socket-library-mt4-mt5.mqh

/* *******************************************************************************

Socket library, for both MT4 and MT5 (32-bit and 64-bit)

Features:

   * Both client and server sockets
   * Both send and receive
   * Both MT4 and MT5 (32-bit and 64-bit)
   * Optional event-driven handling (EAs only, not scripts or indicators),
     offering faster responses to socket events than OnTimer()
   * Direct use of Winsock; no need for a custom DLL sitting 
     between this code and ws2_32.dll

Based on the following forum posts:

   https://www.mql5.com/en/forum/203049#comment_5232176
   https://www.mql5.com/en/forum/160115/page3#comment_3817302


CLIENT SOCKETS
--------------

You create a connection to a server using one of the following two 
constructors for ClientSocket:

   ClientSocket(ushort localport);
   ClientSocket(string HostnameOrIPAddress, ushort port);

The first connects to a port on localhost (127.0.0.1). The second
connects to a remote server, which can be specified either by
passing an IP address such as "123.123.123.123" or a hostname
such as "www.myserver.com".

After creating the instance of the class, and periodically afterwards,
you should check the value of IsSocketConnected(). If false, then 
the connection has failed (or has later been closed). You then need to 
destroy the class and create a new connection. One common pattern of usage
therefore looks like the following:

   ClientSocket * glbConnection = NULL;

   void OnTick()
   {
      // Create a socket if none already exists
      if (!glbConnection) glbConnection = new ClientSocket(12345);
      
      if (glbConnection.IsSocketConnected()) {
         // Socket is okay. Do some action such as sending or receiving
      }
      
      // Socket may already have been dead, or now detected as failed
      // following the attempt above at sending or receiving.
      // If so, delete the socket and try a new one on the next call to OnTick()
      if (!glbConnection.IsSocketConnected()) {
         delete glbConnection;
         glbConnection = NULL;            
      }
   }

You send data down a socket using the simple Send() method, which takes
a string parameter. Any failure to send returns false, which will
also mean that IsSocketConnected() then returns false. The format
of the data which you are sending to the server is obviously
entirely up to you...

You can receive pending incoming data on a socket using Receive(), which
returns either the pending data or an empty string. You will normally want
to call Receive() from OnTimer(), or using the event handling described below.

A non-blank return value from Receive() does not necessarily mean that 
the socket is still active. The server may have sent some data *and* closed 
the socket. 

   string strMessage = MySocket.Receive();
   if (strMessage != "") {
      // Process the message
   }
   
   // Regardless of whether there was any data, the socket may
   // now be dead.
   if (!MySocket.IsSocketConnected()) {
      // ... socket has been closed
   }

You can also give Receive() an optional message terminator, such as "\r\n".
It will then store up data, and only return complete messages (minus the
terminator). If you use a terminator then there may have been multiple
complete messages since your last call to Receive(), and you should
keep calling Receive() until it returns an empty string, in order to collect
all the messages. For example:

   string strMessage;
   do {
      strMessage = MySocket.Receive("\r\n");
      if (strMessage != "") {
         // Do something with the message
      }
   } (while strMessage != "");

You close a socket simply by destroying the ClientSocket object.


SERVER SOCKETS
--------------

For anyone not used to socket programming: the model is that you create
a server socket; you accept connections on it; and each acceptance
creates a new socket for communicating with that client. No data
is sent or received through the server socket itself.

You create a server socket by telling the constructor a port number,
and whether to accept connections only from the local machine or
from any remote computer (subject to firewall rules etc).

   ServerSocket(ushort ServerPort, bool ForLocalhostOnly);

You should check the value of Created() after creating the ServerSocket()
object. Any failure will usually be because something is already 
listening on your chosen port.

   MyServerSocket = new ServerSocket(12345, true);
   if (!MyServerSocket.Created()) {
      // Almost certainly because port 12345 is already in use
   }

You must be careful to destroy any server sockets which you
create. If you don't then the port will remain in use and locked
until MT4/5 is shut down, and you (or any other program) will not
be able to create a new socket on that port. The normal way
of handling this is to do destruction in OnDeinit():

   ServerSocket * glbServerSocket;
   ...
   
   void OnDeinit(const int reason)
   {
      if (glbServerSocket) delete glbServerSocket;
   }

You accept incoming connections using Accept(), typically from
periodic checks in OnTimer() or using the event handling described below.
Accept() returns either NULL if there is no waiting client, or a new
instance of ClientSocket() which you then use for communicating with
the client. There can be multiple simultaneous new connections,
and you will therefore typically want to keep calling Accept()
until it returns NULL. For example:

   ClientSocket * pNewClient;
   do {
      pNewClient = MyServerSocket.Accept();
      if (pNewClient) {
         // Store client socket for future use.
         // Must remember to delete it when finished, to avoid memory leaks.
      }
   } (while pNewClient != NULL);

To repeat the overview above: Accept() gives you a new instance of
ClientSocket (which you must later delete). You then communicate with the 
client using the Send() and Receive() on ClientSocket. No data is
ever sent or received through the server socket itself.


