Use MySqlDataSource in AddMySql by default (#2096)

* Send a MySQL ping packet by default. Fixes #2031

Users can opt in to setting a command that will be executed on the server, but the default is now a more efficient ping.

* Add AddMySql overload for MySqlDataSource.

This pushes users towards good defaults: firstly registering a MySqlDataSource as a singleton in DI, then just calling .AddHealthChecks().AddMySql() with no other arguments to retrieve and use that same data source for health checks.

* Add package README for HealthChecks.MySql.

* Use new MySqlHealthCheckOptions API.

There are two constructors: one to initialise with a MySqlDataSource, and one with a connection string. This helps enforce correct uasge of the API by ensuring that exactly one is set.

src/HealthChecks.MySql/DependencyInjection/MySqlHealthCheckBuilderExtensions.cs

@@ -10,14 +10,50 @@ namespace Microsoft.Extensions.DependencyInjection;
 public static class MySqlHealthCheckBuilderExtensions
 {
     private const string NAME = "mysql";
-    internal const string HEALTH_QUERY = "SELECT 1;";
+
+    /// <summary>
+    /// Add a health check for MySQL databases.
+    /// </summary>
+    /// <param name="builder">The <see cref="IHealthChecksBuilder"/>.</param>
+    /// <param name="dataSourceFactory">An optional factory to create the <see cref="MySqlDataSource"/>. By default, one will be retrieved from the service collection.</param>
+    /// <param name="healthQuery">The optional query to be executed. If this is <c>null</c>, a MySQL "ping" packet will be sent to the server instead of a query.</param>
+    /// <param name="configure">An optional action to allow additional MySQL specific configuration.</param>
+    /// <param name="name">The health check name. Optional. If <c>null</c> the type name 'mysql' 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 AddMySql(
+        this IHealthChecksBuilder builder,
+        Func<IServiceProvider, MySqlDataSource>? dataSourceFactory = null,
+        string? healthQuery = null,
+        Action<MySqlConnection>? configure = null,
+        string? name = default,
+        HealthStatus? failureStatus = default,
+        IEnumerable<string>? tags = default,
+        TimeSpan? timeout = default)
+    {
+        return builder.Add(new HealthCheckRegistration(
+            name ?? NAME,
+            sp => new MySqlHealthCheck(new(dataSourceFactory?.Invoke(sp) ?? sp.GetRequiredService<MySqlDataSource>())
+            {
+                CommandText = healthQuery,
+                Configure = configure,
+            }),
+            failureStatus,
+            tags,
+            timeout));
+    }
 
     /// <summary>
     /// Add a health check for MySQL databases.
     /// </summary>
     /// <param name="builder">The <see cref="IHealthChecksBuilder"/>.</param>
     /// <param name="connectionString">The MySQL connection string to be used.</param>
-    /// <param name="healthQuery">The query to be executed.</param>
+    /// <param name="healthQuery">The optional query to be executed. If this is <c>null</c>, a MySQL "ping" packet will be sent to the server instead of a query.</param>
     /// <param name="configure">An optional action to allow additional MySQL specific configuration.</param>
     /// <param name="name">The health check name. Optional. If <c>null</c> the type name 'mysql' will be used for the name.</param>
     /// <param name="failureStatus">
@@ -30,22 +66,28 @@ public static class MySqlHealthCheckBuilderExtensions
     public static IHealthChecksBuilder AddMySql(
         this IHealthChecksBuilder builder,
         string connectionString,
-        string healthQuery = HEALTH_QUERY,
+        string? healthQuery = null,
         Action<MySqlConnection>? configure = null,
         string? name = default,
         HealthStatus? failureStatus = default,
         IEnumerable<string>? tags = default,
         TimeSpan? timeout = default)
     {
-        return builder.AddMySql(_ => connectionString, healthQuery, configure, name, failureStatus, tags, timeout);
+        Guard.ThrowIfNull(connectionString, throwOnEmptyString: true);
+
+        return builder.AddMySql(new(connectionString)
+        {
+            CommandText = healthQuery,
+            Configure = configure
+        }, name, failureStatus, tags, timeout);
     }
 
