Introduce async factories to Redis health check.

src/HealthChecks.Redis/DependencyInjection/RedisHealthCheckBuilderExtensions.cs

@@ -66,6 +66,37 @@ public static IHealthChecksBuilder AddRedis(
            timeout));
     }
 
+    /// <summary>
+    /// Add a health check for Redis services.
+    /// </summary>
+    /// <param name="builder">The <see cref="IHealthChecksBuilder"/>.</param>
+    /// <param name="connectionStringFactory">A factory to build the Redis connection string to use.</param>
+    /// <param name="name">The health check name. Optional. If <c>null</c> the type name 'redis' will be used for the name.</param>
+    /// <param name="failureStatus">
+    /// The <see cref="HealthStatus"/> that should be reported when the health check fails. Optional. If <c>null</c> then
+    /// the default status of <see cref="HealthStatus.Unhealthy"/> will be reported.
+    /// </param>
+    /// <param name="tags">A list of tags that can be used to filter sets of health checks. Optional.</param>
+    /// <param name="timeout">An optional <see cref="TimeSpan"/> representing the timeout of the check.</param>
+    /// <returns>The specified <paramref name="builder"/>.</returns>
+    public static IHealthChecksBuilder AddRedis(
+        this IHealthChecksBuilder builder,
+        Func<IServiceProvider, CancellationToken, Task<string?>> connectionStringFactory,
+        string? name = default,
+        HealthStatus? failureStatus = default,
+        IEnumerable<string>? tags = default,
+        TimeSpan? timeout = default)
+    {
+        Guard.ThrowIfNull(connectionStringFactory);
+
+        return builder.Add(new HealthCheckRegistration(
+           name ?? NAME,
+           sp => new RedisHealthCheck((ct) => connectionStringFactory(sp, ct)),
+           failureStatus,
+           tags,
+           timeout));
+    }
+
     /// <summary>
     /// Add a health check for Redis services.
     /// </summary>
@@ -120,4 +151,35 @@ public static IHealthChecksBuilder AddRedis(
            tags,
            timeout));
     }
+
+    /// <summary>
+    /// Add a health check for Redis services.
+    /// </summary>
+    /// <param name="builder">The <see cref="IHealthChecksBuilder"/>.</param>
+    /// <param name="connectionMultiplexerFactory">A factory to build the Redis connection to use.</param>
+    /// <param name="name">The health check name. Optional. If <c>null</c> the type name 'redis' will be used for the name.</param>
+    /// <param name="failureStatus">
+    /// The <see cref="HealthStatus"/> that should be reported when the health check fails. Optional. If <c>null</c> then
+    /// the default status of <see cref="HealthStatus.Unhealthy"/> will be reported.
+    /// </param>
+    /// <param name="tags">A list of tags that can be used to filter sets of health checks. Optional.</param>
+    /// <param name="timeout">An optional <see cref="TimeSpan"/> representing the timeout of the check.</param>
+    /// <returns>The specified <paramref name="builder"/>.</returns>
+    public static IHealthChecksBuilder AddRedis(
+        this IHealthChecksBuilder builder,
+        Func<IServiceProvider, CancellationToken, Task<IConnectionMultiplexer>> connectionMultiplexerFactory,
+        string? name = default,
+        HealthStatus? failureStatus = default,
+        IEnumerable<string>? tags = default,
+        TimeSpan? timeout = default)
+    {
+        Guard.ThrowIfNull(connectionMultiplexerFactory);
+
+        return builder.Add(new HealthCheckRegistration(
+           name ?? NAME,
+           sp => new RedisHealthCheck((ct) => connectionMultiplexerFactory(sp, ct)),
+           failureStatus,
+           tags,
+           timeout));
+    }
 }

src/HealthChecks.Redis/RedisHealthCheck.cs

@@ -9,14 +9,19 @@ namespace HealthChecks.Redis;
 /// </summary>
 public class RedisHealthCheck : IHealthCheck
 {
-    private static readonly ConcurrentDictionary<string, IConnectionMultiplexer> _connections = new();
-    private readonly string? _redisConnectionString;
+    private static readonly ConcurrentDictionary<Func<CancellationToken, Task<string?>>, IConnectionMultiplexer> _connections = new();
+    private readonly Func<CancellationToken, Task<string?>>? _redisConnectionStringFactory;
     private readonly IConnectionMultiplexer? _connectionMultiplexer;
-    private readonly Func<IConnectionMultiplexer>? _connectionMultiplexerFactory;
+    private readonly Func<CancellationToken, Task<IConnectionMultiplexer>>? _connectionMultiplexerFactory;
 
