Add method for appending relative paths to urls

Sadly we can't just do this: new Uri(url, path); because you get
different results if the url ends with "/" or not. So we need to make
absolutely sure it _does_ end with "/".

Author: haacked

src/GitHub.Extensions/UriExtensions.cs

@@ -5,6 +5,22 @@ namespace GitHub.Extensions
 {
     public static class UriExtensions
     {
+        /// <summary>
+        /// Appends a relative path to the URL.
+        /// </summary>
+        /// <remarks>
+        /// The Uri constructor for combining relative URLs have a different behavior with URLs that end with /
+        /// than those that don't.
+        /// </remarks>
+        public static Uri Append(this Uri uri, string relativePath)
+        {
+            if (!uri.AbsolutePath.EndsWith("/", StringComparison.Ordinal))
+            {
+                uri = new Uri(uri + "/");
+            }
+            return new Uri(uri, new Uri(relativePath, UriKind.Relative));
+        }
+
         public static bool IsHypertextTransferProtocol(this Uri uri)
         {
             return uri.Scheme == "http" || uri.Scheme == "https";

src/UnitTests/GitHub.Extensions/UriExtensionTests.cs

@@ -0,0 +1,25 @@
+using System;
+using GitHub.Extensions;
+using Xunit;
+
+public class UriExtensionTests
+{
+    public class TheAppendMethod
+    {
+        [Theory]
+        [InlineData("https://github.com/foo/bar", "graphs", "https://github.com/foo/bar/graphs")]
+        [InlineData("https://github.com/foo/bar/", "graphs", "https://github.com/foo/bar/graphs")]
+        [InlineData("https://github.com", "bippety/boppety", "https://github.com/bippety/boppety")]
+        [InlineData("https://github.com/", "bippety/boppety", "https://github.com/bippety/boppety")]
+        [InlineData("https://github.com/foo/bar", "bippety/boppety", "https://github.com/foo/bar/bippety/boppety")]
+        public void AppendsRelativePath(string url, string relativePath, string expected)
+        {
+            var uri = new Uri(url, UriKind.Absolute);
+            var expectedUri = new Uri(expected, UriKind.Absolute);
+
+            var result = uri.Append(relativePath);
+
+            Assert.Equal(expectedUri, result);
+        }
+    }
+}

src/UnitTests/UnitTests.csproj

@@ -141,6 +141,7 @@
     <Compile Include="GitHub.App\ViewModels\RepositoryCreationViewModelTests.cs" />
     <Compile Include="GitHub.App\ViewModels\RepositoryPublishViewModelTests.cs" />
     <Compile Include="GitHub.Exports\VSServicesTests.cs" />
+    <Compile Include="GitHub.Extensions\UriExtensionTests.cs" />
     <Compile Include="GitHub.Extensions\URITests.cs" />
     <Compile Include="GitHub.Primitives\UriStringTests.cs" />
     <Compile Include="GitHub.UI\TwoFactorInputTests.cs" />