Add support for options validation (#266)

src/Microsoft.Extensions.Options/IValidateOptions.cs

@@ -0,0 +1,20 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.Extensions.Options
+{
+    /// <summary>
+    /// Interface used to validate options.
+    /// </summary>
+    /// <typeparam name="TOptions">The options type to validate.</typeparam>
+    public interface IValidateOptions<TOptions> where TOptions : class
+    {
+        /// <summary>
+        /// Validates a specific named options instance (or all when name is null).
+        /// </summary>
+        /// <param name="name">The name of the options instance being validated.</param>
+        /// <param name="options">The options instance.</param>
+        /// <returns>The <see cref="ValidateOptionsResult"/> result.</returns>
+        ValidateOptionsResult Validate(string name, TOptions options);
+    }
+}

src/Microsoft.Extensions.Options/OptionsBuilder.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.Extensions.Options
@@ -255,5 +256,25 @@ public virtual OptionsBuilder<TOptions> PostConfigure<TDep>(Action<TOptions, TDe
                     configureOptions));
             return this;
         }
+
+        public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation)
+            => Validate(name: Options.DefaultName, validation: validation, failureMessage: "A validation error has occured.");
+
+        public virtual OptionsBuilder<TOptions> Validate(string name, Func<TOptions, bool> validation)
+            => Validate(name: name, validation: validation, failureMessage: "A validation error has occured.");
+
+        public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation, string failureMessage)
+            => Validate(name: Options.DefaultName, validation: validation, failureMessage: failureMessage);
+
+        public virtual OptionsBuilder<TOptions> Validate(string name, Func<TOptions, bool> validation, string failureMessage)
+        {
+            if (validation == null)
+            {
+                throw new ArgumentNullException(nameof(validation));
+            }
+
+            Services.AddSingleton<IValidateOptions<TOptions>>(new ValidateOptions<TOptions>(name, validation, failureMessage));
+            return this;
+        }
     }
 }

src/Microsoft.Extensions.Options/OptionsFactory.cs

@@ -13,16 +13,27 @@ public class OptionsFactory<TOptions> : IOptionsFactory<TOptions> where TOptions
     {
         private readonly IEnumerable<IConfigureOptions<TOptions>> _setups;
         private readonly IEnumerable<IPostConfigureOptions<TOptions>> _postConfigures;
+        private readonly IEnumerable<IValidateOptions<TOptions>> _validations;
 
         /// <summary>
         /// Initializes a new instance with the specified options configurations.
         /// </summary>
         /// <param name="setups">The configuration actions to run.</param>
         /// <param name="postConfigures">The initialization actions to run.</param>
-        public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures)
+        public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures) : this(setups, postConfigures, validations: null)
+        { }
+
+        /// <summary>
+        /// Initializes a new instance with the specified options configurations.
+        /// </summary>
+        /// <param name="setups">The configuration actions to run.</param>
+        /// <param name="postConfigures">The initialization actions to run.</param>
+        /// <param name="validations">The validations to run.</param>
+        public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures, IEnumerable<IValidateOptions<TOptions>> validations)
         {
             _setups = setups;
             _postConfigures = postConfigures;
+            _validations = validations;
         }
 
         public TOptions Create(string name)
@@ -43,6 +54,24 @@ public TOptions Create(string name)
             {
                 post.PostConfigure(name, options);
             }
+
+            if (_validations != null)
+            {
+                var failures = new List<string>();
+                foreach (var validate in _validations)
+                {
+                    var result = validate.Validate(name, options);
+                    if (result.Failed)
+                    {
+                        failures.Add(result.FailureMessage);
+                    }
+                }
+                if (failures.Count > 0)
+                {
+                    throw new OptionsValidationException(failures);
+                }
+            }
+
             return options;
         }
     }

src/Microsoft.Extensions.Options/OptionsValidationException.cs

@@ -0,0 +1,26 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+
+namespace Microsoft.Extensions.Options
+{
+    /// <summary>
+    /// Thrown when options validation fails.
+    /// </summary>
+    public class OptionsValidationException : Exception
+    {
+        /// <summary>
+        /// Constructor.
+        /// </summary>
+        /// <param name="failureMessages">The validation failure messages.</param>
+        public OptionsValidationException(IEnumerable<string> failureMessages)
+            => Failures = failureMessages ?? new List<string>();
+
+        /// <summary>
+        /// The validation failures.
+        /// </summary>
+        public IEnumerable<string> Failures { get; }
+    }
+}

src/Microsoft.Extensions.Options/ValidateOptions.cs

@@ -0,0 +1,52 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.Extensions.Options
+{
+    /// <summary>
+    /// Implementation of <see cref="IValidateOptions{TOptions}"/>
+    /// </summary>
+    /// <typeparam name="TOptions">The instance being validated.</typeparam>
+    public class ValidateOptions<TOptions> : IValidateOptions<TOptions> where TOptions : class
+    {
+        public ValidateOptions(string name, Func<TOptions, bool> validation, string failureMessage)
+        {
+            Name = name;
+            Validation = validation;
+            FailureMessage = failureMessage;
+        }
+
+        /// <summary>
+        /// The options name.
+        /// </summary>
+        public string Name { get; }
+
+        /// <summary>
+        /// The validation action.
+        /// </summary>
+        public Func<TOptions, bool> Validation { get; }
+
+        /// <summary>
+        /// The error to return when validation fails.
+        /// </summary>
+        public string FailureMessage { get; }
+
+        public ValidateOptionsResult Validate(string name, TOptions options)
+        {
+            // Null name is used to configure all named options.
+            if (Name == null || name == Name)
+            {
+                if ((Validation?.Invoke(options)).Value)
+                {
+                    return ValidateOptionsResult.Success;
+                }
+                return ValidateOptionsResult.Fail(FailureMessage);
+            }
+
+            // Ignored if not validating this instance.
+            return ValidateOptionsResult.Skip;
+        }
+    }
+}

src/Microsoft.Extensions.Options/ValidateOptionsResult.cs

@@ -0,0 +1,49 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.Extensions.Options
+{
+    /// <summary>
+    /// Represents the result of an options validation.
+    /// </summary>
+    public class ValidateOptionsResult
+    {
+        /// <summary>
+        /// Result when validation was skipped due to name not matching.
+        /// </summary>
+        public static readonly ValidateOptionsResult Skip = new ValidateOptionsResult() { Skipped = true };
+
+        /// <summary>
+        /// Validation was successful.
+        /// </summary>
+        public static readonly ValidateOptionsResult Success = new ValidateOptionsResult() { Skipped = true };
+
+        /// <summary>
+        /// True if validation was successful.
+        /// </summary>
+        public bool Succeeded { get; protected set; }
+
+        /// <summary>
+        /// True if validation was not run.
+        /// </summary>
+        public bool Skipped { get; protected set; }
+
+        /// <summary>
+        /// True if validation failed.
+        /// </summary>
+        public bool Failed { get; protected set; }
+
+        /// <summary>
+        /// Used to describe why validation failed.
+        /// </summary>
+        public string FailureMessage { get; protected set; }
+
+        /// <summary>
+        /// Returns a failure result.
+        /// </summary>
+        /// <param name="failureMessage">The reason for the failure.</param>
+        /// <returns>The failure result.</returns>
+        public static ValidateOptionsResult Fail(string failureMessage)
+            => new ValidateOptionsResult { Failed = true, FailureMessage = failureMessage };
+    }
+}