http: refactor agent 'free' handler

Remove nesting in favor of early returns.

PR-URL: #32801
Reviewed-By: Zeyu Yang <himself65@outlook.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

lib/_http_agent.js

@@ -37,6 +37,8 @@ const {
     ERR_INVALID_ARG_TYPE,
   },
 } = require('internal/errors');
+const { once } = require('internal/util');
+
 const kOnKeylog = Symbol('onkeylog');
 // New Agent code.
 
@@ -94,52 +96,55 @@ function Agent(options) {
     // case of socket.destroy() below this 'error' has no handler
     // and could cause unhandled exception.
 
-    if (socket.writable &&
-        this.requests[name] && this.requests[name].length) {
-      const req = this.requests[name].shift();
+    if (!socket.writable) {
+      socket.destroy();
+      return;
+    }
+
+    const requests = this.requests[name];
+    if (requests && requests.length) {
+      const req = requests.shift();
       setRequestSocket(this, req, socket);
-      if (this.requests[name].length === 0) {
-        // don't leak
+      if (requests.length === 0) {
         delete this.requests[name];
       }
-    } else {
-      // If there are no pending requests, then put it in
-      // the freeSockets pool, but only if we're allowed to do so.
-      const req = socket._httpMessage;
-      if (req &&
-          req.shouldKeepAlive &&
-          socket.writable &&
-          this.keepAlive) {
-        let freeSockets = this.freeSockets[name];
-        const freeLen = freeSockets ? freeSockets.length : 0;
-        let count = freeLen;
-        if (this.sockets[name])
-          count += this.sockets[name].length;
-
-        if (count > this.maxSockets || freeLen >= this.maxFreeSockets) {
-          socket.destroy();
-        } else if (this.keepSocketAlive(socket)) {
-          freeSockets = freeSockets || [];
-          this.freeSockets[name] = freeSockets;
-          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);
-          }
-
-          socket.once('error', freeSocketErrorListener);
-          freeSockets.push(socket);
-        } else {
-          // Implementation doesn't want to keep socket alive
-          socket.destroy();
-        }
-      } else {
-        socket.destroy();
-      }
+      return;
+    }
+
+    // If there are no pending requests, then put it in
+    // the freeSockets pool, but only if we're allowed to do so.
+    const req = socket._httpMessage;
+    if (!req || !req.shouldKeepAlive || !this.keepAlive) {
+      socket.destroy();
+      return;
     }
+
+    let freeSockets = this.freeSockets[name];
+    const freeLen = freeSockets ? freeSockets.length : 0;
+    let count = freeLen;
+    if (this.sockets[name])
+      count += this.sockets[name].length;
+
+    if (count > this.maxSockets ||
+        freeLen >= this.maxFreeSockets ||
+        !this.keepSocketAlive(socket)) {
+      socket.destroy();
+      return;
+    }
+
+    freeSockets = freeSockets || [];
+    this.freeSockets[name] = freeSockets;
+    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);
+    }
+
+    socket.once('error', freeSocketErrorListener);
+    freeSockets.push(socket);
   });
 
   // Don't emit keylog events unless there is a listener for them.
@@ -266,12 +271,8 @@ Agent.prototype.createSocket = function createSocket(req, options, cb) {
 
   debug('createConnection', name, options);
   options.encoding = null;
-  let called = false;
 
-  const oncreate = (err, s) => {
-    if (called)
-      return;
-    called = true;
+  const oncreate = once((err, s) => {
     if (err)
       return cb(err);
     if (!this.sockets[name]) {
@@ -281,7 +282,7 @@ Agent.prototype.createSocket = function createSocket(req, options, cb) {
     debug('sockets', name, this.sockets[name].length);
     installListeners(this, s, options);
     cb(null, s);
-  };
+  });
 
   const newSocket = this.createConnection(options, oncreate);
   if (newSocket)