !== agentTimeout) {
-        socket.setTimeout(agentTimeout);
-      }
-    });
-  });
 }
 
 function emitErrorNT(emitter, err) {

test/parallel/test-http-agent-timeout-option.js

@@ -18,6 +18,6 @@ request.on('socket', mustCall((socket) => {
 
   const listeners = socket.listeners('timeout');
 
-  strictEqual(listeners.length, 1);
-  strictEqual(listeners[0], request.timeoutCb);
+  strictEqual(listeners.length, 2);
+  strictEqual(listeners[1], request.timeoutCb);
 }));

test/parallel/test-http-agent-timeout.js

@@ -0,0 +1,96 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+
+{
+  // Ensure reuse of successful sockets.
+
+  const agent = new http.Agent({ keepAlive: true });
+
+  const server = http.createServer((req, res) => {
+    res.end();
+  });
+
+  server.listen(0, common.mustCall(() => {
+    let socket;
+    http.get({ port: server.address().port, agent })
+      .on('response', common.mustCall((res) => {
+        socket = res.socket;
+        assert(socket);
+        res.resume();
+        socket.on('free', common.mustCall(() => {
+          http.get({ port: server.address().port, agent })
+            .on('response', common.mustCall((res) => {
+              assert.strictEqual(socket, res.socket);
+              assert(socket);
+              agent.destroy();
+              server.close();
+            }));
+        }));
+      }));
+  }));
+}
+
+{
+  // Ensure that timeouted sockets are not reused.
+
+  const agent = new http.Agent({ keepAlive: true, timeout: 50 });
+
+  const server = http.createServer((req, res) => {
+    res.end();
+  });
+
+  server.listen(0, common.mustCall(() => {
+    let socket;
+    http.get({ port: server.address().port, agent })
+      .on('response', common.mustCall((res) => {
+        socket = res.socket;
+        assert(socket);
+        res.resume();
+        socket.on('free', common.mustCall(() => {
+          socket.on('timeout', common.mustCall(() => {
+            http.get({ port: server.address().port, agent })
+              .on('response', common.mustCall((res) => {
+                assert.notStrictEqual(socket, res.socket);
+                assert.strictEqual(socket.destroyed, true);
+                assert(socket);
+                agent.destroy();
+                server.close();
+              }));
+          }));
+        }));
+      }));
+  }));
+}
+
+{
+  // Ensure that destroyed sockets are not reused.
+
+  const agent = new http.Agent({ keepAlive: true });
+
+  const server = http.createServer((req, res) => {
+    res.end();
+  });
+
+  server.listen(0, common.mustCall(() => {
+    let socket;
+    http.get({ port: server.address().port, agent })
+      .on('response', common.mustCall((res) => {
+        socket = res.socket;
+        assert(socket);
+        res.resume();
+        socket.on('free', common.mustCall(() => {
+          socket.destroy();
+          http.get({ port: server.address().port, agent })
+            .on('response', common.mustCall((res) => {
+              assert.notStrictEqual(socket, res.socket);
+              assert(socket);
+              agent.destroy();
+              server.close();
+            }));
+        }));
+      }));
+  }));
+}

test/parallel/test-http-client-set-timeout-after-end.js

@@ -20,7 +20,7 @@ server.listen(0, () => {
   const req = get({ agent, port }, (res) => {
     res.on('end', () => {
       strictEqual(req.setTimeout(0), req);
-      strictEqual(socket.listenerCount('timeout'), 0);
+      strictEqual(socket.listenerCount('timeout'), 1);
       agent.destroy();
       server.close();
     });

test/parallel/test-http-client-set-timeout.js

@@ -42,7 +42,7 @@ server.listen(0, mustCall(() => {
   }));
 
   req.on('timeout', mustCall(() => {
-    strictEqual(req.socket.listenerCount('timeout'), 0);
+    strictEqual(req.socket.listenerCount('timeout'), 1);
     req.destroy();
   }));
 }));

test/parallel/test-http-client-timeout-option-listeners.js

@@ -24,9 +24,9 @@ const options = {
 server.listen(0, options.host, common.mustCall(() => {
   options.port = server.address().port;
   doRequest(common.mustCall((numListeners) => {
-    assert.strictEqual(numListeners, 1);
+    assert.strictEqual(numListeners, 2);
     doRequest(common.mustCall((numListeners) => {
-      assert.strictEqual(numListeners, 1);
+      assert.strictEqual(numListeners, 2);
       server.close();
       agent.destroy();
     }));

test/parallel/test-http-client-timeout-option-with-agent.js

@@ -18,6 +18,6 @@ request.on('socket', mustCall((socket) => {
 
   const listeners = socket.listeners('timeout');
 
-  strictEqual(listeners.length, 1);
-  strictEqual(listeners[0], request.timeoutCb);
+  strictEqual(listeners.length, 2);
+  strictEqual(listeners[1], request.timeoutCb);
 }));