Wire ITranscodeSessionStore to Redis-backed impl with NullTranscodeSessionStore fallback and DI registration (#21)

* Initial plan * feat: add Redis-backed ITranscodeSessionStore with NullTranscodeSessionStore fallback and DI registration Co-authored-by: ZoltyMat <177592743+ZoltyMat@users.noreply.github.com> * refactor: add code review improvements - lease expiry comment, Redis connection error handling Co-authored-by: ZoltyMat <177592743+ZoltyMat@users.noreply.github.com> --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: ZoltyMat <177592743+ZoltyMat@users.noreply.github.com>
2026-03-09 23:04:04 -04:00
parent a187ab18b8
commit d60ae43b59
8 changed files with 452 additions and 0 deletions
@@ -0,0 +1,143 @@
+using System;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+using MediaBrowser.Controller.MediaEncoding;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using StackExchange.Redis;
+
+namespace Emby.Server.Implementations.MediaEncoding;
+
+/// <summary>
+/// A Redis-backed implementation of <see cref="ITranscodeSessionStore"/> that provides
+/// durable, distributed session tracking with lease-based ownership between pods.
+/// </summary>
+public sealed class RedisTranscodeSessionStore : ITranscodeSessionStore
+{
+    private const string KeyPrefix = "jellyfin:transcode:";
+
+    /// <summary>
+    /// Lua script for atomic takeover: reads the stored session, checks whether the lease has
+    /// expired (comparing <c>LeaseExpiresUtc.Ticks</c> against the caller-supplied current ticks),
+    /// and if expired, updates the owner and expiry before returning 1; returns 0 otherwise.
+    /// </summary>
+    private const string TakeoverScript = @"
+local raw = redis.call('GET', KEYS[1])
+if not raw then return 0 end
+local session = cjson.decode(raw)
+local currentTicks = tonumber(ARGV[1])
+if session['LeaseExpiresUtc'] > currentTicks then return 0 end
+session['OwnerPod'] = ARGV[2]
+local leaseDurationMs = tonumber(ARGV[3])
+local newTicks = currentTicks + (leaseDurationMs * 10000)
+session['LeaseExpiresUtc'] = newTicks
+redis.call('SET', KEYS[1], cjson.encode(session), 'PX', leaseDurationMs)
+return 1";
+
+    private readonly IDatabase _db;
+    private readonly TranscodeStoreOptions _options;
+    private readonly ILogger<RedisTranscodeSessionStore> _logger;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RedisTranscodeSessionStore"/> class.
+    /// </summary>
+    /// <param name="redis">The Redis connection multiplexer.</param>
+    /// <param name="options">The transcode store configuration options.</param>
+    /// <param name="logger">The logger.</param>
+    public RedisTranscodeSessionStore(
+        IConnectionMultiplexer redis,
+        IOptions<TranscodeStoreOptions> options,
+        ILogger<RedisTranscodeSessionStore> logger)
+    {
+        _db = redis.GetDatabase();
+        _options = options.Value;
+        _logger = logger;
+    }
+
+    /// <inheritdoc />
+    public async Task SetAsync(TranscodeSession session, CancellationToken cancellationToken = default)
+    {
+        var key = GetKey(session.PlaySessionId);
+        var json = JsonSerializer.Serialize(session);
+        var leaseDurationMs = (long)_options.LeaseDurationSeconds * 1000;
+        await _db.StringSetAsync(key, json, TimeSpan.FromMilliseconds(leaseDurationMs)).ConfigureAwait(false);
+        _logger.LogDebug("Set transcode session {PlaySessionId} in Redis.", session.PlaySessionId);
+    }
+
+    /// <inheritdoc />
+    public async Task<TranscodeSession?> TryGetAsync(string playSessionId, CancellationToken cancellationToken = default)
+    {
+        var key = GetKey(playSessionId);
+        var raw = await _db.StringGetAsync(key).ConfigureAwait(false);
+        if (!raw.HasValue)
+        {
+            return null;
+        }
+
+        var session = JsonSerializer.Deserialize<TranscodeSession>(raw.ToString());
+
+        // Check LeaseExpiresUtc in addition to Redis TTL to guard against the window between
+        // Redis TTL evaluation and the GET result being returned to the caller.
+        if (session is null || session.LeaseExpiresUtc <= DateTime.UtcNow)
+        {
+            return null;
+        }
+
+        return session;
+    }
+
+    /// <inheritdoc />
+    public async Task RenewLeaseAsync(string playSessionId, CancellationToken cancellationToken = default)
+    {
+        var key = GetKey(playSessionId);
+        var raw = await _db.StringGetAsync(key).ConfigureAwait(false);
+        if (!raw.HasValue)
+        {
+            return;
+        }
+
+        var session = JsonSerializer.Deserialize<TranscodeSession>(raw.ToString());
+        if (session is null)
+        {
+            return;
+        }
+
+        var leaseDurationMs = (long)_options.LeaseDurationSeconds * 1000;
+        session.LeaseExpiresUtc = DateTime.UtcNow.AddMilliseconds(leaseDurationMs);
+        var json = JsonSerializer.Serialize(session);
+        await _db.StringSetAsync(key, json, TimeSpan.FromMilliseconds(leaseDurationMs)).ConfigureAwait(false);
+        _logger.LogDebug("Renewed lease for transcode session {PlaySessionId}.", playSessionId);
+    }
+
+    /// <inheritdoc />
+    public async Task DeleteAsync(string playSessionId, CancellationToken cancellationToken = default)
+    {
+        var key = GetKey(playSessionId);
+        await _db.KeyDeleteAsync(key).ConfigureAwait(false);
+        _logger.LogDebug("Deleted transcode session {PlaySessionId} from Redis.", playSessionId);
+    }
+
+    /// <inheritdoc />
+    public async Task<bool> TryTakeoverAsync(string playSessionId, string claimingPod, CancellationToken cancellationToken = default)
+    {
+        var key = GetKey(playSessionId);
+        var leaseDurationMs = (long)_options.LeaseDurationSeconds * 1000;
+        var currentTicks = DateTime.UtcNow.Ticks;
+
+        var result = (long?)await _db.ScriptEvaluateAsync(
+            TakeoverScript,
+            keys: new RedisKey[] { key },
+            values: new RedisValue[] { currentTicks, claimingPod, leaseDurationMs }).ConfigureAwait(false);
+
+        var succeeded = result == 1;
+        if (succeeded)
+        {
+            _logger.LogInformation("Pod {ClaimingPod} successfully took over transcode session {PlaySessionId}.", claimingPod, playSessionId);
+        }
+
+        return succeeded;
+    }
+
+    private static string GetKey(string playSessionId) => KeyPrefix + playSessionId;
+}