feat(server): implement sealed share lifecycle

Signed-off-by: JustMe <mr.toing@outlook.com>

server/src/WebDrop.Core/Errors.cs

@@ -0,0 +1,75 @@
+namespace WebDrop.Core;
+
+public enum ErrorCode
+{
+    BadRequest,
+    Unauthorized,
+    Forbidden,
+    NotJoined,
+    SeatsFull,
+    ModeMismatch,
+    NotFound,
+    Conflict,
+    Gone,
+    TooLarge,
+    CaptchaRequired,
+    CaptchaUnavailable,
+    RateLimited,
+    VisitorsFull,
+    Sealed,
+}
+
+/// <summary>预期内的业务失败。消息只含错误码,绝不回显用户提交的内容。</summary>
+public sealed class WebDropException : Exception
+{
+    public ErrorCode Code { get; }
+
+    /// <summary>仅在 410 日志续传失败时有值,见 api.md。</summary>
+    public long? OldestSeq { get; }
+
+    public WebDropException(ErrorCode code, long? oldestSeq = null) : base(code.ToWire())
+    {
+        Code = code;
+        OldestSeq = oldestSeq;
+    }
+}
+
+public static class ErrorCodes
+{
+    public static string ToWire(this ErrorCode code) => code switch
+    {
+        ErrorCode.BadRequest => "bad_request",
+        ErrorCode.Unauthorized => "unauthorized",
+        ErrorCode.Forbidden => "forbidden",
+        ErrorCode.NotJoined => "not_joined",
+        ErrorCode.SeatsFull => "seats_full",
+        ErrorCode.ModeMismatch => "mode_mismatch",
+        ErrorCode.NotFound => "not_found",
+        ErrorCode.Conflict => "conflict",
+        ErrorCode.Gone => "gone",
+        ErrorCode.TooLarge => "too_large",
+        ErrorCode.CaptchaRequired => "captcha_required",
+        ErrorCode.CaptchaUnavailable => "captcha_unavailable",
+        ErrorCode.RateLimited => "rate_limited",
+        ErrorCode.VisitorsFull => "visitors_full",
+        ErrorCode.Sealed => "sealed",
+        _ => "bad_request",
+    };
+
+    public static int ToStatus(this ErrorCode code) => code switch
+    {
+        ErrorCode.BadRequest => 400,
+        ErrorCode.Unauthorized => 401,
+        ErrorCode.Forbidden or ErrorCode.NotJoined or ErrorCode.SeatsFull or ErrorCode.ModeMismatch => 403,
+        ErrorCode.NotFound => 404,
+        ErrorCode.Conflict => 409,
+        ErrorCode.Sealed => 409,
+        ErrorCode.Gone => 410,
+        ErrorCode.TooLarge => 413,
+        ErrorCode.CaptchaRequired => 428,
+        ErrorCode.CaptchaUnavailable => 503,
+        ErrorCode.RateLimited => 429,
+        ErrorCode.VisitorsFull => 403,
+        _ => 400,
+    };
+}