QTcpSocket sends more data than wanted - Qt/C++ - c++

first of all a little background on my situation:
- Qt/C++ UI desktop application
- embedded device (Stm32l4xx family) +ATWINC1500 wifi module
I'm developing the gui application in order to send commands and files to the emdedded device via sockets.
For simple commands I've done all successfully, but for sending files (text files in GCODE format) I am stuck with some issues.
The embedded device has already a socket management(not written by me, so I have not the possibility to modify the way sockets are managed, coming from third party company), and the reception of that type of files is managed in a way that the API waits for every single line of the file being sent, and then wrotes it into a reserved portion of the flash.
My problem is that when I send file from qt Application(by reading each line and and calling write() on the line, in reality my socket sends an entire chunk of the file, like 50 lines, resulting in my device not managing the file reception.
My sending code is this:
void sendGCODE(const QString fileName)
{
QFile *file = new QFile(fileName,this);
bool result = true;
if (file->open(QIODevice::ReadOnly))
{
while (!file->atEnd())
{
QByteArray bytes(file->readLine());
result = communicationSocket->write(bytes);
communicationSocket->flush();
if(result)
{
console->append("-> GCODE line sent:"+ QString(bytes));
}
else
{
console->append("-> Error sending GCODE line!");
}
}
file->close();
}
}
Have anyone of you guys any hints on what I am doing wrong?
I've already searched and someone suggests on other topic that for this purpose it should be better to use UDP instead of TCP sockets, but unfortunately I cannot touch the embedded-device-side code.
thank you all!
EDIT
After suggestions from comments, I've sniffed tcp packets and the packets are sent correctly(i.e. each packet contains a single line). BUT... at the receiver(device), I understood that there is something regarding memory which is not well managed. an example:
sender sends the line "G1 X470.492 Y599.623 F1000" ; receiver receives correctly the string "G1 X470.492 Y599.623 F1000"
next, if the line length is less than the previous sent, i.e. sending "G1 Z5", the receiver receives: "G1 Z5\n\n.492 Y599.623 F1000", so it is clear that the buffer used to store the data packet is not re-initialized from previous packet content, and the new part overwrites the previous values where the remaining part is from the previous packet
I'm trying to figure out how I could reset that part of memory.

This is all wrong. TCP is not a message-oriented protocol. There is no way to ensure that the TCP packets contain any particular amount of data. The receiver code on the device mustn't expect that either - you perhaps misunderstood the receiver's code, or are otherwise doing something wrong (or the vendor is). What the receiver must do is wait for a packet, add the packet's data to a buffer, then extract and process as many complete lines as it can, then move the remaining data to the beginning of the buffer. And repeat that on every packet.
Thus you're looking for the wrong problem at the wrong place, unless your device never ever had a chance of working. If that device works OK with other software, then your "packetized" TCP assumption doesn't hold any water.
Here's how to proceed:
If the device is commercially available and has been tested to work, then you're looking in the wrong place.
If the device is a new product and still in development, then someone somewhere did something particularly stupid and you either need to fix that stupidity, or have the vendor fix it, or hire a consultant to fix it. But just to be completely clear: that's not how TCP works, and you cannot just accept that "it's how it is".

Related

I need help figuring out tcp sockets (clsocket)

