Can't get more than 3 active TCP connections in Mini-OS? - sockets

Question

I'm writing an TCP server in Mini-OS(an operation system in xen), it can connect to multiple TCP clients. I wrote a simple code for handling multiple TCP clients , but there is an issue with the code. The issue is I can't get the server to connect more than three active connections. The 4th or more clients could not connect for unknown reasons. I looked around the forums and tried increasing the number limit for MEMP_NUM_TCP_PCB in opt.h (stubdom\lwip-x86_64\include\lwip\opt.h) and it didn't help either.
I'm running a TCP client on Ubuntu. Based on what I saw, the 4th client did seem connected, but an exception was thrown during the "write" function: "Resolver Error 0 (no error)"
How can I solve this problem?
//server code
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define MYPORT 1234 // the port users will be connecting to
#define BACKLOG 2// how many pending connections queue will hold
#define BUF_SIZE 1024
int fd_A[BACKLOG]; // accepted connection fd
int conn_amount; // current connection amount
void showclient()
{
int i;
printf("-----> client amount: %d\n", conn_amount);
for (i = 0; i < BACKLOG; i++) {
printf("BACKLOG%d ---> fd = %d\n", i, fd_A[i]);
}
printf("\n\n");
}
int main(void)
{
sleep(1);
printf("start server\n");
int sock_fd, new_fd; // listen on sock_fd, new connection on new_fd
struct sockaddr_in server_addr; // server address information
struct sockaddr_in client_addr; // connector's address information
socklen_t sin_size;
int yes = 1;
char buf[BUF_SIZE];
int ret;
int i;
if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
perror("socket");
exit(1);
}
//if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
/*if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
//perror("setsockopt");
//exit(1);
}
if (fcntl(sock_fd, F_SETFL, O_NONBLOCK) == -1) {
printf("Set server socket nonblock failed\n");
exit(1);
}*/
memset(&server_addr, 0, sizeof(server_addr));
server_addr.sin_family = AF_INET; // host byte order
server_addr.sin_port = htons(MYPORT); // short, network byte order
server_addr.sin_addr.s_addr = htonl(INADDR_ANY); // automatically fill with my IP
//memset(server_addr.sin_zero, '0', sizeof(server_addr.sin_zero));
if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
perror("bind");
exit(1);
}
printf("listen...\n");
if (listen(sock_fd, BACKLOG) == -1) {
perror("listen");
exit(1);
}
printf("listen port %d\n", MYPORT);
fd_set fdsr, wfds, efds;
int maxsock;
struct timeval tv;
conn_amount = 0;
sin_size = sizeof(client_addr);
maxsock = sock_fd;
while (1)
{
sleep(1); // it's necessary
// initialize file descriptor set
FD_ZERO(&fdsr);
FD_ZERO(&wfds);
//FD_ZERO(&efds);
FD_SET(sock_fd, &fdsr); // add fd
FD_SET(sock_fd, &wfds); // add fd
//FD_SET(sock_fd, &efds); // add fd
// timeout setting
tv.tv_sec = 30;
tv.tv_usec = 0;
// add active connection to fd set
for (i = 0; i < BACKLOG; i++) {
if (fd_A[i] != 0) {
FD_SET(fd_A[i], &fdsr);
}
}
//printf("before select!!!!!!!!!!!! ret = %d\n", ret);
if ((select(maxsock + 1, &fdsr, &wfds, (fd_set*) 0, (struct timeval*) 0)) < 0) {
perror("select");
break;
}
// check every fd in the set
for (i = 0; i < conn_amount; i++)
{
if (FD_ISSET(fd_A[i], &fdsr)) // check which fd is ready
{
ret = recv(fd_A[i], buf, sizeof(buf), 0);
if (ret <= 0)
{ // client close
printf("ret : %d and client[%d] close\n", ret, i);
close(fd_A[i]);
FD_CLR(fd_A[i], &fdsr); // delete fd
fd_A[i] = 0;
conn_amount--;
}
else
{ // receive data
if (ret < BUF_SIZE)
memset(&buf[ret], '\0', 1); // add NULL('/0')
printf("client[%d] send:%s\n", i, buf);
}
}
}
// check whether a new connection comes
if (FD_ISSET(sock_fd, &fdsr)) // accept new connection
{
new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size);
if (new_fd <= 0)
{
perror("accept");
continue;
}
// add to fd queue
if (conn_amount < BACKLOG)
{
fd_A[conn_amount++] = new_fd;
printf("------> new connection client[%d] %s:%d\n", conn_amount,
inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
if (new_fd > maxsock) // update the maxsock fd for select function
maxsock = new_fd;
}
else
{
printf("max connections arrive, exit\n");
send(new_fd, "bye", 4, 0);
close(new_fd);
break;
}
}
//showclient();
}
// close other connections
for (i = 0; i < BACKLOG; i++)
{
if (fd_A[i] != 0)
{
close(fd_A[i]);
}
}
exit(0);
}
//client code
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <stdio.h>
#include <malloc.h>
#include <netdb.h>
#include <fcntl.h>
#include <unistd.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#define RES_LENGTH 10240
int connect_socket(char * server,int serverPort);
int send_msg(int sockfd,char * sendBuff);
char * recv_msg(int sockfd);
int close_socket(int sockfd);
int main(int argc, char ** argv)
{
int sockfd[1024] = {0};
char sendMsg[30]="zhangchengfei\r\n\r";
char* res;
int port = 1234;
char ip[128] = {0};
strncpy(ip, "10.107.19.62", 128);
if(argc > 2)
{
strncpy(ip, argv[1], 128);
port = atoi(argv[2]);
printf("Input IP: %s, port : %d\n", ip, port);
}
else if(argc > 1)
{
//port = atoi(argv[1]);
//printf("Input port : %d\n", port);
//
int num_client = atoi(argv[1]);
int i = 0;
for (i = 0; i <= num_client; i++) {
printf("start connect %d\n", i + 1);
sockfd[i]=connect_socket(ip, port);
printf("connect %d OK\n", i + 1);
getchar();
}
for (i = 0; i <= num_client; i++) {
send_msg(sockfd[i], sendMsg);
/* res=recv_msg(sockfd); */
printf("client %d send msg = %s\n", i + 1, sendMsg);
//printf(res);
//free(res);
getchar();
}
for (i = 0; i <= num_client; i++) {
close_socket(sockfd[i]);
printf("close socket %d\n", i + 1);
}
}
return 0;
}
int connect_socket(char * server,int serverPort){
int sockfd=0;
struct sockaddr_in addr;
struct hostent * phost;
if((sockfd=socket(AF_INET,SOCK_STREAM,0))<0){
herror("Init socket error!");
return -1;
}
bzero(&addr,sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(serverPort);
addr.sin_addr.s_addr = inet_addr(server);
if(addr.sin_addr.s_addr == INADDR_NONE){
phost = (struct hostent*)gethostbyname(server);
if(phost==NULL){
herror("Init socket s_addr error!");
return -1;
}
addr.sin_addr.s_addr =((struct in_addr*)phost->h_addr)->s_addr;
}
if(connect(sockfd,(struct sockaddr*)&addr, sizeof(addr))<0)
{
perror("Connect server fail!");
return -1;
}
else
return sockfd;
}
int send_msg(int sockfd,char * sendBuff)
{
int sendSize=0;
if((sendSize=send(sockfd,sendBuff,strlen(sendBuff),0))<=0){
herror("Send msg error!");
return -1;
}else
return sendSize;
}
char* recv_msg(int sockfd){
char * response;
int flag=0,recLenth=0;
response=(char *)malloc(RES_LENGTH);
memset(response,0,RES_LENGTH);
for(flag=0;;)
{
printf("======recv data:\n");
if(( recLenth=recv(sockfd,response+flag,RES_LENGTH-flag,0))==-1 )
{
free(response);
printf("Return value : %d\n", recLenth);
perror("Recv msg error : ");
return NULL;
}
else if(recLenth==0)
break;
else
{
printf("%d char recieved data : %s.\n", recLenth, response+flag);
flag+=recLenth;
recLenth=0;
}
}
printf("Return value : %d\n", recLenth);
response[flag]='0';
return response;
}
int close_socket(int sockfd)
{
close(sockfd);
return 0;
}

