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Type: Bug
Resolution: Duplicate
Priority: P2: Important
Fix Version/s: None
Affects Version/s: 5.0.0 Beta 1
Component/s: Network: Sockets
Labels:
None
Environment:
{noformat}
$ uname -a
Linux sjinks 3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:31:23 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -rd
Description: Ubuntu 12.10
Release: 12.10
{noformat}

Sample code:

#include <QtCore/QCoreApplication>
#include <QtCore/QDebug>
#include <QtNetwork/QHostAddress>
#include <QtNetwork/QTcpSocket>
#include "sockettester.h"

SocketTester::SocketTester(QObject* parent)
    : QObject(parent), socket(new QTcpSocket())
{
    QObject::connect(socket, SIGNAL(connected()), this, SLOT(connected()));
    QObject::connect(socket, SIGNAL(disconnected()), this, SLOT(disconnected()));
    QObject::connect(socket, SIGNAL(error(QAbstractSocket::SocketError)), this, SLOT(error(QAbstractSocket::SocketError)));
    QObject::connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
    QObject::connect(socket, SIGNAL(stateChanged(QAbstractSocket::SocketState)), this, SLOT(stateChanged(QAbstractSocket::SocketState)));
}

void SocketTester::run(void)
{
    this->socket->bind(QHostAddress(QLatin1String("72.251.207.223")), 0);
    this->socket->connectToHost(QLatin1String("aspmx.l.google.com."), 25);
}

void SocketTester::connected(void)
{
    qDebug() << "CONNECTED" << this->socket->localAddress() << this->socket->localPort();
}

void SocketTester::disconnected(void)
{
    qDebug() << "DISCONNECTED";
    QCoreApplication::quit();
}

void SocketTester::error(QAbstractSocket::SocketError e)
{
    qDebug() << "ERROR" << e << this->socket->errorString();
}

void SocketTester::readyRead(void)
{
    static int f = 0;
    qDebug() << "READYREAD" << this->socket->readAll();
    if (!f) {
        f = 1;
        this->socket->write("EHLO localhost\r\n");
    }
    else if (1 == f) {
        this->socket->write("QUIT\r\n");
        f = 2;
    }
}

void SocketTester::stateChanged(QAbstractSocket::SocketState s)
{
    qDebug() << "STATECHANGED" << s << this->socket->localAddress() << this->socket->localPort();
}

Output (Qt built in debug mode):

QTcpSocket::QTcpSocket()
QAbstractSocketPrivate::resetSocketLayer()
QAbstractSocketPrivate::initSocketLayer(TcpSocket, IPv4Protocol) success
QNativeSocketEnginePrivate::nativeBind(72.251.207.223, 0) == true
QNativeSocketEnginePrivate::fetchConnectionParameters() local == 72.251.207.223:46140, peer == :0, socket == TcpSocket - IPv4Protocol
STATECHANGED QAbstractSocket::BoundState  QHostAddress( "72.251.207.223" )  46140 
QAbstractSocket::connectToHost("aspmx.l.google.com.", 25, 3)...
STATECHANGED QAbstractSocket::HostLookupState  QHostAddress( "" )  0 
QHostInfo::lookupHost("aspmx.l.google.com.", 0x17d0bb0, _q_startConnecting(QHostInfo))
QAbstractSocket::connectToHost("aspmx.l.google.com.", 25) == false (connection in progress)
QAbstractSocketPrivate::canReadNotification()
QNativeSocketEnginePrivate::nativeBytesAvailable() == 0
QAbstractSocketPrivate::readFromSocket() about to read 4096 bytes
QHostInfoAgent::fromName(aspmx.l.google.com.) looking up...
QNativeSocketEnginePrivate::nativeRead(0x17d2a40 "", 4096) == -1
QNativeSocketEngine::nativeClose()
QAbstractSocketPrivate::readFromSocket() got -1 bytes, buffer size = 0
ERROR QAbstractSocket::NetworkError "Transport endpoint is not connected" 
QAbstractSocketPrivate::readFromSocket() read failed: Transport endpoint is not connected
QAbstractSocketPrivate::resetSocketLayer()
QAbstractSocketPrivate::canReadNotification() disconnecting socket
QAbstractSocket::disconnectFromHost()
QAbstractSocket::disconnectFromHost() but we're still connecting
getaddrinfo node: flags: 32 family: 2 ai_socktype: 1 ai_protocol: 6 ai_addrlen: 16 
getaddrinfo node: flags: 32 family: 2 ai_socktype: 2 ai_protocol: 17 ai_addrlen: 16 
getaddrinfo node: flags: 32 family: 2 ai_socktype: 3 ai_protocol: 0 ai_addrlen: 16 
QHostInfoAgent::fromName(): found 1 entries for "aspmx.l.google.com.": {173.194.65.26}
QAbstractSocketPrivate::_q_startConnecting(hostInfo == {173.194.65.26})
STATECHANGED QAbstractSocket::ConnectingState  QHostAddress( "" )  0 
QAbstractSocketPrivate::_q_connectToNextAddress(), connecting to 173.194.65.26:25, 1 left to try
QAbstractSocketPrivate::resetSocketLayer()
QAbstractSocketPrivate::initSocketLayer(TcpSocket, IPv4Protocol) success
QNativeSocketEnginePrivate::nativeConnect() : 4 
QNativeSocketEnginePrivate::nativeConnect(173.194.65.26, 25) == false (Connection in progress)
QNativeSocketEnginePrivate::nativeConnect() : 4 
QNativeSocketEnginePrivate::nativeConnect(173.194.65.26, 25) == true
QNativeSocketEnginePrivate::fetchConnectionParameters() local == 78.30.235.66:49951, peer == 173.194.65.26:25, socket == TcpSocket - IPv4Protocol
QAbstractSocketPrivate::connectionNotification() testing connection
STATECHANGED QAbstractSocket::ConnectedState  QHostAddress( "78.30.235.66" )  49951 
CONNECTED  QHostAddress( "78.30.235.66" )  49951 
QAbstractSocketPrivate::fetchConnectionParameters() connection to 173.194.65.26:25 established
QAbstractSocket::disconnectFromHost()
QAbstractSocket::disconnectFromHost() emits stateChanged()(ClosingState)
STATECHANGED QAbstractSocket::ClosingState  QHostAddress( "78.30.235.66" )  49951 
QAbstractSocket::disconnectFromHost() disconnecting immediately
QAbstractSocketPrivate::resetSocketLayer()
QNativeSocketEngine::nativeClose()
STATECHANGED QAbstractSocket::UnconnectedState  QHostAddress( "78.30.235.66" )  49951 
DISCONNECTED 
QAbstractSocket::disconnectFromHost() disconnected!

