Pass base pipeline, add sample

sdk/keyvault/Azure.Security.KeyVault.Secrets/samples/README.md

@@ -14,3 +14,4 @@ description: Samples for the Azure.Security.KeyVault.Secrets client library.
 - [Creating, getting, updating, and deleting secrets](https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/keyvault/Azure.Security.KeyVault.Secrets/samples/Sample1_HelloWorld.md)
 - [Back up and restore a secret](https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/keyvault/Azure.Security.KeyVault.Secrets/samples/Sample2_BackupAndRestore.md)
 - [Listing secrets, secret versions, and deleted secrets](https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/keyvault/Azure.Security.KeyVault.Secrets/samples/Sample3_GetSecrets.md)
+- [Get a secret without throwing if it is not defined](https://github.com/heaths/azure-sdk-for-net/blob/main/sdk/keyvault/Azure.Security.KeyVault.Secrets/samples/Sample4_GetSecretIfExists.md)

sdk/keyvault/Azure.Security.KeyVault.Secrets/samples/Sample4_GetSecretIfExists.md

@@ -0,0 +1,55 @@
+# Get a secret without throwing if it is not defined
+
+This sample demonstrates how to get a secret without throwing an exception if it is not defined.
+This may be useful in some application configuration managers that attempt to fetch key/value pairs from a collection of providers and when exceptions may break startup or are otherwise costly.
+To better configure ASP.NET applications or other applications that use common [.NET Configuration], see our documentation on [Azure.Extensions.AspNetCore.Configuration.Secrets].
+To get started, you'll need a URI to an Azure Key Vault. See the [README](https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/keyvault/Azure.Security.KeyVault.Secrets/README.md) for links and instructions.
+
+## Creating a SecretClient
+
+To create a new `SecretClient` to create get a secret, you need the endpoint to an Azure Key Vault and credentials.
+You can use the [DefaultAzureCredential] to try a number of common authentication methods optimized for both running as a service and development.
+
+In the sample below, you can set `keyVaultUrl` based on an environment variable, configuration setting, or any way that works for your application.
+
+```C# Snippet:SecretsSample4SecretClient
+var client = new SecretClient(new Uri(keyVaultUrl), new DefaultAzureCredential());
+```
+
+## Get a secret
+
+To prevent throwing a `RequestFailedException` when a secret does not exist, or to alter other behaviors of a specific API call, you can create a `RequestContext` and pass that to the API call:
+
+```C# Snippet:SecretsSample4GetSecretIfExists
+// Do not treat HTTP 404 responses as errors.
+RequestContext context = new RequestContext();
+context.AddClassifier(404, false);
+
+// Try getting the latest application connection string using the context above.
+NullableResponse<KeyVaultSecret> response = client.GetSecret("appConnectionString", null, context);
+if (response.HasValue)
+{
+    KeyVaultSecret secret = response.Value;
+    Debug.WriteLine($"Secret is returned with name {secret.Name} and value {secret.Value}");
+}
+```
+
+You can also do this asynchronously:
+
+```C# Snippet:SecretsSample4GetSecretIfExistsAsync
+// Do not treat HTTP 404 responses as errors.
+RequestContext context = new RequestContext();
+context.AddClassifier(404, false);
+
+// Try getting the latest application connection string using the context above.
+NullableResponse<KeyVaultSecret> response = await client.GetSecretAsync("appConnectionString", null, context);
+if (response.HasValue)
+{
+    KeyVaultSecret secret = response.Value;
+    Debug.WriteLine($"Secret is returned with name {secret.Name} and value {secret.Value}");
+}
+```
+
+[.NET Configuration]: https://learn.microsoft.com/dotnet/core/extensions/configuration
+[Azure.Extensions.AspNetCore.Configuration.Secrets]: https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/extensions/Azure.Extensions.AspNetCore.Configuration.Secrets/README.md
+[DefaultAzureCredential]: https://github.com/Azure/azure-sdk-for-net/blob/main/sdk/identity/Azure.Identity/README.md

sdk/keyvault/Azure.Security.KeyVault.Secrets/tests/SampleFixture.cs

@@ -22,6 +22,7 @@ public class SampleFixture: SamplesBase<KeyVaultTestEnvironment>
     public partial class HelloWorld : SampleFixture { }
     public partial class BackupAndRestore : SampleFixture { }
     public partial class GetSecrets : SampleFixture { }
+    public partial class GetSecretIfExists : SampleFixture { }
     public partial class Snippets : SampleFixture { }
 #pragma warning restore SA1402 // File may only contain a single type
 }

sdk/keyvault/Azure.Security.KeyVault.Secrets/tests/samples/Sample4_GetSecretIfExists.cs