I am having trouble figuring out sockets i am just asking the server for data at a position (glm::i64vec4) and expecting a response but the position gets way off when i get the response and the data for that position reflects that (aka my voxel game make a kinda cool looking but useless mess)
It's probably just me not understanding sockets whatsoever or maybe something weird with this library
one thought i had is it was maybe something to do with mismatching blocking and non blocking on the server and client
but when i switched the server to blocking (and put each client in a seperate thread from each other and the accepting process) it did nothing
if i'm doing something really stupid please tell me i know next to nothing about sockets
here is some code that probably looks horrible
Server Code
std::deque <CActiveSocket*> clients;
CPassiveSocket socket;
socket.Initialize();
socket.SetNonblocking();//I'm doing this so i don't need multiple threads for clients
socket.Listen("0.0.0.0",port);
while (1){
{
CActiveSocket* c;
if ((c = socket.Accept()) != NULL){
clients.emplace_back(c);
}
}
for (CActiveSocket*& c : clients){
c->Receive(sizeof(glm::i64vec4));
if (c->GetBytesReceived() == sizeof(glm::i64vec4)){
chkpkt chk;
chk.pos = *(glm::i64vec4*)c->GetData();
LOOP3D(chksize+2){
chk.data(i,j,k).val = chk.pos.y*chksize+j;
chk.data(i,j,k).id=0;
}
while (c->Send((uint8*)&chk,sizeof(chkpkt)) != sizeof(chkpkt)){}
}
}
}
Client Code
//v is a glm::i64vec4
//fsock is set to Blocking
if(fsock.Send((uint8*)&v,sizeof(glm::i64vec4)))
if (fsock.Receive(sizeof(chkpkt))){
tthread::lock_guard<tthread::fast_mutex> lock(wld->filemut);
wld->ichks[v]=(*(chkpkt*)fsock.GetData()).data;//i tried using the position i get back from the server to set this (instead of v) but that made it to where nothing loaded
//i checked it and the chunks position never lines up with what i sent
}
Without your complete application codes it's unrealistic to offer any suggestions of any particular lines of code correction.
But it seems like you are using this library. It doesn't matter if not, because most of time when doing network programming, socket's weird behavior make some problems somewhat universal. Thus there are a few suggestions for the portion of socket application in your project:
It suffices to have BLOCKING sockets.
Most of time socket's read have somewhat weird behavior, that is, it might not receive the requested size of bytes at a time. Due to this, you need to repeatedly call read until the receiving buffer is read thoroughly. For a complete and robust solution you can refer to Stevens's readn routine ([Ref.1], page122).
If you are using exactly the library mentioned above, you can see that your fsock.Receive eventually calls recv. And recv is just an variant of read[Ref.2], thus the solutions for both of them are just identical. And this pattern might help:
while(fsock.Receive(sizeof(chkpkt))>0)
{
// ...
}
Ref.1: https://mathcs.clarku.edu/~jbreecher/cs280/UNIX%20Network%20Programming(Volume1,3rd).pdf
Ref.2: https://man7.org/linux/man-pages/man2/recv.2.html#DESCRIPTION

c++ streaming udp data into a queue?

I am streaming data as a string over UDP, into a Socket class inside Unreal engine. This is threaded, and runs in the background.
My read function is:
float translate;
void FdataThread::ReceiveUDP()
{
uint32 Size;
TArray<uint8> ReceivedData;
if (ReceiverSocket->HasPendingData(Size))
{
int32 Read = 0;
ReceivedData.SetNumUninitialized(FMath::Min(Size, 65507u));
ReceiverSocket->RecvFrom(ReceivedData.GetData(), ReceivedData.Num(), Read, *targetAddr);
}
FString str = FString(bytesRead, UTF8_TO_TCHAR((const UTF8CHAR *)ReceivedData));
translate = FCString::Atof(*str);
}
I then call the translate variable from another class, on a Tick, or timer.
My test case sends an incrementing number from another application.
If I print this number from inside the above Read function, it looks as expected, counting up incrementally.
When i print it from the other thread, it is missing some of the numbers.
I believe this is because I call it on the Tick, so it misses out some data due to processing time.
My question is:
Is there a way to queue the incoming data, so that when i pull the value, it is the next incremental value and not the current one? What is the best way to go about this?
Thank you, please let me know if I have not been clear.
Is this the complete code? ReceivedData isn't used after it's filled with data from the socket. Instead, an (in this code) undefined variable 'buffer' is being used.
Also, it seems that the while loop could run multiple times, overwriting old data in the ReceivedData buffer. Add some debugging messages to see whether RecvFrom actually reads all bytes from the socket. I believe it reads only one 'packet'.
Finally, especially when you're using UDP sockets over the network, note that the UDP protocol isn't guaranteed to actually deliver its packets. However, I doubt this is causing your problems if you're using it on a single computer or a local network.
Your read loop doesn't make sense. You are reading and throwing away all datagrams but the last in any given sequence that happen to be in the socket receive buffer at the same time. The translate call should be inside the loop, and the loop should be while(true), or while (running), or similar.