A call to QAbstractSocketPrivate::resetSocketLayer() closes the socket and thus the binding is lost. QAbstractSocketPrivate::_q_connectToNextAddress() calls resetSocketLayer() again.

If we replace

this->socket->connectToHost(QLatin1String("aspmx.l.google.com."), 25);

with

this->socket->connectToHost(QLatin1String("173.194.65.26"), 25);

the binding will still be lost but the picture will be different ("Transport endpoint is not connected" error will be gone and we will actually be able to connect to the host):

QAbstractSocket::QAbstractSocket(TcpSocket, QAbstractSocketPrivate == 0x1599ba0, parent == 0x0)
QTcpSocket::QTcpSocket()
QAbstractSocketPrivate::resetSocketLayer()
QAbstractSocketPrivate::initSocketLayer(TcpSocket, IPv4Protocol) success
QNativeSocketEnginePrivate::nativeBind(72.251.207.223, 0) == true
QNativeSocketEnginePrivate::fetchConnectionParameters() local == 72.251.207.223:40649, peer == :0, socket == TcpSocket - IPv4Protocol
STATECHANGED QAbstractSocket::BoundState  QHostAddress( "72.251.207.223" )  40649 
QAbstractSocket::connectToHost("173.194.65.26", 25, 3)...
STATECHANGED QAbstractSocket::HostLookupState  QHostAddress( "" )  0 
QAbstractSocketPrivate::_q_startConnecting(hostInfo == {173.194.65.26})
STATECHANGED QAbstractSocket::ConnectingState  QHostAddress( "" )  0 
QAbstractSocketPrivate::_q_connectToNextAddress(), connecting to 173.194.65.26:25, 1 left to try
QAbstractSocketPrivate::resetSocketLayer()
QNativeSocketEngine::nativeClose()
QAbstractSocketPrivate::initSocketLayer(TcpSocket, IPv4Protocol) success
QNativeSocketEnginePrivate::nativeConnect() : 4 
QNativeSocketEnginePrivate::nativeConnect(173.194.65.26, 25) == false (Connection in progress)
QAbstractSocket::connectToHost("173.194.65.26", 25) == false (connection in progress)
QNativeSocketEnginePrivate::nativeConnect() : 4 
QNativeSocketEnginePrivate::nativeConnect(173.194.65.26, 25) == true
QNativeSocketEnginePrivate::fetchConnectionParameters() local == 78.30.235.66:50044, peer == 173.194.65.26:25, socket == TcpSocket - IPv4Protocol
QAbstractSocketPrivate::connectionNotification() testing connection
STATECHANGED QAbstractSocket::ConnectedState  QHostAddress( "78.30.235.66" )  50044 
CONNECTED  QHostAddress( "78.30.235.66" )  50044 
QAbstractSocketPrivate::fetchConnectionParameters() connection to 173.194.65.26:25 established
QAbstractSocketPrivate::canWriteNotification() flushing
QAbstractSocketPrivate::flush() nothing to do: valid ? yes, writeBuffer.isEmpty() ? yes
QAbstractSocketPrivate::canReadNotification()
QNativeSocketEnginePrivate::nativeBytesAvailable() == 44
QAbstractSocketPrivate::readFromSocket() about to read 44 bytes
QNativeSocketEnginePrivate::nativeRead(0x159b570 "220 mx.google.co...", 44) == 44
QAbstractSocketPrivate::readFromSocket() got 44 bytes, buffer size = 44
READYREAD "220 mx.google.com ESMTP n49si4070759eeo.97
" 
QAbstractSocket::writeData(0x40352d "EHLO localhost\r\n", 16) == 16
