44 lines
2.0 KiB
C#
44 lines
2.0 KiB
C#
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using System.Security.Cryptography;
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namespace MusicBridge.Agent.Media;
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internal sealed record Artwork(string Id, string ContentType, byte[] Bytes);
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// Only the current cover is retained. IDs are content hashes, never file paths or URLs.
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internal sealed class ArtworkCache
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{
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public const int MaxBytes = 2 * 1024 * 1024;
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private Artwork? current;
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public Artwork? Current => Volatile.Read(ref current);
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public Artwork? Get(string id) => Current is { } artwork && artwork.Id == id ? artwork : null;
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public void Clear() => Volatile.Write(ref current, null);
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public async Task<Artwork> LoadAsync(Stream stream, CancellationToken cancellationToken)
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{
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Clear(); // A failed/new cover must not leave the previous track's image attached.
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using var output = new MemoryStream();
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var buffer = new byte[16 * 1024];
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while (true)
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{
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var count = await stream.ReadAsync(buffer, cancellationToken);
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if (count == 0) break;
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if (output.Length + count > MaxBytes) throw new InvalidDataException("Обложка больше 2 МиБ.");
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output.Write(buffer, 0, count);
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}
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var bytes = output.ToArray();
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var type = DetectType(bytes) ?? throw new InvalidDataException("Неподдерживаемый формат обложки.");
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var artwork = new Artwork(Convert.ToHexString(SHA256.HashData(bytes)), type, bytes);
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Volatile.Write(ref current, artwork);
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return artwork;
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}
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private static string? DetectType(ReadOnlySpan<byte> data)
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{
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if (data.StartsWith(new byte[] { 137, 80, 78, 71, 13, 10, 26, 10 })) return "image/png";
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if (data.StartsWith(new byte[] { 255, 216, 255 })) return "image/jpeg";
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if (data.StartsWith("GIF87a"u8) || data.StartsWith("GIF89a"u8)) return "image/gif";
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if (data.Length >= 12 && data[..4].SequenceEqual("RIFF"u8) && data.Slice(8, 4).SequenceEqual("WEBP"u8)) return "image/webp";
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return null;
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}
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}
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