WebDrop/server/src/WebDrop.Storage/Blobs/DiskBlobStore.cs

using WebDrop.Core;

namespace WebDrop.Storage;

/// <summary>
/// 磁盘 blob 存储。键形如 "channelHex/itemHex/index.digest",直接映射为目录与文件。
/// 键只能由服务生成(十六进制和数字),这里仍做路径逃逸检查作为纵深防御。
/// </summary>
public sealed class DiskBlobStore : IBlobStore
{
    private readonly string _root;

    public DiskBlobStore(string root)
    {
        _root = Path.GetFullPath(root);
        Directory.CreateDirectory(_root);
    }

    public async ValueTask PutAsync(string key, ReadOnlyMemory<byte> data, CancellationToken ct = default)
    {
        string path = Resolve(key);
        // 键里含内容摘要:文件已存在就意味着内容相同,无需重写(也避免并发覆盖在 Windows 上冲突)
        if (File.Exists(path)) return;
        Directory.CreateDirectory(Path.GetDirectoryName(path)!);

        // 先写临时文件再重命名,读者永远看不到半个文件
        string tmp = path + "." + Guid.NewGuid().ToString("N") + ".tmp";
        await using (var fs = new FileStream(tmp, FileMode.CreateNew, FileAccess.Write, FileShare.None, 4096, FileOptions.Asynchronous))
        {
            await fs.WriteAsync(data, ct).ConfigureAwait(false);
        }

        try
        {
            File.Move(tmp, path, overwrite: false);
        }
        catch (Exception e) when (e is IOException or UnauthorizedAccessException && File.Exists(path))
        {
            File.Delete(tmp); // 并发写入同一内容,对方先到了
        }
    }

    public async ValueTask<byte[]?> ReadAsync(string key, CancellationToken ct = default)
    {
        string path = Resolve(key);
        try
        {
            return await File.ReadAllBytesAsync(path, ct).ConfigureAwait(false);
        }
        catch (FileNotFoundException)
        {
            return null;
        }
        catch (DirectoryNotFoundException)
        {
            return null;
        }
    }

    public void Delete(string key)
    {
        try { File.Delete(Resolve(key)); }
        catch (DirectoryNotFoundException) { }
    }

    public void DeletePrefix(string prefix)
    {
        string dir = Resolve(prefix);
        try { if (Directory.Exists(dir)) Directory.Delete(dir, recursive: true); }
        catch (DirectoryNotFoundException) { }
    }

    public IEnumerable<(string Key, DateTimeOffset LastWrite)> Enumerate()
    {
        foreach (string file in Directory.EnumerateFiles(_root, "*", SearchOption.AllDirectories))
        {
            if (file.EndsWith(".tmp", StringComparison.Ordinal)) continue;
            string key = Path.GetRelativePath(_root, file).Replace('\\', '/');
            yield return (key, new DateTimeOffset(File.GetLastWriteTimeUtc(file), TimeSpan.Zero));
        }
    }

    private string Resolve(string key)
    {
        string full = Path.GetFullPath(Path.Combine(_root, key));
        if (!full.StartsWith(_root + Path.DirectorySeparatorChar, StringComparison.Ordinal))
            throw new ArgumentException("非法 blob 键", nameof(key));
        return full;
    }
}