MQTT connect with activeMQ - c++

Question

I have written a client code for mqtt which is supposed to connect (just connect to server for now) to a active mq server. following is the code:
#include "stdafx.h"
#include<iostream>
#include<winsock2.h>
#include "mqtt.h"
#pragma comment(lib,"ws2_32.lib") //Winsock Library
#include <stdlib.h>
#include <winsock2.h>
void mqtt_init(mqtt_broker_handle_t* broker, const char* clientid) {
// Connection options
broker->alive = 300; // 300 seconds = 5 minutes
broker->seq = 1; // Sequence for message identifiers
// Client options
memset(broker->clientid, 0, sizeof(broker->clientid));
memset(broker->username, 0, sizeof(broker->username));
memset(broker->password, 0, sizeof(broker->password));
if(clientid) {
strncpy_s(broker->clientid, clientid, sizeof(broker->clientid));
} else {
strcpy_s(broker->clientid, "emqtt");
}
// Will topic
broker->clean_session = 1;
}
void mqtt_init_auth(mqtt_broker_handle_t* broker, const char* username, const char* password)
{
if(username && username[0] != '\0')
strncpy_s(broker->username, username, sizeof(broker->username)-1);
if(password && password[0] != '\0')
strncpy_s(broker->password, password, sizeof(broker->password)-1);
}
using namespace std;
int main(int argc , char *argv[])
{
WSADATA wsa;
SOCKET s;
struct sockaddr_in server;
char message[1000] , server_reply[2000];
int recv_size;
int packet_length;
uint16_t msg_id, msg_id_rcv;
mqtt_broker_handle_t broker;
mqtt_init(&broker, "localhost");
mqtt_init_auth(&broker, "cid", "campeador");
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0) {
cout<<"Failed. Error Code : "<<WSAGetLastError();
return 1;
}
cout<<"Initialised.\n";
//Create a socket
if((s = socket(AF_INET , SOCK_STREAM , 0 )) == INVALID_SOCKET)
{
cout<<"Could not create socket : " << WSAGetLastError();
}
cout<<"Socket created.\n";
server.sin_addr.s_addr = inet_addr("127.0.0.1");
server.sin_family = AF_INET;
server.sin_port = htons( 1993);
//Connect to remote server
if (connect(s , (struct sockaddr *)&server , sizeof(server)) < 0)
{
puts("connect error");
return 1;
}
puts("Connected");
mqtt_connect(&broker);
recv_size = recv(s, server_reply, 2000, 0);
server_reply[recv_size] = '\0';
while ( server_reply != "end"){
cout<<server_reply<<endl;
recv_size = recv(s, server_reply, 2000, 0);
server_reply[recv_size] = '\0';
}
closesocket(s);
WSACleanup();
return 0;
}
And also the following is the code for mqtt.h
#ifndef __LIBEMQTT_H__
#define __LIBEMQTT_H__
#endif
#include <stdint.h>
#include <string.h>
#ifndef MQTT_CONF_USERNAME_LENGTH
#define MQTT_CONF_USERNAME_LENGTH 13 // Recommended by MQTT Specification (12 + '\0')
#endif
#ifndef MQTT_CONF_PASSWORD_LENGTH
#define MQTT_CONF_PASSWORD_LENGTH 13 // Recommended by MQTT Specification (12 + '\0')
#endif
#define MQTT_MSG_CONNECT 1<<4
#define MQTT_MSG_CONNACK 2<<4
#define MQTT_MSG_PUBLISH 3<<4
#define MQTT_MSG_PUBACK 4<<4
#define MQTT_MSG_PUBREC 5<<4
#define MQTT_MSG_PUBREL 6<<4
#define MQTT_MSG_PUBCOMP 7<<4
#define MQTT_MSG_SUBSCRIBE 8<<4
#define MQTT_MSG_SUBACK 9<<4
#define MQTT_MSG_UNSUBSCRIBE 10<<4
#define MQTT_MSG_UNSUBACK 11<<4
#define MQTT_MSG_PINGREQ 12<<4
#define MQTT_MSG_PINGRESP 13<<4
#define MQTT_MSG_DISCONNECT 14<<4
#define MQTT_DUP_FLAG 1<<3
#define MQTT_QOS0_FLAG 0<<1
#define MQTT_QOS1_FLAG 1<<1
#define MQTT_QOS2_FLAG 2<<1
#define MQTT_RETAIN_FLAG 1
#define MQTT_CLEAN_SESSION 1<<1
#define MQTT_WILL_FLAG 1<<2
