How read() / write() works with FIFO? - Issue in a client/server program

I have a client/server program.

Client does the following in a loop.

• writes string1 on a pipe.
• read a string from another pipe.
• writes string2 on the pipe.

Server does the following in a loop.

• reads the string.
• writes the same data to client on other pipe.

1. For some iterations this works fine, after approx 10 iterations only string2 is seen to be read on both client and server. Why this so? Also, in in client program in while() loop if read() is called after 2nd write() everything works fine.

2. In client, from second iteration read() should return the whole data in pipe because pipe does not have message boundaries. But it just reads only the data written by 1 write() call in server.

Below is my code for reference.

server.c

#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>

int main()
{
 client_to_server;
char *myfifo = "/tmp/client_to_server_fifo";
int server_to_client;
char *myfifo2 = "/tmp/server_to_client_fifo";

char buf[BUFSIZ];

 /* create the FIFO (named pipe) */
 mkfifo(myfifo, 0666);
 mkfifo(myfifo2, 0666);

 /* open, read, and display the message from the FIFO */
 client_to_server = open(myfifo, O_RDONLY);
 server_to_client = open(myfifo2, O_WRONLY);

 printf("Server ON bufsize=%d.\n", BUFSIZ);

 while (1)
 {
   read(client_to_server, buf, BUFSIZ);
  if (strcmp("exit",buf)==0)
  {
     printf("Server OFF.\n");
     break;
  }
  else if (strcmp("",buf)!=0)
  {
     printf("Received: %s\n", buf);
     printf("Sending back...\n");
     write(server_to_client,buf,BUFSIZ);
  }

  /* clean buf from any data */
  memset(buf, 0, sizeof(buf));
 }

 close(client_to_server);
 close(server_to_client);
 unlink(myfifo);
 unlink(myfifo2);
 return 0;
}

client.c

#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include<string.h>

int main()
{
   int client_to_server;
   char *myfifo = "/tmp/client_to_server_fifo";
   int server_to_client;
   char *myfifo2 = "/tmp/server_to_client_fifo";

   char str[BUFSIZ];

  /* write str to the FIFO */
  client_to_server = open(myfifo, O_WRONLY);
  server_to_client = open(myfifo2, O_RDONLY);

  char buf1[30] = "str1";
  char buf2[30] = "str2";

 while(1){

   //write first string
   write(client_to_server, buf1, sizeof(buf1));
   read(server_to_client,str,sizeof(str));
   perror("Read:"); // Very crude error check
   printf("...received from the server: %s\n",str);

   memset(str, '\0', sizeof(str));

  //write second string
  write(client_to_server, buf2, sizeof(buf2));
 }

 close(client_to_server);
 close(server_to_client);
 return 0;
}

Below is the output: Server output: Server ON bufsize=8192. Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str1 Sending back... Received: str2 Sending back... Received: str2 Sending back... Received: str2 Sending back... Received: str2 Sending back... Received: str2 Sending back... Received: str2 Sending back... Received: str2 Sending back... Received: str2

Below is the output from client: ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str1 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2 ...received from the server: str2