Answer 1

I have solved this problem caused by a Makefile bug in ./stubdom, after executing make crossclean , I found the .o files still existed in lwip-x86_64 folder. So I add a command find . -name "*.o" | xargs rm -f in Makefile and then anything is OK.
The reason is that lwip configure is given by the macro definition, macro definition have been replaced at the pre-compilation stage, so if I modify the lwip configure and did not delete the .o files, there is no effect. Following is the macro definitions I have modified in opt.h.
MEMP_NUM_TCP_PCB 100
MEMP_NUM_TCP_PCB_LISTEN 100
MEMP_NUM_NETCONN 100
Now the server can break through the connection limitations and more than 3 active TCP connections can be established, but sad that we have encountered another problem, the server side only can receive 61 clients of the connection requests. If exceeding the clients number, server side error will be reported as follows:
ASSERTION FAILED: mbox->reader != mbox->writer at lwip-arch.c:124.
Do_exit called!
base is 0x29fe78 caller is 0x4d49d
base is 0x29fe98 caller is 0x5a05a
base is 0x29fec8 caller is 0x5a153
base is 0x29fef8 caller is 0x634a1
base is 0x29ff28 caller is 0x65074
base is 0x29ff78 caller is 0x5d0dd
base is 0x29ffc8 caller is 0x59822
base is 0x29ffe8 caller is 0x33da
How can I solve the above problem?