network programming

hello every body

i am recently working over a mobile robot project. here i need to send an instruction to arduino microcontroller over network. for this i had choosed client server architecture. i modified the server program to read the buffer to device file descriptor ("/dev/ttyACM0" in this case.

i was able to compile the programs and run them. when i send a request from client to server . the server simply closes with out receiving the message.
The led is blinking in this case once

my working environment is
Linux 10.10

in order to execute the client

$ ./client

for serial_server

$ ./serial_server

below is the code of the programs
client code
Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h> 
 
void error(const char *msg)
{
    perror(msg);
    exit(0);
}
 
int main(int argc, char *argv[])
{
    int sockfd, portno, n;
    struct sockaddr_in serv_addr;
    struct hostent *server;
 
    char buffer[256];
    if (argc < 3) {
       fprintf(stderr,"usage %s hostname port\n", argv[0]);
       exit(0);
    }
    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");
    printf("Please enter the message: ");
    bzero(buffer,256);
    fgets(buffer,255,stdin);
    n = write(sockfd,buffer,strlen(buffer));
    if (n < 0) 
         error("ERROR writing to socket");
    bzero(buffer,256);
    n = read(sockfd,buffer,255);
    if (n < 0) 
         error("ERROR reading from socket");
    printf("%s\n",buffer);
    close(sockfd);
    return 0;
}

serial_server code

/* A simple server in the internet domain using TCP
   The port number is passed as an argument */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include<errno.h>
#include<sys/ioctl.h>
#include<termios.h>
#include<fcntl.h>
#include<getopt.h>
void error(const char *msg)
{
    perror(msg);
    exit(1);
}
 
int main(int argc, char *argv[])
{
     int sockfd, newsockfd, portno;
     socklen_t clilen;
     char buffer[256];
     struct sockaddr_in serv_addr, cli_addr;
     int n,k;
// serial data
     int fd;
     int baudrate = B9600;
     int rc;
      
 
     if (argc < 2) {
         fprintf(stderr,"ERROR, no port provided\n");
         exit(1);
     }
     sockfd = socket(AF_INET, SOCK_STREAM, 0);
     if (sockfd < 0)
        error("ERROR 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 = INADDR_ANY;
     serv_addr.sin_port = htons(portno);
     if (bind(sockfd, (struct sockaddr *) &serv_addr,
              sizeof(serv_addr)) < 0)
              error("ERROR on binding");
     listen(sockfd,5);
     clilen = sizeof(cli_addr);
     newsockfd = accept(sockfd,
                 (struct sockaddr *) &cli_addr,
                 &clilen);
     if (newsockfd < 0)
          error("ERROR on accept");
     bzero(buffer,256);
 // serial filedescriptor initializing ;
      fd = open("/dev/ttyACM0", O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd == -1)  {
        perror("init_serialport: Unable to open port ");
        return -1;
 
     n = read(newsockfd,buffer,255);
     if (n < 0) error("ERROR reading from socket");
  
    k= write(fd,buffer,255);
    if(k<0)error("Unable to open the arduino ");
 
     
      
     printf("Here is the message: %s\n",buffer);
     n = write(newsockfd,"I got your message",18);
     if (n < 0) error("ERROR writing to socket");
     k= write(fd,buffer,255);
    if(k<0)error("Unable to send to the arduino ");
     close(newsockfd);
     close(sockfd);
     return 0;
}}

sketch of arduino

void setup()   {                
 Serial.begin(9600);
 pinMode(9, OUTPUT);
 digitalWrite(9,HIGH);
 delay(500);
 digitalWrite(9,LOW);
  pinMode(11,OUTPUT);
  digitalWrite(11,HIGH);
 delay(500);
 digitalWrite(11,LOW);
 
}

 int incomingByte = 0;
void loop()                    
{
   // send data only when you receive data:
	if (Serial.available() > 0) {
                char text = Serial.read();
                Serial.println(text);
                switch(text)
                {
                  case 'a':
                   digitalWrite(9,HIGH);
                   delay(500);
                   digitalWrite(9,LOW);
                  break; 
                   case 'b':
                   digitalWrite(11,HIGH);
                   delay(500);
                   digitalWrite(11,LOW);
                  break; 
                }
                
                
	}

}

Opening a serial port resets the Arduino. In addition to the normal start up time, you are farting around in setup blinking LEDs for a full second.

During that time, your server has send a response, expected a reply, gotten nothing, and quit.

The description of your network is vague. If you are sending info from your pc to the arduino, and the application on the pc opens/closes the serial port each time data is sent, you will need to defeat the arduino auto reset by using a 100 ohm resistor between the arduino +5v and reset pins, or use a large capacitor between the reset pin and ground.