     /// <summary>
     /// Add a health check for MySQL databases.
     /// </summary>
     /// <param name="builder">The <see cref="IHealthChecksBuilder"/>.</param>
     /// <param name="connectionStringFactory">A factory to build the MySQL connection string to use.</param>
-    /// <param name="healthQuery">The query to be executed.</param>
+    /// <param name="healthQuery">The optional query to be executed. If this is <c>null</c>, a MySQL "ping" packet will be sent to the server instead of a query.</param>
     /// <param name="configure">An optional action to allow additional MySQL specific configuration.</param>
     /// <param name="name">The health check name. Optional. If <c>null</c> the type name 'mysql' will be used for the name.</param>
     /// <param name="failureStatus">
@@ -58,7 +100,7 @@ public static IHealthChecksBuilder AddMySql(
     public static IHealthChecksBuilder AddMySql(
         this IHealthChecksBuilder builder,
         Func<IServiceProvider, string> connectionStringFactory,
-        string healthQuery = HEALTH_QUERY,
+        string? healthQuery = null,
         Action<MySqlConnection>? configure = null,
         string? name = default,
         HealthStatus? failureStatus = default,
@@ -69,16 +111,11 @@ public static IHealthChecksBuilder AddMySql(
 
         return builder.Add(new HealthCheckRegistration(
             name ?? NAME,
-            sp =>
+            sp => new MySqlHealthCheck(new(connectionStringFactory(sp))
             {
-                var options = new MySqlHealthCheckOptions
-                {
-                    ConnectionString = connectionStringFactory(sp),
-                    CommandText = healthQuery,
-                    Configure = configure,
-                };
-                return new MySqlHealthCheck(options);
-            },
+                CommandText = healthQuery,
+                Configure = configure,
+            }),
             failureStatus,
             tags,
             timeout));

src/HealthChecks.MySql/MySqlHealthCheck.cs

@@ -12,8 +12,11 @@ public class MySqlHealthCheck : IHealthCheck
 
     public MySqlHealthCheck(MySqlHealthCheckOptions options)
     {
-        Guard.ThrowIfNull(options.ConnectionString, true);
-        Guard.ThrowIfNull(options.CommandText, true);
+        Guard.ThrowIfNull(options);
+        if (options.DataSource is null && options.ConnectionString is null)
+            throw new InvalidOperationException("One of options.DataSource or options.ConnectionString must be specified.");
+        if (options.DataSource is not null && options.ConnectionString is not null)
+            throw new InvalidOperationException("Only one of options.DataSource or options.ConnectionString must be specified.");
         _options = options;
     }
 
@@ -22,18 +25,30 @@ public async Task<HealthCheckResult> CheckHealthAsync(HealthCheckContext context
     {
         try
         {
-            using var connection = new MySqlConnection(_options.ConnectionString);
+            using var connection = _options.DataSource is not null ?
+                _options.DataSource.CreateConnection() :
+                new MySqlConnection(_options.ConnectionString);
 
             _options.Configure?.Invoke(connection);
             await connection.OpenAsync(cancellationToken).ConfigureAwait(false);
 
-            using var command = connection.CreateCommand();
-            command.CommandText = _options.CommandText;
-            object? result = await command.ExecuteScalarAsync(cancellationToken).ConfigureAwait(false);
+            if (_options.CommandText is { } commandText)
+            {
+                using var command = connection.CreateCommand();
+                command.CommandText = _options.CommandText;
+                object? result = await command.ExecuteScalarAsync(cancellationToken).ConfigureAwait(false);
 
-            return _options.HealthCheckResultBuilder == null
-                ? HealthCheckResult.Healthy()
-                : _options.HealthCheckResultBuilder(result);
+                return _options.HealthCheckResultBuilder == null
+                    ? HealthCheckResult.Healthy()
+                    : _options.HealthCheckResultBuilder(result);
+            }
+            else
+            {
+                var success = await connection.PingAsync(cancellationToken).ConfigureAwait(false);
+                return _options.HealthCheckResultBuilder is null
+                    ? (success ? HealthCheckResult.Healthy() : new HealthCheckResult(context.Registration.FailureStatus)) :
+                    _options.HealthCheckResultBuilder(success);
+            }
         }
         catch (Exception ex)
         {

src/HealthChecks.MySql/MySqlHealthCheckOptions.cs

@@ -1,4 +1,3 @@
-using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Diagnostics.HealthChecks;
 using MySqlConnector;
 
