How to send a POST with a JSON in a WebRequest() call using MQL4?
I would like to send a POST from MQL4-script, using a JSON-format to a Node-server.
I\'ve tried the webReque
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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 apython-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 anMQL4-sideWebRequest()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: closeA raw
MQL4-snippet BUT use at one's own risk!
( strongly encourage NOT to use any BLOCKINGWebRequest()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-scriptOnStart()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.
讨论(0) -
Have you tried setting the headers like this:
headers = "Content-Type: application/json\r\n";?
讨论(0) -
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 ""; }讨论(0) -
Allow your [ MetaTrader Terminal 4 ] to communicate with URL via menu:
Tools -> Options -> Expert Advisors ->
1. mark a check-box
[ X ]in front of 'Allow WebReq....'
&
2. type the URL name below the check-box, using the green(+)icon, inside the form.If this doesn't help - try to add
Print()statements to see the possible errors ( incorrectMQL4code or incorrect JSON-format file ).讨论(0)
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