Background:
I have the below C++ code that listens UDP packets on port26009 then outputs the received packets
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
udpSocket.bind(26009); //the port that GUI listens (26009)
connect(&udpSocket, SIGNAL(readyRead()), this, SLOT(readyRead()));
}
void MainWindow::readyRead(){
QByteArray datagram;
do {
datagram.resize(udpSocket.pendingDatagramSize());
udpSocket.readDatagram(datagram.data(), datagram.size());
} while (udpSocket.hasPendingDatagrams());
qDebug() << "Message: " << datagram;
}
On the client side, here is a C code to unicast 20 udp packets: hi0, hi1, ... hi19:
int main(void){
int i;
char msg[5] = {'\0'};
for(i=0; i<20; i++){
snprintf(msg, 4, "hi%d", i);
send_unicast("192.168.5.1", msg, 26009);
memset(msg, 0, sizeof msg);
}
return 0;
}
void send_unicast(char IPaddr[16], char* message, uint16_t destPort){
struct sockaddr_in si_other;
int s, slen = sizeof(si_other);
if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1){
fprintf(stderr, "socket() failed - line817\n");
exit(1);
}
memset((char *) &si_other, 0, sizeof(si_other));
si_other.sin_family = AF_INET;
si_other.sin_port = htons(destPort);
if (inet_aton(IPaddr, &si_other.sin_addr) == 0) {
fprintf(stderr, "inet_aton() failed - line 825\n");
exit(1);
}
if (sendto(s, message, 512, 0, (struct sockaddr *) &si_other, slen) == -1){
fprintf(stderr, "sendto() failed - line830\n");
exit(1);
}
close(s);
}
I run C++ (Server) and C (client) codes on different Linux devices.
Problem:
C code works fine and generates the packets. I can see on Wireshark that the packets are received on receiving end (C++ ).
However, the above C++ code cannot receive (or process) the packets correctly, it is somehow too fast for the code to handle and I see only couple output, e.g.
hi5
hi14
If the frequency of the transmission is significantly slowed down on the C code (adding sleep(1)) then the C++ code outputs the packets fine.
Question:
I use the received UDP packets to update some information on the GUI (Qt). I guess that the slot causes the slowness, and the code would handle the traffic if I used pthread to listen the packets but then how the thread needs to notify the main class so that the GUI can update accordingly?
All in all, how do you recommend to modify C++ code, so that it can handle the fast data traffic and notify GUI to update?
In your readyRead function of MainWindow, I expect this is going to be a problem: -
QByteArray datagram;
do {
qint64 dSize = udpSocket.pendingDatagramSize();
datagram.resize(dSize);
udpSocket.readDatagram(datagram.data(), dSize);
} while (udpSocket.hasPendingDatagrams());
If the first packet of data is, let's say 8 bytes long, you set the QByteArray to 8 bytes and read the data.
While reading 8 bytes, if 6 bytes are received, the second time around that loop you're going to to call resize on the byte array, but this time it's going to reduce it from 8 bytes to 6 and read 6 bytes, throwing away the data you previously read in.
Rather than resizing the QByteArray, I suggest you append the data to it: -
QByteArray datagram;
do
{ datagram.append(udpSocket.pendingDatagramSize());
udpSocket.readDatagram(datagram.data(), datagram.size());
}while (udpSocket.hasPendingDatagrams());
Related
I need some help with a socket program with multiple clients and one server. To simplify, I create
3 socket clients
1 socket server
For each client, it opens a new connection for sending a new message and closes the connection after a response is received.
