Throw UnkownFormatException on Image.Load (#932)

* Throw ImageFormatException on load

* Unseal class and make constructor internal
- This is so that no one can new it up / inherit it outside of the assembly

* Add new exception for distinguish between different exception
- This will be used on image.load operations with invalid image streams

* ImageFormatException -> UnkownImageFormatException

* Add Image.Load throws exception tests

Author: fredeil

src/ImageSharp/Common/Exceptions/ImageFormatException.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -9,14 +9,14 @@ namespace SixLabors.ImageSharp
     /// The exception that is thrown when the library tries to load
     /// an image, which has an invalid format.
     /// </summary>
-    public sealed class ImageFormatException : Exception
+    public class ImageFormatException : Exception
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="ImageFormatException"/> class with the name of the
         /// parameter that causes this exception.
         /// </summary>
         /// <param name="errorMessage">The error message that explains the reason for this exception.</param>
-        public ImageFormatException(string errorMessage)
+        internal ImageFormatException(string errorMessage)
             : base(errorMessage)
         {
         }
@@ -28,7 +28,7 @@ public ImageFormatException(string errorMessage)
         /// <param name="errorMessage">The error message that explains the reason for this exception.</param>
         /// <param name="innerException">The exception that is the cause of the current exception, or a null reference (Nothing in Visual Basic)
         /// if no inner exception is specified.</param>
-        public ImageFormatException(string errorMessage, Exception innerException)
+        internal ImageFormatException(string errorMessage, Exception innerException)
             : base(errorMessage, innerException)
         {
         }

src/ImageSharp/Common/Exceptions/UnknownImageFormatException.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+
+namespace SixLabors.ImageSharp
+{
+    /// <summary>
+    /// The exception that is thrown when the library tries to load
+    /// an image which has an unkown format.
+    /// </summary>
+    public sealed class UnknownImageFormatException : ImageFormatException
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="UnknownImageFormatException"/> class with the name of the
+        /// parameter that causes this exception.
+        /// </summary>
+        /// <param name="errorMessage">The error message that explains the reason for this exception.</param>
+        public UnknownImageFormatException(string errorMessage)
+            : base(errorMessage)
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="UnknownImageFormatException"/> class with a specified
+        /// error message and the exception that is the cause of this exception.
+        /// </summary>
+        /// <param name="errorMessage">The error message that explains the reason for this exception.</param>
+        /// <param name="innerException">The exception that is the cause of the current exception, or a null reference (Nothing in Visual Basic)
+        /// if no inner exception is specified.</param>
+        public UnknownImageFormatException(string errorMessage, Exception innerException)
+            : base(errorMessage, innerException)
+        {
+        }
+    }
+}

src/ImageSharp/Image.FromStream.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
@@ -62,6 +62,7 @@ public static IImageInfo Identify(Configuration config, Stream stream)
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="format">the mime type of the decoded image.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <returns>A new <see cref="Image"/>.</returns>>
         public static Image Load(Stream stream, out IImageFormat format) => Load(Configuration.Default, stream, out format);
 
@@ -71,6 +72,7 @@ public static IImageInfo Identify(Configuration config, Stream stream)
         /// </summary>
         /// <param name="stream">The stream containing image information.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <returns>A new <see cref="Image"/>.</returns>>
         public static Image Load(Stream stream) => Load(Configuration.Default, stream);
 
@@ -81,6 +83,7 @@ public static IImageInfo Identify(Configuration config, Stream stream)
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="decoder">The decoder.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <returns>A new <see cref="Image"/>.</returns>>
         public static Image Load(Stream stream, IImageDecoder decoder) => Load(Configuration.Default, stream, decoder);
 
@@ -92,6 +95,7 @@ public static IImageInfo Identify(Configuration config, Stream stream)
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="decoder">The decoder.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <returns>A new <see cref="Image"/>.</returns>>
         public static Image Load(Configuration config, Stream stream, IImageDecoder decoder) =>
             WithSeekableStream(config, stream, s => decoder.Decode(config, s));
@@ -102,6 +106,7 @@ public static Image Load(Configuration config, Stream stream, IImageDecoder deco
         /// <param name="config">The config for the decoder.</param>
         /// <param name="stream">The stream containing image information.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <returns>A new <see cref="Image"/>.</returns>>
         public static Image Load(Configuration config, Stream stream) => Load(config, stream, out _);
 
