mqd_t, sending and receiving messages

https://stackoverflow.com/questions/13411392

29-11-2021
|

Question

I'm working on a program where I have a one process called server and several processes called client that can connect to the server and send it messages< however for some reason my client won't connect to my server:

This is the header file for the client class:

#ifndef CLIENT_H
#define CLIENT_H

#include <QString>
#include <string>
#include <QByteArray>
#include <mqueue.h>
#include <iostream>
#include "serveredialog.h"
#include "badudialog.h"
#include "../src/messages.h"

class Client
{
public:
    Client();
    void init(QString name);
    void sendMessage(QString mess);
private:
    char *myMailboxName, buf[MSG_SIZE];
    struct mq_attr attr;
    mqd_t mq_ownBox, mq_centralBox;

};

#endif // CLIENT_H

this is the client cpp file:

#include "Client.h"

using namespace std;

Client::Client()
{
    attr.mq_maxmsg = 10;
    attr.mq_msgsize = MSG_SIZE;
    attr.mq_flags = 0;
}

void Client::init(QString name)
{
    //Convert name into char*
    QByteArray byteArray = name.toUtf8();
    char str1[40];
    const char* tempr = byteArray.constData();
    strncpy(str1, tempr, sizeof(str1));
    myMailboxName = str1;

    //Create temp box to check if name available
    string tempS = myMailboxName;
    tempS += "new";
    const char* tempr1 = tempS.data();
    mq_unlink(tempr1);
    mq_ownBox = mq_open(tempr1, O_RDONLY | O_CREAT, S_IRWXU, &attr);
    mq_centralBox = mq_open(CENTRALBOX, O_RDWR);

    //Tell server that you are ready
    string tempS1 = str1;
    string tempS2 = "started:" + tempS1;
    const char* tempr2 = tempS2.data();
    sprintf(buf, tempr2);
    int tempI = mq_send(mq_centralBox, buf, strlen(buf), 0);
    cout << tempI;
    //Check for success
    if(tempI){
        ServerEDialog sd;
        sd.setModal(true);
        sd.exec();
    }
    else
    {
        //If success, wait for response fromserver
        while(1)
        {
            int tempI2 = mq_receive(mq_ownBox, buf, MSG_SIZE, 0);
            if(tempI2 != -1)
            {
                break;
            }
        }
        QString tempS3 = buf;

        //if invalid show error, otherwise create permanent mailbox
        if(tempS3 == "invalidname")
        {
            BadUDialog bd;
            bd.setModal(true);
            bd.exec();
        }
        else
        {
            mq_unlink(myMailboxName);
            mq_ownBox = mq_open(myMailboxName, O_RDONLY | O_CREAT, S_IRWXU, &attr);
        }
    }
}

void Client::sendMessage(QString mess)
{

}

This is my server header file:

#ifndef SERVER_H
#define SERVER_H

#include <QString>
#include <mqueue.h>
#include <QVector>
#include <QStringList>
#include <iostream>
#include "../src/messages.h"

class Server : public QObject
{
    Q_OBJECT
public:
    Server();
    void start();
private:
    void join(QString name);
    char buf[MSG_SIZE], msgSend[MSG_SIZE];
    QVector<mqd_t> mq_external;
    QVector<QString> users;
    mqd_t mq_central;
    struct mq_attr attr;


signals:
    void joined(QString name);

};

#endif // SERVER_H

This is my server cpp file:

#include "Server.h"

using namespace std;

Server::Server()
{
}

void Server::start(){

    attr.mq_maxmsg = 100;
    attr.mq_msgsize = MSG_SIZE;
    attr.mq_flags = 0;

    mq_unlink(CENTRALBOX);
    mq_central = mq_open(CENTRALBOX, O_RDONLY | O_CREAT, S_IRWXU, &attr);
    while(1)
    {
        //Wait to recieve message from user
        int tempMsgVal = mq_receive(mq_central, buf, MSG_SIZE, 0);
        if(tempMsgVal != -1)
        {
            cout << tempMsgVal;
        }

        if(tempMsgVal != -1){
            QString tempS = buf;
            QStringList tempSL = tempS.split(":");
            if(tempSL.size() == 2 && tempSL.at(0) == "started")
            {
                int x = 0;
                bool exists = false;
                for(int i = 0; i < mq_external.size(); i++)
                {
                    x = QString::compare(tempSL[1], users.at(i), Qt::CaseInsensitive);
                    if(x == 0)
                    {
                        exists = true;
                        break;
                    }
                }

                if(!exists)
                {
                    sprintf(buf,"joined");
                    QString tempS1 = tempSL[1] + "new";
                    QByteArray byteArray = tempS1.toUtf8();
                    const char* tempr = byteArray.constData();
                    mqd_t tempMQ = mq_open(tempr, O_RDWR);
                    int tempI = mq_send(tempMQ, buf, strlen(buf), 0);

                    join(tempSL[1]);
                }
                else
                {
                    sprintf(buf,"invalidname");
                    QString tempS1 = tempSL[1] + "new";
                    QByteArray byteArray = tempS1.toUtf8();
                    const char* tempr = byteArray.constData();
                    mqd_t tempMQ = mq_open(tempr, O_RDWR);
                    int tempI = mq_send(tempMQ, buf, strlen(buf), 0);
                }//Endelse
            }//Endif
        }//Endif

    }//Endwhile
}

void Server::join(QString name)
{
    emit joined(name);
}

This is the messages.h file which i include in both classes:

#ifndef MESSAGES_H
#define MESSAGES_H

#define MSG_SIZE 150
#define CENTRALBOX "/CentralMailBox"

#include <stdio.h>
#include <stdlib.h>

#endif // MESSAGES_H

Some of the code in the client and server class have to do with the gui, but I have tested that part and the relevant methods are called at the correct time.

My problem is that when I call in the first call the mq_send method in the client function, it's returning and error and the same for the server class, Is there something I'm doing wrong when it comes to sending and receiving messages because I can't figure it out for the life of me.

Solution

I found out where I was going wrong, it's UN-shown, but the mq_ownbox, used a name that i got from the gui, which i forgot to add '/' to the beginning of, as for mq_central, setting the maxmsg to 100 caused the invalid arguement

OTHER TIPS

As you already found out that the invalid argument showed up because of the too large maxmsg count, I just learned that the maxmsg size on my linux system was only 10. So a none root user only can create message queues with a maximum of 10 slots. The root user can create more than that though.