Receiving sms through gprs shield on Arduino

I have been searching all over the net trying to find some example code to see how to listen for sms and read it. I am new to at commands so I am trying to see some examples. My intentions is to listen for sms and read to content. If the message contained the word: 'forward', I want it to run a certain function. I am using a seeedstudio GPRS v1.4 shield with my arduino uno.
I found a library but I am confused on the readSMS() function. The library is found here: https://github.com/Seeed-Studio/Seeeduino_GPRS.
I have the current code:
GPRS gprsTest(8,7,9,9600,"1818XXXXXXXXX");//TX,RX,PWR,BaudRate,PhoneNumber
void setup() {
Serial.begin(9600);
gprsTest.preInit();
delay(1000);
while(0 != gprsTest.init()) {
delay(1000);
Serial.print("init error\r\n");
}
}
void loop() {
//nothing to do
gprsTest.readSMS();
}
My problem is I am not sure of what to put in the parameters for the readSMS function.
According to the api the function takes a int, string, and another int.
int readSMS(int messageIndex, char *message, int length);
Any ideas? Not really any documentation on receiving sms
I am not familiar with Seeed-studio (whose comments in header files are not maintained very well as well, to give you some help) but here is the basic idea:
The received text messages are stored on independent indexes on the selected message memory (SIM or phone which will be modem in your case). New messages usually take the smallest unused index (indexes starting from 1).
There are two methods to detect a new SMS
1) Modem sends a string on output port to indicate new SMS (like an interrupt)
2) You have to read the count of unread messages yourself (polling)
These methods require a knowledge of hardware dependent AT commands. If you want to understand/learn what's going on, give AT commands CMGR and CMGF a read
That said, the information you have explicitly asked for can be found in the function readSMS of gprs.cpp.
messageIndex is the index of selected memory where the message is stored.
*message is the buffer the message will be read into.
length is the length of bytes to be read.
The return status is always 0 (not a good strategy).
I would recommend distinguishing between read and unread messages using custom code. It depends upon your application

Winsock2 tcp/ip - some data packets are ignored probably due to null terminator from the previous packet

I wrote a simple client-server program. Network.h is a header file which uses Winsock2.h (TCP/IP mode) to create socket, accept/connect in blocking mode, send/recv in non-blocking mode. I made it so that the function string TNetwork::Recv(int size) will return the string "Nothing" if it gets WSAWOULDBLOCK error (no data is received yet)
Here is my main function:
int main(){
string Ans;
TNetwork::StartUp(); //WSA start up, etc
cin >> Ans;
if (Ans == "0"){ // 0 --> server
TNetwork::SetupAsServer(); //accept connection (in blocking mode!)
while (true){
TNetwork::Send("\nAss" + '\0'); //without null terminator, the client may read extra bytes, causing undefined behavior (?)
TNetwork::Send("embly" + '\0');
cin >> Ans;
}
}
else{ // others --> regard Ans as IP address. e.g. I can type "127.0.0.1"
TNetwork::SetupAsClient(Ans);
string Rec;
while (true){
Rec = TNetwork::Recv(1000);
if (Rec != "Nothing"){
cout << Rec;
}
}
}
system("PAUSE");
}
Supposedly, the client would print "Assembly" when connected, and when the server enters anything to its console window. Sometimes, though, the client would only print out "\nAss" in the console without the "embly.
To my understanding, TCP/IP ensures all data to be sent and in the correct order, so I guess what happens is that both packets arrive at the same time, which happen quite often over the unstable internet. And due to this null terminator, the client would ignore the "embly", since the Recv() function stopped reading when it hits a null terminator.
So, how can I ensure that the client will always read all data packets correctly?
Yes, the network stack will send the data in the correct order and doesn't care what termination type you use. This has to do with how you're receiving and processing the data stream (note: not packets, stream). If you receive all 11 bytes and print it to the screen, the print function will stop when it reaches the zero, but the rest of the data is still there.
Note: since it's a stream, what happens if you received only 10 bytes of data from the stream? You need to scan what you receive for the zero to know if you've received a full "zero-terminated string" if that's how you want to communicate your data.
EDIT: Also, I don't think "\nAss" + '\0' is doing what you think it is. Instead of adding a 0 character to the end of the string (which already has one, by the way), it's adding 0 to your string pointer.
As #mark points out, TCP is all about streams, not packets. TCP takes care of ensuring that data is reliably transmitted from A to B and that the data is delivered to the consumer in the order in which it was transmitted. Yes, the data is packetized on the wire, but the TCP stack on the system takes those packets and builds the stream which it makes available to you through the recv() function. The TCP stack handles out-of-order data, missing data, and duplicated data such that by the time your application sees it, the stream is a mirror-copy of when the sender sent.
To properly receive TCP data, you will typically need some kind of loop that reads data from the socket when it becomes available. The way I normally do this is to have a thread that is dedicated to servicing the socket. In the thread function is a loop that reads data from the socket when it becomes available and is idle otherwise. This loop reads data into a buffer of, say, 1 KB. Once the data is received from the socket into this buffer, the buffer is copied to another thread for processing. In the thread function for the processing thread is a loop that receives the 1 KB buffers from the socket thread and adds them to the back end of a master buffer of, say, 1 MB. The processing thread then processes the messages out of this master buffer and makes them available to the application.
For a simple demo application, two threads may be overkill. The two threads I've described could be certainly be combined into one, but for my application, it is more efficient to have two threads and take advantage of the multiple cores on my system. The point is, if you're going to have a front-end UI, there's not going to be a way around using at least one thread and still have the UI be responsive.
One other thing. There are two commonly-used mechanisms for protocol design. You're using one, namely, a marker (e.g., a null terminator, etc.) to signal the begin/end of a message. I don't prefer this mechanism mainly because the marker may actually need to be part of the message at some point. The other mechanism is to have a header on each message that tells, at a minimum, how long the message is. I prefer this mechanism and include in my headers a sync word and the message type as well. For example,
struct Header
{
__int16 _sync; // a hex pattern, e.g., 0xABCD
__int16 _type;
__int32 _length;
}
That's a total of 8 bytes. So when processing from the master buffer, I read the first 8 bytes, verify the sync word, and get the length. I determine if there are 'length' bytes available in the master buffer. If not, I have to wait until the socket thread provides me more data before checking again. If so, I extract 'length' bytes from the master buffer and pass that to an object created according to the specified type, which knows how to interpret that particular message. Then repeat.
As I mentioned, I use a master buffer of 1 MB or so. As messages are processed, it is important to remove them from the master buffer so there is additional space available for new data on the back end. This involves simply copying the unprocessed data, if any, to the beginning of the buffer. In cases where data comes in faster than you can process it, the master buffer may need the ability to resize itself to accommodate the additional data.
I hope that's not overwhelming. Start simple and add as you go.