@@ -110,6 +115,7 @@ public static Image Load(Configuration config, Stream stream, IImageDecoder deco
         /// </summary>
         /// <param name="stream">The stream containing image information.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <returns>A new <see cref="Image{TPixel}"/>.</returns>>
         public static Image<TPixel> Load<TPixel>(Stream stream)
@@ -122,6 +128,7 @@ public static Image<TPixel> Load<TPixel>(Stream stream)
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="format">the mime type of the decoded image.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <returns>A new <see cref="Image{TPixel}"/>.</returns>>
         public static Image<TPixel> Load<TPixel>(Stream stream, out IImageFormat format)
@@ -134,6 +141,7 @@ public static Image<TPixel> Load<TPixel>(Stream stream, out IImageFormat format)
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="decoder">The decoder.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <returns>A new <see cref="Image{TPixel}"/>.</returns>>
         public static Image<TPixel> Load<TPixel>(Stream stream, IImageDecoder decoder)
@@ -147,6 +155,7 @@ public static Image<TPixel> Load<TPixel>(Stream stream, IImageDecoder decoder)
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="decoder">The decoder.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <returns>A new <see cref="Image{TPixel}"/>.</returns>>
         public static Image<TPixel> Load<TPixel>(Configuration config, Stream stream, IImageDecoder decoder)
@@ -159,6 +168,7 @@ public static Image<TPixel> Load<TPixel>(Configuration config, Stream stream, II
         /// <param name="config">The configuration options.</param>
         /// <param name="stream">The stream containing image information.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <returns>A new <see cref="Image{TPixel}"/>.</returns>>
         public static Image<TPixel> Load<TPixel>(Configuration config, Stream stream)
@@ -172,6 +182,7 @@ public static Image<TPixel> Load<TPixel>(Configuration config, Stream stream)
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="format">the mime type of the decoded image.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <typeparam name="TPixel">The pixel format.</typeparam>
         /// <returns>A new <see cref="Image{TPixel}"/>.</returns>>
         public static Image<TPixel> Load<TPixel>(Configuration config, Stream stream, out IImageFormat format)
@@ -195,7 +206,7 @@ public static Image<TPixel> Load<TPixel>(Configuration config, Stream stream, ou
                 sb.AppendLine($" - {val.Key.Name} : {val.Value.GetType().Name}");
             }
 
-            throw new NotSupportedException(sb.ToString());
+            throw new UnknownImageFormatException(sb.ToString());
         }
 
         /// <summary>
@@ -206,6 +217,7 @@ public static Image<TPixel> Load<TPixel>(Configuration config, Stream stream, ou
         /// <param name="stream">The stream containing image information.</param>
         /// <param name="format">the mime type of the decoded image.</param>
         /// <exception cref="NotSupportedException">Thrown if the stream is not readable.</exception>
+        /// <exception cref="UnknownImageFormatException">Image cannot be loaded.</exception>
         /// <returns>A new <see cref="Image{TPixel}"/>.</returns>
         public static Image Load(Configuration config, Stream stream, out IImageFormat format)
         {
@@ -227,7 +239,7 @@ public static Image Load(Configuration config, Stream stream, out IImageFormat f
                 sb.AppendLine($" - {val.Key.Name} : {val.Value.GetType().Name}");
             }
 
-            throw new NotSupportedException(sb.ToString());
+            throw new UnknownImageFormatException(sb.ToString());
         }
 
         private static T WithSeekableStream<T>(Configuration config, Stream stream, Func<Stream, T> action)
@@ -257,4 +269,4 @@ private static T WithSeekableStream<T>(Configuration config, Stream stream, Func
             }
         }
     }
-}
+}

tests/ImageSharp.Tests/Image/ImageTests.Load_FromStream_ThrowsRightException.cs

@@ -0,0 +1,52 @@
+// Copyright (c) Six Labors and contributors.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+using System.IO;
+
+using SixLabors.ImageSharp.Formats;
+using SixLabors.ImageSharp.Formats.Bmp;
+using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.Primitives;
+
+using Xunit;
+
+namespace SixLabors.ImageSharp.Tests
+{
+    public partial class ImageTests
+    {
+        public class Load_FromStream_Throws : IDisposable
+        {
+            private static readonly byte[] Data = new byte[] { 0x01 };
+            
+            private MemoryStream Stream { get; } = new MemoryStream(Data);
+            
+            [Fact]
+            public void Image_Load_Throws_UknownImageFormatException()
+            {
+                Assert.Throws<UnknownImageFormatException>(() =>
+                {
+                    using (var img = Image.Load(Configuration.Default, this.Stream, out IImageFormat format))
+                    {
+                    }
+                });
+            }
+
+            [Fact]
+            public void Image_Load_T_Throws_UknownImageFormatException()
+            {
+                Assert.Throws<UnknownImageFormatException>(() =>
+                {
+                    using (var img = Image.Load<Rgba32>(Configuration.Default, this.Stream, out IImageFormat format))
+                    {
+                    }
+                });
+            }
+
+            public void Dispose()
+            {
+                this.Stream?.Dispose();
+            }
+        }
+    }
+}