MQTT / Mbed OS HelloMQTT

Sample MQTT program - simple send and receive

Dependencies:   C12832 MQTT

Dependents:   MQTT_G_SENSOR

This program and the MQTT libraries it uses are part of the EclipseTM Paho project; specifically the embedded client.

This example and API are working, but are still in progress. Please give us your feedback.

HelloMQTT is an example of using the MQTT API. The MQTT API is portable across network interface stacks. MQTT is designed to be used with TCP/IP, but any transport with similar characteristics should be suitable.

HelloMQTT uses the NetworkInterface APIs in mbed OS 5 to show how this works. The MQTT library contains an MQTTNetwork.h header, which is a wrapper around the mbed networking interface. To switch between connectivity methods (the default is Ethernet) the easy-connect library is provided in this example application. You can change the connectivity method in mbed_app.json.

Adding new connectivity methods to the program is trivial, as long as they implement the mbed OS 5 NetworkStack API.

Linux-example/LinuxIPStack.h

Committer:
Jan Jongboom
Date:
2017-01-10
Revision:
20:49c9daf2b0ff
Parent:
8:a3e3113054a1

File content as of revision 20:49c9daf2b0ff:

#if !defined(LINUX_IPSTACK_H)
#define LINUX_IPSTACK_H

class IPStack 
{
public:    
    IPStack()
    {

    }
    
    int Socket_error(const char* aString)
    {

        if (errno != EINTR && errno != EAGAIN && errno != EINPROGRESS && errno != EWOULDBLOCK)
        {
            if (strcmp(aString, "shutdown") != 0 || (errno != ENOTCONN && errno != ECONNRESET))
                printf("Socket error %s in %s for socket %d\n", strerror(errno), aString, mysock);
        }
        return errno;
    }

    int connect(const char* hostname, int port)
    {
        int type = SOCK_STREAM;
        struct sockaddr_in address;
        int rc = -1;
        sa_family_t family = AF_INET;
        struct addrinfo *result = NULL;
        struct addrinfo hints = {0, AF_UNSPEC, SOCK_STREAM, IPPROTO_TCP, 0, NULL, NULL, NULL};

        if ((rc = getaddrinfo(hostname, NULL, &hints, &result)) == 0)
        {
            struct addrinfo* res = result;

            /* prefer ip4 addresses */
            while (res)
            {
                if (res->ai_family == AF_INET)
                {
                    result = res;
                    break;
                }
                res = res->ai_next;
            }

            if (result->ai_family == AF_INET)
            {
                address.sin_port = htons(port);
                address.sin_family = family = AF_INET;
                address.sin_addr = ((struct sockaddr_in*)(result->ai_addr))->sin_addr;
            }
            else
                rc = -1;

            freeaddrinfo(result);
        }

        if (rc == 0)
        {
            mysock = socket(family, type, 0);
            if (mysock != -1)
            {
                int opt = 1;

                //if (setsockopt(mysock, SOL_SOCKET, SO_NOSIGPIPE, (void*)&opt, sizeof(opt)) != 0)
                //  printf("Could not set SO_NOSIGPIPE for socket %d", mysock);
                
                rc = ::connect(mysock, (struct sockaddr*)&address, sizeof(address));
            }
        }

        return rc;
    }

    int read(char* buffer, int len, int timeout_ms)
    {
        struct timeval interval = {timeout_ms / 1000, (timeout_ms % 1000) * 1000};
        if (interval.tv_sec < 0 || (interval.tv_sec == 0 && interval.tv_usec <= 0))
        {
            interval.tv_sec = 0;
            interval.tv_usec = 100;
        }

        setsockopt(mysock, SOL_SOCKET, SO_RCVTIMEO, (char *)&interval, sizeof(struct timeval));

        //printf("reading %d bytes\n", len);
        int rc = ::recv(mysock, buffer, (size_t)len, 0);
        if (rc == -1)
            Socket_error("read");
        //printf("read %d bytes\n", rc);
        return rc;
    }
    
    int write(char* buffer, int len, int timeout)
    {
        struct timeval tv;

        tv.tv_sec = 0;  /* 30 Secs Timeout */
        tv.tv_usec = timeout * 1000;  // Not init'ing this can cause strange errors

        setsockopt(mysock, SOL_SOCKET, SO_RCVTIMEO, (char *)&tv,sizeof(struct timeval));
        int rc = ::write(mysock, buffer, len);
        //printf("write rc %d\n", rc);
        return rc;
    }

    int disconnect()
    {
        return ::close(mysock);
    }
    
private:

    int mysock; 
    
};

#endif