Unable to send char array via Write and Read Functions over socket in C

Question

I'm writing a set of client/server programs that are meant to get file information over the local network. I am attempting to allow the client to have the path defined and send it to the server, however my server read function is constantly returning a negative value, meaning error. I have even attempted to hard code in the number of bytes I am sending, in order to possibly rule out a blocking issue. Any help is appreciated.

Server #include #include #include #include #include #include #include #include

#define DEFAULT_PROTOCOL 0

char* path;

main()
{
    int serverFd, clientFd, serverLen, clientLen;
    struct sockaddr_un serverAddress;
    struct sockaddr_un clientAddress;
    struct sockaddr* serverSockAddrPtr;
    struct sockaddr* clientSockAddrPtr;

    signal(SIGCHLD, SIG_IGN);

    serverSockAddrPtr = (struct sockaddr*) &serverAddress;
    serverLen = sizeof(serverAddress);

    clientSockAddrPtr = (struct sockaddr*) &clientAddress;
    clientLen = sizeof(clientAddress);

    serverFd = socket(PF_LOCAL, SOCK_STREAM, DEFAULT_PROTOCOL);
    serverAddress.sun_family = PF_LOCAL;
    strcpy (serverAddress.sun_path, "recipe");
    unlink ("recipe");
    bind (serverFd, serverSockAddrPtr, serverLen);
    listen (serverFd, 5);

    while(1)
    {
        clientFd = accept (serverFd, clientSockAddrPtr, &clientLen);

        if (fork() == 0)
        {

            int n = read(clientFd, path, 7);
            printf("%d\n", n);
            printf("Path is %s\n", path);
            writeRecipe(clientFd);
            close (clientFd);
            exit(0);

        } else {
            close (clientFd);
        }

    }
}

writeRecipe(fd)

int fd;

{

    static char str[80];

    DIR *dir;
    struct dirent *ent;
    struct stat fileStat;
    if ((dir = opendir (path)) != NULL) {
      while ((ent = readdir (dir)) != NULL) {

        if(stat(ent->d_name,&fileStat) < 0)    
            printf("fail");
        sprintf(str, "Inode: %d |Link Count: %d   |File Size: %d |Modified: %d\n",fileStat.st_ino, fileStat.st_nlink, fileStat.st_size, fileStat.st_mtime );
        write(fd, str, strlen(str) + 1);
      }
      closedir (dir);
    } else {
      /* could not open directory */
        printf("fail");
    }

}

Client

#include <stdio.h>
#include <signal.h>
#include <sys/types.h>
#include <linux/limits.h>
#include <sys/socket.h>
#include <sys/un.h>

#define DEFAULT_PROTOCOL 0

main (int argc, char* argv[] )

{
    char* path;
    if (argc > 1) {
        path = argv[1];
    } else {
        path = ".";
    }
    printf("Path is %s\n", path);
    int clientFd, serverLen, result;
    struct sockaddr_un serverAddress;
    struct sockaddr* serverSockAddrPtr;

    serverSockAddrPtr = (struct sockaddr*) &serverAddress;
    serverLen = sizeof(serverAddress);

    clientFd = socket (PF_LOCAL, SOCK_STREAM, DEFAULT_PROTOCOL);
    serverAddress.sun_family = PF_LOCAL;
    strcpy (serverAddress.sun_path, "recipe");

    do
        {
            result = connect(clientFd, serverSockAddrPtr, serverLen);
            if (result == -1) sleep (1);
        }
    while (result == -1);
    int n = write(clientFd, path, strlen(path));
    printf("%d\n", n);
    readRecipe (clientFd);
    close (clientFd);
    exit(0);
}

readRecipe(fd)

int fd;

{
    char str[200];
    while (readLine(fd, str))
        printf("%s\n", str);


}

readLine(fd, str)

int fd;
char* str;

{
    int n;

    do
        {
            n = read (fd, str, 1);
        }
    while (n > 0 && *str++ != 0);
    return (n > 0);

}

The value that is returned is negative 1, the errno is 14.

What is errno when read() returns a negative value?

woolstar
– woolstar

2013-12-02 19:47:58 +00:00
Commented Dec 2, 2013 at 19:47 — woolstar
– woolstar, Commented Dec 2, 2013 at 19:47
did you allocate any memory for read to read into?

evil otto
– evil otto

2013-12-02 19:54:47 +00:00
Commented Dec 2, 2013 at 19:54 — evil otto
– evil otto, Commented Dec 2, 2013 at 19:54

Ranma344 · Accepted Answer · 2013-12-02 20:01:10Z

1

Allocating memory was the issue, thanks to evil otto. I changed the server code from char* to a char with allocated memory, and all problems are solved.

answered Dec 2, 2013 at 20:01

Ranma344

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