Avoid unnecessary byte[] allocations

src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarHeader.Read.cs

@@ -518,11 +518,16 @@ private void ReadUstarAttributes(Span<byte> buffer)
         // Throws if end of stream is reached or if an attribute is malformed.
         private void ReadExtendedAttributesBlock(Stream archiveStream)
         {
-            byte[]? buffer = CreateExtendedAttributesBufferIfSizeIsValid();
-            if (buffer != null)
+            if (_size != 0)
             {
-                archiveStream.ReadExactly(buffer);
-                ReadExtendedAttributesFromBuffer(buffer, _name);
+                ValidateSize();
+                byte[] buffer = ArrayPool<byte>.Shared.Rent((int)_size);
+                Span<byte> span = buffer.AsSpan(0, (int)_size);
+
+                archiveStream.ReadExactly(span);
+                ReadExtendedAttributesFromBuffer(span, _name);
+
+                ArrayPool<byte>.Shared.Return(buffer);
             }
         }
 
@@ -531,32 +536,30 @@ private void ReadExtendedAttributesBlock(Stream archiveStream)
         private async ValueTask ReadExtendedAttributesBlockAsync(Stream archiveStream, CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
-            byte[]? buffer = CreateExtendedAttributesBufferIfSizeIsValid();
-            if (buffer != null)
+
+            if (_size != 0)
             {
-                await archiveStream.ReadExactlyAsync(buffer, cancellationToken).ConfigureAwait(false);
-                ReadExtendedAttributesFromBuffer(buffer, _name);
-            }
-        }
+                ValidateSize();
+                byte[] buffer = ArrayPool<byte>.Shared.Rent((int)_size);
+                Memory<byte> memory = buffer.AsMemory(0, (int)_size);
 
-        // Return a byte array if the size field has a valid value for extended attributes. Otherwise, return null, or throw.
-        private byte[]? CreateExtendedAttributesBufferIfSizeIsValid()
-        {
-            Debug.Assert(_typeFlag is TarEntryType.ExtendedAttributes or TarEntryType.GlobalExtendedAttributes);
+                await archiveStream.ReadExactlyAsync(memory, cancellationToken).ConfigureAwait(false);
+                ReadExtendedAttributesFromBuffer(memory.Span, _name);
 
-            // It is not expected that the extended attributes data section will be longer than Array.MaxLength, considering
-            // the size field is 12 bytes long, which fits a number with a value under int.MaxValue.
-            if (_size > Array.MaxLength)
-            {
-                throw new InvalidOperationException(string.Format(SR.TarSizeFieldTooLargeForEntryType, _typeFlag.ToString()));
+                ArrayPool<byte>.Shared.Return(buffer);
             }
+        }
 
-            if (_size == 0)
+        private void ValidateSize()
+        {
+            if ((uint)_size > (uint)Array.MaxLength)
             {
-                return null;
+                ThrowSizeFieldTooLarge();
             }
 
-            return new byte[(int)_size];
+            [DoesNotReturn]
+            void ThrowSizeFieldTooLarge() =>
+                throw new InvalidOperationException(string.Format(SR.TarSizeFieldTooLargeForEntryType, _typeFlag.ToString()));
         }
 
         // Returns a dictionary containing the extended attributes collected from the provided byte buffer.
@@ -581,11 +584,16 @@ private void ReadExtendedAttributesFromBuffer(ReadOnlySpan<byte> buffer, string
         // Throws if end of stream is reached.
         private void ReadGnuLongPathDataBlock(Stream archiveStream)
         {
-            byte[]? buffer = CreateGnuLongDataBufferIfSizeIsValid();
-            if (buffer != null)
+            if (_size != 0)
             {
-                archiveStream.ReadExactly(buffer);
-                ReadGnuLongPathDataFromBuffer(buffer);
+                ValidateSize();
+                byte[] buffer = ArrayPool<byte>.Shared.Rent((int)_size);
+                Span<byte> span = buffer.AsSpan(0, (int)_size);
+
+                archiveStream.ReadExactly(span);
+                ReadGnuLongPathDataFromBuffer(span);
+
+                ArrayPool<byte>.Shared.Return(buffer);
             }
         }
 
@@ -595,11 +603,17 @@ private void ReadGnuLongPathDataBlock(Stream archiveStream)
         private async ValueTask ReadGnuLongPathDataBlockAsync(Stream archiveStream, CancellationToken cancellationToken)
         {
             cancellationToken.ThrowIfCancellationRequested();
-            byte[]? buffer = CreateGnuLongDataBufferIfSizeIsValid();
-            if (buffer != null)
+
+            if (_size != 0)
             {
-                await archiveStream.ReadExactlyAsync(buffer, cancellationToken).ConfigureAwait(false);
-                ReadGnuLongPathDataFromBuffer(buffer);
+                ValidateSize();
+                byte[] buffer = ArrayPool<byte>.Shared.Rent((int)_size);
+                Memory<byte> memory = buffer.AsMemory(0, (int)_size);
+
+                await archiveStream.ReadExactlyAsync(memory, cancellationToken).ConfigureAwait(false);
+                ReadGnuLongPathDataFromBuffer(memory.Span);
+
+                ArrayPool<byte>.Shared.Return(buffer);
             }
         }
 
