From e252a6f223120357fe00cc9c3aa842d250b131ad Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=88=B0=E9=98=9F=E7=9A=84=E5=81=B6=E5=83=8F-=E5=B2=9B?=
 =?UTF-8?q?=E9=A3=8E=E9=85=B1!?= <frg2089@outlook.com>
Date: Thu, 14 Dec 2023 21:48:34 +0800
Subject: [PATCH] Using Seek requires consideration of whether this stream
 allows Seek and the case where the stream start position is not 0.

---
 src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
index b888fa400..dcccc8363 100644
--- a/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
+++ b/src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs
@@ -133,6 +133,9 @@ internal sealed class BmpEncoderCore : IImageEncoderInternals
         Guard.NotNull(image, nameof(image));
         Guard.NotNull(stream, nameof(stream));
 
+        // Stream may not at 0.
+        long basePosition = stream.Position;
+
         Configuration configuration = image.Configuration;
         ImageMetadata metadata = image.Metadata;
         BmpMetadata bmpMetadata = metadata.GetBmpMetadata();
@@ -187,7 +190,7 @@ internal sealed class BmpEncoderCore : IImageEncoderInternals
 
         this.WriteBitmapInfoHeader(stream, infoHeader, buffer, infoHeaderSize);
         this.WriteImage(configuration, stream, image);
-        WriteColorProfile(stream, iccProfileData, buffer);
+        WriteColorProfile(stream, iccProfileData, buffer, basePosition);
 
         stream.Flush();
     }
@@ -271,16 +274,20 @@ internal sealed class BmpEncoderCore : IImageEncoderInternals
     /// <param name="stream">The stream to write to.</param>
     /// <param name="iccProfileData">The color profile data.</param>
     /// <param name="buffer">The buffer.</param>
-    private static void WriteColorProfile(Stream stream, byte[]? iccProfileData, Span<byte> buffer)
+    /// <param name="basePosition">The Stream may not be start with 0.</param>
+    private static void WriteColorProfile(Stream stream, byte[]? iccProfileData, Span<byte> buffer, long basePosition)
     {
         if (iccProfileData != null)
         {
             // The offset, in bytes, from the beginning of the BITMAPV5HEADER structure to the start of the profile data.
             int streamPositionAfterImageData = (int)stream.Position - BmpFileHeader.Size;
             stream.Write(iccProfileData);
+            long position = stream.Position; // Storage Position
             BinaryPrimitives.WriteInt32LittleEndian(buffer, streamPositionAfterImageData);
-            stream.Position = BmpFileHeader.Size + 112;
+            _ = stream.Seek(basePosition, SeekOrigin.Begin);
+            _ = stream.Seek(BmpFileHeader.Size + 112, SeekOrigin.Current);
             stream.Write(buffer[..4]);
+            _ = stream.Seek(position, SeekOrigin.Begin); // Reset Position
         }
     }