How to send a POST with a JSON in a WebRequest() call using MQL4?
It works well for me, I have someone like this :
string response = SendResquest("POST", "GetPrediction", "[4, 7]", "Content-Type: application/json", 5000);
string SendResquest(string httpType, string methodName, string bodyData = "", string headers = "", int timeout)
{
uchar bodyDataCharArray[];
ArrayResize(bodyDataCharArray, StringToCharArray(bodyData, bodyDataCharArray)-1);
int response = WebRequest(httpType, this.address+methodName, headers, timeout, bodyDataCharArray, this.resultDataCharArray, this.resultHeader);
string result = CharArrayToString(this.resultDataCharArray);
if(response == 200)
return result;
Print("Error when trying to call API : ", response);
return "";
}
Have you tried setting the headers like this:
headers = "Content-Type: application/json\r\n";
?
So, back to the square No.1:
In the last-year's post, there was a step by step methodology to proceed with a MCVE-based approach to the problem isolation.
Repeating the same steps here, inside MQL4-code,
adding a python-based mock-up WebSERVER, to diagnose the actual working client/server http-protocol exchange & handshaking, ( not the WebSERVER-side interpretation of the delivered POST-request, which is the same, as if one have launched the URL from a WebBROWSER, for all related details ref: BaseHTTPServer.BaseHTTPRequestHandler )
>>> import BaseHTTPServer
>>> server_class = BaseHTTPServer.HTTPServer
>>> handler_class = BaseHTTPServer.BaseHTTPRequestHandler
>>> httpd = server_class( ( '', 8765 ), handler_class )
>>> httpd.handle_request()
127.0.0.1 - - [10/Oct/2016 09:46:45] code 501, message Unsupported method ('GET')
127.0.0.1 - - [10/Oct/2016 09:46:45] "GET /?test=123_from_Chrome HTTP/1.1" 501 -
>>> httpd.handle_request()
127.0.0.1 - - [10/Oct/2016 09:47:23] code 501, message Unsupported method ('GET')
127.0.0.1 - - [10/Oct/2016 09:47:23] "GET /favicon.ico HTTP/1.1" 501 -
>>>
>>>
>>>
>>> httpd = server_class( ( '', 80 ), handler_class )
>>> httpd.handle_request()
127.0.0.1 - - [10/Oct/2016 10:22:05] code 501, message Unsupported method ('GET')
127.0.0.1 - - [10/Oct/2016 10:22:05] "GET /?test=123_from_Chrome_on_port_80 HTTP/1.1" 501 -
>>> httpd.handle_request()
127.0.0.1 - - [10/Oct/2016 10:22:31] code 501, message Unsupported method ('GET')
127.0.0.1 - - [10/Oct/2016 10:22:31] "GET /?test=123_from_Chrome_on_port_80_again HTTP/1.1" 501 -
>>> httpd.handle_request()
127.0.0.1 - - [10/Oct/2016 10:22:34] code 501, message Unsupported method ('GET')
127.0.0.1 - - [10/Oct/2016 10:22:34] "GET /favicon.ico HTTP/1.1" 501 -
>>> httpd.handle_request()
127.0.0.1 - - [10/Oct/2016 11:25:56] code 501, message Unsupported method ('GET')
127.0.0.1 - - [10/Oct/2016 11:26:12] "GET /?test=123_from_Chrome_on_port_80_another_call HTTP/1.1" 501 -
>>>
>>>
127.0.0.1 - - [10/Oct/2016 12:03:03] code 501, message Unsupported method ('POST')
127.0.0.1 - - [10/Oct/2016 12:03:03] "POST / HTTP/1.1" 501 -
>>>
the output is
providing an evidence that the last pair of rows were produced by an MQL4-side WebRequest() that was setup correctly and works fine there and back
[ MetaTrader Terminal 4 ]-Log reads:
2016.10.10 12:03:03.921 ___StackOverflow_WebRequest_DEMO XAUUSD,H1:
DATA:: <head><title>Error response</title></head>
<body>
<h1>Error response</h1><p>Error code 501.<p>
Message: Unsupported method ('POST').<p>
Error code explanation: 501 = Server does not support this operation.
