The administrator's page backs up, downloads, uploads and restores
/clientapi/admin/backups (owner decision 2026-10-07, approving these endpoints in production): the list with what runs, the restore waiting and the last restore's report; back up now; delete; a download for the password, through a ticket good for ten minutes in the link's path, as one tar whose length is known first and which honours Range (BackupTar); an upload in pieces of at most 32 MB, each at the offset already received or refused with it, so a broken upload resumes, read into a backup only when it holds nothing but plain files under one backup's folder; and a restore for the password and the host typed out. Every call checks the administrator against the database. nginx streams downloads for an hour and takes upload pieces unbuffered, rate-limited. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw
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using System.Formats.Tar;
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using System.Text;
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using System.Text.RegularExpressions;
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namespace PrivaPub.Infrastructure.Backup
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{
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// A backup as one tar file, for the administrator to download and to upload again: every file under <id>/, its length
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// known before the first byte (so a download has a Content-Length and resumes with Range), written straight from the
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// backup's files, never held in memory.
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public sealed partial class BackupTar
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{
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const int Block = 512;
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readonly List<Entry> _entries = [];
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public long Length { get; private set; }
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sealed record Entry(string Name, string Path, long Size, DateTime ModifiedAt, long Offset);
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public static BackupTar Of(string backupsRoot, string id)
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{
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var directory = Path.Combine(backupsRoot, id);
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var tar = new BackupTar();
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var offset = 0L;
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foreach (var file in Directory.EnumerateFiles(directory, "*", SearchOption.AllDirectories).OrderBy(f => f, StringComparer.Ordinal))
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{
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var info = new FileInfo(file);
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var name = id + "/" + Path.GetRelativePath(directory, file).Replace('\\', '/');
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tar._entries.Add(new Entry(name, file, info.Length, info.LastWriteTimeUtc, offset));
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offset += Block + Padded(info.Length);
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}
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tar.Length = offset + 2 * Block;
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return tar;
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}
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static long Padded(long size) => (size + Block - 1) / Block * Block;
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/// <summary>Writes bytes from to to (inclusive) of the tar.</summary>
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public async Task Write(Stream output, long from, long to, CancellationToken token)
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{
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var buffer = new byte[81920];
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foreach (var entry in _entries)
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{
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var headerEnd = entry.Offset + Block;
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var dataEnd = headerEnd + entry.Size;
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var entryEnd = headerEnd + Padded(entry.Size);
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if (entryEnd <= from)
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continue;
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if (entry.Offset > to)
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return;
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if (from < headerEnd)
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{
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var header = Header(entry);
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var start = (int)Math.Max(0, from - entry.Offset);
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var end = (int)Math.Min(Block, to - entry.Offset + 1);
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await output.WriteAsync(header.AsMemory(start, end - start), token);
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}
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if (from < dataEnd && to >= headerEnd && entry.Size > 0)
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{
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var start = Math.Max(0, from - headerEnd);
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var end = Math.Min(entry.Size, to - headerEnd + 1);
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await using var file = new FileStream(entry.Path, FileMode.Open, FileAccess.Read, FileShare.Read, 1, FileOptions.SequentialScan);
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file.Seek(start, SeekOrigin.Begin);
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var left = end - start;
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while (left > 0)
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{
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var read = await file.ReadAsync(buffer.AsMemory(0, (int)Math.Min(buffer.Length, left)), token);
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if (read == 0)
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throw new IOException($"{entry.Name} shrank while it was sent");
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await output.WriteAsync(buffer.AsMemory(0, read), token);
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left -= read;
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}
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}
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if (to >= dataEnd && from < entryEnd)
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{
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var start = Math.Max(from, dataEnd);
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var end = Math.Min(entryEnd - 1, to);
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if (end >= start)
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await output.WriteAsync(new byte[end - start + 1], token);
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}
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}
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var trailer = Length - 2 * Block;
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if (to >= trailer)
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await output.WriteAsync(new byte[to - Math.Max(from, trailer) + 1], token);
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}
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// a ustar header (name split into prefix and name past 100 bytes; sizes past 8 GiB in base 256)
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static byte[] Header(Entry entry)
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{
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var header = new byte[Block];
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var name = entry.Name;
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var prefix = string.Empty;
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if (Encoding.UTF8.GetByteCount(name) > 100)
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{
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var cut = name.LastIndexOf('/', Math.Min(name.Length - 1, 155));
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while (cut > 0 && Encoding.UTF8.GetByteCount(name[(cut + 1)..]) > 100)
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cut = name.IndexOf('/', cut + 1);
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if (cut <= 0 || Encoding.UTF8.GetByteCount(name[..cut]) > 155)
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throw new InvalidOperationException($"{name} is too long for a tar header");
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prefix = name[..cut];
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name = name[(cut + 1)..];
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}
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Text(header, 0, 100, name);
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Octal(header, 100, 8, Convert.ToInt32("640", 8));
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Octal(header, 108, 8, 0);
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Octal(header, 116, 8, 0);
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if (entry.Size < 1L << 33)
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Octal(header, 124, 12, entry.Size);
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else
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{