EVENT-DRIVEN HANDLING
---------------------

The timing infrastructure in Windows does not normally have millisecond 
granularity. EventSetMillisecondTimer(1) is usually in fact equivalent 
to EventSetMillisecondTimer(16). Therefore, checks for socket
activity in OnTimer() potentially have a delay of at least 16 milliseconds
before you respond to a new connection or incoming data.

In an EA (but not a script or indicator) you can achieve <1ms response
times using event-driven handling. The way this works is that the 
socket library generates dummy key-down messages to OnChartEvent() 
when socket activity occurs. Responding to these events can be 
significantly faster than a periodic check in OnTimer().

You need to request the event-driven handling by #defining SOCKET_LIBRARY_USE_EVENTS
before including the library. For example:

   #define SOCKET_LIBRARY_USE_EVENTS
   #include <socket-library-mt4-mt5.mqh>

(Note that this has no effect in a custom indicator or script. It only
works with EAs.)

You then process notifications in OnChartEvent as follows:

   void OnChartEvent(const int id, const long& lparam, const double& dparam, const string& sparam)
   {
      if (id == CHARTEVENT_KEYDOWN) {
         // May be a real key press, or a dummy notification
         // resulting from socket activity. If lparam matches
         // any .GetSocketHandle() then it's from a socket.
         // If not, it's a real key press. (If lparam>256 then
         // it's also pretty reliably a socket message rather 
         // than a real key press.)
         
         if (lparam == MyServerSocket.GetSocketHandle()) {
            // Activity on a server socket
         } else if (lparam == MyClientSocket.GetSocketHandle()) {
            // Activity on a client socket
         } else {
            // Doesn't match a socket. Assume real key pres
         }
      }
   }

For a comprehensive example of using the event-driven handling,
see the example socket server code.


NOTES ON MT4/5 CROSS-COMPATIBILITY
----------------------------------

It appears to be safe for a 64-bit application to use 4-byte socket
handles, despite the fact that the Win32 SDK defines SOCKET as 8-byte
on x64. Nevertheless, this code uses 8-byte handles when running
on 64-bit MT5.

The area which definitely does cause problems is gethostbyname(),
because it returns a memory block containing pointers whose size
depends on the environment. (The issue here is 32-bit vs 64-bit,
not MT4 vs MT5.)

This code not only needs to handle 4-byte vs 8-byte memory pointers.
The further problem is that MQL5 has no integer data type whose
size varies with the environment. Therefore, it's necessary to
have two versions of the #import of gethostbyname(), and to
force the compiler to use the applicable one despite the fact
that they only really vary by their return type. Manipulating
the hostent* returned by gethostbyname() is then very ugly,
made doubly so by the need for different paths of execution
on 32-bit and 64-bit, using a range of different #imports of
the RtlMoveMemory() function which the code uses to
process the pointers.

******************************************************************************* */

#property strict


// -------------------------------------------------------------
// Winsock constants and structures
// -------------------------------------------------------------

#define SOCKET_HANDLE32       uint
#define SOCKET_HANDLE64       ulong
#define AF_INET               2
#define SOCK_STREAM           1
#define IPPROTO_TCP           6
#define INVALID_SOCKET32      0xFFFFFFFF
#define INVALID_SOCKET64      0xFFFFFFFFFFFFFFFF
#define SOCKET_ERROR          -1
#define INADDR_NONE           0xFFFFFFFF
#define FIONBIO               0x8004667E
#define WSAWOULDBLOCK         10035

struct sockaddr {
   short family;
   ushort port;
   uint address;
   ulong ignore;
};

struct linger {
   ushort onoff;
   ushort linger_seconds;
};

// -------------------------------------------------------------
// DLL imports
// -------------------------------------------------------------

#import "ws2_32.dll"
   // Imports for 32-bit environment
   SOCKET_HANDLE32 socket(int, int, int); // Artificially differs from 64-bit version based on 3rd parameter
   int connect(SOCKET_HANDLE32, sockaddr&, int);
   int closesocket(SOCKET_HANDLE32);
   int send(SOCKET_HANDLE32, uchar&[],int,int);
   int recv(SOCKET_HANDLE32, uchar&[], int, int);
   int ioctlsocket(SOCKET_HANDLE32, uint, uint&);
   int bind(SOCKET_HANDLE32, sockaddr&, int);
   int listen(SOCKET_HANDLE32, int);
   SOCKET_HANDLE32 accept(SOCKET_HANDLE32, int, int);
   int WSAAsyncSelect(SOCKET_HANDLE32, int, uint, int);
   int shutdown(SOCKET_HANDLE32, int);
   
