CSHARP-2357: Add ReadConcern Available.

Author: rstam

src/MongoDB.Driver.Core/ReadConcern.cs

@@ -25,11 +25,18 @@ namespace MongoDB.Driver
     /// </summary>
     public sealed class ReadConcern : IEquatable<ReadConcern>, IConvertibleToBsonDocument
     {
+        private static readonly ReadConcern __available = new ReadConcern(ReadConcernLevel.Available);
         private static readonly ReadConcern __default = new ReadConcern();
         private static readonly ReadConcern __linearizable = new ReadConcern(ReadConcernLevel.Linearizable);
         private static readonly ReadConcern __local = new ReadConcern(ReadConcernLevel.Local);
         private static readonly ReadConcern __majority = new ReadConcern(ReadConcernLevel.Majority);
         private static readonly ReadConcern __snapshot = new ReadConcern(ReadConcernLevel.Snapshot);
+
+        /// <summary>
+        /// Gets an available read concern.
+        /// </summary>
+        public static ReadConcern Available => __available;
+
         /// <summary>
         /// Gets a default read concern.
         /// </summary>
@@ -70,6 +77,8 @@ public static ReadConcern FromBsonDocument(BsonDocument document)
                 var level = (ReadConcernLevel)Enum.Parse(typeof(ReadConcernLevel), (string)levelValue, true);
                 switch (level)
                 {
+                    case ReadConcernLevel.Available:
+                        return ReadConcern.Available;
                     case ReadConcernLevel.Linearizable:
                         return ReadConcern.Linearizable;
                     case ReadConcernLevel.Local:
@@ -155,6 +164,9 @@ public BsonDocument ToBsonDocument()
             {
                 switch (_level.Value)
                 {
+                    case ReadConcernLevel.Available:
+                        level = "available";
+                        break;
                     case ReadConcernLevel.Linearizable:
                         level = "linearizable";
                         break;

src/MongoDB.Driver.Core/ReadConcernLevel.cs

@@ -26,6 +26,11 @@ namespace MongoDB.Driver
     /// </summary>
     public enum ReadConcernLevel
     {
+        /// <summary>
+        /// Reads available data.
+        /// </summary>
+        Available,
+
         /// <summary>
         /// Reads data committed locally.
         /// </summary>

tests/MongoDB.Driver.Core.Tests/Core/Configuration/ConnectionStringTests.cs

@@ -666,8 +666,11 @@ public void When_password_is_specified(string connectionString, string password)
         }
 
         [Theory]
+        [InlineData("mongodb://localhost?readConcernLevel=available", ReadConcernLevel.Available)]
+        [InlineData("mongodb://localhost?readConcernLevel=linearizable", ReadConcernLevel.Linearizable)]
         [InlineData("mongodb://localhost?readConcernLevel=local", ReadConcernLevel.Local)]
         [InlineData("mongodb://localhost?readConcernLevel=majority", ReadConcernLevel.Majority)]
+        [InlineData("mongodb://localhost?readConcernLevel=snapshot", ReadConcernLevel.Snapshot)]
         public void When_readConcernLevel_is_specified(string connectionString, ReadConcernLevel readConcernLevel)
         {
             var subject = new ConnectionString(connectionString);

tests/MongoDB.Driver.Core.Tests/ReadConcernTests.cs

@@ -28,6 +28,14 @@ namespace MongoDB.Driver
 {
     public class ReadConcernTests
     {
+        [Fact]
+        public void Available_should_return_expected_result()
+        {
+            var result = ReadConcern.Available;
+
+            result.Level.Should().Be(ReadConcernLevel.Available);
+        }
+
         [Fact]
         public void Default_should_return_expected_result()
         {
@@ -103,6 +111,7 @@ public void Equals_should_return_true_when_level_is_equal()
         }
 
         [Theory]
+        [InlineData(ReadConcernLevel.Available, "{ level: 'available' }")]
         [InlineData(ReadConcernLevel.Linearizable, "{ level: 'linearizable' }")]
         [InlineData(ReadConcernLevel.Local, "{ level: 'local' }")]
         [InlineData(ReadConcernLevel.Majority, "{ level: 'majority' }")]

tests/MongoDB.Driver.Tests/MongoUrlBuilderTests.cs

@@ -802,8 +802,11 @@ public void TestMinConnectionPoolSize_Range()
         }
 
         [Theory]
+        [InlineData("mongodb://localhost/?readConcernLevel=available", ReadConcernLevel.Available)]
+        [InlineData("mongodb://localhost/?readConcernLevel=linearizable", ReadConcernLevel.Linearizable)]
         [InlineData("mongodb://localhost/?readConcernLevel=local", ReadConcernLevel.Local)]
         [InlineData("mongodb://localhost/?readConcernLevel=majority", ReadConcernLevel.Majority)]
+        [InlineData("mongodb://localhost/?readConcernLevel=snapshot", ReadConcernLevel.Snapshot)]
         public void TestReadConcernLevel(string connectionString, ReadConcernLevel readConcernLevel)
         {
             var built = new MongoUrlBuilder { ReadConcernLevel = readConcernLevel };