Still having trouble deserializing binary data from another UDP source (non-qt)

[RobbieP]

@JonB I'm getting the correct names and the size...the doubles are off though...does the second readRawData start where the previous readRawData left off? calling readRawData back to back like that doesn't reset the position does it?

[RobbieP]

@JonB I ask because I'm curious if it's possible the second readRawData isn't tryign to convert the 200 64 character names into doubles.

[JonB]

@RobbieP
No, your readRawData()s run sequentially, carrying on from where they got to.

Possibilities:

• Sender does have some pad between end of Name and start of Value.
• Sender saves doubles as something other than write(&double, sizeof(double)).
• Sender is different architecture which represents doubles differently. Though I kind of doubt this, I believe there is some standard for how doubles are represented which is cross-architecture.
• QDataStream encodes double with some extra information. Though I doubt this.

the doubles are off though

How "off" is "off"? Slightly wrong, or way out there?

Suggestions:

• You really should put those checks in on return result of QDataStream::readRawData().
• Can you get the sender to send just with inPacket.Size = 1 while you get it sorted out?
• Try it with plain read()s and no QDataStream. Though if that does not work you're a bit stuck.
• Do you have the source code of the sender's write()ing code to examine?

[RobbieP]

@JonB

/* This method writes data to the UDP socket and returns the number of
* bytes written or -1 for an error.  Pass in the IP and port youare sending to. */

int PCSBSocketUDP::WriteData(
				void *				inBuf,
				int				inBufLength,
				unsigned int		inDstIP,
				unsigned short		inDstPort)
{
	sockaddr_in destAddress;
	int tolen = sizeof(destAddress);
	destAddress.sin_family = AF_INET;
	destAddress.sin_port = htons(inDstPort);
	destAddress.sin_addr.s_addr = htonl(inDstIP);
	int result = sendto(mWinSocket,
						 (char*)inBuf,
						 inBufLength,
						 0,
						 (sockaddr*)&destAddress,
						 tolen);

	if (result == -1)
	{
		return -1;
	}
	else
	{
		return result;
	}
}

and I'm sending the struct from the top of my first post with that using:

m_SendSocket->WriteData((char *)&m_Packet, sizeof (fennecPacketStruct), ntohl(inet_addr(m_ipaddress.c_str())), 46456);

the sender is running on this same linux machine, but it's a plugin to a flight simulator. I'll see what the return value is for readRawData next.

[JonB]

@RobbieP said in Still having trouble deserializing binary data from another UDP source (non-qt):

m_SendSocket->WriteData((char *)&m_Packet, sizeof (fennecPacketStruct), ntohl(inet_addr(m_ipaddress.c_str())), 46456);

Since this sends a fennecPacketStruct in one chunk of bytes, why in the world are you trying to deserialize field-by-field? Assuming same machine architecture and same compiler and same definition of fennecPacketStruct with same constants for sizes, you want to just do the opposite read, like read(&inPacket, sizeof(fennecPacketStruct)).

Meanwhile I am "unconvinced" your sender size really has an identical declaration of struct fennecPacketStruct as you showed? Or does it? That uses a fixed size SP_PACKET_SIZE constant. But earlier your code read inPacket.Size from the data stream, and used that to affect how much it read where. Something is fishy...

[RobbieP]

That's what I was originally thinking a long time ago, but I can't seem to do it...it gives me this error:

/home/robbie/Documents/Programming/Fennec/mainwindow.cpp:36: error: no matching function for call to ‘QUdpSocket::read(MainWindow::fennecPacketStruct*, long unsigned int)’
../Fennec/mainwindow.cpp: In member function ‘void MainWindow::readPendingDatagrams()’:
../Fennec/mainwindow.cpp:36:24: error: no matching function for call to ‘QUdpSocket::read(MainWindow::fennecPacketStruct*, long unsigned int)’
36 | udpSocket->read(&inPacket, sizeof(fennecPacketStruct));
| ~^~~~~~~~~~~~~~~~~~~~~~~~~

[JonB]

@RobbieP
Of course that won't match. The writer code does not use fennecPacketStruct in WriteData() either. For qint64 QIODevice::read(char *data, qint64 maxSize) it expects a char *, so cast it....

[RobbieP]

@JonB the writer is using fennecPacketStruct though isn't it? m_Packet is a fennecPacketStruct, and the writer is sending sizeof(fennecPacketStruct).

Do I cast it in the read block using another reinterpret_cast? I'm not sure how that would work, because even casting it doesn't seem to like it. Also I need to use ReadDataGram, not Read because I need the host and port that it's coming from.

[RobbieP]

@JonB got it!

the correct cast was (char *)&inPacket

All my values are now correct!

I'll do some sanity checking and add some value logs as well to make sure this is goign to stay consistent in the lab. Thanks much for your incredible patience and help.

[JonB]

@RobbieP said in Still having trouble deserializing binary data from another UDP source (non-qt):

the correct cast was (char *)&inPacket

Yeah. Which should have gone through as reinterpret_cast<char *>(&inPacket) ? Not that it's much different, but keeps the wolves at bay.

the writer is using fennecPacketStruct though isn't it?

But not in the definition of PCSBSocketUDP::WriteData(void *inBuf, ...), or sendTo(..., (char*)inBuf), which are the equivalent of your udpSocket->read(&inPacket, ...).