   // Imports for 64-bit environment
   SOCKET_HANDLE64 socket(int, int, uint); // Artificially differs from 32-bit version based on 3rd parameter
   int connect(SOCKET_HANDLE64, sockaddr&, int);
   int closesocket(SOCKET_HANDLE64);
   int send(SOCKET_HANDLE64, uchar&[], int, int);
   int recv(SOCKET_HANDLE64, uchar&[], int, int);
   int ioctlsocket(SOCKET_HANDLE64, uint, uint&);
   int bind(SOCKET_HANDLE64, sockaddr&, int);
   int listen(SOCKET_HANDLE64, int);
   SOCKET_HANDLE64 accept(SOCKET_HANDLE64, int, int);
   int WSAAsyncSelect(SOCKET_HANDLE64, long, uint, int);
   int shutdown(SOCKET_HANDLE64, int);

   // gethostbyname() has to vary between 32/64-bit, because
   // it returns a memory pointer whose size will be either
   // 4 bytes or 8 bytes. In order to keep the compiler
   // happy, we therefore need versions which take 
   // artificially-different parameters on 32/64-bit
   uint gethostbyname(uchar&[]); // For 32-bit
   ulong gethostbyname(char&[]); // For 64-bit

   // Neutral; no difference between 32-bit and 64-bit
   uint inet_addr(uchar&[]);
   int WSAGetLastError();
   uint htonl(uint);
   ushort htons(ushort);
#import

// For navigating the Winsock hostent structure, with indescribably horrible
// variation between 32-bit and 64-bit
#import "kernel32.dll"
   void RtlMoveMemory(uint&, uint, int);
   void RtlMoveMemory(ushort&, uint, int);
   void RtlMoveMemory(ulong&, ulong, int);
   void RtlMoveMemory(ushort&, ulong, int);
#import

// -------------------------------------------------------------
// Forward definitions of classes
// -------------------------------------------------------------

class ClientSocket;
class ServerSocket;


// -------------------------------------------------------------
// Client socket class
// -------------------------------------------------------------

class ClientSocket
{
   private:
      // Need different socket handles for 32-bit and 64-bit environments
      SOCKET_HANDLE32 mSocket32;
      SOCKET_HANDLE64 mSocket64;
      
      // Other state variables
      bool mConnected;
      int mLastWSAError;
      string mPendingReceiveData; // Backlog of incoming data, if using a message-terminator in Receive()
      
      // Event handling
      bool mDoneEventHandling;
      void SetupSocketEventHandling();
      
   public:
      // Constructors for connecting to a server, either locally or remotely
      ClientSocket(ushort localport);
      ClientSocket(string HostnameOrIPAddress, ushort port);

      // Constructors used by ServerSocket() when accepting a client connection
      ClientSocket(ServerSocket* ForInternalUseOnly, SOCKET_HANDLE32 ForInternalUseOnly_clientsocket32);
      ClientSocket(ServerSocket* ForInternalUseOnly, SOCKET_HANDLE64 ForInternalUseOnly_clientsocket64);

      // Destructor
      ~ClientSocket();
      
      // Simple send and receive methods
      bool Send(string strMsg);
      bool Send(uchar & callerBuffer[], int startAt = 0, int szToSend = -1);
      string Receive(string MessageSeparator = "");
      int Receive(uchar & callerBuffer[]);
      
      // State information
      bool IsSocketConnected() {return mConnected;}
      int GetLastSocketError() {return mLastWSAError;}
      ulong GetSocketHandle() {return (mSocket32 ? mSocket32 : mSocket64);}
      
      // Buffer sizes, overwriteable once the class has been created
      int ReceiveBufferSize;
      int SendBufferSize;
};


// -------------------------------------------------------------
// Constructor for a simple connection to 127.0.0.1
// -------------------------------------------------------------

ClientSocket::ClientSocket(ushort localport)
{
   // Default buffer sizes
   ReceiveBufferSize = 10000;
   SendBufferSize = 999999999;
   
   // Need to create either a 32-bit or 64-bit socket handle
   mConnected = false;
   mLastWSAError = 0;
   if (TerminalInfoInteger(TERMINAL_X64)) {
      uint proto = IPPROTO_TCP;
      mSocket64 = socket(AF_INET, SOCK_STREAM, proto);
      if (mSocket64 == INVALID_SOCKET64) {
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("socket() failed, 64-bit, error: ", mLastWSAError);
         #endif
         return;
      }
   } else {
      int proto = IPPROTO_TCP;
      mSocket32 = socket(AF_INET, SOCK_STREAM, proto);
      if (mSocket32 == INVALID_SOCKET32) {
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("socket() failed, 32-bit, error: ", mLastWSAError);
         #endif
         return;
      }
   }
   
   // Fixed definition for connecting to 127.0.0.1, with variable port
   sockaddr server;
   server.family = AF_INET;
   server.port = htons(localport);
   server.address = 0x100007f; // 127.0.0.1
   