@@ -8,16 +7,55 @@ namespace HealthChecks.MySql;
 /// Options for <see cref="MySqlHealthCheck"/>.
 /// </summary>
 public class MySqlHealthCheckOptions
-{
+{
+    /// <summary>
+    /// Creates an instance of <see cref="MySqlHealthCheckOptions"/>.
+    /// </summary>
+    /// <param name="dataSource">The <see cref="MySqlDataSource" /> to be used.</param>
+    /// <remarks>
+    /// Depending on how the <see cref="MySqlDataSource" /> was configured, the connections it hands out may be pooled.
+    /// That is why it should be the exact same <see cref="MySqlDataSource" /> that is used by other parts of your app.
+    /// </remarks>
+    public MySqlHealthCheckOptions(MySqlDataSource dataSource)
+    {
+        DataSource = Guard.ThrowIfNull(dataSource);
+    }
+
+    /// <summary>
+    /// Creates an instance of <see cref="MySqlHealthCheckOptions"/>.
+    /// </summary>
+    /// <param name="connectionString">The MySQL connection string to be used.</param>
+    /// <remarks>
+    /// <see cref="MySqlDataSource"/> supports additional configuration beyond the connection string, such as logging and naming pools for diagnostics.
+    /// To specify a data source, use <see cref=" MySqlDataSourceBuilder"/> and the <see cref="MySqlHealthCheckOptions(MySqlDataSource)"/> constructor.
+    /// </remarks>
+    public MySqlHealthCheckOptions(string connectionString)
+    {
+        ConnectionString = Guard.ThrowIfNull(connectionString, throwOnEmptyString: true);
+    }
+
+    /// <summary>
+    /// The MySQL data source to be used.
+    /// </summary>
+    /// <remarks>
+    /// Depending on how the <see cref="MySqlDataSource" /> was configured, the connections it hands out may be pooled.
+    /// That is why it should be the exact same <see cref="MySqlDataSource" /> that is used by other parts of your app.
+    /// </remarks>
+    public MySqlDataSource? DataSource { get; }
+
     /// <summary>
-    /// The MySQL connection string to be used.
+    /// The MySQL connection string to be used, if <see cref="DataSource"/> isn't set.
     /// </summary>
-    public string ConnectionString { get; set; } = null!;
+    /// <remarks>
+    /// <see cref="MySqlDataSource"/> supports additional configuration beyond the connection string, such as logging and naming pools for diagnostics.
+    /// To specify a data source, use <see cref=" MySqlDataSourceBuilder"/> and the <see cref="MySqlHealthCheckOptions(MySqlDataSource)"/> constructor.
+    /// </remarks>
+    public string? ConnectionString { get; }
 
     /// <summary>
     /// The query to be executed.
     /// </summary>
-    public string CommandText { get; set; } = MySqlHealthCheckBuilderExtensions.HEALTH_QUERY;
+    public string? CommandText { get; set; }
 
     /// <summary>
     /// An optional action executed before the connection is opened in the health check.

src/HealthChecks.MySql/README.md

@@ -0,0 +1,59 @@
+## MySQL Health Check
+
+This health check verifies the ability to communicate with a MySQL Server.
+It uses the provided [MySqlDataSource](https://mysqlconnector.net/api/mysqlconnector/mysqldatasourcetype/) or a connection string to connect to the server.
+
+### Defaults
+
+By default, the `MySqlDataSource` instance is resolved from service provider.
+(This should be the same as the instance being used by the application; do not create a new `MySqlDataSource` just for the health check.)
+The health check will send a MySQL "ping" packet to the server to verify connectivity.
+
+```csharp
+builder.Services
+    .AddMySqlDataSource(builder.Configuration.GetConnectionString("mysql")) // using the MySqlConnector.DependencyInjection package
+    .AddHealthChecks().AddMySql();
+```
+
+### Connection String
+
+You can also specify a connection string directly:
+
+```csharp
+builder.Services.AddHealthChecks().AddMySql(connectionString: "Server=...;User Id=...;Password=...");
+```
+
+This can be useful if you're not using `MySqlDataSource` in your application.
+
+### Customization
+
+You can additionally add the following parameters:
+
+- `healthQuery`: A query to run against the server. If `null` (the default), the health check will send a MySQL "ping" packet to the server.
+- `configure`: An action to configure the `MySqlConnection` object. This is called after the `MySqlConnection` is created but before the connection is opened.
+- `name`: The health check name. The default is `mysql`.
+- `failureStatus`: The `HealthStatus` that should be reported when the health check fails. Default is `HealthStatus.Unhealthy`.
+- `tags`: A list of tags that can be used to filter sets of health checks.
+- `timeout`: A `System.TimeSpan` representing the timeout of the check.
+
+```csharp
+builder.Services
+    .AddMySqlDataSource(builder.Configuration.GetConnectionString("mysql"))
+    .AddHealthChecks().AddMySql(
+        healthQuery: "SELECT 1;",
+        configure: conn => conn.ConnectTimeout = 3,
+        name: "MySQL"
+    );
+```
+
+### Breaking changes
+
+In previous versions, `MySqlHealthCheck` defaulted to testing connectivity by sending a `SELECT 1;` query to the server.
+It has been changed to send a more efficient "ping" packet instead.
+To restore the previous behavior, specify `healthQuery: "SELECT 1;"` when registering the health check.
+
+While not a breaking change, it's now preferred to use `MySqlDataSource` instead of a connection string.
+This allows the health check to use the same connection pool as the rest of the application.
+This can be achieved by calling the `.AddMySql()` overload that has no required parameters.
+The health check assumes that a `MySqlDataSource` instance has been registered with the service provider and will retrieve it automatically.
+

