How to have gwan send no reply to some requests, i.e. make a servlet closed silently without building and sending a reply?
It is useful to reduce the out-going bandwidth from the server side.
For collecting data only, there's no need to respond anything to the client.
You can also close the connection from the servlet by doing something like (untested):
#include <sys/socket.h>
char buf[1024];
int s = (int)get_env(argv, CLIENT_SOCKET);
shutdown(s, SHUT_WR);
while(read(s, buf, sizeof(buf)) > 0);
close(s);
return 500;
Then return something like 500 like above so you don't have to build a reply.
You can do that with a gwan connection handler.
I think this is the event that you need to catch on the handler. Since you want the servlet to run then close the connection after.
HDL_BEFORE_WRITE, // after a reply was built, but before it is sent
Here is a sample code for the connection handler. You still need to add your filter. This code will close all requests after the reply was built.
int init(int argc, char *argv[])
{
u32 *states = (u32*)get_env(argv, US_HANDLER_STATES);
*states = (1 << HDL_BEFORE_WRITE)
}
int main(int argc, char *argv[])
{
long state = (long)argv[0];
if(state == HDL_BEFORE_WRITE)
{
return 0; // Close connection
}
return(255); // continue G-WAN's default execution path
}
Related
I wanted to write a client server thing using gio socket in gtk and I found a sample code to send data to server but, the more thing i want is to read the data/reply sent by the server. The below is sample code
#include <glib.h>
#include <gio/gio.h>
int main (int argc, char *argv[])
{
/* initialize glib */
g_type_init ();
GError * error = NULL;
/* create a new connection */
GSocketConnection * connection = NULL;
GSocketClient * client = g_socket_client_new();
/* connect to the host */
connection = g_socket_client_connect_to_host (client,
(gchar*)"localhost",
1500, /* your port goes here */
NULL,
&error);
/* don't forget to check for errors */
if (error != NULL)
{
g_error (error->message);
}
else
{
g_print ("Connection successful!\n");
}
/* use the connection */
GInputStream * istream = g_io_stream_get_input_stream (G_IO_STREAM (connection));
GOutputStream * ostream = g_io_stream_get_output_stream (G_IO_STREAM (connection));
g_output_stream_write (ostream,
"Hello server!", /* your message goes here */
13, /* length of your message */
NULL,
&error);
/* don't forget to check for errors */
if (error != NULL)
{
g_error (error->message);
}
return 0;
}
The above code works fine for the sending data to server but when i try to read it form input stream it goes in to block state. My read message function look like this
void readMessage()
{
char buffer[2048];
GInputStream * istream = g_io_stream_get_input_stream (G_IO_STREAM(connection));
gssize bytes;
bytes = g_input_stream_read(istream, buffer, sizeof buffer, NULL, NULL);
buffer[bytes] = '\0';
g_print ("%"G_GSSIZE_FORMAT" bytes read: %s\n", bytes, buffer);
}
g_input_stream_read() is documented as blocking until it receives as many bytes as you request (in this case, 2048), or until the connection is closed. Presumably, neither of those things are happening. How big is the reply from the server? Does it close the connection after sending its reply?
Bear in mind that g_socket_client_connect_to_host() opens a TCP connection, so you should expect to be doing stream-based I/O here, rather than message-based I/O. If you expect to be sending messages to and from the server, you will need a framing protocol within TCP.
I am trying to write a simple socket program which reads a file name in client and sends it to the server. The contents of file are sent to the Client back if present. The client and server are able to successfully able to connect but when I read a file name I don't get any output(program doesn't terminates). Please tell me what is going wrong.
