[tests] Add XYX slippy map to test QGIS server

Plus: multi-threading server side (for speed)

This is useful for testing various authentication
shemes on a slippy-map server (that uses multi-threading
in QGIS desktop)

tests/src/python/qgis_wrapped_server.py

@@ -6,6 +6,11 @@ This script launches a QGIS Server listening on port 8081 or on the port
 specified on the environment variable QGIS_SERVER_PORT.
 QGIS_SERVER_HOST (defaults to 127.0.0.1)
 
+A XYZ slippy maps service is also available for multithreading testing:
+
+  ?MAP=/path/to/projects.qgs&SERVICE=XYZ&X=1&Y=0&Z=1&LAYERS=world
+
+
 For testing purposes, HTTP Basic can be enabled by setting the following
 environment variables:
 
@@ -49,9 +54,13 @@ os.environ['QT_HASH_SEED'] = '1'
 import sys
 import signal
 import ssl
+import math
 import urllib.parse
 from http.server import BaseHTTPRequestHandler, HTTPServer
-from qgis.core import QgsApplication
+from socketserver import ThreadingMixIn
+import threading
+
+from qgis.core import QgsApplication, QgsCoordinateTransform, QgsCoordinateReferenceSystem
 from qgis.server import QgsServer, QgsServerRequest, QgsBufferServerRequest, QgsBufferServerResponse
 
 QGIS_SERVER_PORT = int(os.environ.get('QGIS_SERVER_PORT', '8081'))
@@ -100,6 +109,42 @@ if os.environ.get('QGIS_SERVER_HTTP_BASIC_AUTH') is not None:
     qgs_server.serverInterface().registerFilter(filter)
 
 
+def num2deg(xtile, ytile, zoom):
+    """This returns the NW-corner of the square. Use the function with xtile+1 and/or ytile+1 
+    to get the other corners. With xtile+0.5 & ytile+0.5 it will return the center of the tile."""
+    n = 2.0 ** zoom
+    lon_deg = xtile / n * 360.0 - 180.0
+    lat_rad = math.atan(math.sinh(math.pi * (1 - 2 * ytile / n)))
+    lat_deg = math.degrees(lat_rad)
+    return (lat_deg, lon_deg)
+
+
+class XYZFilter(QgsServerFilter):
+    """XYZ server, example: ?MAP=/path/to/projects.qgs&SERVICE=XYZ&X=1&Y=0&Z=1&LAYERS=world"""
+
+    def requestReady(self):
+        handler = self.serverInterface().requestHandler()
+        if handler.parameter('SERVICE') == 'XYZ':
+            x = int(handler.parameter('X'))
+            y = int(handler.parameter('Y'))
+            z = int(handler.parameter('Z'))
+            # NW corner
+            lat_deg, lon_deg = num2deg(x, y, z)
+            # SE corner
+            lat_deg2, lon_deg2 = num2deg(x + 1, y + 1, z)
+            handler.setParameter('SERVICE', 'WMS')
+            handler.setParameter('REQUEST', 'GetMap')
+            handler.setParameter('VERSION', '1.3.0')
+            handler.setParameter('SRS', 'EPSG:4326')
+            handler.setParameter('HEIGHT', '256')
+            handler.setParameter('WIDTH', '256')
+            handler.setParameter('BBOX', "{},{},{},{}".format(lat_deg2, lon_deg, lat_deg, lon_deg2))
+
+
+xyzfilter = XYZFilter(qgs_server.serverInterface())
+qgs_server.serverInterface().registerFilter(xyzfilter)
+
+
 class Handler(BaseHTTPRequestHandler):
 
     def do_GET(self, post_body=None):
@@ -128,8 +173,13 @@ class Handler(BaseHTTPRequestHandler):
         return self.do_GET(post_body)
 
 
+class ThreadedHTTPServer(ThreadingMixIn, HTTPServer):
+    """Handle requests in a separate thread."""
+    pass
+
+
 if __name__ == '__main__':
-    server = HTTPServer((QGIS_SERVER_HOST, QGIS_SERVER_PORT), Handler)
+    server = ThreadedHTTPServer((QGIS_SERVER_HOST, QGIS_SERVER_PORT), Handler)
     if https:
         server.socket = ssl.wrap_socket(server.socket,
                                         certfile=QGIS_SERVER_PKI_CERTIFICATE,