fix: exception on FFmpeg proxy file creation

src/Aurio.FFmpeg.UnitTest/Aurio.FFmpeg.UnitTest.csproj

@@ -18,6 +18,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
+    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
   </ItemGroup>
 
   <ItemGroup>

src/Aurio.FFmpeg.UnitTest/FFmpegSourceStreamTests.cs

@@ -0,0 +1,82 @@
+using System;
+using System.IO;
+using Xunit;
+
+namespace Aurio.FFmpeg.UnitTest
+{
+    public class FFmpegSourceStreamTests
+    {
+        [Fact]
+        public void CreateWaveProxy_ProxyFileInfoIsNull()
+        {
+            FileInfo fileInfo = new("X:\\test.file");
+            FileInfo? proxyFileInfo = null;
+
+            void act() => FFmpegSourceStream.CreateWaveProxy(fileInfo, proxyFileInfo);
+
+            Assert.Throws<ArgumentNullException>(act);
+        }
+
+        [SkippableFact]
+        public void SuggestWaveProxyFileInfo_WithoutDirectory_Windows()
+        {
+            Skip.IfNot(OperatingSystem.IsWindows());
+
+            var fileInfo = new FileInfo("X:\\folder\\file.wav");
+
+            var proxyFileInfo = FFmpegSourceStream.SuggestWaveProxyFileInfo(fileInfo);
+
+            Assert.Equal("X:\\folder\\file.wav.ffproxy.wav", proxyFileInfo.FullName);
+        }
+
+        [SkippableFact]
+        public void SuggestWaveProxyFileInfo_WithoutDirectory_Unix()
+        {
+            Skip.If(OperatingSystem.IsWindows());
+
+            var fileInfo = new FileInfo("/folder/file.wav");
+
+            var proxyFileInfo = FFmpegSourceStream.SuggestWaveProxyFileInfo(fileInfo);
+
+            Assert.Equal("/folder/file.wav.ffproxy.wav", proxyFileInfo.FullName);
+        }
+
+        [SkippableFact]
+        public void SuggestWaveProxyFileInfo_WithDirectory_Windows()
+        {
+            Skip.IfNot(OperatingSystem.IsWindows());
+
+            var fileInfo = new FileInfo("X:\\folder\\file.wav");
+            var directoryInfo = new DirectoryInfo("Y:\\temp\\dir");
+
+            var proxyFileInfo = FFmpegSourceStream.SuggestWaveProxyFileInfo(
+                fileInfo,
+                directoryInfo
+            );
+
+            Assert.Equal(
+                "Y:\\temp\\dir\\87c18cf1c8d8e07552df4ecc1ef629995fca9c59ad47ccf7eb4816de33590af7.ffproxy.wav",
+                proxyFileInfo.FullName
+            );
+        }
+
+        [SkippableFact]
+        public void SuggestWaveProxyFileInfo_WithDirectory_Unix()
+        {
+            Skip.If(OperatingSystem.IsWindows());
+
+            var fileInfo = new FileInfo("/folder/file.wav");
+            var directoryInfo = new DirectoryInfo("/temp/dir");
+
+            var proxyFileInfo = FFmpegSourceStream.SuggestWaveProxyFileInfo(
+                fileInfo,
+                directoryInfo
+            );
+
+            Assert.Equal(
+                "/temp/dir/e2c5b9282d156c5bdbf95639ca2ce2516b096e4828b7aa16620cb317cc90b3d9.ffproxy.wav",
+                proxyFileInfo.FullName
+            );
+        }
+    }
+}

src/Aurio.FFmpeg/FFmpegAudioStreamFactory.cs

@@ -31,6 +31,8 @@ public FFmpegAudioStreamFactory()
 
         public IAudioStream OpenFile(FileInfo fileInfo, FileInfo proxyFileInfo = null)
         {
+            proxyFileInfo ??= FFmpegSourceStream.SuggestWaveProxyFileInfo(fileInfo);
+
             if (FFmpegSourceStream.WaveProxySuggested(fileInfo))
             {
                 Console.WriteLine("File format with known seek problems, creating proxy file...");

src/Aurio.FFmpeg/FFmpegSourceStream.cs

@@ -27,6 +27,8 @@ namespace Aurio.FFmpeg
 {
     public class FFmpegSourceStream : IAudioStream
     {
+        public const string ProxyFileExtension = ".ffproxy.wav";
+
         private Stream sourceStream;
         private FFmpegReader reader;
         private AudioProperties properties;
@@ -287,6 +289,11 @@ public void Dispose()
 
         public static FileInfo CreateWaveProxy(FileInfo fileInfo, FileInfo proxyFileInfo)
         {
+            if (proxyFileInfo == null)
+            {
+                throw new ArgumentNullException(nameof(proxyFileInfo));
+            }
+
             if (proxyFileInfo.Exists)
             {
                 Console.WriteLine("Proxy already existing, using " + proxyFileInfo.Name);
@@ -339,39 +346,16 @@ out Type type
         }
 
