Named Pipe client and server, message truncated on server?

Question

I got a server that is always running, it creates a log file that receives via named pipe one argument and stores it on the log.txt file.

Clients sent a message via argument to the named pipe.

cliente side i guess its ok, if i cat /tmp/talk its there the full message, but on the server its only storing the first char. why is that?

And a simplier question, is there a better way to implement the server cycle to check the pipe?

client

int main(int argc, char const *argv[]){

    char *myfifo = "/tmp/talk";     int fd,n;

    fd = open(myfifo,O_WRONLY);

    write(fd,argv[1],strlen(argv[1])+1);    printf("Sent to server: %s \n",argv[1]);

    close(fd);

}

server

int main(int argc, char const *argv[]){

    char *myfifo = "/tmp/talk";
    char buffer[2024];
    //char *log = "log.txt";
    int fd,n;

    mkfifo(myfifo, 0666);

    int log = open("log.txt",O_CREAT|O_APPEND|O_WRONLY, 0666);
    fd = open(myfifo,O_RDONLY);

    while(1) {
        if(n = read(fd,buffer,1024)>0) {
            write(log,buffer,n);
            write(1,buffer,n);
            //printf("Client connected sent: %s",buffer);
        }
    }   


}

Ctx Ctx · Accepted Answer · 2017-05-02T19:59:34

n = read(fd,buffer,1024)>0

evaluates like

n = (read(fd,buffer,1024)>0)

so 1 is stored in n (instead of the number of bytes read) if read returns a positive value. Use instead:

(n = read(fd,buffer,1024))>0

as conditional, then it should work as expected.

Named Pipe client and server, message truncated on server?

1 Answers