Merge pull request #112 from dotmailer/master

Fix for occasional crash due to unsupported URI schemes

Author: martinnormark

PreMailer.Net/PreMailer.Net.Tests/LinkTagCssSourceTests.cs

@@ -69,6 +69,17 @@ public void GetCSS_AbsoluteUrlInHref_CallsWebDownloader_WithSpecifiedPath()
 			_webDownloader.Verify(w => w.DownloadString(new Uri(path)));
 		}
 
+		[TestMethod]
+		public void GetCSS_DoesNotCallWebDownloader_WhenSchemeNotSupported()
+		{
+			string path = "chrome-extension://fcdjadjbdihbaodagojiomdljhjhjfho/css/atd.css";
+
+			LinkTagCssSource sut = CreateSUT(path: path);
+			sut.GetCss();
+
+			_webDownloader.Verify(w => w.DownloadString(new Uri(path)), Times.Never);
+		}
+
 		private LinkTagCssSource CreateSUT(string baseUrl = "http://a.com", string path = "a.css", string link = "<link href=\"{0}\" />")
 		{
 			var node = new HtmlParser().Parse(String.Format(link, path));

PreMailer.Net/PreMailer.Net/Sources/LinkTagCssSource.cs

@@ -28,7 +28,20 @@ public LinkTagCssSource(IElement node, Uri baseUri)
 
 		public string GetCss()
 		{
-			return _cssContents ?? (_cssContents = WebDownloader.SharedDownloader.DownloadString(_downloadUri));
+			if (IsSupported(_downloadUri.Scheme))
+			{
+				return _cssContents ?? (_cssContents = WebDownloader.SharedDownloader.DownloadString(_downloadUri));
+			}
+			return string.Empty;
+		}
+
+		private bool IsSupported(string scheme)
+		{
+			return
+				scheme == Uri.UriSchemeHttp ||
+				scheme == Uri.UriSchemeHttps ||
+				scheme == Uri.UriSchemeFtp ||
+				scheme == Uri.UriSchemeFile;
 		}
 	}
 }