diff --git a/MediaBrowser.Providers/Music/MusicBrainzAlbumProvider.cs b/MediaBrowser.Providers/Music/MusicBrainzAlbumProvider.cs index b716f40f0..3797f9039 100644 --- a/MediaBrowser.Providers/Music/MusicBrainzAlbumProvider.cs +++ b/MediaBrowser.Providers/Music/MusicBrainzAlbumProvider.cs @@ -32,12 +32,21 @@ namespace MediaBrowser.Providers.Music public readonly string MusicBrainzBaseUrl; - // The Jellyfin user-agent is unrestricted but source IP must not exceed - // one request per second, therefore we rate limit to avoid throttling. - // Be prudent, use a value slightly above the minimun required. - // https://musicbrainz.org/doc/XML_Web_Service/Rate_Limiting + /// + /// The Jellyfin user-agent is unrestricted but source IP must not exceed + /// one request per second, therefore we rate limit to avoid throttling. + /// Be prudent, use a value slightly above the minimun required. + /// https://musicbrainz.org/doc/XML_Web_Service/Rate_Limiting + /// private const long MusicBrainzQueryIntervalMs = 1050u; + /// + /// For each single MB lookup/search, this is the maximum number of + /// attempts that shall be made whilst receiving a 503 Server + /// Unavailable (indicating throttled) response. + /// + private const uint MusicBrainzQueryAttempts = 5u; + public MusicBrainzAlbumProvider( IHttpClient httpClient, IApplicationHost appHost, @@ -717,19 +726,12 @@ namespace MediaBrowser.Providers.Music /// /// Makes request to MusicBrainz server and awaits a response. + /// A 503 Service Unavailable response indicates throttling to maintain a rate limit. + /// A number of retries shall be made in order to try and satisfy the request before + /// giving up and returning null. /// internal async Task GetMusicBrainzResponse(string url, CancellationToken cancellationToken) { - if (_stopWatchMusicBrainz.ElapsedMilliseconds < MusicBrainzQueryIntervalMs) - { - // MusicBrainz is extremely adamant about limiting to one request per second - var delayMs = MusicBrainzQueryIntervalMs - _stopWatchMusicBrainz.ElapsedMilliseconds; - await Task.Delay((int)delayMs, cancellationToken).ConfigureAwait(false); - } - - _logger.LogDebug("MusicBrainz time since previous request: {0}ms", _stopWatchMusicBrainz.ElapsedMilliseconds); - _stopWatchMusicBrainz.Restart(); - var options = new HttpRequestOptions { Url = MusicBrainzBaseUrl.TrimEnd('/') + url, @@ -740,7 +742,38 @@ namespace MediaBrowser.Providers.Music BufferContent = false }; - return await _httpClient.SendAsync(options, "GET").ConfigureAwait(false); + HttpResponseInfo response; + var attempts = 0u; + + do + { + attempts++; + + if (_stopWatchMusicBrainz.ElapsedMilliseconds < MusicBrainzQueryIntervalMs) + { + // MusicBrainz is extremely adamant about limiting to one request per second + var delayMs = MusicBrainzQueryIntervalMs - _stopWatchMusicBrainz.ElapsedMilliseconds; + await Task.Delay((int)delayMs, cancellationToken).ConfigureAwait(false); + } + + // Write time since last request to debug log as evidence we're meeting rate limit + // requirement, before resetting stopwatch back to zero. + _logger.LogDebug("GetMusicBrainzResponse: Time since previous request: {0} ms", _stopWatchMusicBrainz.ElapsedMilliseconds); + _stopWatchMusicBrainz.Restart(); + + response = await _httpClient.SendAsync(options, "GET").ConfigureAwait(false); + + // We retry a finite number of times, and only whilst MB is indcating 503 (throttling) + } + while (attempts < MusicBrainzQueryAttempts && response.StatusCode == HttpStatusCode.ServiceUnavailable); + + // Log error if unable to query MB database due to throttling + if (attempts == MusicBrainzQueryAttempts && response.StatusCode == HttpStatusCode.ServiceUnavailable ) + { + _logger.LogError("GetMusicBrainzResponse: 503 Service Unavailable (throttled) response received {0} times whilst requesting {1}", attempts, options.Url); + } + + return response; } public int Order => 0;