   // connect() call has to differ between 32-bit and 64-bit
   int res;
   if (TerminalInfoInteger(TERMINAL_X64)) {
      res = connect(mSocket64, server, sizeof(sockaddr));
   } else {
      res = connect(mSocket32, server, sizeof(sockaddr));
   }
   if (res == SOCKET_ERROR) {
      // Ooops
      mLastWSAError = WSAGetLastError();
      #ifdef SOCKET_LIBRARY_LOGGING
         Print("connect() to localhost failed, error: ", mLastWSAError);
      #endif
      return;
   } else {
      mConnected = true;   
      
      // Set up event handling. Can fail if called in OnInit() when
      // MT4/5 is still loading, because no window handle is available
      #ifdef SOCKET_LIBRARY_USE_EVENTS
         SetupSocketEventHandling();
      #endif
   }
}

// -------------------------------------------------------------
// Constructor for connection to a hostname or IP address
// -------------------------------------------------------------

ClientSocket::ClientSocket(string HostnameOrIPAddress, ushort port)
{
   // Default buffer sizes
   ReceiveBufferSize = 10000;
   SendBufferSize = 999999999;

   // Need to create either a 32-bit or 64-bit socket handle
   mConnected = false;
   mLastWSAError = 0;
   if (TerminalInfoInteger(TERMINAL_X64)) {
      uint proto = IPPROTO_TCP;
      mSocket64 = socket(AF_INET, SOCK_STREAM, proto);
      if (mSocket64 == INVALID_SOCKET64) {
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("socket() failed, 64-bit, error: ", mLastWSAError);
         #endif
         return;
      }
   } else {
      int proto = IPPROTO_TCP;
      mSocket32 = socket(AF_INET, SOCK_STREAM, proto);
      if (mSocket32 == INVALID_SOCKET32) {
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("socket() failed, 32-bit, error: ", mLastWSAError);
         #endif
         return;
      }
   }

   // Is the host parameter an IP address?
   uchar arrName[];
   StringToCharArray(HostnameOrIPAddress, arrName);
   ArrayResize(arrName, ArraySize(arrName) + 1);
   uint addr = inet_addr(arrName);
   
   if (addr == INADDR_NONE) {
      // Not an IP address. Need to look up the name
      // .......................................................................................
      // Unbelievably horrible handling of the hostent structure depending on whether
      // we're in 32-bit or 64-bit, with different-length memory pointers. 
      // Ultimately, we're having to deal here with extracting a uint** from
      // the memory block provided by Winsock - and with additional 
      // complications such as needing different versions of gethostbyname(),
      // because the return value is a pointer, which is 4 bytes in x86 and
      // 8 bytes in x64. So, we must artifically pass different types of buffer
      // to gethostbyname() depending on the environment, so that the compiler
      // doesn't treat them as imports which differ only by their return type.
      if (TerminalInfoInteger(TERMINAL_X64)) {
         char arrName64[];
         ArrayResize(arrName64, ArraySize(arrName));
         for (int i = 0; i < ArraySize(arrName); i++) arrName64[i] = (char)arrName[i];
         ulong nres = gethostbyname(arrName64);
         if (nres == 0) {
            // Name lookup failed
            mLastWSAError = WSAGetLastError();
            #ifdef SOCKET_LIBRARY_LOGGING
               Print("Name-resolution in gethostbyname() failed, 64-bit, error: ", mLastWSAError);
            #endif
            return;
         } else {
            // Need to navigate the hostent structure. Very, very ugly...
            ushort addrlen;
            RtlMoveMemory(addrlen, nres + 18, 2);
            if (addrlen == 0) {
               // No addresses associated with name
               #ifdef SOCKET_LIBRARY_LOGGING
                  Print("Name-resolution in gethostbyname() returned no addresses, 64-bit, error: ", mLastWSAError);
               #endif
               return;
            } else {
               ulong ptr1, ptr2, ptr3;
               RtlMoveMemory(ptr1, nres + 24, 8);
               RtlMoveMemory(ptr2, ptr1, 8);
               RtlMoveMemory(ptr3, ptr2, 4);
               addr = (uint)ptr3;
            }
         }
      } else {
         uint nres = gethostbyname(arrName);
         if (nres == 0) {
            // Name lookup failed
            mLastWSAError = WSAGetLastError();
            #ifdef SOCKET_LIBRARY_LOGGING
               Print("Name-resolution in gethostbyname() failed, 32-bit, error: ", mLastWSAError);
            #endif
            return;
         } else {
            // Need to navigate the hostent structure. Very, very ugly...
            ushort addrlen;
            RtlMoveMemory(addrlen, nres + 10, 2);
            if (addrlen == 0) {
               // No addresses associated with name
               #ifdef SOCKET_LIBRARY_LOGGING
                  Print("Name-resolution in gethostbyname() returned no addresses, 32-bit, error: ", mLastWSAError);
               #endif
               return;
            } else {
               int ptr1, ptr2;
               RtlMoveMemory(ptr1, nres + 12, 4);
               RtlMoveMemory(ptr2, ptr1, 4);
               RtlMoveMemory(addr, ptr2, 4);
            }
         }
      }
   