@@ -618,24 +632,6 @@ private void ReadGnuLongPathDataFromBuffer(ReadOnlySpan<byte> buffer)
             }
         }
 
-        // Return a byte array if the size field has a valid value for GNU long metadata entry data. Otherwise, return null, or throw.
-        private byte[]? CreateGnuLongDataBufferIfSizeIsValid()
-        {
-            Debug.Assert(_typeFlag is TarEntryType.LongLink or TarEntryType.LongPath);
-
-            if (_size > Array.MaxLength)
-            {
-                throw new InvalidOperationException(string.Format(SR.TarSizeFieldTooLargeForEntryType, _typeFlag.ToString()));
-            }
-
-            if (_size == 0)
-            {
-                return null;
-            }
-
-            return new byte[(int)_size];
-        }
-
         // Tries to collect the next extended attribute from the string wrapped by the specified reader.
         // Extended attributes are saved in the ISO/IEC 10646-1:2000 standard UTF-8 encoding format.
         // https://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html

src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarHeader.Write.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Buffers;
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
@@ -524,8 +525,18 @@ private int WriteGnuFields(Span<byte> buffer)
         private static void WriteData(Stream archiveStream, Stream dataStream, long actualLength)
         {
             dataStream.CopyTo(archiveStream); // The data gets copied from the current position
+
             int paddingAfterData = TarHelpers.CalculatePadding(actualLength);
-            archiveStream.Write(new byte[paddingAfterData]);
+            if (paddingAfterData != 0)
+            {
+                Debug.Assert(paddingAfterData <= TarHelpers.RecordSize);
+
+                Span<byte> padding = stackalloc byte[TarHelpers.RecordSize];
+                padding = padding.Slice(0, paddingAfterData);
+                padding.Clear();
+
+                archiveStream.Write(padding);
+            }
         }
 
         // Asynchronously writes the current header's data stream into the archive stream.
@@ -534,8 +545,17 @@ private static async Task WriteDataAsync(Stream archiveStream, Stream dataStream
             cancellationToken.ThrowIfCancellationRequested();
 
             await dataStream.CopyToAsync(archiveStream, cancellationToken).ConfigureAwait(false); // The data gets copied from the current position
+
             int paddingAfterData = TarHelpers.CalculatePadding(actualLength);
-            await archiveStream.WriteAsync(new byte[paddingAfterData], cancellationToken).ConfigureAwait(false);
+            if (paddingAfterData != 0)
+            {
+                byte[] buffer = ArrayPool<byte>.Shared.Rent(paddingAfterData);
+
+                Array.Clear(buffer, 0, paddingAfterData);
+                await archiveStream.WriteAsync(buffer.AsMemory(0, paddingAfterData), cancellationToken).ConfigureAwait(false);
+
+                ArrayPool<byte>.Shared.Return(buffer);
+            }
         }
 
         // Dumps into the archive stream an extended attribute entry containing metadata of the entry it precedes.

src/libraries/System.Formats.Tar/src/System/Formats/Tar/TarWriter.cs

@@ -364,7 +364,9 @@ private async Task WriteEntryAsyncInternal(TarEntry entry, CancellationToken can
         // by two records consisting entirely of zero bytes.
         private void WriteFinalRecords()
         {
-            byte[] emptyRecord = new byte[TarHelpers.RecordSize];
+            Span<byte> emptyRecord = stackalloc byte[TarHelpers.RecordSize];
+            emptyRecord.Clear();
+
             _archiveStream.Write(emptyRecord);
             _archiveStream.Write(emptyRecord);
         }
@@ -374,9 +376,14 @@ private void WriteFinalRecords()
         // This method is called from DisposeAsync, so we don't want to propagate a cancelled CancellationToken.
         private async ValueTask WriteFinalRecordsAsync()
         {
-            byte[] emptyRecord = new byte[TarHelpers.RecordSize];
-            await _archiveStream.WriteAsync(emptyRecord, cancellationToken: default).ConfigureAwait(false);
-            await _archiveStream.WriteAsync(emptyRecord, cancellationToken: default).ConfigureAwait(false);
+            const int TwoRecordSize = TarHelpers.RecordSize * 2;
+
+            byte[] twoEmptyRecords = ArrayPool<byte>.Shared.Rent(TwoRecordSize);
+            Array.Clear(twoEmptyRecords, 0, TwoRecordSize);
+
+            await _archiveStream.WriteAsync(twoEmptyRecords.AsMemory(0, TwoRecordSize), cancellationToken: default).ConfigureAwait(false);
+
+            ArrayPool<byte>.Shared.Return(twoEmptyRecords);
         }
 
         private (string, string) ValidateWriteEntryArguments(string fileName, string? entryName)