Revert "Fill read buffer in constructor and when IsInReadBuffer() is false"

This reverts commit e066b839.

src/ImageSharp/IO/BufferedReadStream.cs

@@ -49,6 +49,7 @@ internal sealed class BufferedReadStream : Stream
 
         this.BaseStream = stream;
         this.Length = stream.Length;
+        this.Position = (int)stream.Position;
         this.BufferSize = configuration.StreamProcessingBufferSize;
         this.maxBufferIndex = this.BufferSize - 1;
         this.readBuffer = ArrayPool<byte>.Shared.Rent(this.BufferSize);
@@ -58,8 +59,8 @@ internal sealed class BufferedReadStream : Stream
             this.pinnedReadBuffer = (byte*)this.readBufferHandle.Pointer;
         }
 
-        this.Position = (int)stream.Position;
-        this.FillReadBuffer();
+        // This triggers a full read on first attempt.
+        this.readBufferIndex = this.BufferSize;
     }
 
     /// <summary>
@@ -98,7 +99,6 @@ internal sealed class BufferedReadStream : Stream
                 this.BaseStream.Seek(value, SeekOrigin.Begin);
                 this.readerPosition = value;
                 this.readBufferIndex = this.BufferSize;
-                this.FillReadBuffer();
             }
         }
     }

tests/ImageSharp.Tests/IO/BufferedReadStreamTests.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
-using System.IO;
 using SixLabors.ImageSharp.IO;
 
 namespace SixLabors.ImageSharp.Tests.IO;
@@ -10,10 +9,13 @@ public class BufferedReadStreamTests
 {
     private readonly Configuration configuration;
 
-    public BufferedReadStreamTests() => this.configuration = Configuration.CreateDefaultInstance();
+    public BufferedReadStreamTests()
+    {
+        this.configuration = Configuration.CreateDefaultInstance();
+    }
 
     public static readonly TheoryData<int> BufferSizes =
-        new()
+        new TheoryData<int>()
         {
             1, 2, 4, 8,
             16, 97, 503,
@@ -350,31 +352,6 @@ public class BufferedReadStreamTests
         }
     }
 
-    [Fact]
-    public void BufferedStreamSettingPositionWorksMultipleTimes()
-    {
-        // This test replicates an issue, which was caused by setting the stream position multiple times.
-        // This was then lead to the read buffer not being filled correctly.
-        int bufferSize = 16;
-        this.configuration.StreamProcessingBufferSize = bufferSize;
-        using MemoryStream stream = this.CreateTestStream(bufferSize * 2);
-        byte[] expected = stream.ToArray();
-        using var reader = new BufferedReadStream(this.configuration, stream);
-
-        // Read more then fits into the buffer.
-        for (int i = 0; i < 20; i++)
-        {
-            reader.ReadByte();
-        }
-
-        // Set the Position twice.
-        reader.Position = 10;
-        reader.Position = 3;
-
-        int actual = reader.ReadByte();
-        Assert.Equal(expected[3], actual);
-    }
-
     private MemoryStream CreateTestStream(int length)
     {
         var buffer = new byte[length];
@@ -393,6 +370,9 @@ public class BufferedReadStreamTests
         {
         }
 
-        public override int Read(byte[] buffer, int offset, int count) => base.Read(buffer, offset, 1);
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            return base.Read(buffer, offset, 1);
+        }
     }
 }