server.c
int main()
{
int create_socket,new_socket,fd,addlen,n;
int bufsize=1024;
char *buffer=malloc(bufsize);
char fname[255];
struct sockaddr_in address;
//printf("program");
if((create_socket=socket(AF_INET,SOCK_STREAM,0))>0)
printf("socket created");
address.sin_family=AF_INET;
address.sin_port=htons(15000);
address.sin_addr.s_addr=INADDR_ANY;
if(bind(create_socket,(struct sockaddr*)&address,sizeof(address))==0)
printf("socket binded");
while(1)
{
printf("Inside while loop");
listen(create_socket,3);
addlen=sizeof(struct sockaddr_in);
if(new_socket=accept(create_socket,(struct sockaddr*)&address,&addlen)>0)
printf("%d connected",inet_ntoa(address.sin_addr));
else
printf("not connected");
recv(new_socket,fname,255,0);
printf("file name is %s",fname);
if(fd=open(fname,O_RDONLY)<0)
{
strcpy(buffer,"Not such file found");
send(new_socket,buffer,sizeof(buffer),0);
}
else
{
while(n=read(fd,buffer,bufsize)>0)
send(new_socket,buffer,n,0);
}
close(new_socket);
}
close(create_socket);
}
client.c
int main(int argc,char *argv[])
{
int create_socket,n;
int bufsize=1024;
char *buffer=malloc(bufsize);
char fname[255];
struct sockaddr_in address;
if((create_socket=socket(AF_INET,SOCK_STREAM,0))>0)
printf("socket created\n");
address.sin_family=AF_INET;
address.sin_port=htons(15000);
inet_pton(AF_INET,argv[1],&address.sin_addr);
if(connect(create_socket,(struct sockaddr*)&address,sizeof(address))==0)
printf("%s connected\n",argv[1]);
else
printf("not connected\n");
printf("Enter the filename\n");
scanf("%s",fname);
send(create_socket,fname,strlen(fname),0);
printf("get the values");
while(n=recv(create_socket,buffer,bufsize,0)>0)
write(1,buffer,n);
return close(create_socket);
}
With the information provided, two problems with transmitting the file name are apparent:
(1) You do not check the return value of send. You cannot be sure what is sent.
(2) You choose not to send the terminating '\0' over the network. Therefore, the receiver has no way of determining when the complete file name has been received. The receiver also does not check the return value of recv. Additionally, the receiver does not bother to terminate the received filename with a '\0'.
I use sockets in non-blocking mode, and sometimes WSAConnect function returns WSAEINVAL error.
I investigate a problem and found, that it occurs if there is no pause (or it is very small ) between
WSAConnect function calls.
Does anyone know how to avoid this situation?
Below you can found source code, that reproduce the problem. If I increase value of parameter in Sleep function to 50 or great - problem dissapear.
P.S. This problem reproduces only on Windows XP, on Win7 it works well.
#undef UNICODE
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <iostream>
#include <windows.h>
#pragma comment(lib, "Ws2_32.lib")
static int getError(SOCKET sock)
{
DWORD error = WSAGetLastError();
return error;
}
void main()
{
SOCKET sock;
WSADATA wsaData;
if (WSAStartup(MAKEWORD(2, 2), &wsaData) != 0) {
fprintf(stderr, "Socket Initialization Error. Program aborted\n");
return;
}
for (int i = 0; i < 1000; ++i) {
struct addrinfo hints;
struct addrinfo *res = NULL;
memset(&hints, 0, sizeof(hints));
hints.ai_flags = AI_PASSIVE;
hints.ai_socktype = SOCK_STREAM;
hints.ai_family = AF_INET;
hints.ai_protocol = IPPROTO_TCP;
if (0 != getaddrinfo("172.20.1.59", "8091", &hints, &res)) {
fprintf(stderr, "GetAddrInfo Error. Program aborted\n");
closesocket(sock);
WSACleanup();
return;
}
struct addrinfo *ptr = 0;
for (ptr=res; ptr != NULL ;ptr=ptr->ai_next) {
sock = WSASocket(ptr->ai_family, ptr->ai_socktype, ptr->ai_protocol, NULL, 0, NULL); //
if (sock == INVALID_SOCKET)
int err = getError(sock);
else {
u_long noblock = 1;
if (ioctlsocket(sock, FIONBIO, &noblock) == SOCKET_ERROR) {
int err = getError(sock);
closesocket(sock);
sock = INVALID_SOCKET;
}
break;
}
}
int ret;
do {
ret = WSAConnect(sock, ptr->ai_addr, (int)ptr->ai_addrlen, NULL, NULL, NULL, NULL);
if (ret == SOCKET_ERROR) {
int error = getError(sock);
if (error == WSAEWOULDBLOCK) {
Sleep(5);
continue;
}