     public RedisHealthCheck(string redisConnectionString)
     {
-        _redisConnectionString = Guard.ThrowIfNull(redisConnectionString);
+        _redisConnectionStringFactory = (_) => Task.FromResult<string?>(Guard.ThrowIfNull(redisConnectionString));
+    }
+
+    public RedisHealthCheck(Func<CancellationToken, Task<string?>> redisConnectionStringFactory)
+    {
+        _redisConnectionStringFactory = Guard.ThrowIfNull(redisConnectionStringFactory);
     }
 
     public RedisHealthCheck(IConnectionMultiplexer connectionMultiplexer)
@@ -35,6 +40,11 @@ public RedisHealthCheck(IConnectionMultiplexer connectionMultiplexer)
     /// <seealso cref="IConnectionMultiplexer"/> for the first time, so exceptions can be handled gracefully.
     /// </remarks>
     internal RedisHealthCheck(Func<IConnectionMultiplexer> connectionMultiplexerFactory)
+    {
+        _connectionMultiplexerFactory = (ct) => Task.FromResult(connectionMultiplexerFactory());
+    }
+
+    internal RedisHealthCheck(Func<CancellationToken, Task<IConnectionMultiplexer>> connectionMultiplexerFactory)
     {
         _connectionMultiplexerFactory = connectionMultiplexerFactory;
     }
@@ -44,25 +54,31 @@ public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context
     {
         try
         {
-            IConnectionMultiplexer? connection = _connectionMultiplexer ?? _connectionMultiplexerFactory?.Invoke();
+            var connection = (_connectionMultiplexer, _connectionMultiplexerFactory) switch
+            {
+                (not null, _) => _connectionMultiplexer,
+                (null, { } factory) => await factory(cancellationToken).ConfigureAwait(false),
+                _ => null
+            };
 
-            if (_redisConnectionString is not null && !_connections.TryGetValue(_redisConnectionString, out connection))
+            if (_redisConnectionStringFactory is not null && !_connections.TryGetValue(_redisConnectionStringFactory, out connection))
             {
                 try
                 {
-                    var connectionMultiplexerTask = ConnectionMultiplexer.ConnectAsync(_redisConnectionString!);
+                    var redisConnectionString = await _redisConnectionStringFactory(cancellationToken).ConfigureAwait(false);
+                    var connectionMultiplexerTask = ConnectionMultiplexer.ConnectAsync(redisConnectionString!);
                     connection = await TimeoutAsync(connectionMultiplexerTask, cancellationToken).ConfigureAwait(false);
                 }
                 catch (OperationCanceledException)
                 {
                     return new HealthCheckResult(context.Registration.FailureStatus, description: "Healthcheck timed out");
                 }
 
-                if (!_connections.TryAdd(_redisConnectionString, connection))
+                if (!_connections.TryAdd(_redisConnectionStringFactory, connection))
                 {
                     // Dispose new connection which we just created, because we don't need it.
                     connection.Dispose();
-                    connection = _connections[_redisConnectionString];
+                    connection = _connections[_redisConnectionStringFactory];
                 }
             }
 
@@ -99,9 +115,9 @@ public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context
         }
         catch (Exception ex)
         {
-            if (_redisConnectionString is not null)
+            if (_redisConnectionStringFactory is not null)
             {
-                _connections.TryRemove(_redisConnectionString, out var connection);
+                _connections.TryRemove(_redisConnectionStringFactory, out var connection);
 #pragma warning disable IDISP007 // Don't dispose injected [false positive here]
                 connection?.Dispose();
 #pragma warning restore IDISP007 // Don't dispose injected

test/HealthChecks.Redis.Tests/DependencyInjection/RegistrationTests.cs

@@ -62,6 +62,29 @@ public void add_health_check_with_connection_string_factory_when_properly_config
         factoryCalled.ShouldBeTrue();
     }
 