For the server, it does not need to deal with connections concurrently, it can deal with the message one by one
here is my code (runnable), compile it with /usr/bin/g++ mycode.cpp -g -lpthread -lrt -Wall -o mycode
#include <iostream>
#include <arpa/inet.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>
#include <unordered_map>
#include <thread>
using namespace std;
void Warning(string msg) { std::cout<< msg << std::endl; }
namespace mySocket {
class Memcached {
public:
// start a server
static void controller(int port=7111) { std::thread (server, port).detach(); }
// open a new connection to send a message:
// 1. open a connection
// 2. send the message
// 3. read the message
// 4. close the connection
std::string sendMessage(string msg, string host, int port=7111) {
int sock = 0, client_fd;
struct sockaddr_in serv_addr;
char buffer[1024] = { 0 };
if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
std::cout << "Socket creation error, msg: " << msg << ", host: " << host << ", port: " << port << std::endl;
exit(1);
}
serv_addr.sin_family = AF_INET;
serv_addr.sin_port = htons(port);
if (inet_pton(AF_INET, host.c_str(), &serv_addr.sin_addr) <= 0) {
std::cout << "\nInvalid address/ Address not supported, kmsgey: " << msg << ", host: " << host << ", port: " << port << std::endl;
exit(1);
}
while ((client_fd = connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr))) < 0) { sleep(10*1000); }
std::cout << "client sends a message:"<<msg<<", msg size:"<<msg.size()<<std::endl;
send(sock, msg.c_str(), msg.size(), 0);
read(sock, buffer, 1024);
close(client_fd);
return std::string(buffer, strlen(buffer));
}
private:
// start a server
// 1. open a file descriptor
// 2. listen the fd with queue size 10
// 3. accept one connection at a time
// 4. deal with message in the connection
// 5. accept the next connection
// 6. repeat step 3
static void server(int port) {
int server_fd, new_socket;
struct sockaddr_in address;
int opt = 1;
int addrlen = sizeof(address);
char buffer[1024] = { 0 };
unordered_map<string,string> data;
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0) {
Warning("socket failed"); exit(1);
}
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
Warning("setsockopt failed"); exit(1);
}
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(port);
if (bind(server_fd, (struct sockaddr*)&address, sizeof(address)) < 0) {
Warning("bind failed"); exit(1);
}
// the queue size is 10 > 3
if (listen(server_fd, 10) < 0) {
Warning("listen failed"); exit(1);
}
while(1)
{
if ((new_socket = accept(server_fd, (struct sockaddr*)&address, (socklen_t*)&addrlen)) < 0) {
std::cout << "accept failed"; exit(1);
}
memset(&buffer, 0, sizeof(buffer)); //clear the buffer
read(new_socket, buffer, 1024);
std::string msg = std::string(buffer, strlen(buffer));
if (msg.size()==0) {
std::cout<<"I can't believe it"<<std::endl;
}
std::cout<<"received msg from the client:"<<msg<<",msg size:"<<msg.size()<<std::endl;
std::string results="response from the server:["+msg+"]";
send(new_socket, results.c_str(), results.length(), 0);
//usleep(10*1000);
}
if (close(new_socket)<0){
std::cout <<"close error"<<std::endl;
}
shutdown(server_fd, SHUT_RDWR);
}
} ;
}
void operation(int client_id) {
auto obj = new mySocket::Memcached();
for (int i=0; i<10;i++){
int id=client_id*100+i;
std::cout<<obj->sendMessage(std::to_string(id), "127.0.0.1", 7111)<<std::endl<<std::endl;
}
}
int main(int argc, char const* argv[]) {
// start a socket server
mySocket::Memcached::controller();
// start 3 socket clients
std::thread t1(operation, 1);
std::thread t2(operation, 2);
std::thread t3(operation, 3);
t1.join();
t2.join();
t3.join();
}
In the code above, the client always sends a message with a length of 3. However, the server can receive messages with a length of 0 which causes further errors.
I'm struggling with this for several days and can't figure out why it happens. I noticed
if I add a short sleep inside the server while loop, the problem is solved. (uncomment usleep(10*1000); in the code).
or if I only use one client, the problem is also solved.
Any thought helps.
You are using TCP sockets. You may want to use some application-level protocol like HTTP, websockets instead, that will be much easier, because you will not need to worry about how message is sent/received and in which sequence. If you have to stick with TCP sockets, you firstly have to understand few things:
There's two types of TCP sockets you can use: non-blocking and blocking IO (input/output). You are currently using blocking IO. That IO will be sometimes blocked and you won't be able to do anything with sockets. In blocking IO, it can be work arounded by using one socket per thread on server-side. It's not efficient, but it's relatively easy comparing to Non-blocking IO. Non-blocking IO doesn't wait for anything. While in blocking IO you wait for data, in non-blocking IO you create something like events, callbacks, that are used when there's some data. You probably have to read about these types of IO.
