How to copy Buffer bytes block in Poco C++? - c++

Question

Hi i am trying to write a TCP connection in poco. the client sends a packet with this fields :
packetSize : int
date : int
ID : int
so the first 4 bytes contains the packet size. in the receive side i have this code :
int packetSize = 0;
char *bufferHeader = new char[4];
// receive 4 bytes that contains packetsize here
socket().receiveBytes(bufferHeader, sizeof(bufferHeader), MSG_WAITALL);
Poco::MemoryInputStream *inStreamHeader = new Poco::MemoryInputStream(bufferHeader, sizeof(bufferHeader));
Poco::BinaryReader *BinaryReaderHeader = new Poco::BinaryReader(*inStreamHeader);
(*BinaryReaderHeader) >> packetSize; // now we have the full packet size
Now I am trying to store all remaining incoming bytes into one array for future binary reading :
int ID = 0;
int date = 0;
int availableBytes = 0;
int readedBytes = 0;
char *body = new char[packetSize - 4];
do
{
char *bytes = new char[packetSize - 4];
availableBytes = socket().receiveBytes(bytes, sizeof(bytes), MSG_WAITALL);
if (availableBytes == 0)
break;
memcpy(body + readedBytes, bytes, availableBytes);
readedBytes += availableBytes;
} while (availableBytes > 0);
Poco::MemoryInputStream *inStream = new Poco::MemoryInputStream(body, sizeof(body));
Poco::BinaryReader *BinaryReader = new Poco::BinaryReader(*inStream);
(*BinaryReader) >> date;
(*BinaryReader) >> ID;
cout << "date :" << date << endl;
cout << "ID :" << ID << endl;
the problem is the byte block of body is not storing the remaining bytes , it has always only the first 4 bytes (date). so in the out put the date is correct but the ID is not as expected. I tried to Stream it without Block copy and manually receive the each field without loop, it was just fine and had expected data. but when i try to store the incoming bytes into one array and then pass that array to a memorystream to read it, i have only the first block correct and expected!!
I really need to store all incoming bytes into one array and then read whole that array, how should i change my code?
thanks alot

Answer 1

I see two errors in your code. Or, more precisely, an error you do twice.
You confuse sizeof of char[] with sizeof of char *; the first is the number of characters in the array, the second is the size of the pointer: typically 4 or 8 bytes, depending on the memory model.
So, when you write
availableBytes = socket().receiveBytes(bytes, sizeof(bytes), MSG_WAITALL);
you are asking for 4 (I suppose) bytes. This is not serious as you continue to ask other bytes until the message is finished.
The real problem is the following instruction
Poco::MemoryInputStream *inStream = new Poco::MemoryInputStream(body, sizeof(body));
where you transfer only sizeof(char *) bytes in inStream
You should substitute sizeof(body) and sizeof(bytes) with packetSize - 4.
P.s.: sorry for my bad english
Edit: I've seen another error. In this instruction
char *bytes = new char[packetSize - 4];
you allocate packetSize - 4 chars. This memory in never deleted and in allocated in the do ... while() cycle.
You can allocate bytes outside of the cycle (togheter with body).
Edit 2016.03.17
Proposed solution (caution: non tested)
size_t toRead = packetSize - 4U;
size_t totRead = 0U;
size_t nowRead;
char * body = new char[toRead];
do
{
nowRead += socket().receiveBytes(body+totRead, toRead-totRead,
MSG_WAITALL);
if ( 0 == nowRead )
throw std::runtime_error("shutdown from receiveBytes()");
totRead += nowRead;
} while ( totRead < toRead );
Poco::MemoryInputStream *inStream = new Poco::MemoryInputStream(body,
toRead);
delete[] body;
body = NULL;