Request Options : Adds fix to support injecting/appending custom headers into request via RequestOptions.

Microsoft.Azure.Cosmos/src/RequestOptions/RequestOptions.cs

@@ -36,6 +36,16 @@ public class RequestOptions
         /// </summary>
         public IReadOnlyDictionary<string, object> Properties { get; set; }
 
+#if PREVIEW
+        /// <summary>
+        /// Gets or sets a delegate which injects/appends a custom header in the request.
+        /// </summary>
+        public 
+#else
+        internal        
+#endif
+        Action<Headers> AddRequestHeaders { get; set; }
+
         /// <summary>
         /// Gets or sets the boolean to use effective partition key routing in the cosmos db request.
         /// </summary>
@@ -79,6 +89,22 @@ internal virtual void PopulateRequestOptions(RequestMessage request)
             {
                 request.Headers.Add(HttpConstants.HttpHeaders.IfNoneMatch, this.IfNoneMatchEtag);
             }
+
+            this.AddRequestHeaders?.Invoke(request.Headers);
+        }
+
+#if PREVIEW
+        /// <summary>
+        /// Clone RequestOptions.
+        /// </summary>
+        /// <returns> cloned RequestOptions. </returns>
+        public
+#else
+        internal
+#endif
+        RequestOptions ShallowCopy()
+        {
+            return this.MemberwiseClone() as RequestOptions;
         }
 
         /// <summary>

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/CosmosHeaderTests.cs

@@ -46,6 +46,41 @@ public async Task VerifyKnownHeaders()
             }
         }
 
+        [TestMethod]
+        public async Task VerifyRequestOptionCustomRequestHeaders()
+        {
+            CustomHeaderValidationHandler headerValidationHandler = new CustomHeaderValidationHandler();
+            using CosmosClient client = TestCommon.CreateCosmosClient(x => x.AddCustomHandlers(headerValidationHandler));
+            Database database = null;
+            try
+            {
+                database = await client.CreateDatabaseAsync(nameof(VerifyRequestOptionCustomRequestHeaders) + Guid.NewGuid().ToString());
+                Container container = await database.CreateContainerAsync(
+                Guid.NewGuid().ToString(),
+                "/pk");
+
+                ToDoActivity toDoActivity = ToDoActivity.CreateRandomToDoActivity();
+                ItemRequestOptions requestOptions = new ItemRequestOptions
+                {
+                    AddRequestHeaders = (headers) => headers["x-ms-cosmos-database-rid"] = "databaseRidValue",
+                };
+
+                await container.CreateItemAsync(toDoActivity, new PartitionKey(toDoActivity.pk), requestOptions: requestOptions);
+
+                // null pass
+                requestOptions.AddRequestHeaders = null;
+
+                await container.ReadItemAsync<ToDoActivity>(toDoActivity.id, new PartitionKey(toDoActivity.pk), requestOptions: requestOptions);
+            }
+            finally
+            {
+                if (database != null)
+                {
+                    await database.DeleteStreamAsync();
+                }
+            }
+        }
+
         private class HeaderValidationHandler : RequestHandler
         {
             public override async Task<ResponseMessage> SendAsync(RequestMessage request, CancellationToken cancellationToken)
@@ -76,5 +111,28 @@ private void ValidateLazyHeadersAreNotCreated(CosmosMessageHeadersInternal inter
                 }
             }
         }
+
+        private class CustomHeaderValidationHandler : RequestHandler
+        {
+            public override async Task<ResponseMessage> SendAsync(RequestMessage request, CancellationToken cancellationToken)
+            {
+                if (request.ResourceType == Documents.ResourceType.Document)
+                {
+                    this.ValidateCustomHeaders(request.Headers.CosmosMessageHeaders);
+                }
+
+                return await base.SendAsync(request, cancellationToken);
+            }
+
+            private void ValidateCustomHeaders(CosmosMessageHeadersInternal internalHeaders)
+            {
+                string customHeaderValue = internalHeaders.Get("x-ms-cosmos-database-rid");
+
+                if (!string.IsNullOrEmpty(customHeaderValue))
+                {
+                    Assert.AreEqual("databaseRidValue", customHeaderValue);
+                }                
+            }
+        }
     }
 }

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/Contracts/DotNetPreviewSDKAPI.json

@@ -1797,7 +1797,32 @@
           "NestedTypes": {}
         }
       },
-      "Members": {},
+      "Members": {
+        "Microsoft.Azure.Cosmos.RequestOptions ShallowCopy()": {
+          "Type": "Method",
+          "Attributes": [],
+          "MethodInfo": "Microsoft.Azure.Cosmos.RequestOptions ShallowCopy();IsAbstract:False;IsStatic:False;IsVirtual:False;IsGenericMethod:False;IsConstructor:False;IsFinal:False;"
+        },
+        "System.Action`1[Microsoft.Azure.Cosmos.Headers] AddRequestHeaders": {
+          "Type": "Property",
+          "Attributes": [],
+          "MethodInfo": "System.Action`1[Microsoft.Azure.Cosmos.Headers] AddRequestHeaders;CanRead:True;CanWrite:True;System.Action`1[Microsoft.Azure.Cosmos.Headers] get_AddRequestHeaders();IsAbstract:False;IsStatic:False;IsVirtual:False;IsGenericMethod:False;IsConstructor:False;IsFinal:False;Void set_AddRequestHeaders(System.Action`1[Microsoft.Azure.Cosmos.Headers]);IsAbstract:False;IsStatic:False;IsVirtual:False;IsGenericMethod:False;IsConstructor:False;IsFinal:False;"
+        },
+        "System.Action`1[Microsoft.Azure.Cosmos.Headers] get_AddRequestHeaders()[System.Runtime.CompilerServices.CompilerGeneratedAttribute()]": {
+          "Type": "Method",
+          "Attributes": [
+            "CompilerGeneratedAttribute"
+          ],
+          "MethodInfo": "System.Action`1[Microsoft.Azure.Cosmos.Headers] get_AddRequestHeaders();IsAbstract:False;IsStatic:False;IsVirtual:False;IsGenericMethod:False;IsConstructor:False;IsFinal:False;"
+        },
+        "Void set_AddRequestHeaders(System.Action`1[Microsoft.Azure.Cosmos.Headers])[System.Runtime.CompilerServices.CompilerGeneratedAttribute()]": {
+          "Type": "Method",
+          "Attributes": [
+            "CompilerGeneratedAttribute"
+          ],
+          "MethodInfo": "Void set_AddRequestHeaders(System.Action`1[Microsoft.Azure.Cosmos.Headers]);IsAbstract:False;IsStatic:False;IsVirtual:False;IsGenericMethod:False;IsConstructor:False;IsFinal:False;"
+        }
+      },
       "NestedTypes": {}
     },
     "Microsoft.Azure.Cosmos.TransactionalBatch;System.Object;IsAbstract:True;IsSealed:False;IsInterface:False;IsEnum:False;IsClass:True;IsValueType:False;IsNested:False;IsGenericType:False;IsSerializable:False": {