Reset ZLibStreamHandle when parsing concatenated GZip streams (#113587)

* Reset ZLib inflater state where possible
* Add CompressionNative_InflateReset2_ to Unix exports
---------
Co-authored-by: Carlos Sánchez López <[email protected]>

Author: edwardneal

src/libraries/Common/src/Interop/Interop.zlib.cs

@@ -26,6 +26,9 @@ internal static unsafe partial ZLibNative.ErrorCode DeflateInit2_(
         [LibraryImport(Libraries.CompressionNative, EntryPoint = "CompressionNative_InflateInit2_")]
         internal static unsafe partial ZLibNative.ErrorCode InflateInit2_(ZLibNative.ZStream* stream, int windowBits);
 
+        [LibraryImport(Libraries.CompressionNative, EntryPoint = "CompressionNative_InflateReset2_")]
+        internal static unsafe partial ZLibNative.ErrorCode InflateReset2_(ZLibNative.ZStream* stream, int windowBits);
+
         [LibraryImport(Libraries.CompressionNative, EntryPoint = "CompressionNative_Inflate")]
         internal static unsafe partial ZLibNative.ErrorCode Inflate(ZLibNative.ZStream* stream, ZLibNative.FlushCode flush);
 

src/libraries/Common/src/System/IO/Compression/ZLibNative.cs

@@ -280,6 +280,17 @@ public unsafe ErrorCode InflateInit2_(int windowBits)
                 }
             }
 
+            public unsafe ErrorCode InflateReset2_(int windowBits)
+            {
+                EnsureNotDisposed();
+                EnsureState(State.InitializedForInflate);
+
+                fixed (ZStream* stream = &_zStream)
+                {
+                    return Interop.ZLib.InflateReset2_(stream, windowBits);
+                }
+            }
+
             public unsafe ErrorCode Inflate(FlushCode flush)
             {
                 EnsureNotDisposed();

src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateZLib/Inflater.cs

@@ -149,25 +149,18 @@ private unsafe bool ResetStreamForLeftoverInput()
 
             lock (SyncLock)
             {
-                IntPtr nextInPtr = _zlibStream.NextIn;
-                byte* nextInPointer = (byte*)nextInPtr.ToPointer();
+                byte* nextInPointer = (byte*)_zlibStream.NextIn;
                 uint nextAvailIn = _zlibStream.AvailIn;
 
-                // Check the leftover bytes to see if they start with he gzip header ID bytes
+                // Check the leftover bytes to see if they start with the gzip header ID bytes
                 if (*nextInPointer != ZLibNative.GZip_Header_ID1 || (nextAvailIn > 1 && *(nextInPointer + 1) != ZLibNative.GZip_Header_ID2))
                 {
                     return true;
                 }
 
-                // Trash our existing zstream.
-                _zlibStream.Dispose();
+                // Reset our existing zstream.
+                _zlibStream.InflateReset2_(_windowBits);
 
-                // Create a new zstream
-                InflateInit(_windowBits);
-
-                // SetInput on the new stream to the bits remaining from the last stream
-                _zlibStream.NextIn = nextInPtr;
-                _zlibStream.AvailIn = nextAvailIn;
                 _finished = false;
             }
 

src/native/libs/System.IO.Compression.Native/System.IO.Compression.Native.def

@@ -20,3 +20,4 @@ EXPORTS
     CompressionNative_Inflate
     CompressionNative_InflateEnd
     CompressionNative_InflateInit2_
+    CompressionNative_InflateReset2_

src/native/libs/System.IO.Compression.Native/System.IO.Compression.Native_unixexports.src

@@ -20,3 +20,4 @@ CompressionNative_DeflateInit2_
 CompressionNative_Inflate
 CompressionNative_InflateEnd
 CompressionNative_InflateInit2_
+CompressionNative_InflateReset2_

src/native/libs/System.IO.Compression.Native/entrypoints.c

@@ -31,6 +31,7 @@ static const Entry s_compressionNative[] =
     DllImportEntry(CompressionNative_Inflate)
     DllImportEntry(CompressionNative_InflateEnd)
     DllImportEntry(CompressionNative_InflateInit2_)
+    DllImportEntry(CompressionNative_InflateReset2_)
 };
 
 EXTERN_C const void* CompressionResolveDllImport(const char* name);

src/native/libs/System.IO.Compression.Native/pal_zlib.c

@@ -181,6 +181,17 @@ int32_t CompressionNative_InflateEnd(PAL_ZStream* stream)
     return result;
 }
 
+int32_t CompressionNative_InflateReset2_(PAL_ZStream* stream, int32_t windowBits)
+{
+    assert(stream != NULL);
+
+    z_stream* zStream = GetCurrentZStream(stream);
+    int32_t result = inflateReset2(zStream, windowBits);
+    TransferStateToPalZStream(zStream, stream);
+
+    return result;
+}
+
 uint32_t CompressionNative_Crc32(uint32_t crc, uint8_t* buffer, int32_t len)
 {
     assert(buffer != NULL);

src/native/libs/System.IO.Compression.Native/pal_zlib.h

@@ -124,6 +124,15 @@ Returns a PAL_ErrorCode indicating success or an error number on failure.
 */
 FUNCTIONEXPORT int32_t FUNCTIONCALLINGCONVENTION CompressionNative_InflateEnd(PAL_ZStream* stream);
 
+/*
+This function is equivalent to InflateEnd followed by InflateInit, but does not free and reallocate 
+the internal decompression state. The stream's window size will be modified and its memory may be
+reallocated if necessary.
+
+Returns a PAL_ErrorCode indicating success or an error number on failure.
+*/
+FUNCTIONEXPORT int32_t FUNCTIONCALLINGCONVENTION CompressionNative_InflateReset2_(PAL_ZStream* stream, int32_t windowBits);
+
 /*
 Update a running CRC-32 with the bytes buffer[0..len-1] and return the
 updated CRC-32.