Server delay on system command in C - c

Question

I have two programs, one acting as a server and one acting as a client. They are supposed to act like you are connecting to remote system using ssh. The client sends a command and the server executes the command and prints the output to the server. Although my code does exactly that, there is a delay on the output after the first command. For example if the client sents date, the server will return the date. If the client sends date again it will print message was received but not the output. On the third input from client, the second date will be executed and print on the client Here is the message:date and so on. Any ideas would be really apreciated.
Server:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <fcntl.h>
#define MAX_PINS 1
void error(const char *msg){
perror(msg);
exit(1);
}
void exec_comm(int sock,int nerror,char buff[]){
dup2(sock,1);
dup2(nerror,2);
if(system(buff)==-1){
printf("command not found\n");
}
}
int main(int argc, char *argv[]){
int sockfd, newsockfd, portno, pid;
socklen_t clilen;
char buffer[256];
char* comm[20],*cbuff;
struct sockaddr_in serv_addr, cli_addr;
int n,i,done=0,correct=0;
char str[INET_ADDRSTRLEN];
char* args,*pins[MAX_PINS]={"1234"},pin[10];
FILE* fd;
int nerror;
if (argc < 2){
fprintf(stderr, "No port provided\n");
exit(1);
}
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
memset((char *) &serv_addr, 0, 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");
if (inet_ntop(AF_INET, &cli_addr.sin_addr, str, INET_ADDRSTRLEN) == NULL) {
fprintf(stderr, "Could not convert byte to address\n");
exit(1);
}
fprintf(stdout, "The client address is :%s\n", str);
while(1){
bzero(buffer, 256);
n = read(newsockfd, buffer, 255);
sscanf(buffer,"%s\n",buffer);
printf("The message that was read was:\t%s\n",buffer);
if (n < 0) error("ERROR reading from socket");
fprintf(fd,"%s\n",buffer);
if(strcmp(buffer,"exit\n")==0||strcmp(buffer,"exit")==0){
printf("Exiting...\n");
done=1;
break;
}
exec_comm(newsockfd,nerror,buffer);
printf("Here is the message: %s\n", buffer);
n = write(newsockfd, "message received", 17);
if (n < 0) error("ERROR writing to socket");
}
fclose(fd);
close(newsockfd);
close(sockfd);
return 0;
}
Client:
#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");
n = write(sockfd, stdin, sizeof(int));
if (n < 0)
error("ERROR writing to socket");
do{
printf("Please enter the message: ");
bzero(buffer, 256);
fgets(buffer, 255, stdin);
if(strcmp(buffer,"exit\n")==0||strcmp(buffer,"exit")==0){
printf("Exiting...\n");
n = write(sockfd, buffer, strlen(buffer));
if (n < 0)
error("ERROR writing to socket");
close(sockfd);
break;
}
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);
}while(1);
return 0;
}

Answer 1

n = write(sockfd, buffer, strlen(buffer));
That's your problem right here. Calls to write do not result in individual distinguishable messages, one message per call. They result in a single homogenous stream (that's the "stream" in SOCK_STREAM) of bytes with no delimiters.
You have newlines that separate commands, which is nice and all, but read has no idea about newlines. It will just wait until the buffer is full, or enough time has passed, or whatever. You have no control over it.
You basically have 2 ways to fix this.
Read character by character (pass the length of 1) and stop as soon as you see a newline. Accumulate the characters in a buffer, then execute it.
Send the length of each message before the message itself, in a fixed-length record, so that the server can safely read the length and then use it to read the message itself.