In your server function, would be better, if you listen for incoming connections in one thread, and when there's incoming connection, move this connection into another thread and function, that will handle other things. This may solve your problem related to multiple clients at the same time.
In function operation, instead of allocating memory using raw pointer, use static allocation or smart pointers to avoid memory leaks. If you don't want to, then at least, do delete obj; in the end of function.
And the last one thing. You can use some TCP socket wrapper like sockpp to make things a lot easier. You will have anything TCP sockets have, but in C++ style and a little bit easier to understand and maintain. If you can't use application-level protocol, I strongly suggest you to use some wrapper at least.
Update
As was stated by commenters, there are more things you need to know:
TCP sockets are streams. This means that if you send your message with length of 1024 bytes, it can be divided into several TCP data packets and you can't know if it will be divided or not, how much packets other side will receive etc. You have to read in a while loop using recv() and wait for data. There's some tricks which can help you to properly receive data:
You can send length of your message first, so other side will know how much bytes it needs to receive.
You can place some terminating symbol or sequence of terminating symbols in the end of your message and read until these will be received. This can be a little risky, because there's chance that you would not receive these symbols at all and will be reading next.
You have to join client threads only when you know, that server is already started and listening for incoming connections. You can use some variable as a flag for these purposes, but make note, that you have to pay a lot of attention, when reading/writing variable from two or more different threads. For these purposes, you can use mutexes, which are some mechanism that will allow you safely access one variable from several threads.
I am making a 3d application that works with the data of the accelerometer and gyroscope of the mobile. The problem is that the mobile sends data faster than the computer reads. The application increasingly makes the movements of the mobile with more delay as time passes. For example, at the beginning 2~3s is faithful to what the mobile does in reality, but over 10s it is making the movements that I did 6 seconds before.
I understand that it is reading data from the beginning buffer while the front of the most current data grows and never reaches it. I think the problem is how I read the data that comes to me.
Here is an example code that is implemented in the application. What could I do?
#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <string.h>
#include <fcntl.h>
#include <algorithm>
#define PORT 8080
int main(int argc, char const *argv[])
{
int server_fd, new_socket, valread;
struct sockaddr_in address;
int opt = 1;
int addrlen = sizeof(address);
char buffer[1024] = {0};
const char *ACK = "ACKDAT\n";
std::string data;
socklen_t len;
char *error;
if ((server_fd = socket(AF_INET, SOCK_STREAM, 0)) == 0)
{
perror("socket failed");
exit(EXIT_FAILURE);
}
if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,&opt, sizeof(opt)))
{
perror("setsockopt");
exit(EXIT_FAILURE);
}
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons( PORT );
if (bind(server_fd, (struct sockaddr *)&address, sizeof(address))<0)
{
perror("bind failed");
exit(EXIT_FAILURE);
}
if (listen(server_fd, 3) < 0)
{
perror("listen");
exit(EXIT_FAILURE);
}
if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen))<0)
{
perror("accept");
exit(EXIT_FAILURE);
}
fcntl(new_socket, F_SETFL, O_NONBLOCK);
while(true){
valread = read( new_socket , buffer, 1024);
for(int i = 0;i < 1024 ; i++){
if(buffer[i]!=0){
data = data + buffer[i];
}
buffer[i]=0;
}
if(!data.empty()){
//remove /n from data
data.erase(std::remove(data.begin(), data.end(), '\n'), data.end());
std::cout<<"#"<<data<<"#"<<std::endl;
send(new_socket , ACK , strlen(ACK) , 0 );
}
data.clear();
}
return 0;
}
While Sam Varshavchik's suggestion of using a thread is good, there's another option.
You already set your socket to non-blocking with fcntl(new_socket, F_SETFL, O_NONBLOCK);. So, at each loop you should read everything there is to read and send everything there is to send. If you don't tie one-to-one the reading and writing, both sides will be able to catch up.
The main hint that you need to fix this is that you don't use the read return value, valread. Your code should look like:
while(true){ // main loop
...
valread = read( new_socket , buffer, 1024);
while(valread > 0)
{
// deal with the read values.