   } else {
      // The HostnameOrIPAddress parameter is an IP address,
      // which we have stored in addr
   }

   // Fill in the address and port into a sockaddr_in structure
   sockaddr server;
   server.family = AF_INET;
   server.port = htons(port);
   server.address = addr; // Already in network-byte-order

   // connect() call has to differ between 32-bit and 64-bit
   int res;
   if (TerminalInfoInteger(TERMINAL_X64)) {
      res = connect(mSocket64, server, sizeof(sockaddr));
   } else {
      res = connect(mSocket32, server, sizeof(sockaddr));
   }
   if (res == SOCKET_ERROR) {
      // Ooops
      mLastWSAError = WSAGetLastError();
      #ifdef SOCKET_LIBRARY_LOGGING
         Print("connect() to server failed, error: ", mLastWSAError);
      #endif
   } else {
      mConnected = true;   

      // Set up event handling. Can fail if called in OnInit() when
      // MT4/5 is still loading, because no window handle is available
      #ifdef SOCKET_LIBRARY_USE_EVENTS
         SetupSocketEventHandling();
      #endif
   }
}

// -------------------------------------------------------------
// Constructors for internal use only, when accepting connections
// on a server socket
// -------------------------------------------------------------

ClientSocket::ClientSocket(ServerSocket* ForInternalUseOnly, SOCKET_HANDLE32 ForInternalUseOnly_clientsocket32)
{
   // Constructor ror "internal" use only, when accepting an incoming connection
   // on a server socket
   mConnected = true;
   ReceiveBufferSize = 10000;
   SendBufferSize = 999999999;

   mSocket32 = ForInternalUseOnly_clientsocket32;
}

ClientSocket::ClientSocket(ServerSocket* ForInternalUseOnly, SOCKET_HANDLE64 ForInternalUseOnly_clientsocket64)
{
   // Constructor ror "internal" use only, when accepting an incoming connection
   // on a server socket
   mConnected = true;
   ReceiveBufferSize = 10000;
   SendBufferSize = 999999999;

   mSocket64 = ForInternalUseOnly_clientsocket64;
}


// -------------------------------------------------------------
// Destructor. Close the socket if created
// -------------------------------------------------------------

ClientSocket::~ClientSocket()
{
   if (TerminalInfoInteger(TERMINAL_X64)) {
      if (mSocket64 != 0) {
         shutdown(mSocket64, 2);
         closesocket(mSocket64);
      }
   } else {
      if (mSocket32 != 0) {
         shutdown(mSocket32, 2);
         closesocket(mSocket32);
      }
   }   
}

// -------------------------------------------------------------
// Simple send function which takes a string parameter
// -------------------------------------------------------------

bool ClientSocket::Send(string strMsg)
{
   if (!mConnected) return false;

   // Make sure that event handling is set up, if requested
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      SetupSocketEventHandling();
   #endif 

   int szToSend = StringLen(strMsg);
   if (szToSend == 0) return true; // Ignore empty strings
      
   bool bRetval = true;
   uchar arr[];
   StringToCharArray(strMsg, arr);
   
   while (szToSend > 0) {
      int res, szAmountToSend = (szToSend > SendBufferSize ? SendBufferSize : szToSend);
      if (TerminalInfoInteger(TERMINAL_X64)) {
         res = send(mSocket64, arr, szToSend, 0);
      } else {
         res = send(mSocket32, arr, szToSend, 0);
      }
      
      if (res == SOCKET_ERROR || res == 0) {
         mLastWSAError = WSAGetLastError();
         if (mLastWSAError == WSAWOULDBLOCK) {
            // Blocking operation. Retry.
         } else {
            #ifdef SOCKET_LIBRARY_LOGGING
               Print("send() failed, error: ", mLastWSAError);
            #endif

            // Assume death of socket for any other type of error
            szToSend = -1;
            bRetval = false;
            mConnected = false;
         }
      } else {
         szToSend -= res;
         if (szToSend > 0) {
            // If further data remains to be sent, shuffle the array downwards
            // by copying it onto itself. Note that the MQL4/5 documentation
            // says that the result of this is "undefined", but it seems
            // to work reliably in real life (because it almost certainly
            // just translates inside MT4/5 into a simple call to RtlMoveMemory,
            // which does allow overlapping source & destination).
            ArrayCopy(arr, arr, 0, res, szToSend);
         }
      }
   }

   return bRetval;
}


// -------------------------------------------------------------
// Simple send function which takes an array of uchar[], 
// instead of a string. Can optionally be given a start-index
// within the array (rather then default zero) and a number 
// of bytes to send.
// -------------------------------------------------------------

bool ClientSocket::Send(uchar & callerBuffer[], int startAt = 0, int szToSend = -1)
{
   if (!mConnected) return false;

