50 lines
1.3 KiB
C#
50 lines
1.3 KiB
C#
namespace MareSynchronos.Utils;
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public class PngHdr
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{
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private static readonly byte[] _magicSignature = [137, 80, 78, 71, 13, 10, 26, 10];
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private static readonly byte[] _IHDR = [(byte)'I', (byte)'H', (byte)'D', (byte)'R'];
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public static readonly (int Width, int Height) InvalidSize = (0, 0);
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public static (int Width, int Height) TryExtractDimensions(Stream stream)
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{
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Span<byte> buffer = stackalloc byte[8];
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try
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{
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stream.ReadExactly(buffer[..8]);
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// All PNG files start with the same 8 bytes
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if (!buffer.SequenceEqual(_magicSignature))
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return InvalidSize;
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stream.ReadExactly(buffer[..8]);
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uint ihdrLength = BitConverter.ToUInt32(buffer);
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// The next four bytes will be the length of the IHDR section (it should be 13 bytes but we only need 8)
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if (ihdrLength < 8)
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return InvalidSize;
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// followed by ASCII "IHDR"
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if (!buffer[4..].SequenceEqual(_IHDR))
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return InvalidSize;
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stream.ReadExactly(buffer[..8]);
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uint width = BitConverter.ToUInt32(buffer);
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uint height = BitConverter.ToUInt32(buffer[4..]);
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// Validate the width/height are non-negative and... that's all we care about!
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if (width > int.MaxValue || height > int.MaxValue)
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return InvalidSize;
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return ((int)width, (int)height);
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}
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catch (EndOfStreamException)
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{
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return InvalidSize;
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}
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}
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}
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