7.6 KiB
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 2000-2024, MetaQuotes Ltd."
#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\nUser-Agent: MT5\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