   // Make sure that event handling is set up, if requested
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      SetupSocketEventHandling();
   #endif 

   // Process the start-at and send-size parameters
   int arraySize = ArraySize(callerBuffer);
   if (!arraySize) return true; // Ignore empty arrays 
   if (startAt >= arraySize) return true; // Not a valid start point; nothing to send
   if (szToSend <= 0) szToSend = arraySize;
   if (startAt + szToSend > arraySize) szToSend = arraySize - startAt;
   
   // Take a copy of the array 
   uchar arr[];
   ArrayResize(arr, szToSend);
   ArrayCopy(arr, callerBuffer, 0, startAt, szToSend);   
      
   bool bRetval = true;
   
   while (szToSend > 0) {
      int res, szAmountToSend = (szToSend > SendBufferSize ? SendBufferSize : szToSend);
      if (TerminalInfoInteger(TERMINAL_X64)) {
         res = send(mSocket64, arr, szToSend, 0);
      } else {
         res = send(mSocket32, arr, szToSend, 0);
      }
      
      if (res == SOCKET_ERROR || res == 0) {
         mLastWSAError = WSAGetLastError();
         if (mLastWSAError == WSAWOULDBLOCK) {
            // Blocking operation. Retry.
         } else {
            #ifdef SOCKET_LIBRARY_LOGGING
               Print("send() failed, error: ", mLastWSAError);
            #endif

            // Assume death of socket for any other type of error
            szToSend = -1;
            bRetval = false;
            mConnected = false;
         }
      } else {
         szToSend -= res;
         if (szToSend > 0) {
            // If further data remains to be sent, shuffle the array downwards
            // by copying it onto itself. Note that the MQL4/5 documentation
            // says that the result of this is "undefined", but it seems
            // to work reliably in real life (because it almost certainly
            // just translates inside MT4/5 into a simple call to RtlMoveMemory,
            // which does allow overlapping source & destination).
            ArrayCopy(arr, arr, 0, res, szToSend);
         }
      }
   }

   return bRetval;
}


// -------------------------------------------------------------
// Simple receive function. Without a message separator,
// it simply returns all the data sitting on the socket.
// With a separator, it stores up incoming data until
// it sees the separator, and then returns the text minus
// the separator.
// Returns a blank string once no (more) data is waiting
// for collection.
// -------------------------------------------------------------

string ClientSocket::Receive(string MessageSeparator = "")
{
   if (!mConnected) return "";

   // Make sure that event handling is set up, if requested
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      SetupSocketEventHandling();
   #endif
   
   string strRetval = "";
   
   uchar arrBuffer[];
   ArrayResize(arrBuffer, ReceiveBufferSize);

   uint nonblock = 1;
   if (TerminalInfoInteger(TERMINAL_X64)) {
      ioctlsocket(mSocket64, FIONBIO, nonblock);
 
      int res = 1;
      while (res > 0) {
         res = recv(mSocket64, arrBuffer, ReceiveBufferSize, 0);
         if (res > 0) {
            StringAdd(mPendingReceiveData, CharArrayToString(arrBuffer, 0, res));

         } else if (res == 0) {
            // No data

         } else {
            mLastWSAError = WSAGetLastError();

            if (mLastWSAError != WSAWOULDBLOCK) {
               #ifdef SOCKET_LIBRARY_LOGGING
                  Print("recv() failed, result:, " , res, ", error: ", mLastWSAError, " queued bytes: " , StringLen(mPendingReceiveData));
               #endif
               mConnected = false;
            }
         }
      }
   } else {
      ioctlsocket(mSocket32, FIONBIO, nonblock);

      int res = 1;
      while (res > 0) {
         res = recv(mSocket32, arrBuffer, ReceiveBufferSize, 0);
         if (res > 0) {
            StringAdd(mPendingReceiveData, CharArrayToString(arrBuffer, 0, res));

         } else if (res == 0) {
            // No data
         
         } else {
            mLastWSAError = WSAGetLastError();

            if (mLastWSAError != WSAWOULDBLOCK) {
               #ifdef SOCKET_LIBRARY_LOGGING
                  Print("recv() failed, result:, " , res, ", error: ", mLastWSAError, " queued bytes: " , StringLen(mPendingReceiveData));
               #endif
               mConnected = false;
            }
         }
      }
   }   
   
   if (mPendingReceiveData == "") {
      // No data
      
   } else if (MessageSeparator == "") {
      // No requested message separator to wait for
      strRetval = mPendingReceiveData;
      mPendingReceiveData = "";
   