+    [Fact]
+    public void add_health_check_with_async_connection_string_factory_when_properly_configured()
+    {
+        var services = new ServiceCollection();
+        var factoryCalled = false;
+        services.AddHealthChecks()
+            .AddRedis((sp, ct) =>
+            {
+                factoryCalled = true;
+                return Task.FromResult<string?>("connectionstring");
+            });
+
+        using var serviceProvider = services.BuildServiceProvider();
+        var options = serviceProvider.GetRequiredService<IOptions<HealthCheckServiceOptions>>();
+
+        var registration = options.Value.Registrations.First();
+        var check = registration.Factory(serviceProvider);
+
+        registration.Name.ShouldBe("redis");
+        check.ShouldBeOfType<RedisHealthCheck>();
+        factoryCalled.ShouldBeFalse();
+    }
+
     [Fact]
     public void add_named_health_check_with_connection_multiplexer_when_properly_configured()
     {
@@ -109,4 +132,33 @@ public void add_health_check_with_connection_multiplexer_when_properly_configure
         // the factory is called when it's used for the first time, as it can throw
         factoryCalled.ShouldBeFalse();
     }
+
+    [Fact]
+    public void add_health_check_with_async_connection_multiplexer_when_properly_configured()
+    {
+        var connectionMultiplexer = Substitute.For<IConnectionMultiplexer>();
+        var services = new ServiceCollection();
+
+        services.AddSingleton(connectionMultiplexer);
+        var factoryCalled = false;
+
+        services.AddHealthChecks()
+            .AddRedis((sp, _) =>
+            {
+                factoryCalled = true;
+                var multiplexer = sp.GetRequiredService<IConnectionMultiplexer>();
+                return Task.FromResult(multiplexer);
+            });
+
+        using var serviceProvider = services.BuildServiceProvider();
+        var options = serviceProvider.GetRequiredService<IOptions<HealthCheckServiceOptions>>();
+
+        var registration = options.Value.Registrations.First();
+        var check = registration.Factory(serviceProvider);
+
+        registration.Name.ShouldBe("redis");
+        check.ShouldBeOfType<RedisHealthCheck>();
+        // the factory is called when it's used for the first time, as it can throw
+        factoryCalled.ShouldBeFalse();
+    }
 }

test/HealthChecks.Redis.Tests/HealthChecks.Redis.approved.txt

@@ -3,6 +3,7 @@ namespace HealthChecks.Redis
     public class RedisHealthCheck : Microsoft.Extensions.Diagnostics.HealthChecks.IHealthCheck
     {
         public RedisHealthCheck(StackExchange.Redis.IConnectionMultiplexer connectionMultiplexer) { }
+        public RedisHealthCheck(System.Func<System.Threading.CancellationToken, System.Threading.Tasks.Task<string?>> redisConnectionStringFactory) { }
         public RedisHealthCheck(string redisConnectionString) { }
         public System.Threading.Tasks.Task<Microsoft.Extensions.Diagnostics.HealthChecks.HealthCheckResult> CheckHealthAsync(Microsoft.Extensions.Diagnostics.HealthChecks.HealthCheckContext context, System.Threading.CancellationToken cancellationToken = default) { }
     }
@@ -14,6 +15,8 @@ namespace Microsoft.Extensions.DependencyInjection
         public static Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder AddRedis(this Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder builder, StackExchange.Redis.IConnectionMultiplexer connectionMultiplexer, string? name = null, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
         public static Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder AddRedis(this Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder builder, System.Func<System.IServiceProvider, StackExchange.Redis.IConnectionMultiplexer> connectionMultiplexerFactory, string? name = null, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
         public static Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder AddRedis(this Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder builder, System.Func<System.IServiceProvider, string> connectionStringFactory, string? name = null, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
+        public static Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder AddRedis(this Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder builder, System.Func<System.IServiceProvider, System.Threading.CancellationToken, System.Threading.Tasks.Task<StackExchange.Redis.IConnectionMultiplexer>> connectionMultiplexerFactory, string? name = null, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
+        public static Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder AddRedis(this Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder builder, System.Func<System.IServiceProvider, System.Threading.CancellationToken, System.Threading.Tasks.Task<string?>> connectionStringFactory, string? name = null, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
         public static Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder AddRedis(this Microsoft.Extensions.DependencyInjection.IHealthChecksBuilder builder, string redisConnectionString, string? name = null, Microsoft.Extensions.Diagnostics.HealthChecks.HealthStatus? failureStatus = default, System.Collections.Generic.IEnumerable<string>? tags = null, System.TimeSpan? timeout = default) { }
     }
 }