else if (error == WSAEISCONN) {
fprintf(stderr, "+");
closesocket(sock);
sock = SOCKET_ERROR;
break;
}
else if (error == 10037) {
fprintf(stderr, "-");
closesocket(sock);
sock = SOCKET_ERROR;
break;
}
else {
fprintf(stderr, "Connect Error. [%d]\n", error);
closesocket(sock);
sock = SOCKET_ERROR;
break;
}
}
else {
int one = 1;
setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, (char*)&one, sizeof(one));
fprintf(stderr, "OK\n");
break;
}
}
while (1);
}
std::cout<<"end";
char ch;
std::cin >> ch;
}
You've got a whole basketful of errors and questionable design and coding decisions here. I'm going to have to break them up into two groups:
Outright Errors
I expect if you fix all of the items in this section, your symptom will disappear, but I wouldn't want to speculate about which one is the critical fix:
Calling connect() in a loop on a single socket is simply wrong.
If you mean to establish a connection, drop it, and reestablish it 1000 times, you need to call closesocket() at the end of each loop, then call socket() again to get a fresh socket. You can't keep re-connecting the same socket. Think of it like a power plug: if you want to plug it in twice, you have to unplug (closesocket()) between times.
If instead you mean to establish 1000 simultaneous connections, you need to allocate a new socket with socket() on each iteration, connect() it, then go back around again to get another socket. It's basically the same loop as for the previous case, except without the closesocket() call.
Beware that since XP is a client version of Windows, it's not optimized for handling thousands of simultaneous sockets.
Calling connect() again is not the correct response to WSAEWOULDBLOCK:
if (error == WSAEWOULDBLOCK) {
Sleep(5);
continue; /// WRONG!
}
That continue code effectively commits the same error as above, but worse, if you only fix the previous error and leave this, this usage will then make your code start leaking sockets.
WSAEWOULDBLOCK is not an error. All it means after a connect() on a nonblcoking socket is that the connection didn't get established immediately. The stack will notify your program when it does.
You get that notification by calling one of select(), WSAEventSelect(), or WSAAsyncSelect(). If you use select(), the socket will be marked writable when the connection gets established. With the other two, you will get an FD_CONNECT event when the connection gets established.
Which of these three APIs to call depends on why you want nonblocking sockets in the first place, and what the rest of the program will look like. What I see so far doesn't need nonblocking sockets at all, but I suppose you have some future plan that will inform your decision. I've written an article, Which I/O Strategy Should I Use (part of the Winsock Programmers' FAQ) which will help you decide which of these options to use; it may instead guide you to another option entirely.
You shouldn't use AI_PASSIVE and connect() on the same socket. Your use of AI_PASSIVE with getaddrinfo() tells the stack you intend to use this socket to accept incoming connections. Then you go and use that socket to make an outgoing connection.
You've basically lied to the stack here. Computers find ways to get revenge when you lie to them.
Sleep() is never the right way to fix problems with Winsock. There are built-in delays within the stack that your program can see, such as TIME_WAIT and the Nagle algorithm, but Sleep() is not the right way to cope with these, either.
Questionable Coding/Design Decisions
This section is for things I don't expect to make your symptom go away, but you should consider fixing them anyway:
The main reason to use getaddrinfo() — as opposed to older, simpler functions like inet_addr() — is if you have to support IPv6. That kind of conflicts with your wish to support XP, since XP's IPv6 stack wasn't nearly as heavily tested during the time XP was the current version of Windows as its IPv4 stack. I would expect XP's IPv6 stack to still have bugs as a result, even if you've got all the patches installed.