#define MQTT_WILL_RETAIN 1<<5
#define MQTT_USERNAME_FLAG 1<<7
#define MQTT_PASSWORD_FLAG 1<<6
typedef struct {
void* socket_info;
int (*send)(void* socket_info, const void* buf, unsigned int count);
// Connection info
char clientid[50];
// Auth fields
char username[MQTT_CONF_USERNAME_LENGTH];
char password[MQTT_CONF_PASSWORD_LENGTH];
// Will topic
uint8_t will_retain;
uint8_t will_qos;
uint8_t clean_session;
// Management fields
uint16_t seq;
uint16_t alive;
} mqtt_broker_handle_t;
int mqtt_connect(mqtt_broker_handle_t* broker)
{
uint8_t flags = 0x00;
uint16_t clientidlen = strlen(broker->clientid);
uint16_t usernamelen = strlen(broker->username);
uint16_t passwordlen = strlen(broker->password);
uint16_t payload_len = clientidlen + 2;
// Preparing the flags
if(usernamelen) {
payload_len += usernamelen + 2;
flags |= MQTT_USERNAME_FLAG;
}
if(passwordlen) {
payload_len += passwordlen + 2;
flags |= MQTT_PASSWORD_FLAG;
}
if(broker->clean_session) {
flags |= MQTT_CLEAN_SESSION;
}
// Variable header
uint8_t var_header[] = {
0x00,0x06,0x4d,0x51,0x49,0x73,0x64,0x70, // Protocol name: MQTT
0x03, // Protocol version
flags, // Connect flags
broker->alive>>8, broker->alive&0xFF, // Keep alive
};
// Fixed header
uint8_t fixedHeaderSize = 2; // Default size = one byte Message Type + one byte Remaining Length
uint8_t remainLen = sizeof(var_header)+payload_len;
if (remainLen > 127) {
fixedHeaderSize++; // add an additional byte for Remaining Length
}
uint8_t fixed_header[2];
// Message Type
fixed_header[0] = MQTT_MSG_CONNECT;
// Remaining Length
if (remainLen <= 127) {
fixed_header[1] = remainLen;
} else {
// first byte is remainder (mod) of 128, then set the MSB to indicate more bytes
fixed_header[1] = remainLen % 128;
fixed_header[1] = fixed_header[1] | 0x80;
// second byte is number of 128s
fixed_header[2] = remainLen / 128;
}
uint16_t offset = 0;
uint8_t packet[sizeof(fixed_header)+sizeof(var_header)+ sizeof(payload_len)];
memset(packet, 0, sizeof(packet));
memcpy(packet, fixed_header, sizeof(fixed_header));
offset += sizeof(fixed_header);
memcpy(packet+offset, var_header, sizeof(var_header));
offset += sizeof(var_header);
// Client ID - UTF encoded
packet[offset++] = clientidlen>>8;
packet[offset++] = clientidlen&0xFF;
memcpy(packet+offset, broker->clientid, clientidlen);
offset += clientidlen;
if(usernamelen) {
// Username - UTF encoded
packet[offset++] = usernamelen>>8;
packet[offset++] = usernamelen&0xFF;
memcpy(packet+offset, broker->username, usernamelen);
offset += usernamelen;
}
if(passwordlen) {
// Password - UTF encoded
packet[offset++] = passwordlen>>8;
packet[offset++] = passwordlen&0xFF;
memcpy(packet+offset, broker->password, passwordlen);
offset += passwordlen;
}
return 1;
}
When I debug the code there are no errors however when I run the code I get error stating that "the stack around the variable 'packet' is corrupt". I am very new to socket programming and mqtt in general so any help would be great.

Answer 1

What you've shown is derived from libemqtt (which is GPL licensed by the way, don't forget that :), have you tried starting from the examples that they provide?
libemqtt isn't actively developed and has a notice saying "DO NOT USE". Unless you're particularly interested in solving the problem of using MQTT for yourself, I'd suggest you look at something different, like the Paho or mosquitto client libraries.