Unix Domain Socket (C ++) - client server crash

Question

I have a problem. I recently started with daemon and sockets. My current setup consists of a daemon that creates a socket and a client that writes messages and reads the processed response.
Well, read the answer.

The daemon demonizes itself, creates a socket, and even processes the message (I can check through the log entries that I make), but as soon as I try to send a response to the client, the daemon is blocked; the client never receives a response, and if I am a ctrl-cclient, the daemon also shuts down.
This is a completely strange behavior for me, and I can’t explain what is happening, so I ask you for any hints.

Brief summary:
 - the type of socket AF_UNIX, therefore local and non-connected networks - The daemon successfully receives a message, but cannot write back - the client cannot read (since the send()server is blocked) and if I am a ctrl-cclient, the daemon also exits (but this signal is not sent to the daemon )

Below is my code, divided into an interesting and non-working part.
Thanks a lot in advance for tips, help and suggestions!

UPDATE:

Client code added!

int main()
{
    //those two work just fine
    createSocket();
    daemonize();

    //declare some variables needed in the big loop
    FILE *client_fd;
    int fd;
    socklen_t len;
    string tmp;
    char *buf = new char[1024];
    while(1)
    {
        struct sockaddr_un saun;
        len = sizeof(saun);

        //receive an fd for the incoming connection
        if((fd = accept(m_socket, (sockaddr*)&saun, &len)) < 0)
        {
            writeLog("Accepting connection failed!");
            continue;
        }
        //i wanted to use fgets, therefore obtain a FILE object here
        client_fd = fdopen(fd, "r");
        if(client_fd == NULL)
        {
            writeLog("fdopen() failed!");
            continue;
        }
        while(fgets(buf, bufferSize, client_fd) != NULL)
        {
            //message read succeeds (verified)
            writeLog(buf);
            tmp = evaluateMsg(buf);

            //tmp is not empty (verified)
            writeLog(tmp);

            //send seems to block, nothing happens from now on
            //I don't even get in one of the if-else branches
            if(send(fd, (tmp + "\n").c_str(), tmp.size() + 1, 0) < 0)
            {
                writeLog("Could not write message back!");
                continue;
            }
            else
                writeLog("bytes written!");
        }
        close(fd);
    }
}

Below is the customer code:

int main()
{
    int sockfd;
    sockaddr_un addr;

    sockfd = socket(AF_UNIX, SOCK_STREAM, 0);
    addr.sun_family = AF_UNIX;
    strcpy(addr.sun_path, SOCKET_PATH);

    //the connection is successfull
    if(connect(sockfd, (sockaddr*)&addr, sizeof(addr)) < 0)
    {
        cerr<<"Connection failed!"<<endl;
        exit(1);
    }
    //message is written successfully
    write(sockfd, "hello", 5);
    char *buf = new char[1024];

    //same as for the server, I wanted to use fgets
    //therefore need to obtain a FILE object
    FILE *fd = fdopen(sockfd, "r");
    fgets(buf, 1024, fd);
    cout<<buf<<endl;

    close(sockfd);
}

Answer 1

Ok, I found a solution myself.

() fgets(); read(), .
, read() , , , , ...
!