rabbitmq-c send nlohmann json

Question

Want to send image through RabbitMQ-C but the image file too big. Receiver cannot retrieve the image. So, I converted image to base64 then put it in JSON.

const char *msg;


FILE *image1;
    if (image1 = fopen(path, "rb")) {
        fseek(image1, 0, SEEK_END); //used to move file pointer to a specific position
                                    // if fseek(0 success, return 0; not successful, return non-zero value
                                    //SEEK_END: end of file
        
        length = ftell(image1); //ftell(): used to get total size of file after moving the file pointer at the end of the file
        sprintf(tmp, "size of file: %d  bytes", length);

//convert image to base64
        std::string line;
        std::ifstream myfile;
        myfile.open(path, std::ifstream::binary);
        std::vector<char> data((std::istreambuf_iterator<char>(myfile)), std::istreambuf_iterator<char>() );
        std::string base64_encode(unsigned char const* bytes_to_encode, unsigned int in_len);
        std::string code = base64_encode((unsigned char*)&data[0], (unsigned int)data.size());
        
//convert std::string to const char 
        const char* base64_Image = code.c_str();
        

        
        json j ;
    
        
        j.push_back("Title");
        j.push_back("content");
        j.push_back(base64_Image);
        
        std::string sa = j.dump();

        msg = sa.c_str();       //convert std::string to const char*
        
    }
    else {
        return;
    }

Using RabbitMQ-C to send the message(msg) to receiver but failed [error point to here]

is const char* cannot use amqp_cstring_bytes(msg) to convert to amqp_bytes_t??

    respo = amqp_basic_publish(conn, 1, amqp_cstring_bytes(exchange), amqp_cstring_bytes(routing_key),0, 0, NULL, amqp_cstring_bytes(msg));

and get this error

If there is a handler for this exception, the program may be safely continued.```


Anyone know how to send image as JSON using RabbitMQ-C & C++ ?

Answer 1

amqp_cstring_bytes expects a C string, which is normally terminated by a NUL byte. Your PNG file is almost guaranteed to contain a NUL byte, so that explains why your message got cut off midway through.

As for the code in your paste: the pointer returned by sa.c_str() is only valid while sa is alive and unmodified. Once you exit the block containing sa's definition, the variable is dead and buried.

Instead, get a buffer of the appropriate size with amqp_bytes_alloc and return that:

amqp_bytes_t bytes = amqp_bytes_malloc(sa.length());
strncpy((char *)bytes.bytes, sa.c_str(), sa.length());

then pass the bytes object to amqp_basic_publish. Don't forget to ampqp_bytes_free it when you're done.