Add check for dependency on linux

Google.Authenticator.Tests/QRCodeTest.cs

@@ -0,0 +1,17 @@
+using System;
+using Xunit;
+using Shouldly;
+
+namespace Google.Authenticator.Tests
+{
+    public class QRCodeTest
+    {
+        [Fact]
+        public void CanGenerateQRCode()
+        {
+            var subject = new TwoFactorAuthenticator();
+            var setupCodeInfo = subject.GenerateSetupCode("issuer","[email protected]","secret", false, 2);
+            setupCodeInfo.QrCodeSetupImageUrl.ShouldNotBeNull();
+        }
+    }
+}

Google.Authenticator/Google.Authenticator.csproj

@@ -7,7 +7,7 @@
     <Description>Google Authenticator Two-Factor Authentication Library (Not officially affiliated with Google.)</Description>
     <Authors>Brandon Potter</Authors>
     <Company>Brandon Potter</Company>
-    <Version>2.0.2</Version>
+    <Version>2.1.0</Version>
     <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
     <PackageProjectUrl>https://github.com/BrandonPotter/GoogleAuthenticator</PackageProjectUrl>
     <PackageId>GoogleAuthenticator</PackageId>

Google.Authenticator/MissingDependencyException.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Google.Authenticator
+{
+    public class MissingDependencyException : Exception
+    {
+        public MissingDependencyException(string message) : base(message)
+        {
+        }
+
+        public MissingDependencyException(string message, Exception innerException) : base(message, innerException)
+        {
+        }
+    }
+}

Google.Authenticator/TwoFactorAuthenticator.cs

@@ -68,15 +68,28 @@ public SetupCode GenerateSetupCode(string issuer, string accountTitleNoSpaces, b
             string qrCodeUrl = string.Empty;
             if (generateQrCode)
             {
-                using (QRCodeGenerator qrGenerator = new QRCodeGenerator())
-                using (QRCodeData qrCodeData = qrGenerator.CreateQrCode(provisionUrl, QRCodeGenerator.ECCLevel.Q))
-                using (QRCode qrCode = new QRCode(qrCodeData))
-                using (Bitmap qrCodeImage = qrCode.GetGraphic(QRPixelsPerModule))
-                using (MemoryStream ms = new MemoryStream())
+                try
                 {
-                    qrCodeImage.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
+                    using (QRCodeGenerator qrGenerator = new QRCodeGenerator())
+                    using (QRCodeData qrCodeData = qrGenerator.CreateQrCode(provisionUrl, QRCodeGenerator.ECCLevel.Q))
+                    using (QRCode qrCode = new QRCode(qrCodeData))
+                    using (Bitmap qrCodeImage = qrCode.GetGraphic(QRPixelsPerModule))
+                    using (MemoryStream ms = new MemoryStream())
+                    {
+                        qrCodeImage.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
+
+                        qrCodeUrl = String.Format("data:image/png;base64,{0}", Convert.ToBase64String(ms.ToArray()));
+                    }
+                }
+                catch (System.TypeInitializationException e)  
+                {
+                    if (e.InnerException != null 
+                        && e.InnerException.GetType() == typeof(System.DllNotFoundException)
+                        && e.InnerException.Message.Contains("libgdiplus"))
+                    {
+                        throw new MissingDependencyException("It looks like libgdiplus has not been installed - see https://github.com/codebude/QRCoder/issues/227", e);
+                    }
 
-                    qrCodeUrl = String.Format("data:image/png;base64,{0}", Convert.ToBase64String(ms.ToArray()));
                 }
             }
 

README.md

@@ -8,3 +8,6 @@ Simple, easy to use server-side two-factor authentication library for .NET that
 See blog post for usage instructions:
 
 https://csharprookie.wordpress.com/2015/03/17/implementing-free-two-factor-authentication-in-net-using-google-authenticator/
+
+# Notes
+On linux, you need to ensure `libgdiplus` is installed if you want to generate QR Codes. See [https://github.com/codebude/QRCoder/issues/227](https://github.com/codebude/QRCoder/issues/227).