Sending user defined struct through Apache Qpid - c++

Question

I try to send a user defined struct which contains substructs over AMQP from one node to another. I am using the Apache Qpid library at the moment.
(I'm currently still testing my code on the PC before i rebuild it for my other devices)
my current method consist of a conversion from the struct to a bytestring and sending that over AMQP to deconverse it on the other side.
I do the following
//user defined struct
enum Quality
{
/// <summary>Value is reliable.</summary>
QUALITY_GOOD,
/// <summary>Value not reliable.</summary>
/// <remarks>
/// A variable may be declared unreliable if a sensor is not calibrated or
/// if the last query failed but older samples are still usable.
/// </remarks>
QUALITY_UNCERTAIN,
/// <summary>Value is invalid.</summary>
/// <remarks>
/// A variable may be declared bad if the measured value is out of range or
/// if a timeout occured.
/// </remarks>
QUALITY_BAD
};
struct Payload
{
/// <summary>Identifier that uniquely points to a single instance.</summary>
DdsInterface::Id id = DdsInterface::Id();
/// <summary>Human readable short name.</summary>
std::string name = "default";
/// <summary>Actual value.</summary>
long long value;
/// <summary>Quality of the Value.</summary>
Quality quality = QUALITY_GOOD;
/// <summary>Detailed quality of the variable.</summary>
QualityDetail qualityDetail = 0;
/// <summary>Unit of measure.</summary>
PhysicalQuantity quantity = 0;
Payload();
Payload(const DdsInterface::Id id, const std::string topic, const uint64_t counter);
};
//sender function
void QpidAMQP::AMQPPublish(const Payload& payload, bool durability, bool sync)
{
// Publish to MQTT broker
qpid::messaging::Message message;
message.setDurable(durability);
char b[sizeof (payload)];
memcpy(b, &payload, sizeof(payload));
//create stream of bytes to send over the line
message.setContent(b);
//message.setContent("testIfSend");
std::string temp = message.getContent();
print_bytes(temp.c_str(), sizeof (temp));// used to check the byte data
this->sender.send(message);
this->session.sync(sync);
}
//receiver functions
void *check_for_incoming_messages(QpidAMQP* amqp_instance) //called via pthread
{
qpid::messaging::Message message;
std::cout << "check for incoming messages" << std::endl;
while(amqp_instance->getReceiver()->fetch(message, qpid::messaging::Duration::FOREVER))
{
amqp_instance->on_message(&message);
}
return nullptr;
}
void QpidAMQP::on_message(qpid::messaging::Message *message)
{
/// make sure message topic and payload are copied!!!
if (this->handler)
{
std::string temp = message->getContent();
print_bytes(temp.c_str(), sizeof (temp)); // used to check the byte data
Payload payload; //Re-make the struct
memcpy(&payload, message->getContent().c_str(), message->getContentSize());
handler->ReceivedIntegerValue(payload.id.variableId, payload.value);
}
}
I did check the byte data and they where vastly different.
sender:
[ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 63 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 60 32 bf 74 ff 7f 00 00 05 00 00 00 00 00 00 00 74 6f 70 69 63 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ]
receiver:
>[ 74 65 73 74 49 66 53 65 6e 64 00 00 00 7f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 a0 ed ff 43 57 7f 00 00 07 00 00 00 00 00 00 00 64 65 66 61 75 6c 74 00 6d 05 77 4b 57 7f 00 00 ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00 ]
I used the following code to print this out
void print_bytes(const void *object, size_t size)
{
// This is for C++; in C just drop the static_cast<>() and assign.
const unsigned char * const bytes = static_cast<const unsigned char *>(object);
size_t i;
printf("[ ");
for(i = 0; i < size; i++)
{
printf("%02x ", bytes[i]);
}
printf("]\n");
}
When i send only a string instead of the payload it receives on the other end. But for some reason a user defined struct doesn't work.
i want to avoid remapping everything against the qpid map because i will lose the depth of my Payload.id.
If someone has any sugestions to overcome this i would appreciatie it.
Thanks in advance,
Nick

Answer 1

I solved the issue.
the problem was that instead of the string instance it copied a pointer instance. By making the std::string name = "default"; into char name[20] = "default"; it copies the real character string.
This is how the publisher and subscriber encode en decode the message now.
void QpidAMQP::AMQPPublish(const Payload& payload, bool durability, bool sync)
{
// Publish to MQTT broker
//create stream of bytes to send over the line
qpid::messaging::Message message;
message.setDurable(durability);
std::string b;
b.resize(sizeof(Payload));
std::memcpy(const_cast<char*>(b.c_str()), &payload, b.size());
message.setContent(b);
std::string temp = message.getContent();
print_bytes(temp.c_str(), temp.size());
this->sender.send(message);
this->session.sync(sync);
}
void QpidAMQP::on_message(qpid::messaging::Message *message)
{
/// make sure message topic and payload are copied!!!
if (this->handler != nullptr)
{
const std::string temp = message->getContent();
print_bytes(temp.c_str(), temp.size());
Payload payload;
std::memcpy(&payload, temp.c_str(), temp.size());//sizeof(message->getContentBytes().c_str()));
handler->ReceivedIntegerValue(payload.id.variableId, payload.value);
}
}