         /// <summary>
-        /// Creates a Wave format proxy file in the same directory and with the same name as the specified file,
-        /// if no storage directory is specified (i.e. if it is null). If a storage directory is specified, the proxy
-        /// file will be stored in the specified directory with a hashed file name to avoid name collisions and
-        /// file overwrites. The story directory option is convenient for the usage of temporary or working directories.
+        /// Creates a Wave format proxy file for the given file and optional directory according
+        /// to <see cref="SuggestWaveProxyFileInfo(FileInfo, DirectoryInfo)"/>.
         /// </summary>
         /// <param name="fileInfo">the file for which a proxy file should be created</param>
         /// <param name="storageDirectory">optional directory where the proxy file will be stored, can be null</param>
         /// <returns>the FileInfo of the proxy file</returns>
         public static FileInfo CreateWaveProxy(FileInfo fileInfo, DirectoryInfo storageDirectory)
         {
-            if (storageDirectory == null)
-            {
-                // Without a storage directory, store the proxy file beside the original file
-                var proxyFileInfo = new FileInfo(fileInfo.FullName + ".ffproxy.wav");
-                return CreateWaveProxy(fileInfo, proxyFileInfo);
-            }
-            else
-            {
-                // With a storage directory specified, store the proxy file with a hashed name
-                // (to avoid name collision / overwrites) in the target directory (e.g. a temp or working directory)
-                using (var sha256 = SHA256.Create())
-                {
-                    byte[] hash = sha256.ComputeHash(Encoding.Unicode.GetBytes(fileInfo.FullName));
-                    string hashString = BitConverter
-                        .ToString(hash)
-                        .Replace("-", "")
-                        .ToLowerInvariant();
-                    var proxyFileInfo = new FileInfo(
-                        Path.Combine(storageDirectory.FullName, hashString + ".ffproxy.wav")
-                    );
-                    return CreateWaveProxy(fileInfo, proxyFileInfo);
-                }
-            }
+            var proxyFileInfo = SuggestWaveProxyFileInfo(fileInfo, storageDirectory);
+            return CreateWaveProxy(fileInfo, proxyFileInfo);
         }
 
         /// <summary>
@@ -399,6 +383,42 @@ public static bool WaveProxySuggested(FileInfo fileInfo)
             );
         }
 
+        /// <summary>
+        /// Creates a proxy file info for the provided file with the <see cref="ProxyFileExtension"/>.
+        ///
+        /// If a storage directory is specified, the proxy file will be located in the specified directory
+        /// with a hashed file name to avoid name collisions. This option is is convenient when using
+        /// temporary or working directories.
+        ///
+        /// If no storage diretory is specified, the proxy file will be located in the same directory and
+        /// with the same name as the specified file.
+        /// </summary>
+        /// <param name="fileInfo">the file for which a proxy file should be created</param>
+        /// <param name="storageDirectory">optional directory where the proxy file will be stored (can be null)</param>
+        /// <returns>the FileInfo of the suggested proxy file</returns>
+        public static FileInfo SuggestWaveProxyFileInfo(
+            FileInfo fileInfo,
+            DirectoryInfo storageDirectory = null
+        )
+        {
+            if (storageDirectory == null)
+            {
+                // Without a storage directory, store the proxy file beside the original file
+                return new FileInfo(fileInfo.FullName + ProxyFileExtension);
+            }
+            else
+            {
+                // With a storage directory specified, store the proxy file with a hashed name
+                // (to avoid name collision / overwrites) in the target directory (e.g. a temp or working directory)
+                using var sha256 = SHA256.Create();
+                byte[] hash = sha256.ComputeHash(Encoding.Unicode.GetBytes(fileInfo.FullName));
+                string hashString = BitConverter.ToString(hash).Replace("-", "").ToLowerInvariant();
+                return new FileInfo(
+                    Path.Combine(storageDirectory.FullName, hashString + ProxyFileExtension)
+                );
+            }
+        }
+
         public class FileNotSeekableException : Exception
         {
             public FileNotSeekableException()