// deal with receiving more than one packet per iteration
}
// send code done a single time per loop.
There still plenty of architecture you need to have a clean resilient main loop that sends and receives, but I hope that points you in a useful direction.
You can have all reading from the socket done in a separate std::thread, that does nothing but read from the socket and save the data in your program's internal buffer. Your existing program reads from the internal buffer, rather than a socket, whenever it is capable of doing so.
If the internal buffer is full you'll have to figure out what to do about it, probably discard unwanted data. Perhaps stash a copy of the most recent received record, in a safe place, and put it into the buffer when things get unclogged. The dedicated execution thread will likely need to do some minimal processing, to parse the raw data from the socket into some meaningful, logical form. It's unlikely that you can simply throw away random parts of the raw data stream from the socket. It will need to be logically parsed, in some form or fashion that's particular to your application, so this can be done in a meaningful way.
You will need to implement your application's buffer in a thread-safe manner, so that it can be simultaneously accessed by multiple execution threads. If you're not familiar with multi-threaded programming in C++, you will find more information in your C++ textbook, on this topic.
I'm trying to develop a streaming system sending multiple images to a receiving socket, which displays them. However, for some reason I can't understand, my code gets blocked at the send function after sending about 3 images. This is a snippet of my code so far:
portno = atoi(argv[2]);
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr,"ERROR, no such host\n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr));
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
if (connect(sockfd,(struct sockaddr *) &serv_addr,sizeof(serv_addr)) < 0)
error("ERROR connecting");
bzero(buffer,256);
for(int i=10;i<51;i++){
std::stringstream sstm;
sstm << filename << i << ext;
result = sstm.str();
cout << result << endl;
Mat image = imread(result, CV_LOAD_IMAGE_COLOR);
image = (image.reshape(0,1));
int imgSize = image.total()*image.elemSize();
n = send(sockfd, image.data, imgSize, 0);
}
Tried to debug it, and, as I said, it gets blocket at the last line, the send function. I wonder if there's a limit on how much information can you transmit through a socket. If I move the for sentence back before the socket creation, it works like a charm, but i'm not going to create a bizillion sockets. Any help?
The send() call will block if the TCP window size goes to zero. This is almost always a result of the other side of the connection not consuming the data from a recv() call.
It's also entirely possible that imgSize is extremely huge and it just simply takes that long for the receiver to consume the stream.
You didn't share any code from the receiver side, so it's difficult to say.
I would suggest more debug spew (print statements) showing the value of imgSize and the return value of the send call. Ditto for the recv side.
Do note - that just because you sent imgSize bytes in one send call, the remote receiver may not receiver all those bytes within a single call to recv().
I've been trying to send a packet from a client to a server via sockets. With the help of some of the tips I have made quite bit of progress in my code. However, the server only receives eight bytes from the client and prints them on the console whereas at my client side, It seems that it has sent everything.
Now I am not sure whether the problem is at the sending side or the receiving side. My hunch is that something is wrong at my client side. Could someone please help in verifying my assumption?
