add example of using Qt for a POST request to a cgi script

examples/X-extras/server-request.lisp

@@ -0,0 +1,50 @@
+;;; this is just a snippet to show how to use Qt for POST requests to
+;;; a cgi script (using e.g. python for cgi)
+;;;
+;;; this is here to have an alternative to Lisp solutions, which don't
+;;; work well in ECL on some platforms (namely Windows)
+;;;
+;;; example usage:
+;;;
+;;; (server-request "booking.py"
+;;;                 (list (cons "from" "2020-08-01")
+;;;                       (cons "to    "2020-08-08")))
+
+(qrequire :network)
+
+;; for testing, using e.g. python3 -m http.server 8080 --cgi
+(defparameter *server* "http://localhost:8080/cgi-bin/")
+
+(defun http-part (parameter)
+  (let ((part (qnew "QHttpPart")))
+    (qlet ((name "QVariant(QString)"
+                 (format nil "form-data; name=~S" (car parameter))))
+      (|setHeader| part |QNetworkRequest.ContentDispositionHeader| name)
+      (|setBody| part (x:string-to-bytes (cdr parameter))))
+    part))
+
+(defun server-request (script &optional parameters)
+  "Make a http POST request to a cgi script, forcing synchronous behaviour,
+  which simplifies things and is preferable in many cases."
+  (start-busy-animation) ; pseudo code
+  (let (response)
+    (qlet ((ev-loop "QEventLoop")
+           (manager "QNetworkAccessManager"))
+      (qconnect manager "finished(QNetworkReply*)"
+                (lambda (reply)
+                  (|deleteLater| reply)
+                  (let ((err (|error| reply)))
+                    (when (= |QNetworkReply.NoError| err)
+                      (setf response (qfrom-utf8 (|readAll| reply)))))
+                  (|exit| ev-loop)))
+      (qlet ((multi   "QHttpMultiPart")
+             (qurl    "QUrl(QString)" (x:cc *server* script))
+             (request "QNetworkRequest(QUrl)" qurl))
+        (dolist (param parameters)
+          (qlet ((part (http-part param)))
+            (|append| multi part)))
+        (|post| manager request multi)
+        (|exec| ev-loop |QEventLoop.ExcludeUserInputEvents|)
+        (stop-busy-animation) ; pseudo code
+        response))))
+