Call native BrotliEncoderMaxCompressedSize method for BrotliEncoder.GetMaxCompressedLength

src/libraries/Common/src/Interop/Interop.Brotli.cs

@@ -41,6 +41,9 @@ internal static unsafe partial BOOL BrotliEncoderCompressStream(
         [LibraryImport(Libraries.CompressionNative)]
         internal static partial BOOL BrotliEncoderHasMoreOutput(SafeBrotliEncoderHandle state);
 
+        [LibraryImport(Libraries.CompressionNative)]
+        internal static partial nuint BrotliEncoderMaxCompressedSize(nuint inputSize);
+
         [LibraryImport(Libraries.CompressionNative)]
         internal static partial void BrotliEncoderDestroyInstance(IntPtr state);
 

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/BrotliUtils.cs

@@ -11,7 +11,7 @@ internal static partial class BrotliUtils
         public const int Quality_Min = 0;
         public const int Quality_Default = 4;
         public const int Quality_Max = 11;
-        public const int MaxInputSize = int.MaxValue - 515; // 515 is the max compressed extra bytes
+        public const int MaxInputSize = int.MaxValue - 524_166; // 524_166 is the max compressed extra bytes
 
         internal static int GetQualityFromCompressionLevel(CompressionLevel compressionLevel) =>
             compressionLevel switch

src/libraries/System.IO.Compression.Brotli/src/System/IO/Compression/enc/BrotliEncoder.cs

@@ -103,26 +103,16 @@ internal void SetWindow(int window)
         }
 
         /// <summary>Gets the maximum expected compressed length for the provided input size.</summary>
-        /// <param name="inputSize">The input size to get the maximum expected compressed length from. Must be greater or equal than 0 and less or equal than <see cref="int.MaxValue" /> - 515.</param>
+        /// <param name="inputSize">The input size to get the maximum expected compressed length from. Must be greater or equal than 0 and less or equal than <see cref="int.MaxValue" /> - 524166.</param>
         /// <returns>A number representing the maximum compressed length for the provided input size.</returns>
-        /// <remarks>Returns 1 if <paramref name="inputSize" /> is 0.</remarks>
-        /// <exception cref="System.ArgumentOutOfRangeException"><paramref name="inputSize" /> is less than 0, the minimum allowed input size, or greater than <see cref="int.MaxValue" /> - 515, the maximum allowed input size.</exception>
+        /// <remarks>Returns 2 if <paramref name="inputSize" /> is 0.</remarks>
+        /// <exception cref="System.ArgumentOutOfRangeException"><paramref name="inputSize" /> is less than 0, the minimum allowed input size, or greater than <see cref="int.MaxValue" /> - 524166, the maximum allowed input size.</exception>
         public static int GetMaxCompressedLength(int inputSize)
         {
             ArgumentOutOfRangeException.ThrowIfNegative(inputSize);
             ArgumentOutOfRangeException.ThrowIfGreaterThan(inputSize, BrotliUtils.MaxInputSize);
 
-            if (inputSize == 0)
-            {
-                return 1;
-            }
-
-            int numLargeBlocks = inputSize >> 24;
-            int tail = inputSize & 0xFFFFFF;
-            int tailOverhead = (tail > (1 << 20)) ? 4 : 3;
-            int overhead = 2 + (4 * numLargeBlocks) + tailOverhead + 1;
-            int result = inputSize + overhead;
-            return result;
+            return (int)Interop.Brotli.BrotliEncoderMaxCompressedSize((nuint)inputSize);
         }
 
         internal OperationStatus Flush(Memory<byte> destination, out int bytesWritten) => Flush(destination.Span, out bytesWritten);

src/libraries/System.IO.Compression.Brotli/tests/CompressionStreamUnitTests.Brotli.cs

@@ -78,9 +78,23 @@ public void InvalidWindow()
         public void GetMaxCompressedSize_Basic()
         {
             Assert.Throws<ArgumentOutOfRangeException>("inputSize", () => BrotliEncoder.GetMaxCompressedLength(-1));
-            Assert.Throws<ArgumentOutOfRangeException>("inputSize", () => BrotliEncoder.GetMaxCompressedLength(2147483133));
-            Assert.InRange(BrotliEncoder.GetMaxCompressedLength(2147483132), 0, int.MaxValue);
-            Assert.Equal(1, BrotliEncoder.GetMaxCompressedLength(0));
+            Assert.Throws<ArgumentOutOfRangeException>("inputSize", () => BrotliEncoder.GetMaxCompressedLength(2_146_959_482));
+            Assert.InRange(BrotliEncoder.GetMaxCompressedLength(2_146_959_481), 0, int.MaxValue); // 2_146_959_481 produces int.MaxValue
+            Assert.Equal(2, BrotliEncoder.GetMaxCompressedLength(0));
+        }
+
+        [Fact]
+        public void DestinationBufferWithSizeEqualToMaxCompressedLength_ShouldAlwaysSucceed()
+        {
+            byte[] source = new byte[256000];
+            var rng = new Random(1234);
+            rng.NextBytes(source);
+
+            int maxLength = BrotliEncoder.GetMaxCompressedLength(source.Length);
+            var resultBuffer = new byte[maxLength];
+
+            Assert.True(BrotliEncoder.TryCompress(source, resultBuffer, out int bytesWritten, quality: 5, window: 10));
+            Assert.True(maxLength >= bytesWritten);
         }
 
         [Fact]

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

@@ -11,6 +11,7 @@ EXPORTS
     BrotliEncoderCreateInstance
     BrotliEncoderDestroyInstance
     BrotliEncoderHasMoreOutput
+    BrotliEncoderMaxCompressedSize
     BrotliEncoderSetParameter
     CompressionNative_Crc32
     CompressionNative_Deflate

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

@@ -11,6 +11,7 @@ BrotliEncoderCompressStream
 BrotliEncoderCreateInstance
 BrotliEncoderDestroyInstance
 BrotliEncoderHasMoreOutput
+BrotliEncoderMaxCompressedSize
 BrotliEncoderSetParameter
 CompressionNative_Crc32
 CompressionNative_Deflate

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

@@ -22,6 +22,7 @@ static const Entry s_compressionNative[] =
     DllImportEntry(BrotliEncoderCreateInstance)
     DllImportEntry(BrotliEncoderDestroyInstance)
     DllImportEntry(BrotliEncoderHasMoreOutput)
+    DllImportEntry(BrotliEncoderMaxCompressedSize)
     DllImportEntry(BrotliEncoderSetParameter)
     DllImportEntry(CompressionNative_Crc32)
     DllImportEntry(CompressionNative_Deflate)