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

@@ -1,3 +1,5 @@
+using MySqlConnector;
+
 namespace HealthChecks.MySql.Tests.DependencyInjection;
 
 public class mysql_registration_should
@@ -18,6 +20,7 @@ public void add_health_check_when_properly_configured()
         registration.Name.ShouldBe("mysql");
         check.ShouldBeOfType<MySqlHealthCheck>();
     }
+
     [Fact]
     public void add_named_health_check_when_properly_configured()
     {
@@ -34,4 +37,22 @@ public void add_named_health_check_when_properly_configured()
         registration.Name.ShouldBe("my-mysql-group");
         check.ShouldBeOfType<MySqlHealthCheck>();
     }
+
+    [Fact]
+    public void add_health_check_for_data_source()
+    {
+        var services = new ServiceCollection();
+        services
+            .AddMySqlDataSource("Server=example")
+            .AddHealthChecks().AddMySql();
+
+        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("mysql");
+        check.ShouldBeOfType<MySqlHealthCheck>();
+    }
 }

test/HealthChecks.MySql.Tests/Functional/MySqlHealthCheckTests.cs

@@ -1,11 +1,39 @@
 using System.Net;
+using MySqlConnector;
 
 namespace HealthChecks.MySql.Tests.Functional;
 
 public class mysql_healthcheck_should
 {
     [Fact]
-    public async Task be_healthy_when_mysql_server_is_available()
+    public async Task be_healthy_when_mysql_server_is_available_using_data_source()
+    {
+        var connectionString = "server=localhost;port=3306;database=information_schema;uid=root;password=Password12!";
+
+        var webHostBuilder = new WebHostBuilder()
+            .ConfigureServices(services =>
+            {
+                services
+                    .AddMySqlDataSource(connectionString)
+                    .AddHealthChecks().AddMySql(tags: new string[] { "mysql" });
+            })
+            .Configure(app =>
+            {
+                app.UseHealthChecks("/health", new HealthCheckOptions
+                {
+                    Predicate = r => r.Tags.Contains("mysql")
+                });
+            });
+
+        using var server = new TestServer(webHostBuilder);
+
+        using var response = await server.CreateRequest("/health").GetAsync();
+
+        response.StatusCode.ShouldBe(HttpStatusCode.OK);
+    }
+
+    [Fact]
+    public async Task be_healthy_when_mysql_server_is_available_using_connection_string()
     {
         var connectionString = "server=localhost;port=3306;database=information_schema;uid=root;password=Password12!";
 
@@ -64,10 +92,7 @@ public async Task be_unhealthy_when_mysql_server_is_unavailable_using_options()
         var webHostBuilder = new WebHostBuilder()
             .ConfigureServices(services =>
             {
-                var mysqlOptions = new MySqlHealthCheckOptions
-                {
-                    ConnectionString = connectionString
-                };
+                var mysqlOptions = new MySqlHealthCheckOptions(connectionString);
                 services.AddHealthChecks()
                     .AddMySql(mysqlOptions, tags: new string[] { "mysql" });
             })

test/HealthChecks.MySql.Tests/HealthChecks.MySql.Tests.csproj

@@ -1,5 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+  <ItemGroup>
+    <PackageReference Include="MySqlConnector.DependencyInjection" Version="2.3.1" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\..\src\HealthChecks.MySql\HealthChecks.MySql.csproj" />
   </ItemGroup>