Client code:
int main(int argc, char *argv[])
{
int sockfd, portno, n;
struct sockaddr_in serv_addr;
struct hostent *server;
data_struct client_data;
struct packet
{
long int srcID;
long int destID;
int pver;
int profiles;
int length;
long int data;
};
if (argc < 3) {
fprintf(stderr,"usage: %s hostname port\n", argv[0]);
exit(0);
}
portno = atoi(argv[2]); //Convert ASCII to integer
sockfd = socket(AF_INET, SOCK_STREAM, 0); // socket file descriptor
if (sockfd < 0)
error("ERROR DETECTED !!! Problem in opening socket\n");
server = gethostbyname(argv[1]);
if (server == NULL) {
fprintf(stderr,"ERROR DETECTED !!!, no such server found \n");
exit(0);
}
bzero((char *) &serv_addr, sizeof(serv_addr)); //clear the memory for server address
serv_addr.sin_family = AF_INET;
bcopy((char *)server->h_addr,
(char *)&serv_addr.sin_addr.s_addr,
server->h_length);
serv_addr.sin_port = htons(portno);
printf("Client 1 trying to connect with server host %s on port %d\n", argv[1], portno);
if (connect(sockfd,(struct sockaddr *)&serv_addr,sizeof(serv_addr)) < 0)
error("ERROR in connection");
printf("SUCCESS !!! Connection established \n");
char buffer[256];
struct packet *pkt = (struct packet *) buffer;
char *payload = buffer + sizeof(struct packet);
long double packet_size;
printf("Started Creating packet\n");
pkt->srcID = 01;
pkt->destID = 02;
pkt->pver = 03;
pkt->profiles = 01;
pkt->length = 16;
pkt->data = 1; 2; 3; 4; 5; 6; 7; 8;
{
if (send(sockfd,pkt,sizeof(packet_size),0) <0)
printf ("error\n");
else
printf ("packet send done");
}
return 0;
}
Server code:
int main(int argc, char *argv[])
{
int sockfd, newsockfd, portno, clilen;
struct sockaddr_in serv_addr, cli_addr;
int n;
char wish;
long int SrcID;
long int DestID;
int Pver;
int Profiles;
long int Data;
int Length;
char bytes_to_receive;
int received_bytes;
struct packet
{
long int srcID;
long int destID;
int pver;
int profiles;
int length;
long int data;
};
if (argc < 2) {
fprintf(stderr,"usage: %s port_number1",argv[0]);
exit(1);
}
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR DETECTED !!! Problem in opening socket");
bzero((char *) &serv_addr, sizeof(serv_addr));
portno = atoi(argv[1]);
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
serv_addr.sin_port = htons(portno);
if (bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0)
error("ERROR DETECTED !!! There was a problem in binding");
listen(sockfd, 10);
clilen = sizeof(cli_addr);
printf("Server listening on port number %d...\n", serv_addr.sin_port);
newsockfd = accept(sockfd,(struct sockaddr *) &cli_addr, &clilen);
if (newsockfd < 0)
error("ERROR DETECTED !!! the connection request was not accepted");
char buffer[256];
struct packet *pkt = (struct packet *) buffer;
char *payload = buffer + sizeof(struct packet);
long double packet_size;
bytes_to_receive = sizeof(packet_size);
received_bytes = 0;
int rc =0;
while ((rc = recv(newsockfd,pkt,sizeof(packet_size),0)) > 0)
{
received_bytes+=rc;
SrcID = pkt->srcID;
DestID = pkt->destID;
Pver = pkt->pver ;
Profiles = pkt->profiles;
Length = pkt->length;
Data = pkt->data;
printf("Data Received from Client_1 are :\n");
printf("Source ID: %ld\n", SrcID);
printf("Destination ID: %ld\n", DestID);
printf("profile Version: %d\n", Pver);
printf("No of Profiles: %d\n", Profiles);
printf("Length: %d\n", Length);
printf("data : %ld\n", Data);
}
if (rc == 0)
{
printf("Connection closed by Server\n");
printf("Bytes received: %d\n",received_bytes);
}
if (rc == -1)
{
perror("recv");
}
{
if (close(newsockfd) == -1) {
error("Error closing connection with client 1");
}
printf("Connection with client 1 has been closed\n");
}
return 0;
}
The output that I see on the client's console is:
Client Side: Client 1 trying to connect with server host 130.191.166.230 on port 1234
SUCCESS !!! Connection established
Started Creating packet
packet send done
and on the server's console I see:
Server Side: Data Received from Client_1 are :
Source ID: 1
Destination ID: 2
profile Version: 0
No of Profiles: 1074462536
Length: 0
data : 0
Connection closed by Server
Bytes received: 8
Connection with client 1 has been closed
First of all
recv(newsockfd,pkt,sizeof(packet_size),0)) /* What is packet_size ? */
recv(newsockfd,pkt,sizeof(struct packet),0)) /* You probably mean this. */
That might solve your problems, but there are a few issues with the way you are using TCP sockets.
But at my client side, it prints that it has sent everything
Where ? I don't see you actually checking the number of bytes sent. send(2) can return after sending less that you asked it to.
It shows me that only 8 bytes were sent by Client and prints them out.