   } else {
      int idx = StringFind(mPendingReceiveData, MessageSeparator);
      if (idx >= 0) {
         while (idx == 0) {
            mPendingReceiveData = StringSubstr(mPendingReceiveData, idx + StringLen(MessageSeparator));
            idx = StringFind(mPendingReceiveData, MessageSeparator);
         }
         
         strRetval = StringSubstr(mPendingReceiveData, 0, idx);
         mPendingReceiveData = StringSubstr(mPendingReceiveData, idx + StringLen(MessageSeparator));
      }
   }
   
   return strRetval;
}

// -------------------------------------------------------------
// Receive function which fills an array, provided by reference.
// Always clears the array. Returns the number of bytes 
// put into the array.
// If you send and receive binary data, then you can no longer 
// use the built-in messaging protocol provided by this library's
// option to process a message terminator such as \r\n. You have
// to implement the messaging yourself.
// -------------------------------------------------------------

int ClientSocket::Receive(uchar & callerBuffer[])
{
   if (!mConnected) return 0;

   ArrayResize(callerBuffer, 0);
   int ctTotalReceived = 0;
   
   // Make sure that event handling is set up, if requested
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      SetupSocketEventHandling();
   #endif
   
   uchar arrBuffer[];
   ArrayResize(arrBuffer, ReceiveBufferSize);

   uint nonblock = 1;
   if (TerminalInfoInteger(TERMINAL_X64)) {
      ioctlsocket(mSocket64, FIONBIO, nonblock);
   } else {
      ioctlsocket(mSocket32, FIONBIO, nonblock);
   }

   int res = 1;
   while (res > 0) {
      if (TerminalInfoInteger(TERMINAL_X64)) {
         res = recv(mSocket64, arrBuffer, ReceiveBufferSize, 0);
      } else {
         res = recv(mSocket32, arrBuffer, ReceiveBufferSize, 0);
      }
      
      if (res > 0) {
         ArrayResize(callerBuffer, ctTotalReceived + res);
         ArrayCopy(callerBuffer, arrBuffer, ctTotalReceived, 0, res);
         ctTotalReceived += res;

      } else if (res == 0) {
         // No data

      } else {
         mLastWSAError = WSAGetLastError();

         if (mLastWSAError != WSAWOULDBLOCK) {
            #ifdef SOCKET_LIBRARY_LOGGING
               Print("recv() failed, result:, " , res, ", error: ", mLastWSAError);
            #endif
            mConnected = false;
         }
      }
   }
   
   return ctTotalReceived;
}

// -------------------------------------------------------------
// Event handling in client socket
// -------------------------------------------------------------

void ClientSocket::SetupSocketEventHandling()
{
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      if (mDoneEventHandling) return;
      
      // Can only do event handling in an EA. Ignore otherwise.
      if (MQLInfoInteger(MQL_PROGRAM_TYPE) != PROGRAM_EXPERT) {
         mDoneEventHandling = true;
         return;
      }
      
      long hWnd = ChartGetInteger(0, CHART_WINDOW_HANDLE);
      if (!hWnd) return;
      mDoneEventHandling = true; // Don't actually care whether it succeeds.
      
      if (TerminalInfoInteger(TERMINAL_X64)) {
         WSAAsyncSelect(mSocket64, hWnd, 0x100 /* WM_KEYDOWN */, 0xFF /* All events */);
      } else {
         WSAAsyncSelect(mSocket32, (int)hWnd, 0x100 /* WM_KEYDOWN */, 0xFF /* All events */);
      }
   #endif
}


// -------------------------------------------------------------
// Server socket class
// -------------------------------------------------------------

class ServerSocket
{
   private:
      // Need different socket handles for 32-bit and 64-bit environments
      SOCKET_HANDLE32 mSocket32;
      SOCKET_HANDLE64 mSocket64;

      // Other state variables
      bool mCreated;
      int mLastWSAError;
      
      // Optional event handling
      void SetupSocketEventHandling();
      bool mDoneEventHandling;
                 
   public:
      // Constructor, specifying whether we allow remote connections
      ServerSocket(ushort ServerPort, bool ForLocalhostOnly);
      
      // Destructor
      ~ServerSocket();
      
      // Accept function, which returns NULL if no waiting client, or
      // a new instace of ClientSocket()
      ClientSocket * Accept();

      // Access to state information
      bool Created() {return mCreated;}
      int GetLastSocketError() {return mLastWSAError;}
      ulong GetSocketHandle() {return (mSocket32 ? mSocket32 : mSocket64);}
};


// -------------------------------------------------------------
// Constructor for server socket
// -------------------------------------------------------------

ServerSocket::ServerSocket(ushort serverport, bool ForLocalhostOnly)
{
   // Create socket and make it non-blocking
   mCreated = false;
   mLastWSAError = 0;
   if (TerminalInfoInteger(TERMINAL_X64)) {
      // Force compiler to use the 64-bit version of socket() 
      // by passing it a uint 3rd parameter 
      uint proto = IPPROTO_TCP;
      mSocket64 = socket(AF_INET, SOCK_STREAM, proto);
      
      if (mSocket64 == INVALID_SOCKET64) {
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("socket() failed, 64-bit, error: ", mLastWSAError);
         #endif
         return;
      }
      uint nonblock = 1;
      ioctlsocket(mSocket64, FIONBIO, nonblock);

