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ZhijuCen
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# SocketIsWritable
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Check whether data can be written to a socket at the current time.
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```
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bool SocketIsWritable(
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const int socket // socket handle
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);
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```
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Parameters
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socket
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[in] Socket handle returned by the [SocketCreate](/en/docs/network/socketcreate) function. When an incorrect handle is passed, the error 5270 (ERR_NETSOCKET_INVALIDHANDLE) is written to [_LastError](/en/docs/predefined/_lasterror).
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Return Value
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Return true if writing is possible, otherwise false.
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Note
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This function allows you to check whether it is possible to write data to a socket right now.
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If an error occurs on a system socket when executing the function, connection established via [SocketConnect](/en/docs/network/socketconnect) is discontinued.
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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()](/en/docs/check/getlasterror) returns the error 4014 – "Function is not allowed for call".
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Example:
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```
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//+------------------------------------------------------------------+
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//| SocketIsWritable.mq5 |
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//| Copyright 2024, MetaQuotes Ltd. |
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//| https://www.mql5.com |
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//+------------------------------------------------------------------+
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#property copyright "Copyright 2024, MetaQuotes Ltd."
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#property link "https://www.mql5.com
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#property version "1.00"
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#property description "Add Address to the list of allowed ones in the terminal settings to let the example work"
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#property script_show_inputs
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input string Address ="www.mql5.com";
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input int Port =80;
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bool ExtTLS =false;
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//+------------------------------------------------------------------+
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//| Script program start function |
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//+------------------------------------------------------------------+
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void OnStart(void)
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{
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//--- create a socket and get its handle
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int socket=SocketCreate();
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//--- check the handle
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if(socket!=INVALID_HANDLE)
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{
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//--- if all is well, connect
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if(SocketConnect(socket,Address,Port,1000))
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{
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PrintFormat("Established connection to %s:%d",Address,Port);
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string subject,issuer,serial,thumbprint;
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datetime expiration;
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//--- if connection is protected by certificate, display its data
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if(SocketTlsCertificate(socket,subject,issuer,serial,thumbprint,expiration))
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{
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Print("TLS certificate:");
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Print(" Owner: ",subject);
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Print(" Issuer: ",issuer);
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Print(" Number: ",serial);
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Print(" Print: ",thumbprint);
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Print(" Expiration: ",expiration);
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ExtTLS=true;
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}
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//--- send GET request to the server
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if(HTTPSend(socket,"GET / HTTP/1.1\r\nHost: www.mql5.com\r\nUser-Agent: MT5\r\n\r\n"))
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{
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Print("GET request sent");
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//--- read response
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if(!HTTPRecv(socket,1000))
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Print("Failed to get a response, error ",GetLastError());
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}
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else
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Print("Failed to send GET request, error ",GetLastError());
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}
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else
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{
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PrintFormat("Connection to %s:%d failed, error %d",Address,Port,GetLastError());
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}
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//--- display the ability to write data to the socket at the current moment in time in the journal
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if(SocketIsWritable(socket))
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Print("At the current moment in time, writing data to the socket is possible");
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else
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Print("It is not possible to write data to the socket at the current time");
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//--- close the socket after use
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if(SocketClose(socket))
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Print("Now the socket is closed");
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}
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else
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Print("Failed to create a socket, error ",GetLastError());
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/*
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result:
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At the current moment in time, writing data to the socket is possible
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Socket is closed now
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*/
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}
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//+------------------------------------------------------------------+
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//| Send command to server |
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//+------------------------------------------------------------------+
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bool HTTPSend(int socket,string request)
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{
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//--- convert the string to a character array, discard the terminating zero
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char req[];
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int len=StringToCharArray(request,req)-1;
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if(len<0)
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return(false);
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//--- if a secure TLS connection via port 443 is used
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if(ExtTLS)
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return(SocketTlsSend(socket,req,len)==len);
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//--- if a regular TCP connection is used
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return(SocketSend(socket,req,len)==len);
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}
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//+------------------------------------------------------------------+
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//| Read server response |
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//+------------------------------------------------------------------+
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bool HTTPRecv(int socket,uint timeout_ms)
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{
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char rsp[];
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string result;
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ulong timeout_check=GetTickCount64()+timeout_ms;
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//--- read data from the socket while there is some, but not longer than timeout
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do
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{
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uint len=SocketIsReadable(socket);
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if(len)
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{
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int rsp_len;
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//--- different read commands depending on whether the connection is secure or not
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if(ExtTLS)
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rsp_len=SocketTlsRead(socket,rsp,len);
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else
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rsp_len=SocketRead(socket,rsp,len,timeout_ms);
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//--- parse response
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if(rsp_len>0)
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{
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result+=CharArrayToString(rsp,0,rsp_len);
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//--- display response header only
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int header_end=StringFind(result,"\r\n\r\n");
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if(header_end>0)
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{
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Print("HTTP answer header received:");
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Print(StringSubstr(result,0,header_end));
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return(true);
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}
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//--- update read timeout expiration time
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timeout_check=GetTickCount64()+timeout_ms;
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}
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}
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}
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while(GetTickCount64()<timeout_check && !IsStopped());
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return(false);
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}
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```
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