I have a server that receives commands from various other local processes.
I chose the most simplest form (endless loop with accept-read), but here the socket-connections remain open and I soon run out of them (running on a virtual host). Then, on a client, socket() fails with the error message "Cannot allocate memory". (However memory is not the problem, it surely is some socket-limitation from the virtual host.)
I also tried to have the whole thing (unlink-socket-bind-accept-listen-read-close) in an endless loop, which also does not solve the problem. One of these commands seems to grab a socket-connection that never gets released. (Only killing and restarting the server process allows the clients to connect again) Using shutdown() before close() also does not help.
The type of the socket is AF_UNIX / SOCK_SEQPACKET.
How can I use a socket without leaking system ressources?
Edit: As requested the endless loop in the server:
while(1)
{
unlink(SOCKET_FILE_PATH);
if((socket_fd = socket(AF_UNIX, SOCK_SEQPACKET, 0)) < 0)
{
perror("socket() failed");
return 1;
}
if(bind(socket_fd, (const struct sockaddr *) &server_address, sizeof(server_address)) < 0)
{
close(socket_fd);
perror("bind() failed");
return 1;
}
listen(socket_fd, 10);
newsockfd = accept(socket_fd, (struct sockaddr *)&cli_addr, &clilen);
if (newsockfd < 0)
{
perror("ERROR on accept");
return 1;
}
bzero(buffer,256);
n = read( newsockfd,buffer,255 );
if (n < 0)
{
perror("ERROR reading from socket");
return 1;
}
printf("buffer: \"%s\"\n",buffer);
shutdown(socket_fd, SHUT_RDWR);
close(socket_fd);
}
Where do you close 'newsockfd'? Also, there is no guarantee that the buffer contains a null-terminated string, so calling printf(%s..) on it will likely segfault or some other UB.
Related
I have a server written in plain-old C accepting TCP connections using kqueue on FreeBSD.
Incoming connections are accepted and added to a simple connection pool to keep track of the file handle.
When data is received (on EVFILT_READ), I call recv() and then I put the payload in a message queue for a different thread to process it.
Receiving and processing data this way works perfect.
When the processing thread is done, it may need to send something back to the client. Since the processing thread has access to the connection pool and can easily get the file handle, I'm simply calling send() from the processing thread.
This works 99% of the time, but every now and then kqueue gives me a EV_EOF flag, and the connection is dropped.
There is a clear correlation between the frequency of the calls to send() and the number of EV_EOF errors, so I have a feeling the EV_EOF due to some race condition between my kqueue thread and the processing thread.
The calls to send() always returns the expected byte count, so I'm not filling up the tx buffer.
So my question; Is it acceptable to call send() from a separate thread as described here? If not, what would be the right way to send data back to the clients asynchronously?
All the examples I find calls send() in the same context as the kqueue loop, but my processing threads may need to send back data at any time - even minutes after the last received data from the client - so obviously I can't block the kqueue loop for that time..
Relevant code snippets:
void *tcp_srvthread(void *arg)
{
[[...Bunch of declarations...]]
tcp_serversocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
...
setsockopt(tcp_serversocket, SOL_SOCKET, SO_REUSEADDR, &i, sizeof(int));
...
err = bind(tcp_serversocket, (const struct sockaddr*)&sa, sizeof(sa));
...
err = listen(tcp_serversocket, 10);
...
kq = kqueue();
EV_SET(&evSet, tcp_serversocket, EVFILT_READ | EV_CLEAR, EV_ADD, 0, 0, NULL);
...
while(!fTerminated) {
timeout.tv_sec = 2; timeout.tv_nsec = 0;
nev = kevent(kq, &evSet, 0, evList, NLIST, &timeout);
for (i=0; i<nev; i++) {
if (evList[i].ident == tcp_serversocket) { // new connection?
socklen = sizeof(addr);
fd = accept(evList[i].ident, &addr, &socklen); // accept it
if(fd > 0) { // accept ok?
uidx = conn_add(fd, (struct sockaddr_in *)&addr); // Add it to connected controllers
if(uidx >= 0) { // add ok?
EV_SET(&evSet, fd, EVFILT_READ | EV_CLEAR, EV_ADD, 0, 0, (void*)(uint64_t)(0x00E20000 | uidx)); // monitor events from it
if (kevent(kq, &evSet, 1, NULL, 0, NULL) == -1) { // monitor ok?
conn_delete(uidx); // ..no, so delete it from my list also
}
} else { // no room on server?
close(fd);
}
}
else Log(0, "ERR: accept fd=%d", fd);
}
else
if (evList[i].flags & EV_EOF) {
[[ ** THIS IS CALLED SOMETIMES AFTER CALLING SEND - WHY?? ** ]]
uidx = (uint32_t)evList[i].udata;
conn_delete( uidx );
}
else
if (evList[i].filter == EVFILT_READ) {
if((nr = recv(evList[i].ident, buf, sizeof(buf)-2, 0)) > 0) {
uidx = (uint32_t)evList[i].udata;
recv_data(uidx, buf, nr); // This will queue the message for the processing thread
}
}
}
else {
// should not get here.
}
}
}
The processing thread looks something like this (obviously there's a lot of data manipulation going on in addition to what's shown) :
void *parsethread(void *arg)
{
int len;
tmsg_Queue mq;
char is_ok;
while(!fTerminated) {
if((len = msgrcv(msgRxQ, &mq, sizeof(tmsg_Queue), 0, 0)) > 0) {
if( process_message(mq) ) {
[[ processing will find the uidx of the client and build the return data ]]
send( ctl[uidx].fd, replydata, replydataLen, 0 );
}
}
}
}
Appreciate any ideas or nudges in the right direction. Thanks.