   } else {
      // Force compiler to use the 32-bit version of socket() 
      // by passing it a int 3rd parameter 
      int proto = IPPROTO_TCP;
      mSocket32 = socket(AF_INET, SOCK_STREAM, proto);
      
      if (mSocket32 == INVALID_SOCKET32) {
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("socket() failed, 32-bit, error: ", mLastWSAError);
         #endif
         return;
      }
      uint nonblock = 1;
      ioctlsocket(mSocket32, FIONBIO, nonblock);
   }

   // Try a bind
   sockaddr server;
   server.family = AF_INET;
   server.port = htons(serverport);
   server.address = (ForLocalhostOnly ? 0x100007f : 0); // 127.0.0.1 or INADDR_ANY

   if (TerminalInfoInteger(TERMINAL_X64)) {
      int bindres = bind(mSocket64, server, sizeof(sockaddr));
      if (bindres != 0) {
         // Bind failed
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("bind() failed, 64-bit, port probably already in use, error: ", mLastWSAError);
         #endif
         return;
         
      } else {
         int listenres = listen(mSocket64, 10);
         if (listenres != 0) {
            // Listen failed
            mLastWSAError = WSAGetLastError();
            #ifdef SOCKET_LIBRARY_LOGGING
               Print("listen() failed, 64-bit, error: ", mLastWSAError);
            #endif
            return;
            
         } else {
            mCreated = true;         
         }
      }
   } else {
      int bindres = bind(mSocket32, server, sizeof(sockaddr));
      if (bindres != 0) {
         // Bind failed
         mLastWSAError = WSAGetLastError();
         #ifdef SOCKET_LIBRARY_LOGGING
            Print("bind() failed, 32-bit, port probably already in use, error: ", mLastWSAError);
         #endif
         return;
         
      } else {
         int listenres = listen(mSocket32, 10);
         if (listenres != 0) {
            // Listen failed
            mLastWSAError = WSAGetLastError();
            #ifdef SOCKET_LIBRARY_LOGGING
               Print("listen() failed, 32-bit, error: ", mLastWSAError);
            #endif
            return;
            
         } else {
            mCreated = true;         
         }
      }
   }
   
   // Try settig up event handling; can fail here in constructor
   // if no window handle is available because it's being called 
   // from OnInit() while MT4/5 is loading
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      SetupSocketEventHandling();
   #endif
}


// -------------------------------------------------------------
// Destructor. Close the socket if created
// -------------------------------------------------------------

ServerSocket::~ServerSocket()
{
   if (TerminalInfoInteger(TERMINAL_X64)) {
      if (mSocket64 != 0)  closesocket(mSocket64);
   } else {
      if (mSocket32 != 0)  closesocket(mSocket32);
   }   
}

// -------------------------------------------------------------
// Accepts any incoming connection. Returns either NULL,
// or an instance of ClientSocket
// -------------------------------------------------------------

ClientSocket * ServerSocket::Accept()
{
   if (!mCreated) return NULL;
   
   // Make sure that event handling is in place; can fail in constructor
   // if no window handle is available because it's being called 
   // from OnInit() while MT4/5 is loading
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      SetupSocketEventHandling();
   #endif
   
   ClientSocket * pClient = NULL;

   if (TerminalInfoInteger(TERMINAL_X64)) {
      SOCKET_HANDLE64 acc = accept(mSocket64, 0, 0);
      if (acc != INVALID_SOCKET64) {
         pClient = new ClientSocket(NULL, acc);
      }
   } else {
      SOCKET_HANDLE32 acc = accept(mSocket32, 0, 0);
      if (acc != INVALID_SOCKET32) {
         pClient = new ClientSocket(NULL, acc);
      }
   }

   return pClient;
}

// -------------------------------------------------------------
// Event handling
// -------------------------------------------------------------

void ServerSocket::SetupSocketEventHandling()
{
   #ifdef SOCKET_LIBRARY_USE_EVENTS
      if (mDoneEventHandling) return;
   
      // Can only do event handling in an EA. Ignore otherwise.
      if (MQLInfoInteger(MQL_PROGRAM_TYPE) != PROGRAM_EXPERT) {
         mDoneEventHandling = true;
         return;
      }
    
      long hWnd = ChartGetInteger(0, CHART_WINDOW_HANDLE);
      if (!hWnd) return;
      mDoneEventHandling = true; // Don't actually care whether it succeeds.
      
      if (TerminalInfoInteger(TERMINAL_X64)) {
         WSAAsyncSelect(mSocket64, hWnd, 0x100 /* WM_KEYDOWN */, 0xFF /* All events */);
      } else {
         WSAAsyncSelect(mSocket32, (int)hWnd, 0x100 /* WM_KEYDOWN */, 0xFF /* All events */);
      }
   #endif
}