feat: add bounded compatible session browser (#8)

Closes #8
2026-07-16 06:06:29 +02:00
parent 49564c7e7e
commit a9a2b3db35
14 changed files with 786 additions and 10 deletions
@@ -0,0 +1,181 @@
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.State;
+
+namespace FinalFactory.Rendezvous.Server.Browser;
+
+internal sealed class SessionBrowserCursorCodec : IDisposable
+{
+    private const string Prefix = "rvc1";
+    private readonly byte[] _key = RandomNumberGenerator.GetBytes(32);
+    private bool _disposed;
+
+    public string Encode(VisibleListingQuery query, SessionListingId after, DateTimeOffset now)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        BrowserCursorPayload payload = new()
+        {
+            GameId = query.Scope.GameId.Value,
+            EnvironmentId = query.Scope.EnvironmentId.Value,
+            ProtocolVersion = query.ProtocolVersion,
+            RegionId = query.RegionId?.Value,
+            ExcludeFull = query.ExcludeFull,
+            AfterListingId = after.ToString(),
+            ExpiresAtUnixSeconds = now.AddMinutes(5).ToUnixTimeSeconds(),
+        };
+        string encoded = EncodeBytes(JsonSerializer.SerializeToUtf8Bytes(payload, ContractJson.Options));
+        string content = $"{Prefix}.{encoded}";
+        byte[] signature = HMACSHA256.HashData(_key, Encoding.ASCII.GetBytes(content));
+        try
+        {
+            string cursor = $"{content}.{EncodeBytes(signature)}";
+            return ContractValidation.IsCursorValid(cursor)
+                ? cursor
+                : throw new InvalidOperationException("The browser cursor exceeds its contract limit.");
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(signature);
+        }
+    }
+
+    public bool TryDecode(
+        string? cursor,
+        TenantScope scope,
+        uint protocolVersion,
+        RegionId? regionId,
+        bool excludeFull,
+        DateTimeOffset now,
+        out SessionListingId? after)
+    {
+        after = null;
+        if (cursor is null)
+        {
+            return true;
+        }
+
+        if (_disposed || !ContractValidation.IsCursorValid(cursor))
+        {
+            return false;
+        }
+
+        string[] segments = cursor.Split('.');
+        if (segments.Length != 3 || !string.Equals(segments[0], Prefix, StringComparison.Ordinal))
+        {
+            return false;
+        }
+
+        byte[] expected = HMACSHA256.HashData(
+            _key,
+            Encoding.ASCII.GetBytes($"{segments[0]}.{segments[1]}"));
+        if (!TryDecodeBytes(segments[2], out byte[] supplied))
+        {
+            CryptographicOperations.ZeroMemory(expected);
+            return false;
+        }
+
+        bool validSignature = supplied.Length == expected.Length
+            && CryptographicOperations.FixedTimeEquals(supplied, expected);
+        CryptographicOperations.ZeroMemory(supplied);
+        CryptographicOperations.ZeroMemory(expected);
+        if (!validSignature || !TryDecodeBytes(segments[1], out byte[] encodedPayload))
+        {
+            return false;
+        }
+
+        BrowserCursorPayload? payload;
+        try
+        {
+            payload = JsonSerializer.Deserialize<BrowserCursorPayload>(
+                encodedPayload,
+                ContractJson.Options);
+        }
+        catch (JsonException)
+        {
+            payload = null;
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(encodedPayload);
+        }
+
+        if (payload is null
+            || payload.ExpiresAtUnixSeconds <= now.ToUnixTimeSeconds()
+            || !string.Equals(payload.GameId, scope.GameId.Value, StringComparison.Ordinal)
+            || !string.Equals(payload.EnvironmentId, scope.EnvironmentId.Value, StringComparison.Ordinal)
+            || payload.ProtocolVersion != protocolVersion
+            || !string.Equals(payload.RegionId, regionId?.Value, StringComparison.Ordinal)
+            || payload.ExcludeFull != excludeFull
+            || !SessionListingId.TryParse(payload.AfterListingId, out SessionListingId listingId))
+        {
+            return false;
+        }
+
+        after = listingId;
+        return true;
+    }
+
+    public void Dispose()
+    {
+        if (!_disposed)
+        {
+            _disposed = true;
+            CryptographicOperations.ZeroMemory(_key);
+        }
+    }
+
+    public override string ToString() => "[SessionBrowserCursorCodec: key and cursors redacted]";
+
+    private static string EncodeBytes(ReadOnlySpan<byte> bytes) => Convert
+        .ToBase64String(bytes)
+        .TrimEnd('=')
+        .Replace('+', '-')
+        .Replace('/', '_');
+
+    private static bool TryDecodeBytes(string value, out byte[] bytes)
+    {
+        bytes = [];
+        if (string.IsNullOrEmpty(value)
+            || value.Any(static character =>
+                character is not (>= 'A' and <= 'Z')
+                and not (>= 'a' and <= 'z')
+                and not (>= '0' and <= '9')
+                and not '-'
+                and not '_'))
+        {
+            return false;
+        }
+
+        string padded = value.Replace('-', '+').Replace('_', '/');
+        padded += (padded.Length % 4) switch { 0 => "", 2 => "==", 3 => "=", _ => "!" };
+        try
+        {
+            bytes = Convert.FromBase64String(padded);
+            return true;
+        }
+        catch (FormatException)
+        {
+            return false;
+        }
+    }
+}
+
+internal sealed class BrowserCursorPayload
+{
+    [JsonRequired]
+    public string GameId { get; set; } = string.Empty;
+    [JsonRequired]
+    public string EnvironmentId { get; set; } = string.Empty;
+    [JsonRequired]
+    public uint ProtocolVersion { get; set; }
+    public string? RegionId { get; set; }
+    [JsonRequired]
+    public bool ExcludeFull { get; set; }
+    [JsonRequired]
+    public string AfterListingId { get; set; } = string.Empty;
+    [JsonRequired]
+    public long ExpiresAtUnixSeconds { get; set; }
+}