class EE::Network::Packet¶

Overview¶

Utility class to build blocks of data to transfer over the network. More…

#include <packet.hpp>

class Packet {
public:
    // construction

    virtual ~Packet();

    // methods

    void append(const void* data, std::size_t sizeInBytes);
    void clear();
    const void* getData() const;
    std::size_t getDataSize() const;
    bool endOfPacket() const;
    operator BoolType() const;
    Packet& operator>>(bool& data);
    Packet& operator>>(Int8& data);
    Packet& operator>>(Uint8& data);
    Packet& operator>>(Int16& data);
    Packet& operator>>(Uint16& data);
    Packet& operator>>(Int32& data);
    Packet& operator>>(Uint32& data);
    Packet& operator>>(float& data);
    Packet& operator>>(double& data);
    Packet& operator>>(char* data);
    Packet& operator>>(std::string& data);
    Packet& operator>>(wchar_t* data);
    Packet& operator>>(std::wstring& data);
    Packet& operator>>(String& data);
    Packet& operator<<(bool data);
    Packet& operator<<(Int8 data);
    Packet& operator<<(Uint8 data);
    Packet& operator<<(Int16 data);
    Packet& operator<<(Uint16 data);
    Packet& operator<<(Int32 data);
    Packet& operator<<(Uint32 data);
    Packet& operator<<(float data);
    Packet& operator<<(double data);
    Packet& operator<<(const char* data);
    Packet& operator<<(const std::string& data);
    Packet& operator<<(const wchar_t* data);
    Packet& operator<<(const std::wstring& data);
    Packet& operator<<(const String& data);
};

Detailed Documentation¶

Utility class to build blocks of data to transfer over the network.

Packets provide a safe and easy way to serialize data, in order to send it over the network using sockets (TcpSocket, UdpSocket).

Packets solve 2 fundamental problems that arise when transfering data over the network:

data is interpreted correctly according to the endianness
the bounds of the packet are preserved (one send == one receive)

The Packet class provides both input and output modes. It is designed to follow the behaviour of standard C++ streams, using operators >> and << to extract and insert data.

It is recommended to use only fixed-size types (like Int32, etc.), to avoid possible differences between the sender and the receiver. Indeed, the native C++ types may have different sizes on two platforms and your data may be corrupted if that happens.

Usage example:

Uint32 x = 24;
std::string s = "hello";
double d = 5.89;

// Group the variables to send into a packet
Packet packet;
packet << x << s << d;

// Send it over the network (socket is a valid TcpSocket)
socket.send(packet);

-----------------------------------------------------------------

// Receive the packet at the other end
Packet packet;
socket.receive(packet);

// Extract the variables contained in the packet
Uint32 x;
std::string s;
double d;
if (packet >> x >> s >> d) {
     // Data extracted successfully...
}

Packets have built-in operator >> and << overloads for standard types:

bool
fixed-size integer types (Int8/16/32, Uint8/16/32)
floating point numbers (float, double)
string types (char*, wchar_t*, std::string, std::wstring, String)

Like standard streams, it is also possible to define your own overloads of operators >> and << in order to handle your custom types.

struct MyStruct {
     float     number;
     Int8   integer;
     std::string str;
};

Packet& operator <<(Packet& packet, const MyStruct& m) {
     return packet << m.number << m.integer << m.str;
}

Packet& operator >>(Packet& packet, MyStruct& m) {
     return packet >> m.number >> m.integer >> m.str;
}

Packets also provide an extra feature that allows to apply custom transformations to the data before it is sent, and after it is received. This is typically used to handle automatic compression or encryption of the data. This is achieved by inheriting from Packet, and overriding the onSend and onReceive functions.

Here is an example:

class ZipPacket : public Packet {
     virtual const void* onSend(std::size_t& size) {
         const void* srcData = getData();
         std::size_t srcSize = getDataSize();

         return MySuperZipFunction(srcData, srcSize, &size);
     }

     virtual void onReceive(const void* data, std::size_t size) {
         std::size_t dstSize;
         const void* dstData = MySuperUnzipFunction(data, size, &dstSize);

         append(dstData, dstSize);
     }
};

// Use like regular packets:
ZipPacket packet;
packet << x << s << d;
...

Construction¶

virtual ~Packet()

Virtual destructor.

Methods¶

void append(const void* data, std::size_t sizeInBytes)

Append data to the end of the packet.

Parameters:

data	Pointer to the sequence of bytes to append
sizeInBytes	Number of bytes to append

See also:

Clear

void clear()

Clear the packet After calling Clear, the packet is empty.

See also:

Append

const void* getData() const

Get a pointer to the data contained in the packet Warning: the returned pointer may become invalid after you append data to the packet, therefore it should never be stored. The return pointer is NULL if the packet is empty.

Returns:

Pointer to the data

See also:

GetDataSize

std::size_t getDataSize() const

Get the size of the data contained in the packet This function returns the number of bytes pointed to by what GetData returns.

Returns:

Data size, in bytes

See also:

GetData

bool endOfPacket() const

Tell if the reading position has reached the / end of the packet This function is useful to know if there is some data left to be read, without actually reading it.

Returns:

True if all data was read, false otherwise

See also:

operator bool

operator BoolType() const

Test the validity of the packet, for reading This operator allows to test the packet as a boolean variable, to check if a reading operation was successful. A packet will be in an invalid state if it has no more data to read. This behaviour is the same as standard C++ streams. Usage example:

    float x;
    packet >> x;
    if (packet)
    {
/// // ok, x was extracted successfully
    }
///
    // -- or --
///
    float x;
    if (packet >> x)
    {
/// // ok, x was extracted successfully
    }

/ Don’t focus on the return type, it’s equivalent to bool but it disallows unwanted implicit conversions to integer or pointer types. /

Returns:

True if last data extraction from packet was successful /

See also:

EndOfPacket

Packet& operator>>(bool& data)

Overloads of operator >> to read data from the packet

Packet& operator<<(bool data)

Overloads of operator << to write data into the packet