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header[124] = 0x80;
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for (var i = 0; i < 8; i++)
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header[135 - i] = (byte)(entry.Size >> (8 * i));
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}
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Octal(header, 136, 12, new DateTimeOffset(entry.ModifiedAt).ToUnixTimeSeconds());
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header[156] = (byte)'0';
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Text(header, 257, 6, "ustar");
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Text(header, 263, 2, "00");
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Text(header, 265, 32, "privapub");
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Text(header, 297, 32, "privapub");
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Text(header, 345, 155, prefix);
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for (var i = 148; i < 156; i++)
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header[i] = (byte)' ';
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var sum = header.Sum(b => (long)b);
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Text(header, 148, 7, Convert.ToString(sum, 8).PadLeft(6, '0'));
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header[155] = (byte)' ';
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return header;
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}
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static void Text(byte[] header, int at, int length, string value)
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{
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var bytes = Encoding.UTF8.GetBytes(value);
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Array.Copy(bytes, 0, header, at, Math.Min(bytes.Length, length));
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}
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static void Octal(byte[] header, int at, int length, long value) =>
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Text(header, at, length - 1, Convert.ToString(value, 8).PadLeft(length - 1, '0'));
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[GeneratedRegex(@"^\d{8}-\d{6}-[a-z-]{1,20}$")]
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public static partial Regex BackupId();
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/// <summary>
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/// A backup read from an uploaded tar into the backups' root: refused when it holds anything but plain files and
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/// folders under one backup's folder, a path leaving it, or more than the disk can take. The backup, or why not.
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/// </summary>
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public static async Task<(BackupInfo Backup, string Error)> Import(Stream tar, string backupsRoot, CancellationToken token)
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{
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const int MaxEntries = 2_000_000;
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var id = default(string);
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var partial = default(string);
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var entries = 0;
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var free = new DriveInfo(Path.GetFullPath(backupsRoot)).AvailableFreeSpace;
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var written = 0L;
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try
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{
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await using var reader = new TarReader(tar, leaveOpen: true);
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while (await reader.GetNextEntryAsync(copyData: false, token) is { } entry)
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{
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if (++entries > MaxEntries)
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return (default, "too many files");
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var name = entry.Name.TrimEnd('/');
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var slash = name.IndexOf('/');
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var top = slash < 0 ? name : name[..slash];
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if (id == default)
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{
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if (!BackupId().IsMatch(top))
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return (default, $"{top} is not a backup's folder");
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id = top;
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if (Directory.Exists(Path.Combine(backupsRoot, id)))
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return (default, $"{id} is already here");
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partial = Path.Combine(backupsRoot, id + ServerBackup.PartialSuffix);
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if (Directory.Exists(partial))
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Directory.Delete(partial, recursive: true);
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ServerBackup.MakeDirectory(partial);
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}
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if (top != id)
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return (default, $"{name} is outside {id}");
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if (entry.EntryType is TarEntryType.Directory)
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continue;
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if (entry.EntryType is not (TarEntryType.RegularFile or TarEntryType.V7RegularFile))
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return (default, $"{name} is not a plain file");
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if (slash < 0)
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return (default, $"{name} is not inside a folder");
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written += entry.Length;
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if (written > free - 512L * 1024 * 1024)
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return (default, "not enough free disk");
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var path = ServerBackup.Inside(partial, name[(slash + 1)..]);
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Directory.CreateDirectory(Path.GetDirectoryName(path)!);
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await using var file = OperatingSystem.IsWindows()
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? new FileStream(path, FileMode.CreateNew, FileAccess.Write)
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: new FileStream(path, new FileStreamOptions { Mode = FileMode.CreateNew, Access = FileAccess.Write,
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UnixCreateMode = UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.GroupRead });
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if (entry.DataStream != default)
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await entry.DataStream.CopyToAsync(file, token);
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}
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if (id == default)
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return (default, "the file holds nothing");
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var manifest = ArchiveManifest.Read(partial);
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if (manifest == default)
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return (default, "it has no manifest");
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manifest.Kind = "uploaded";
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manifest.Write(partial);
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Directory.Move(partial, Path.Combine(backupsRoot, id));
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partial = default;
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var problems = await ServerBackup.Verify(backupsRoot, id, token);
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if (problems.Count > 0)
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{
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ServerBackup.Delete(backupsRoot, id);
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return (default, string.Join("; ", problems.Take(5)));
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}
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return (ServerBackup.Find(backupsRoot, id), default);
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}
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catch (Exception ex) when (ex is FormatException or InvalidDataException or InvalidOperationException or EndOfStreamException or System.Text.Json.JsonException)
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{
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return (default, $"not a backup: {ex.Message}");
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}
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finally
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{
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if (partial != default && Directory.Exists(partial))
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Directory.Delete(partial, recursive: true);
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}
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}
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}
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}
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