Change Feed Processor with Datetime.MinValue and Multi master accounts

Microsoft.Azure.Cosmos/src/ChangeFeedProcessor/Utils/ResultSetIteratorUtils.cs

@@ -23,7 +23,7 @@ public static ChangeFeedPartitionKeyResultSetIteratorCore BuildResultSetIterator
             }
             else if (startFromBeginning)
             {
-                requestOptions.StartTime = DateTime.MinValue;
+                requestOptions.StartTime = ChangeFeedRequestOptions.DateTimeStartFromBeginning;
             }
 
             return new ChangeFeedPartitionKeyResultSetIteratorCore(

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

@@ -15,6 +15,7 @@ namespace Microsoft.Azure.Cosmos
     internal class ChangeFeedRequestOptions : RequestOptions
     {
         internal const string IfNoneMatchAllHeaderValue = "*";
+        internal static readonly DateTime DateTimeStartFromBeginning = DateTime.MinValue.ToUniversalTime();
 
         /// <summary>
         /// Specifies a particular point in time to start to read the change feed.
@@ -37,7 +38,8 @@ internal override void PopulateRequestOptions(RequestMessage request)
                 {
                     request.Headers.IfNoneMatch = ChangeFeedRequestOptions.IfNoneMatchAllHeaderValue;
                 }
-                else if (this.StartTime != null)
+                else if (this.StartTime != null
+                    && this.StartTime != ChangeFeedRequestOptions.DateTimeStartFromBeginning)
                 {
                     request.Headers.Add(HttpConstants.HttpHeaders.IfModifiedSince, this.StartTime.Value.ToUniversalTime().ToString("r", CultureInfo.InvariantCulture));
                 }

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.Tests/StandByFeedContinuationTokenTests.cs

@@ -244,6 +244,18 @@ public void ChangeFeedRequestOptions_DefaultValues()
             Assert.IsNull(request.Headers[Documents.HttpConstants.HttpHeaders.IfModifiedSince]);
         }
 
+        [TestMethod]
+        public void ChangeFeedRequestOptions_StartFromBeginning()
+        {
+            RequestMessage request = new RequestMessage();
+            ChangeFeedRequestOptions requestOptions = new ChangeFeedRequestOptions() { StartTime = DateTime.MinValue.ToUniversalTime() };
+
+            requestOptions.PopulateRequestOptions(request);
+
+            Assert.IsNull(request.Headers.IfNoneMatch);
+            Assert.IsNull(request.Headers[Documents.HttpConstants.HttpHeaders.IfModifiedSince]);
+        }
+
         [TestMethod]
         public void ChangeFeedRequestOptions_MaxItemSizeIsSet()
         {

changelog.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - [#944](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/944) Change Feed Processor won't use user serializer for internal operations
 - [#988](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/988) Fixed query mutating due to retry of gone / name cache is stale.
+- [#954](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/954) Support "Start from Beginning" for Change Feed Processor in multi master accounts
 - [#999](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/999) Fixed grabbing extra page, updated continuation token on exception path, and non ascii character in order by continuation token.
 - [#1013](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/1013) Gateway OperationCanceledException are now returned as request timeouts
 - [#1023](https://github.com/Azure/azure-cosmos-dotnet-v3/pull/1023) Fixed ThroughputResponse.IsReplacePending header mapping