Implement Page.XPathAsync (a.k.a. Page.$x) (#200)

Author: Meir017

lib/PuppeteerSharp.Tests/Page/XPathTests.cs

@@ -0,0 +1,33 @@
+using System.Threading.Tasks;
+using Xunit;
+
+namespace PuppeteerSharp.Tests.Page
+{
+    [Collection("PuppeteerLoaderFixture collection")]
+    public class XPathTests : PuppeteerPageBaseTest
+    {
+        [Fact]
+        public async Task ShouldQueryExistingElement()
+        {
+            await Page.SetContentAsync("<section>test</section>");
+            var elements = await Page.XPathAsync("/html/body/section");
+            Assert.NotNull(elements[0]);
+            Assert.Single(elements);
+        }
+
+        [Fact]
+        public async Task ShouldReturnEmptyArrayForNonExistingElement()
+        {
+            var elements = await Page.XPathAsync("/html/body/non-existing-element");
+            Assert.Empty(elements);
+        }
+
+        [Fact]
+        public async Task ShouldReturnMultipleElements()
+        {
+            await Page.SetContentAsync("<div></div><div></div>");
+            var elements = await Page.XPathAsync("/html/body/div");
+            Assert.Equal(2, elements.Length);
+        }
+    }
+}

lib/PuppeteerSharp/ElementHandle.cs

@@ -136,16 +136,28 @@ internal async Task<ElementHandle[]> QuerySelectorAllAsync(string selector)
 
             var properties = await arrayHandle.GetPropertiesAsync();
             await arrayHandle.DisposeAsync();
-            var result = new List<ElementHandle>();
-            foreach(var property in properties.Values)
-            {
-                var elementHandle = property.AsElement();
-                if(elementHandle != null)
-                {
-                    result.Add(elementHandle);
-                }
-            }
-            return result.ToArray();
+
+            return properties.Values.OfType<ElementHandle>().ToArray();
+        }
+
+        internal async Task<ElementHandle[]> XPathAsync(string expression)
+        {
+            var arrayHandle = await ExecutionContext.EvaluateFunctionHandleAsync(
+                @"(element, expression) => {
+                    const document = element.ownerDocument || element;
+                    const iterator = document.evaluate(expression, element, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE);
+                    const array = [];
+                    let item;
+                    while ((item = iterator.iterateNext()))
+                        array.push(item);
+                    return array;
+                }",
+                this, expression
+            );
+            var properties = await arrayHandle.GetPropertiesAsync();
+            await arrayHandle.DisposeAsync();
+
+            return properties.Values.OfType<ElementHandle>().ToArray();
         }
 
         private async Task<(decimal x, decimal y)> VisibleCenterAsync()

lib/PuppeteerSharp/Frame.cs

@@ -152,6 +152,13 @@ internal async Task<ElementHandle[]> QuerySelectorAllAsync(string selector)
             return value;
         }
 
+        internal async Task<ElementHandle[]> XPathAsync(string expression)
+        {
+            var document = await GetDocument();
+            var value = await document.XPathAsync(expression);
+            return value;
+        }
+
         internal Task<ElementHandle> AddStyleTag(dynamic options)
         {
             throw new NotImplementedException();

lib/PuppeteerSharp/Page.cs

@@ -188,6 +188,16 @@ public Task<ElementHandle[]> QuerySelectorAllAsync(string selector)
         public Task<JSHandle> QuerySelectorAllHandleAsync(string selector)
             => EvaluateFunctionHandleAsync("selector => Array.from(document.querySelectorAll(selector))", selector);
 
+        /// <summary>
+        /// Evaluates the XPath expression
+        /// </summary>
+        /// <param name="expression">Expression to evaluate <see cref="https://developer.mozilla.org/en-US/docs/Web/API/Document/evaluate"/></param>
+        /// <returns>Task which resolves to an array of <see cref="ElementHandle"/></returns>
+        /// <remarks>
+        /// Shortcut for <c>page.MainFrame.XPathAsync(expression)</c>
+        /// </remarks>
+        public Task<ElementHandle[]> XPathAsync(string expression) => MainFrame.XPathAsync(expression);
+
         /// <summary>
         /// Executes a script in browser context
         /// </summary>