deflatestream-uses-native-apis-for-decompression.md

DeflateStream uses native APIs for decompression

Scope

Minor

Version Introduced

4.7.2

Source Analyzer Status

NotPlanned

Change Description

Starting with the .NET Framework 4.7.2, the implementation of decompression in the T:System.IO.Compression.DeflateStream class has changed to use native Windows APIs by default. Typically, this results in a substantial performance improvement. All .NET applications targeting the .NET Framework version 4.7.2 or higher use the native implementation.

This change might result in some differences in behavior, which include:

• Exception messages may be different. However, the type of exception thrown remains the same.

• Some special situations, such as not having enough memory to complete an operation, may be handled differently.

• There are known differences for parsing gzip header (note: only GZipStream set for decompression is affected):

  • Exceptions when parsing invalid headers may be thrown at different times.
  • The native implementation enforces that values for some reserved flags inside the gzip header (i.e. FLG) are set according to the specification, which may cause it to throw an exception where previously invalid values were ignored.

• Quirked

• Build-time break

Recommended Action

If decompression with native APIs has adversely affected the behavior of your app, you can opt out of this feature by adding the Switch.System.IO.Compression.DoNotUseNativeZipLibraryForDecompression switch to the runtime section of your app.config file and setting it to true:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <runtime>
       <AppContextSwitchOverrides
          value="Switch.System.IO.Compression.DoNotUseNativeZipLibraryForDecompression=true" />
    </runtime>
</configuration>

Affected APIs

T:System.IO.Compression.DeflateStream T:System.IO.Compression.GZipStream

Category

Core