Throw DirectoryNotFoundException on Image.Save with bad directory

src/libraries/System.Drawing.Common/src/Resources/Strings.resx

@@ -455,4 +455,7 @@
   <data name="ValueNotOneOfValues" xml:space="preserve">
     <value>The value of the {0} property is not one of the {1} values</value>
   </data>
+  <data name="TargetDirectoryDoesNotExist" xml:space="preserve">
+    <value>The directory {0} of the filename {1} does not exist.</value>
+  </data>
 </root>

src/libraries/System.Drawing.Common/src/System/Drawing/Image.Unix.cs

@@ -189,6 +189,11 @@ public void Save(string filename, ImageFormat format)
 
         public void Save(string filename, ImageCodecInfo encoder, EncoderParameters? encoderParams)
         {
+            if (filename == null)
+                throw new ArgumentNullException(nameof(filename));
+
+            ThrowIfDirectoryDoesntExist(filename);
+
             int st;
             Guid guid = encoder.Clsid;
 

src/libraries/System.Drawing.Common/src/System/Drawing/Image.Windows.cs

@@ -135,6 +135,8 @@ public void Save(string filename, ImageCodecInfo encoder, EncoderParameters? enc
             if (encoder == null)
                 throw new ArgumentNullException(nameof(encoder));
 
+            ThrowIfDirectoryDoesntExist(filename);
+
             IntPtr encoderParamsMemory = IntPtr.Zero;
 
             if (encoderParams != null)

src/libraries/System.Drawing.Common/src/System/Drawing/Image.cs

@@ -153,6 +153,15 @@ public void Dispose()
         /// </summary>
         public void Save(string filename) => Save(filename, RawFormat);
 
+        private static void ThrowIfDirectoryDoesntExist(string filename)
+        {
+            var directoryPart = System.IO.Path.GetDirectoryName(filename);
+            if (!string.IsNullOrEmpty(directoryPart) && !System.IO.Directory.Exists(directoryPart))
+            {
+                throw new DirectoryNotFoundException(SR.Format(SR.TargetDirectoryDoesNotExist, directoryPart, filename));
+            }
+        }
+
         /// <summary>
         /// Gets the width and height of this <see cref='Image'/>.
         /// </summary>

src/libraries/System.Drawing.Common/tests/ImageTests.cs

@@ -199,5 +199,16 @@ public void GetEncoderParameterList_ReturnsExpected(ImageFormat format, Guid[] e
                     paramList.Param.Select(p => p.Encoder.Guid));
             }
         }
+
+        [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, ".NET Framework throws ExternalException")]
+        [ConditionalFact(Helpers.IsDrawingSupported)]
+        public void Save_InvalidDirectory_ThrowsDirectoryNotFoundException()
+        {
+            using (var bitmap = new Bitmap(1, 1))
+            {
+                var badTarget = System.IO.Path.Combine("NoSuchDirectory", "NoSuchFile");
+                AssertExtensions.Throws<DirectoryNotFoundException>(() => bitmap.Save(badTarget), $"The directory NoSuchDirectory of the filename {badTarget} does not exist.");
+            }
+        }
     }
 }