@@ -0,0 +1,61 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System;
+using System.Diagnostics;
+using System.Threading.Tasks;
+using NUnit.Framework;
+
+namespace Azure.Security.KeyVault.Secrets.Samples
+{
+    public partial class GetSecretIfExists
+    {
+        [Test]
+        public void GetSecretIfExistsSync()
+        {
+            // Environment variable with the Key Vault endpoint.
+            string keyVaultUrl = TestEnvironment.KeyVaultUrl;
+
+            #region Snippet:SecretsSample4SecretClient
+            var client = new SecretClient(new Uri(keyVaultUrl), new DefaultAzureCredential());
+            #endregion
+
+            #region Snippet:SecretsSample4GetSecretIfExists
+            // Do not treat HTTP 404 responses as errors.
+            RequestContext context = new RequestContext();
+            context.AddClassifier(404, false);
+
+            // Try getting the latest application connection string using the context above.
+            NullableResponse<KeyVaultSecret> response = client.GetSecret("appConnectionString", null, context);
+            if (response.HasValue)
+            {
+                KeyVaultSecret secret = response.Value;
+                Debug.WriteLine($"Secret is returned with name {secret.Name} and value {secret.Value}");
+            }
+            #endregion
+        }
+
+        [Test]
+        public async Task GetSecretIfExistsAsync()
+        {
+            // Environment variable with the Key Vault endpoint.
+            string keyVaultUrl = TestEnvironment.KeyVaultUrl;
+
+            var client = new SecretClient(new Uri(keyVaultUrl), new DefaultAzureCredential());
+
+            #region Snippet:SecretsSample4GetSecretIfExistsAsync
+            // Do not treat HTTP 404 responses as errors.
+            RequestContext context = new RequestContext();
+            context.AddClassifier(404, false);
+
+            // Try getting the latest application connection string using the context above.
+            NullableResponse<KeyVaultSecret> response = await client.GetSecretAsync("appConnectionString", null, context);
+            if (response.HasValue)
+            {
+                KeyVaultSecret secret = response.Value;
+                Debug.WriteLine($"Secret is returned with name {secret.Name} and value {secret.Value}");
+            }
+            #endregion
+        }
+    }
+}

sdk/keyvault/Azure.Security.KeyVault.Shared/src/KeyVaultPipeline.cs

@@ -78,7 +78,7 @@ public HttpMessage CreateMessage(RequestMethod method, Uri uri, bool appendApiVe
         public HttpMessage CreateMessage(RequestMethod method, RequestContext context, params string[] path)
         {
             // See comment in CreateMessage overload above for future design consideration.
-            HttpMessage message = _pipeline.CreateMessage(context);
+            HttpMessage message = _pipeline.CreateMessage(context, DefaultResponseClassifier);
             Request request = message.Request;
 
             request.Headers.Add(HttpHeader.Common.JsonContentType);
@@ -294,7 +294,6 @@ public Response GetResponse(RequestMethod method, CancellationToken cancellation
 
         private async ValueTask SendRequestAsync(HttpMessage message, CancellationToken cancellationToken)
         {
-            message.ResponseClassifier ??= ResponseClassifier200201202204;
             await _pipeline.SendAsync(message, cancellationToken).ConfigureAwait(false);
 
             if (message.ResponseClassifier.IsErrorResponse(message))
@@ -305,7 +304,6 @@ private async ValueTask SendRequestAsync(HttpMessage message, CancellationToken
 
         private void SendRequest(HttpMessage message, CancellationToken cancellationToken)
         {
-            message.ResponseClassifier ??= ResponseClassifier200201202204;
             _pipeline.Send(message, cancellationToken);
 
             if (message.ResponseClassifier.IsErrorResponse(message))
@@ -314,8 +312,8 @@ private void SendRequest(HttpMessage message, CancellationToken cancellationToke
             }
         }
 
-        private static ResponseClassifier s_responseClassifier200201202204;
-        private static ResponseClassifier ResponseClassifier200201202204 => s_responseClassifier200201202204 ??= new StatusCodeClassifier(stackalloc ushort[]
+        private static ResponseClassifier s_defaultResponseClassifier;
+        private static ResponseClassifier DefaultResponseClassifier => s_defaultResponseClassifier ??= new StatusCodeClassifier(stackalloc ushort[]
         {
             200,
             201,