QAbstractSocketPrivate::canWriteNotification() flushing
QNativeSocketEnginePrivate::nativeWrite(0x159b588 "EHLO localhost\r\n", 16) == 16
QAbstractSocketPrivate::flush() 16 bytes written to the network
QAbstractSocketPrivate::canReadNotification()
QNativeSocketEnginePrivate::nativeBytesAvailable() == 123
QAbstractSocketPrivate::readFromSocket() about to read 123 bytes
QNativeSocketEnginePrivate::nativeRead(0x159b570 "250-mx.google.co...", 123) == 123
QAbstractSocketPrivate::readFromSocket() got 123 bytes, buffer size = 123
READYREAD "250-mx.google.com at your service, [78.30.235.66]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250 ENHANCEDSTATUSCODES
" 
QAbstractSocket::writeData(0x40353e "QUIT\r\n", 6) == 6
QAbstractSocketPrivate::canWriteNotification() flushing
QNativeSocketEnginePrivate::nativeWrite(0x159b588 "QUIT\r\n", 6) == 6
QAbstractSocketPrivate::flush() 6 bytes written to the network
QAbstractSocketPrivate::canReadNotification()
QNativeSocketEnginePrivate::nativeBytesAvailable() == 49
QAbstractSocketPrivate::readFromSocket() about to read 49 bytes
QNativeSocketEnginePrivate::nativeRead(0x159b570 "221 2.0.0 closin...", 49) == 49
QAbstractSocketPrivate::readFromSocket() got 49 bytes, buffer size = 49
READYREAD "221 2.0.0 closing connection n49si4070759eeo.97
" 
QAbstractSocketPrivate::canReadNotification()
QNativeSocketEnginePrivate::nativeBytesAvailable() == 0
QAbstractSocketPrivate::readFromSocket() about to read 4096 bytes
QNativeSocketEnginePrivate::nativeRead(0x159b570 "", 4096) == 0
QNativeSocketEngine::nativeClose()
QAbstractSocketPrivate::readFromSocket() got -1 bytes, buffer size = 0
ERROR QAbstractSocket::RemoteHostClosedError "The remote host closed the connection" 
QAbstractSocketPrivate::readFromSocket() read failed: The remote host closed the connection
QAbstractSocketPrivate::resetSocketLayer()
QAbstractSocketPrivate::canReadNotification() disconnecting socket
QAbstractSocket::disconnectFromHost()
QAbstractSocket::disconnectFromHost() emits stateChanged()(ClosingState)
STATECHANGED QAbstractSocket::ClosingState  QHostAddress( "78.30.235.66" )  50044 
QAbstractSocket::disconnectFromHost() disconnecting immediately
QAbstractSocketPrivate::resetSocketLayer()
STATECHANGED QAbstractSocket::UnconnectedState  QHostAddress( "78.30.235.66" )  50044 
DISCONNECTED 
QAbstractSocket::disconnectFromHost() disconnected!

The expected behavior is:

when connecting to the host by name:
- we should not try to read from the not connected socket (resulting in "Transport endpoint is not connected" error)
- socket binding must be preserved
- we should eventually be able to connect to the host
when connecting to the host by IP:
- socket binding must be preserved - QAbstractSocketPrivate::_q_connectToNextAddress() probably should not call resetSocketLayer()

relates to

QTBUG-26538 QUdpSocket: connectToHost() resets local port number specified by bind()

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