我写了一个客户端/服务器TCP / IP程序，它工作正常，直到服务器生成一个更大的文件。在那一刻它破裂了，而不是所有的时间，但往往足以使它成为一个真正的问题。我只用TCP / IP编写了一个小版本，它重现了我发现相当令人印象深刻的问题。
我尝试了各种各样的方法来解决问题，但我不太确定下一步该做什么！
/*
* Test showing that at times a socket close() + exit(0) prevents all the
* data from reaching the client.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <QCoreApplication>
#include <QByteArray>
#include <QFile>
#include <QTcpSocket>
#include <QTcpServer>
#include <QHostAddress>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/socket.h>
void
client()
{
QHostAddress a("192.168.2.1");
int port = 4004;
QTcpSocket socket;
socket.connectToHost(a, port);
if(socket.waitForConnected())
{
// if we get here then we can just copy the output of the child to Apache2
// the wait will flush all the writes as necessary
if(!socket.waitForReadyRead())
{
fprintf(stderr, "error: waitForReadyRead() timed out.\n");
exit(1);
}
// buffer somewhere to check the output validity
FILE *f = fopen("/tmp/out.html", "w");
if(f == NULL)
{
fprintf(stderr, "error: could not create /tmp/out.html file.\n");
exit(1);
}
for(;;)
{
char buf[64 * 1024];
qint64 r(socket.read(buf, sizeof(buf)));
if(r > 0)
{
fwrite(buf, r, 1, f);
}
else if(r == -1)
{
fprintf(stderr, "error: an error occured while read()'ing from the socket.\n");
break;
}
else if(r == 0)
{
// no more data (since our socket is blocking this really
// only happens when no more data is available)
break;
}
}
fclose(f);
return;
}
fprintf(stderr, "error: client could not connect to server.\n");
exit(1);
}
void
server()
{
QTcpServer s;
QHostAddress a("0.0.0.0");
if(!s.listen(a, 4004))
{
fprintf(stderr, "error: server is not able to listen, port 4004 not available?\n");
exit(1);
}
pid_t pid(0);
for(;;)
{
if(pid > 0)
{
int status;
if(waitpid(pid, &status, WNOHANG) == pid)
{
pid = 0;
}
}
s.waitForNewConnection(-1);
if(pid > 0)
{
int status;
if(waitpid(pid, &status, 0) == pid)
{
pid = 0;
}
}
QTcpSocket *socket(s.nextPendingConnection());
pid = fork();
if(pid == 0)
{
// this makes it work a bit better but we still have the
// early disconnection
int optval(1);
socklen_t optlen(sizeof(optval));
if(setsockopt(socket->socketDescriptor(), SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) {
fprintf(stderr, "warning: could not mark the new connection with keepalive flag.\n");
}
// we are the child, write in the socket and close it
QFile f("example.html");
f.open(QIODevice::ReadOnly);
QByteArray buffer(f.readAll());
f.close();
socket->write(buffer);
// the sleep makes it slow, but it doesn't make any difference
//sleep(2);
socket->flush();
// extra sleep/flush don't make any difference
//sleep(1);
//socket->flush();
//sleep(1);
//socket->flush();
// the read doesn't seem to fix anything
socket->waitForReadyRead();
socket->disconnectFromHost();
delete socket;
exit(0);
}
else {
if(pid == -1) {
fprintf(stderr, "error: could not create child process to handle the socket.\n");
}
socket->close();
}
}
}
int
main(int argc, char *argv[])
{
if(argc == 1)
{
client();
}
else if(strcmp(argv[1], "-s") == 0)
{
server();
}
else
{
printf("Usage: %s [-s]\n", argv[0]);
exit(1);
}
exit(0);
}
我使用CMakeLists.txt文件编译服务器＆amp;客户。编译完成后，我们有一个可执行文件：tcp-bug。以-s作为服务器启动它。然后在不带-s的不同控制台中启动相同的可执行文件。我写了一个shell脚本来重复测试，因为它通常不是第一次发生，虽然它通常不到20次点击。
有我的CMakeLists.txt文件：
cmake_minimum_required(VERSION 2.8)
project(tcp-bug)
find_package(Qt4 4.8.1 REQUIRED QtCore QtNetwork)
include(${QT_USE_FILE})
include_directories(${QT_INCLUDES})
add_definitions(${QT_DEFINITIONS})
add_executable(tcp-bug tcp-bug.cpp)
target_link_libraries(tcp-bug ${QT_LIBRARIES})
set(CPACK_PACKAGE_NAME "tcp-bug")
set(CPACK_SOURCE_IGNORE_FILES ".swp$;/BUILD/")
include(CPack)
我的shell脚本：
#!/bin/sh
for g in a b c d e f g h i j k l m n o p q r s t u v w x y z
do
for f in 1 2 3 4 5 6 7 8 9 10
do
BUILD/tcp-bug
if [ `stat -c %s /tmp/out.html` -ne 41812 ]
then
echo "Error occured! Iteration: $g - $f"
ls -l /tmp/out.html
exit 1
fi
done
done
请注意，脚本需要在下一页的.tar.gz中提供正好41,812字节的文件（您还可以创建自己的example.html文件，服务器读取并发送给客户端的内容）：< / p>
http://linux.m2osw.com/breaking-tcpip-simple-clientserver-implementation-qt