TCP is a stream-oriented protocol. You send bytes and they arrive, in the same order. So when you recv(2) something, you might get less (or more than you wrote). So, the following can be true:
client:
send 100 bytes
send 400 bytes
server:
recv 50 bytes
recv 150 bytes
recv 250 bytes
recv 50 bytes
The number of send and recv calls need not be identical when using TCP.
When you call send the function returns the number of bytes actually sent and this number can be less than the number of bytes you wanted to send. So every time you want to send something there must be a loop like the following
bool sendBuffer(SOCKET s, unsigned char *buf, int size)
{
while (size > 0)
{
int sz = send(s, buf, size,0);
if (sz < 0) return false; // Failure
size -= sz; // Decrement number of bytes to send
buf += sz; // Advance read pointer
}
return true; // All buffer has been sent
}
and a similar loop must be done when receiving (in other words recv can return less bytes than what you are asking for).
If you don't make these loops the risk is that everything apparently will work anyway (until the size of an ethernet packet) when you work on your local machine or even over a LAN, but things will not work when working across the internet.
Note also that as other answers pointed out you asked to send sizeof(packet_size) i.e. the number of bytes required to store that variable, not the size of the structure.
There is an informal rule that nobody is allowed to write any software that uses TCP until they memorize this sentence and can fully explain what it means: "TCP is a byte-stream protocol that does not preserve application message boundaries."
What that means is that TCP only ensures that you get out the same bytes you put in and in the same order. It does not "glue" the bytes together in any way.
Before you write any code that uses TCP, you should either use a protocol that is already designed (such as IMAP or HTTP) or design one yourself. If you design one yourself, you should write out a protocol specification. It should specifically define what a protocol-level message will consist of at the byte level. It should specifically state how the receiver finds the ends of messages, and so on.
This may seem a little silly for simple applications, but trust me, it will pay off massively. Otherwise, it's almost impossible to figure out why things aren't work because if the server and client don't quite get along, there's no arbiter to say what's right.
I don't specialise in socket programming but there are a few things I've noticed. As far as I'm aware, I don't think you can send structs over sockets that easily. You may wish to consider a different method.
NB, when using send/recv you're also determing the sizeof packet_size, and not the sizeof the struct.
Googling brought up this about sending structs over sockets: http://ubuntuforums.org/showthread.php?t=613906
I am trying to use non-blocking TCP sockets. The problem is that they are still blocking. The code is below -
server code -
struct sockaddr name;
char buf[80];
void set_nonblock(int socket) {
int flags;
flags = fcntl(socket,F_GETFL,0);
assert(flags != -1);
fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}
int main(int agrc, char** argv) {
int sock, new_sd, adrlen; //sock is this socket, new_sd is connection socket
name.sa_family = AF_UNIX;
strcpy(name.sa_data, "127.0.0.1");
adrlen = strlen(name.sa_data) + sizeof(name.sa_family);
//make socket
sock = socket(AF_UNIX, SOCK_STREAM, 0);
if (sock < 0) {
printf("\nBind error %m", errno);
exit(1);
}
//unlink and bind
unlink("127.0.0.1");
if(bind (sock, &name, adrlen) < 0)
printf("\nBind error %m", errno);
//listen
if(listen(sock, 5) < 0)
printf("\nListen error %m", errno);
//accept
new_sd = accept(sock, &name, (socklen_t*)&adrlen);
if( new_sd < 0) {
cout<<"\nserver accept failure "<<errno;
exit(1);
}
//set nonblock
set_nonblock(new_sd);
char* in = new char[80];
std::string out = "Got it";
int numSent;
int numRead;
while( !(in[0] == 'q' && in[1] == 'u' && in[2] == 'i' && in[3] == 't') ) {
//clear in buffer
for(int i=0;i<80;i++)
in[i] = ' ';
cin>>out;
cin.get();
//if we typed something, send it
if(strlen(out.c_str()) > 0) {
numSent = send(new_sd, out.c_str(), strlen(out.c_str()), 0);
cout<<"\n"<<numSent<<" bytes sent";
}
numRead = recv(new_sd, in, 80, 0);
if(numRead > 0)
cout<<"\nData read from client - "<<in;
} //end while
cout<<"\nExiting normally\n";
return 0;
}
client code -
struct sockaddr name;