If you don't really need IPv6 support, doing it the old way might make your symptoms disappear. You might end up needing an IPv4-only build for XP.
This code:
for (int i = 0; i < 1000; ++i) {
// ...
if (0 != getaddrinfo("172.20.1.59", "8091", &hints, &res)) {
...is inefficient. There is no reason you need to keep reinitializing res on each loop.
Even if there is some reason I'm not seeing, you're leaking memory by not calling freeaddrinfo() on res.
You should initialize this data structure once before you enter the loop, then reuse it on each iteration.
else if (error == 10037) {
Why aren't you using WSAEALREADY here?
You don't need to use WSAConnect() here. You're using the 3-argument subset that Winsock shares with BSD sockets. You might as well use connect() here instead.
There's no sense making your code any more complex than it has to be.
Why aren't you using a switch statement for this?
if (error == WSAEWOULDBLOCK) {
// ...
}
else if (error == WSAEISCONN) {
// ...
}
// etc.
You shouldn't disable the Nagle algorithm:
setsockopt(sock, IPPROTO_TCP, TCP_NODELAY, ...);
I have implemented a TCP server using boost::asio. This server uses basic_stream_socket::read_some function to read data. I know that read_some does not guarantee that supplied buffer will be full before it returns.
In my project I am sending strings separated by a delimiter(if that matters). At client side I am using WinSock::send() function to send data. Now my problem is on server side I am not able to get all the strings which were sent from client side. My suspect is that read_some is receiving some data and discarding leftover data for some reason. Than again in next call its receiving another string.
Is it really possible in TCP/IP ?
I tried to use async_receive but that is eating up all my CPU, also since buffer has to be cleaned up by callback function its causing serious memory leak in my program. (I am using IoService::poll() to call handler. That handler is getting called at a very slow rate compared to calling rate of async_read()).
Again I tried to use free function read but that will not solve my purpose as it blocks for too much time with the buffer size I am supplying.
My previous implementation of the server was with WinSock API where I was able to receive all data using WinSock::recv().
Please give me some leads so that I can receive complete data using boost::asio.
here is my server side thread loop
void
TCPObject::receive()
{
if (!_asyncModeEnabled)
{
std::string recvString;
if ( !_tcpSocket->receiveData( _maxBufferSize, recvString ) )
{
LOG_ERROR("Error Occurred while receiving data on socket.");
}
else
_parseAndPopulateQueue ( recvString );
}
else
{
if ( !_tcpSocket->receiveDataAsync( _maxBufferSize ) )
{
LOG_ERROR("Error Occurred while receiving data on socket.");
}
}
}
receiveData() in TCPSocket
bool
TCPSocket::receiveData( unsigned int bufferSize, std::string& dataString )
{
boost::system::error_code error;
char *buf = new char[bufferSize + 1];
size_t len = _tcpSocket->read_some( boost::asio::buffer((void*)buf, bufferSize), error);
if(error)
{
LOG_ERROR("Error in receiving data.");
LOG_ERROR( error.message() );
_tcpSocket->close();
delete [] buf;
return false;
}
buf[len] ='\0';
dataString.insert( 0, buf );
delete [] buf;
return true;
}
receiveDataAsync in TCP Socket
bool
TCPSocket::receiveDataAsync( unsigned int bufferSize )
{
char *buf = new char[bufferSize + 1];
try
{
_tcpSocket->async_read_some( boost::asio::buffer( (void*)buf, bufferSize ),
boost::bind(&TCPSocket::_handleAsyncReceive,
this,
buf,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred) );
//! Asks io_service to execute callback
_ioService->poll();
}
catch (std::exception& e)
{
LOG_ERROR("Error Receiving Data Asynchronously");
LOG_ERROR( e.what() );
delete [] buf;
return false;
}
//we dont delete buf here as it will be deleted by callback _handleAsyncReceive
return true;
}
Asynch Receive handler
void
TCPSocket::_handleAsyncReceive(char *buf, const boost::system::error_code& ec, size_t size)
{
if(ec)
{
LOG_ERROR ("Error occurred while sending data Asynchronously.");
LOG_ERROR ( ec.message() );
}
else if ( size > 0 )
{
buf[size] = '\0';
emit _asyncDataReceivedSignal( QString::fromLocal8Bit( buf ) );
}
delete [] buf;
}
Client Side sendData function.