</body>
2016.10.10 12:03:03.921 ___StackOverflow_WebRequest_DEMO XAUUSD,H1:
HDRs:: HTTP/1.0 501 Unsupported method ('POST')
Server: BaseHTTP/0.3 Python/2.7.6
Date: Mon, 10 Oct 2016 20:03:03 GMT
Content-Type: text/html
Connection: close
A raw MQL4-snippet BUT use at one's own risk!
( strongly encourage NOT to use any BLOCKING WebRequest() calls
in any Production-grade code...for NON-BLOCKING tools see my other posts and how to or read into internal details on high-performance, low-latency, non-blocking integration tools for distributed heterogeneous systems processing alike ZeroMQ or nanomsg )
All have been warned, so:
Last years setup picture is still valid:
The mock-up WebSERVER had inside the dotted form-field input of:
http://localhost/
One shall also bear in mind, that trying to set a specific port designation in the URL will violate the MetaQuotes Inc. design rule, that a port is being derived from the protocol pragma at the beginning of the URL declaration, so:
http://localhost:8765/
will not work, as MQL4 WebRequest() CANNOT use other port but either of { 80 | 443 }, given by protocol pragma stated in URL: { http: | https: }
Thus for any port-numbering gymnastics, one has to setup and tune a proper set of port-forwarding services, that would leave MetaTrader Terminal 4 live inside this design-cage, using just either of { 80 | 443 }.
The simplest MQL4-script OnStart() demonstrator looks this way:
//+------------------------------------------------------------------+
//| ___StackOverflow_WebRequest_DEMO.mq4 |
//| Copyright © 1987-2016 [MS] |
//| nowhere.no |
//+------------------------------------------------------------------+ >>> https://stackoverflow.com/questions/39954177/how-to-send-a-post-with-a-json-in-a-webrequest-call-using-mql4
#property copyright "Copyright © 1987-2016 [MS]"
#property link "nowhere.no"
#property version "1.00"
#property strict
//+------------------------------------------------------------------+
//| Script program start function |
//+------------------------------------------------------------------+
void OnStart(){
/* A BRIGHTER WAY:
string JSON_string = StringFormat( "{\"currency\": \"%s\", \"timeframe\": \"%d\", \"ticktime\": \"%s\", \"bid\": %f, \"ask\": %f, \"spread\": %s }", _Symbol,
Period(),
TimeToString( TimeLocal(), TIME_DATE | TIME_SECONDS ),
MarketInfo( _Symbol, MODE_BID ),
MarketInfo( _Symbol, MODE_ASK ),
MarketInfo( _Symbol, MODE_SPREAD )
);
// A SMARTER WAY & THE FASTEST PROCESSING TIMES:
// --------------
#define MQL4_COMPILE_TIME_JSON_TEMPLATE "{\"currency\": \"%s\", \"timeframe\": \"%d\", \"ticktime\": \"%s\", \"bid\": %f, \"ask\": %f, \"spread\": %s }" // CONSTANT TEMPLATE TO FILL-IN AD-HOC VALUES:
// +
string JSON_string = StringFormat( MQL4_COMPILE_TIME_JSON_TEMPLATE", _Symbol,
Period(),
TimeToString( TimeLocal(), TIME_DATE | TIME_SECONDS ),
MarketInfo( _Symbol, MODE_BID ),
MarketInfo( _Symbol, MODE_ASK ),
MarketInfo( _Symbol, MODE_SPREAD )
);
*/
string JSON_string = StringConcatenate( "{", // **** MQL4 can concat max 63 items
"\"currency\"",
":",
"\"",
Symbol(),
"\"",
",",
"\"timeframe\"",
":",
"\"",
IntegerToString( Period() ),
"\"",
",",
"\"ticktime\"",
":",
"\"",
TimeToString( TimeLocal(), TIME_DATE | TIME_SECONDS ),
"\"",
",",
"\"bid\"",
":",
DoubleToString( MarketInfo( Symbol(), MODE_BID ), 4 ),
",",
"\"ask\"",
":",
DoubleToString( MarketInfo( Symbol(), MODE_ASK ), 4 ),
",",