void set_nonblock(int socket) {
int flags;
flags = fcntl(socket,F_GETFL,0);
assert(flags != -1);
fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}
int main(int agrc, char** argv) {
int sock, new_sd, adrlen;
sock = socket(AF_UNIX, SOCK_STREAM, 0);
if (sock < 0) {
printf("\nserver socket failure %m", errno);
exit(1);
}
//stuff for server socket
name.sa_family = AF_UNIX;
strcpy(name.sa_data, "127.0.0.1");
adrlen = strlen(name.sa_data) + sizeof(name.sa_family);
if(connect(sock, &name, adrlen) < 0) {
printf("\nclient connection failure %m", errno);
exit(1);
}
cout<<"\nSuccessful connection\n";
//set nonblock
set_nonblock(sock);
std::string out;
char* in = new char[80];
int numRead;
int numSent;
while(out.compare("quit")) {
//clear in
for(int i=0;i<80;i++)
in[i] = '\0';
numRead = recv(sock, in, 80, 0);
if(numRead > 0)
cout<<"\nData read from server - "<<in;
cout<<"\n";
out.clear();
cin>>out;
cin.get();
//if we typed something, send it
if(strlen(out.c_str())) {
numSent = send(sock, out.c_str(), strlen(out.c_str()), 0);
cout<<"\n"<<numSent<<" bytes sent";
}
} //end while
cout<<"\nExiting normally\n";
return 0;
}
Whenever I run it, the server still waits for me to send something before it will read and output what the client has sent. I want either the server or client to be able to send the message as soon as I type it, and have the other read and output the message at that time. I thought non-blocking sockets was the answer, but maybe I am just doing something wrong?
Also, I was using a file instead of my 127.0.0.1 address as the sockaddr's data. If that is not how it should be properly used, feel free to say so (it worked how it worked previously with a file so I just kept it like that).
Any help is appreciated.
General approach for a TCP server where you want to handle many connections at the same time:
make listening socket non-blocking
add it to select(2) or poll(2) read event set
enter select(2)/poll(2) loop
on wakeup check if it's the listening socket, then
accept(2)
check for failure (the client might've dropped the connection attempt by now)
make newly created client socket non-blocking, add it to the polling event set
else, if it's one of the client sockets
consume input, process it
watch out for EAGAIN error code - it's not really an error, but indication that there's no input now
if read zero bytes - client closed connection, close(2) client socket, remove it from event set
re-init event set (omitting this is a common error with select(2))
repeat the loop
Client side is a little simpler since you only have one socket. Advanced applications like web browsers that handle many connections often do non-blocking connect(2) though.
Whenever I run it, the server still waits for me to send something before it will read and output what the client has sent.
Well, that is how you wrote it. You block on IO from stdin, and then and only then do you send/receive.
cin>>out;
cin.get();
Also, you are using a local socket (AF_UNIX) which creates a special file in your filesystem for interprocess communication - this is a different mechanism than IP, and is definitely not TCP as you indicate in your question. I suppose you could name the file 127.0.0.1, but that really doesn't make sense and implies confusion on your part, because that is an IP loopback address. You'll want to use AF_INET for IP.
For an excellent starter guide on unix networking, I'd recommend http://beej.us/guide/bgnet/
If you want the display of messages received to be independant of your cin statements, either fork() off a seperate process to handle your network IO, or use a separate thread.
You might be interested in select(). In my opinion non-blocking sockets are usually a hack, and proper usage of select() or poll() is generally much better design and more flexible (and more portable). try
man select_tut
for more information.
I think you have to set non-block sooner (ie get the socket then set it non block)
also check that the fcntl to set it actually worked
If you want non-blocking i/o, you want to use select. You can set it with stdin as one of the sockets it is listening on, along with the client sockets (just add file descriptor 1, which is stdin, to the fd_set).
http://beej.us/guide/bgnet/output/html/multipage/advanced.html
I would recommend reading through what beej has to say about select. It looks a little intimidating but is really useful and simple to use if you take a little time to wrap your head around it.