Make WMS server selection deterministic, by using a real number hashing algorithm on the parameter string to select the server URL. Also, patch TMS since it doesn't use getFullParameterString(). Passes all tests. Fixes #410.

git-svn-id: http://svn.openlayers.org/trunk/openlayers@2821 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Layer/HTTPRequest.js

@@ -90,6 +90,18 @@ OpenLayers.Layer.HTTPRequest.prototype =
         this.params = OpenLayers.Util.extend(this.params, newParams);
     },
     
+    /**
+     * @param {String} paramString
+     * @param {Array(String)} urls
+     */
+    selectUrl: function(paramString, urls) {
+        var product = 1;
+        for (var i = 0; i < paramString.length; i++) { 
+            product *= paramString.charCodeAt(i) * (Math.sqrt(5) - 1) / Math.sqrt(3);
+            product -= Math.floor(product); 
+        }
+        return urls[Math.floor(product * urls.length)];
+    },
 
     /** combine url with layer's params and these newParams. 
      *   
@@ -109,15 +121,6 @@ OpenLayers.Layer.HTTPRequest.prototype =
         // use layer's url unless altUrl passed in
         var url = (altUrl == null) ? this.url : altUrl;
         
-        // if url is not a string, it should be an array of strings, 
-        //  in which case we will randomly select one of them in order
-        //  to evenly distribute requests to different urls.
-        if (typeof url == "object") {
-            url = url[Math.floor(Math.random()*url.length)];
-        }   
-        // requestString always starts with url
-        var requestString = url;        
-
         // create a new params hashtable with all the layer params and the 
         // new params together. then convert to string
         var allParams = OpenLayers.Util.extend(new Object(), this.params);
@@ -131,6 +134,17 @@ OpenLayers.Layer.HTTPRequest.prototype =
             }
         }
         var paramsString = OpenLayers.Util.getParameterString(allParams);
+        
+        // if url is not a string, it should be an array of strings, 
+        // in which case we will deterministically select one of them in 
+        // order to evenly distribute requests to different urls.
+        if (url instanceof Array) {
+            url = this.selectUrl(paramsString, url);
+        }   
+        
+        // requestString always starts with url
+        var requestString = url;        
+        
         if (paramsString != "") {
             var lastServerChar = url.charAt(url.length - 1);
             if ((lastServerChar == "&") || (lastServerChar == "?")) {

lib/OpenLayers/Layer/TMS.js

@@ -75,7 +75,12 @@ OpenLayers.Layer.TMS.prototype =
         var x = (bounds.left - this.tileOrigin.lon) / (res * this.tileSize.w);
         var y = (bounds.bottom - this.tileOrigin.lat) / (res * this.tileSize.h);
         var z = this.map.getZoom();
-        return this.url + "1.0.0" + "/" + this.layername + "/" + z + "/" + x + "/" + y + "." + this.type; 
+        var path = "1.0.0" + "/" + this.layername + "/" + z + "/" + x + "/" + y + "." + this.type; 
+        var url = this.url;
+        if (url instanceof Array) {
+            url = this.selectUrl(path, url);
+        }
+        return url + path;
     },
 
     /**

tests/Layer/test_HTTPRequest.html

@@ -89,7 +89,7 @@
         tParams = { layers: 'basic', 
                    format: 'image/png'};
         
-        t.plan( 9 );
+        t.plan( 12 );
 
   // without ?        
         tUrl = "http://octo.metacarta.com/cgi-bin/mapserv";
@@ -147,9 +147,35 @@
         layer = new OpenLayers.Layer.HTTPRequest(name, "chicken", tParams, null);
         str = layer.getFullRequestString(null, tUrl);
         t.eq(str, tUrl + '?' + OpenLayers.Util.getParameterString(tParams), "getFullRequestString() works for url sans ?");
+  
+  // single url object        
+        tUrl = ["http://octo.metacarta.com/cgi-bin/mapserv"];
+        layer = new OpenLayers.Layer.HTTPRequest(name, tUrl, tParams, null);
+        str = layer.getFullRequestString();
+        t.eq(str, tUrl[0] + '?' + OpenLayers.Util.getParameterString(tParams), "getFullRequestString() works for list of one url");
+  
+  // two url object        
+        tUrl = ["http://octo.metacarta.com/cgi-bin/mapserv","http://labs.metacarta.com/cgi-bin/mapserv"];
+        layer = new OpenLayers.Layer.HTTPRequest(name, tUrl, tParams, null);
+        str = layer.getFullRequestString();
+        t.eq(str, tUrl[0] + '?' + OpenLayers.Util.getParameterString(tParams), "getFullRequestString() works for list of two urls");
+        str = layer.getFullRequestString({'a':'f'});
+        t.eq(str, tUrl[1] + '?' + OpenLayers.Util.getParameterString(OpenLayers.Util.extend(tParams,{'a':'f'})), "getFullRequestString() works for list of two urls and is deterministic");
 
     }
 
+    function test_04_Layer_HTTPRequest_selectUrl (t) { 
+        t.plan( 4 ); 
+
+        layer = new OpenLayers.Layer.HTTPRequest(name, url, params, options); 
+
+        urls = ["wms1", "wms2", "wms3", "wms4"]; 
+        t.eq( layer.selectUrl("bbox=-180,0,0,90",  urls), "wms4", "selectUrl(-90,-180) returns 4" ); 
+        t.eq( layer.selectUrl("bbox=-180,-90,0,0", urls), "wms3", "selectUrl(90,-180) returns 3" ); 
+        t.eq( layer.selectUrl("bbox=0,90,180,0",   urls), "wms1", "selectUrl(-90,180) returns 1" ); 
+        t.eq( layer.selectUrl("bbox=0,0,180,90",   urls), "wms2", "selectUrl(90,180) returns 2" ); 
+    }
+
     function test_99_Layer_HTTPRequest_destroy (t) {
         t.plan( 6 );    
 

tests/Layer/test_TMS.html

@@ -106,7 +106,7 @@
      */
     function test_10_Layer_TMS_getURL(t) {
 
-        t.plan(1);
+        t.plan(2);
         
         var map = new OpenLayers.Map('map', options);
         var options = {'layername':'basic', 'type':'png'}; 
@@ -115,6 +115,10 @@
         map.setCenter(new OpenLayers.LonLat(0,0), 9);
         var tileurl = layer.getURL(new OpenLayers.Bounds(3.515625,45,4.21875,45.703125));
         t.eq(tileurl, "http://labs.metacarta.com/wms-c/Basic.py/1.0.0/basic/9/261/192.png", "Tile URL is correct");
+
+        layer.url = ["http://tilecache1/", "http://tilecache2/", "http://tilecache3/"];
+        tileurl = layer.getURL(new OpenLayers.Bounds(3.515625,45,4.21875,45.703125));
+        t.eq(tileurl, "http://tilecache2/1.0.0/basic/9/261/192.png", "Tile URL is deterministic");
     }
 
     function test_11_Layer_TMS_setMap(t) {