Improve connection handling

1. Previously unhandled connections will stay in pending state. It won't
be closed until timeout happened. This may lead to wasting system
resources. Now the (over-limit) connection is actively rejected.

2. When out-of-memory occurs here, reject the new connection instead of
throwing exception and crash.

3. Also clean up some unused bits.

PR #20961.

src/base/http/connection.cpp

@@ -44,6 +44,7 @@ Connection::Connection(QTcpSocket *socket, IRequestHandler *requestHandler, QObj
     , m_requestHandler(requestHandler)
 {
     m_socket->setParent(this);
+    connect(m_socket, &QAbstractSocket::disconnected, this, &Connection::closed);
 
     // reserve common size for requests, don't use the max allowed size which is too big for
     // memory constrained platforms
@@ -62,11 +63,6 @@ Connection::Connection(QTcpSocket *socket, IRequestHandler *requestHandler, QObj
     });
 }
 
-Connection::~Connection()
-{
-    m_socket->close();
-}
-
 void Connection::read()
 {
     // reuse existing buffer and avoid unnecessary memory allocation/relocation
@@ -182,11 +178,6 @@ bool Connection::hasExpired(const qint64 timeout) const
         && m_idleTimer.hasExpired(timeout);
 }
 
-bool Connection::isClosed() const
-{
-    return (m_socket->state() == QAbstractSocket::UnconnectedState);
-}
-
 bool Connection::acceptsGzipEncoding(QString codings)
 {
     // [rfc7231] 5.3.4. Accept-Encoding