EV_EOF
If you write to a socket after the peer closed the reading part of it, you will receive a RST, which triggered EVFILT_READ with EV_EOF set.
Async
You should try aio_read and aio_write.
I have an application that sends a GET request using winsock on port 80 using a TCP socket. A few users have reported an issue where no response is received, looking at network logs and seeing the network device is getting the data just the app isn't it was clear that the firewall was blocking it.
Having disabled the firewall it then worked fine but what I don't understand is why it was getting blocked. The connection is created from the users computer, it connects fine and sends (which I assumes automatically opens a port) so how can data be lost on the same connection when received? Should I be providing additional winsock settings? Or is there simply no way around stopping the firewall blocking an already active connection?
Here is a stripped down version of the winsock code
SOCKET sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (sock == INVALID_SOCKET)
return -1;
struct sockaddr_in client;
memset(&client, 0, sizeof(client));
client.sin_family = AF_INET;
client.sin_port = htons(80);
client.sin_addr.s_addr = inet_addr(inet_ntoa(*addr_list[0]));
if (connect(sock, (struct sockaddr *)&client, sizeof(client)) < 0){
closesocket(sock);
return -1;
}
if (send(sock, buffer, buflength, 0) != buflength){
closesocket(sock);
return -1;
}
//get response
response = "";
int resp_leng = BUFFERSIZE;
while (resp_leng == BUFFERSIZE)
{
resp_leng = recv(sock, (char*)&buffer, BUFFERSIZE, 0);
if (resp_leng > 0)
response += std::string(buffer).substr(0, resp_leng);
else
return -1;
}
closesocket(sock);
Your while loop exits if a recv() returns less than BUFFERSIZE. This is wrong -- you must always assume that recv() can return any amount of data from 1 byte up to and including the supplied buffer size.
I've been writing a server and every time I quit it and re-open it, it seems to fail to bind to the socket. I'm connecting 2 clients and then disconnecting them with close() before I shut down the server, I also then quit the clients before opening the server just in case, however it still seems to fail and I have to restart my computer. Here is my code:
listenSocket = device = app = 0;
struct sockaddr_in server_addr;
char buffer[1024];
listenSocket = socket(AF_INET, SOCK_STREAM, 0);
memset(&server_addr, '0', sizeof(server_addr));
memset(buffer, '0', sizeof(buffer));
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
server_addr.sin_port = htons(35565);
//bind the socket
if (bind(listenSocket,(struct sockaddr*)&server_addr, sizeof(server_addr)) == -1) {
NSLog(#"Error binding to socket");
}
if (listen(listenSocket, 5) == -1) {
NSLog(#"Failed to listen");
}
//launch thread for console
[NSThread detachNewThreadSelector:#selector(console) toTarget:self withObject:nil];
NSLog(#"Starting server");
//socket open, ask for clients
while (true) {
int client = -1;
if (!device || !app)
client = accept(listenSocket, (struct sockaddr*)NULL, NULL);
//handshake omitted for length
}
And the code to close the server:
close(listenSocket);
close(device);
close(app);
NSLog(#"Clean");
Is there something I'm doing wrong? Any help would be appreciated. Thanks.
EDIT: Here is my error checking code:
NSLog(#"%s",strerror(errno));
int e = bind(listenSocket,(struct sockaddr*)&server_addr, sizeof(server_addr));
NSLog(#"%s",strerror(errno));
You need to set the SO_REUSEADDR option. Otherwise, once you grab the port in a process, there is a significant timeout before the kernel will let you have it again. Much detail to be found in an existing question; I've voted to close as a duplicate.
I had a similar problem which was caused by another process holding on to the ports. Killing that process solved the problem.
I have multiple threads who have a socket open with a client application each. Each of those threads receive an instruction from a main thread to send commands to the client (commands could be run test, stop test, terminate session, exit....). Those threads are generic, they just have a socket per client and just send a command when the main thread asks it to.
The client could exit or crash, or network could be bad.
I have been trying to see how to figure out that my TCP session has ended per client. Two solutions that I have found that seem appropriate here.
1) Implement my own heartbeat system
2) Use keepAlive using setsockopt.
I have tried 2) as it sounds faster to implement, but I am not sure of one thing: Will SO_KEEPALIVE generate a SIGPIPE when connection is interrupted please? I saw that it should be the case but never received a SIGPIPE.
This is how my code looks:
void setKeepAlive(int sockfd) {
int optval;
optval = 1;
setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &optval, sizeof(optval));
optval = 1;
setsockopt(sockfd, SOL_TCP, TCP_KEEPIDLE, &optval, sizeof(optval));
optval = 1;
setsockopt(sockfd, SOL_TCP, TCP_KEEPCNT, &optval, sizeof(optval));
optval = 1;
setsockopt(sockfd, SOL_TCP, TCP_KEEPINTVL, &optval, sizeof(optval));
}
And my code that accepts connection is as follows:
for (mNumberConnectedClients = 0; mNumberConnectedClients < maxConnections; ++mNumberConnectedClients) {
clientSocket = accept(sockfd, (struct sockaddr *) &client_addr, &clientLength);
// set KeepAlive on socket
setKeepAlive(clientSocket);
pthread_create(&mThread_pool[mNumberConnectedClients], NULL, controlClient, (void*) &clientSocket);
}
signal(SIGPIPE, test);
....
And the test function:
void test(int n) {
printf("Socket broken: %d\n", n);
}
test() never gets triggered. Is it my understanding that is wrong please? I am not sure if SIGPIPE gets generated or not. Thanks a lot.
If a keep-alive fails, the connection will simply be invalidated by the OS, and any subsequent read/write operations on that socket will fail with an appropriate error code. You need to make sure your reading/writing code is handling errors so it can close the socket, if it is not already doing so.
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, ...);