Server's NonBlocking TCP socket taking time to stream content

Problem
- I am working on a Streaming server & created a nonblocking socket using:
flag=fcntl(m_fd,F_GETFL);
flag|=O_NONBLOCK;
fcntl(m_fd,F_SETFL,flag);
Server then sends the Media file contents using code:
bool SendData(const char *pData,long nSize)
{
int fd=m_pSock->get_fd();
fd_set write_flag;
while(1)
{
FD_ZERO(&write_flag);
FD_SET(fd,&write_flag);
struct timeval tout;
tout.tv_sec=0;
tout.tv_usec=500000;
int res=select(fd+1,0,&write_flag,0,&tout);
if(-1==res)
{
print("select() failure\n");
return false;
}
if(1==res)
{
unsigned long sndLen=0;
if(!m_pSock->send(pData,nSize,&sndLen))
{
print(socket send() failure\n");
return false;
}
nSize-=sndLen;
if(!nSize)
return true; //everything is sent
}
}
}
Using above code, I am streaming a say 200sec audio file, which I expect that Server should stream it in 2-3secs using full n/w available bandwidth(Throttle off), but the problem is that Server is taking 199~200secs to stream full contents.
While debugging, I commented the
m_pSock->send()
section & tried to dump the file locally. It takes 1~2secs to dump the file.
Questions
- If I am using a NonBlocking TCP socket, why does send() taking so much time?
Since the data is always available, select() will return immediately (as we have seen while dumping the file). Does that mean send() is affected by the recv() on the client side?
Any inputs on this would be helpul. Client behavior is not in our scope.
Your client is probably doing some buffering to avoid network jitter, but it is likely still playing the audio file in real time. So, the file transfer rate is matched to the rate that the client is consuming the data. Since it is a 200 second audio file, it will take about 200 seconds to complete the transfer.
Because TCP output and input buffers are propably much smaller than the audio file, reading speed of the receiving application can slow down the sending speed.
When both the TCP output buffer of sender and the input buffer of receiver are both full, TCP stack of the sender is not able to receive any data from the sender. So sending will be blocked, until there is space.
If the receiver reads the TCP stream same speed as data is needed for playing. Then the transfer takes about 200 seconds. Or little bit less.
This can be avoided by using application layer buffering in the receiving end.
The problem could be that if the client side is using blocking TCP, plus is processing all the data on a single thread with no no buffer/queue etc right through to the "player" of the file, then your side being non-blocking will only speed things until you reach the point where the TCP/IP protocol stack buffers, NIC buffers etc are full. Then you will ultimately still only be able to send data as fast as the client side is consuming it. Remember TCP is a reliable, point-to-point protocol.
Where does your client code come from in your testing? Is it some sort of simple test client someone has written?