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



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


[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).


[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).


[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.


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".


//|                                                SocketExample.mq5 |
//|                        Copyright 2018, MetaQuotes Software Corp. |
//|                                    |
#property copyright   "Copyright 2018, MetaQuotes Software Corp."
#property link        ""
#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="";
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 secure TLS connection is used via the port 443
//--- if standard TCP connection is used
//| 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
      uint len=SocketIsReadable(socket);
         int rsp_len;
         //--- various reading commands depending on whether the connection is secure or not
         //--- analyze the response
            //--- print only the response header
            int header_end=StringFind(result,"\r\n\r\n");
               Print("HTTP answer header received:");
   while(GetTickCount()<timeout_check && !IsStopped());
//| Script program start function                                    |
void OnStart()
   int socket=SocketCreate();
//--- check the handle
      //--- connect if all is well
         Print("Established connection to ",Address,":",Port);
         string   subject,issuer,serial,thumbprint;
         datetime expiration;
         //--- if connection is secured by the certificate, display its data
            Print("TLS certificate:");
            Print("   Owner:  ",subject);
            Print("   Issuer:  ",issuer);
            Print("   Number:     ",serial);
            Print("   Print: ",thumbprint);
            Print("   Expiration: ",expiration);
         //--- send GET request to the server
         if(HTTPSend(socket,"GET / HTTP/1.1\r\nHost:\r\n\r\n"))
            Print("GET request sent");
            //--- read the response
               Print("Failed to get a response, error ",GetLastError());
            Print("Failed to send GET request, error ",GetLastError());
         Print("Connection to ",Address,":",Port," failed, error ",GetLastError());
      //--- close a socket after using
      Print("Failed to create a socket, error ",GetLastError());

See also

SocketTimeouts, MathSwap