sendData(std::string data)
{
if(!_connected)
{
return;
}
const char *pBuffer = data.c_str();
int bytes = data.length() + 1;
int i = 0,j;
while (i < bytes)
{
j = send(_connectSocket, pBuffer+i, bytes-i, 0);
if(j == SOCKET_ERROR)
{
_connected = false;
if(!_bNetworkErrNotified)
{
_bNetworkErrNotified=true;
emit networkErrorSignal(j);
}
LOG_ERROR( "Unable to send Network Packet" );
break;
}
i += j;
}
}
Boost.Asio's TCP capabilities are pretty well used, so I would be hesitant to suspect it is the source of the problem. In most cases of data loss, the problem is the result of application code.
In this case, there is a problem in the receiver code. The sender is delimiting strings with \0. However, the receiver fails to proper handle the delimiter in cases where multiple strings are read in a single read operation, as string::insert() will cause truncation of the char* when it reaches the first delimiter.
For example, the sender writes two strings "Test string\0" and "Another test string\0". In TCPSocket::receiveData(), the receiver reads "Test string\0Another test string\0" into buf. dataString is then populated with dataString.insert(0, buf). This particular overload will copy up to the delimiter, so dataString will contain "Test string". To resolve this, consider using the string::insert() overload that takes the number of characters to insert: dataString.insert(0, buf, len).
I have not used the poll function before. What I did is create a worker thread that is dedicated to processing ASIO handlers with the run function, which blocks. The Boost documentation says that each thread that is to be made available to process async event handlers must first call the io_service:run or io_service:poll method. I'm not sure what else you are doing with the thread that calls poll.
So, I would suggest dedicating at least one worker thread for the async ASIO event handlers and use run instead of poll. If you want that worker thread to continue to process all async messages without returning and exiting, then add a work object to the io_service object. See this link for an example.
I want to establish tcp connection between iphone and PC. On PC QTspServer is running and working (was tested with other client application).
Here is the connection method i'm using on iphone:
- (IBAction)connectToServer:(id)sender {
CFReadStreamRef read = NULL;
CFWriteStreamRef write = NULL;
NSString *host = #"192.168.1.169";
CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (CFStringRef)host, 1000, &read, &write);
CFWriteStreamOpen(write);
int k = 0;
}
The server on PC is not reacting. Any help is appropriate
By the way: Server is nothing more then a QTcpServer with replemented incomingConnection method. Here is the main function on server side:
int main(int argc, char **argv)
{
QApplication app(argc, argv);
AbstractServer server;
server.listen(QHostAddress::Any, 1000);
QLabel label("Hello server");
label.setFixedSize(400, 400);
label.show();
return app.exec();
}
The connection is established after something was sent to the server
Check that write isn't NULL after the call to CFStreamCreatePairWithSocketToHost. If it is, the socket connection is failing.
-(IBAction)connectToServer:(id)sender {
CFWriteStreamRef write = NULL;
NSString *host = #"192.168.1.169";
int port = 1000;
CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, (CFStringRef)host, port, NULL, &write);
if (!write) {
// connection failed.
NSLog(#"Connection to %#:%d failed.",host,port);
} else {
CFWriteStreamOpen(write);
// keep a reference to the output stream for later use.
self.output = (NSOutputStream*)write;
// the function that made the output stream has "Create" in its name, so
// this method owns the write stream & should release it.
CFRelease(write);
}
}
Note that I store the output stream in a property of self. In your sample code, the stream isn't saved anywhere. You don't release it, so it still exists when the method exits, but there's no way of accessing it. If the sample -connectToServer: is representative, that error will prevent your object from sending anything to the server.