SocketRead

Read data from a socket.

int  SocketRead(
   int           socket,               // socket
   uchar&        buffer[],             // buffer for reading data from socket
   uint          buffer_maxlen,        // number of bytes to read
   uint          timeout_ms            // reading timeout
   );

Parameters

socket

[in]  Socket handle returned by the SocketCreate function. When an incorrect handle is passed to _LastError, the error 5270 (ERR_NETSOCKET_INVALIDHANDLE) is activated.

buffer

[out]  Reference to the uchar type array the data is read in. Dynamic array size is increased by the number of read bytes. The array size cannot exceed INT_MAX (2147483647).

buffer_maxlen

[in]  Number of bytes to read to the buffer[] array. Data not fitting into the array remain in the socket. They can be received by the next SocketRead call. buffer_maxlen cannot exceed INT_MAX (2147483647).

timeout_ms

[in]  Data reading timeout in milliseconds. If data is not obtained within this time, attempts are stopped and the function returns -1.

Return Value

If successful, return the number of read bytes. In case of an error, -1 is returned.

Note

If an error occurs on a system socket when executing the function, connection established via SocketConnect is discontinued.

In case of a data reading error, the error 5273 (ERR_NETSOCKET_IO_ERROR) is written in _LastError.

The function can be called only from Expert Advisors and scripts, as they run in their own execution threads. If calling from an indicator, GetLastError() returns the error 4014 – "Function is not allowed for call".

Example:

//+------------------------------------------------------------------+
//|                                                SocketExample.mq5 |
//|                        Copyright 2018, MetaQuotes Software Corp. |
//|                                             https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright   "Copyright 2018, MetaQuotes Software Corp."
#property link        "https://www.mql5.com"
#property version     "1.00"
#property description "Add Address to the list of allowed ones in the terminal settings to let the example work"
#property script_show_inputs
 
input string Address="www.mql5.com";
input int    Port   =80;
bool         ExtTLS =false;
//+------------------------------------------------------------------+
//| Send command to the server                                       |
//+------------------------------------------------------------------+
bool HTTPSend(int socket,string request)
  {
   char req[];
   int  len=StringToCharArray(request,req)-1;
   if(len<0)
      return(false);
//--- if secure TLS connection is used via the port 443
   if(ExtTLS)
      return(SocketTlsSend(socket,req,len)==len);
//--- if standard TCP connection is used
   return(SocketSend(socket,req,len)==len);
  }
//+------------------------------------------------------------------+
//| Read server response                                             |
//+------------------------------------------------------------------+
bool HTTPRecv(int socket,uint timeout)
  {
   char   rsp[];
   string result;
   uint   timeout_check=GetTickCount()+timeout;
//--- read data from sockets till they are still present but not longer than timeout
   do
     {
      uint len=SocketIsReadable(socket);
      if(len)
        {
         int rsp_len;
         //--- various reading commands depending on whether the connection is secure or not
         if(ExtTLS)
            rsp_len=SocketTlsRead(socket,rsp,len);
         else
            rsp_len=SocketRead(socket,rsp,len,timeout);
         //--- analyze the response
         if(rsp_len>0)
           {
            result+=CharArrayToString(rsp,0,rsp_len);
            //--- print only the response header
            int header_end=StringFind(result,"\r\n\r\n");
            if(header_end>0)
              {
               Print("HTTP answer header received:");
               Print(StringSubstr(result,0,header_end));
               return(true);
              }
           }
        }
     }
   while(GetTickCount()<timeout_check && !IsStopped());
   return(false);
  }
//+------------------------------------------------------------------+
//| Script program start function                                    |
//+------------------------------------------------------------------+
void OnStart()
  {
   int socket=SocketCreate();
//--- check the handle
   if(socket!=INVALID_HANDLE)
     {
      //--- connect if all is well
      if(SocketConnect(socket,Address,Port,1000))
        {
         Print("Established connection to ",Address,":",Port);
 
         string   subject,issuer,serial,thumbprint;
         datetime expiration;
         //--- if connection is secured by the certificate, display its data
         if(SocketTlsCertificate(socket,subject,issuer,serial,thumbprint,expiration))
           {
            Print("TLS certificate:");
            Print("   Owner:  ",subject);
            Print("   Issuer:  ",issuer);
            Print("   Number:     ",serial);
            Print("   Print: ",thumbprint);
            Print("   Expiration: ",expiration);
            ExtTLS=true;
           }
         //--- send GET request to the server
         if(HTTPSend(socket,"GET / HTTP/1.1\r\nHost: www.mql5.com\r\n\r\n"))
           {
            Print("GET request sent");
            //--- read the response
            if(!HTTPRecv(socket,1000))
               Print("Failed to get a response, error ",GetLastError());
           }
         else
            Print("Failed to send GET request, error ",GetLastError());
        }
      else
        {
         Print("Connection to ",Address,":",Port," failed, error ",GetLastError());
        }
      //--- close a socket after using
      SocketClose(socket);
     }
   else
      Print("Failed to create a socket, error ",GetLastError());
  }
//+------------------------------------------------------------------+

See also

SocketTimeouts, MathSwap