"\"spread\"",
":",
DoubleToString( MarketInfo( Symbol(), MODE_SPREAD ), 0 ),
"}"
);
// */
/* off-topic: a JSON-string VALIDATOR -----------------------------------------------------------------------------------------------------------------------------------
#include <Json\hash.mqh>
#include <Json\KoulJSONMgmt.mqh>
JSONParser *parser = new JSONParser();
JSONValue *jv = parser.parse(strParam);
string strJson = jv.toString();
if ( jv == NULL ) Print( "ERROR:" + (string) parser.getErrorCode()
+ parser.getErrorMessage()
);
else Print( "PARSED:" + strJson );
// Example of a journalled Print() for an above setup JSON String :
// EURUSD,M15: PARSED:{"bid" : 1.1152,"ask" : 1.1154,"spread" : 13,"ticktime" : "2016.10.10 16:24:01","currency" : "EURUSD","timeframe" : "15"}
*/ // off-topic: a JSON-string VALIDATOR -----------------------------------------------------------------------------------------------------------------------------------
// string ReqSERVER_URL = "http://localhost:8765/", // **** MQL4 WebRequest CANNOT use other port but either of { 80 | 443 } given by protocol pragma stated in URL: { http: | https: }
string ReqSERVER_URL = "http://localhost/", // ---- MQL4 WebRequst
ReqCOOKIE = NULL,
// ReqHEADERs = "application/json"; // **** MQL4 WebRequest MUST use [in] Request headers of type "key: value", separated by a line break "\r\n".
ReqHEADERs = "Content-Type: application/json\r\n";
int ReqTIMEOUT = 5000; // ---- MQL4 WebRequest SHALL use [in] Timeouts below 1000 (1 sec.) are not enough for slow Internet connection;
// ================================================= // ~~~~ MQL4 WebRequest SHALL be AVOIDED as an un-control-able BLOCKING-SHOW-STOPPER, any professional need shall use NON-BLOCKING tools
char POSTed_DATA[],
result_RECVed_DATA_FromSERVER[];
int result_RetCODE;
string result_DecodedFromSERVER,
result_RECVed_HDRs_FromSERVER;
// int intHostNameLength = StringLen( ReqSERVER_URL );
// StringToCharArray( ReqSERVER_URL, POSTed_DATA, 0, StringLen( ReqSERVER_URL ) );
// StringToCharArray( prmParameter, post, 0, intHostNameLength );
StringToCharArray( JSON_string, POSTed_DATA, 0, StringLen( JSON_string ) );
ResetLastError();
result_RetCODE = WebRequest( "POST",
ReqSERVER_URL,
ReqHEADERs,
ReqTIMEOUT,
POSTed_DATA,
result_RECVed_DATA_FromSERVER,
result_RECVed_HDRs_FromSERVER
);
if ( result_RetCODE == -1 ) Print( "Error in WebRequest. Error code =", GetLastError() ); // returns error 4060 – "Function is not allowed for call" unless permitted -- ref. Picture in >>> https://stackoverflow.com/questions/39954177/how-to-send-a-post-with-a-json-in-a-webrequest-call-using-mql4
else {
for ( int i = 0; i < ArraySize( result_RECVed_DATA_FromSERVER ); i++ ) {
if ( ( result_RECVed_DATA_FromSERVER[i] == 10 ) // == '\n' // <LF>
|| ( result_RECVed_DATA_FromSERVER[i] == 13 ) // == '\r' // <CR>
)
continue;
else result_DecodedFromSERVER += CharToStr( result_RECVed_DATA_FromSERVER[i] );
}
Print( "DATA:: ", result_DecodedFromSERVER );
Print( "HDRs:: ", result_RECVed_HDRs_FromSERVER );
}
}
//+------------------------------------------------------------------+
Deviations from documented steps are easily visible in the source and were left for clarity.
Epilogue:
If documentation says something, it is worth keeping that advice ( with some tests, sure ).
If a sponsored Community advice says something, it is worth giving it at least a try, before asking for more.