Max segment size (#110)

* add MaxSegmentSizeBytes configuration when creating a stream.
* add MaxSegmentSizeBytes and MaxLengthBytes in stream creation test.
* add documentation  max segment size

Author: simone-fariselli

README.md

@@ -197,6 +197,18 @@ await system.CreateStream(new StreamSpec(stream)
 
 Set a policy is highly recommended.
 
+RabbitMQ does not store the whole stream in a single file, but splits it in segment files. 
+This is also used for truncate the stream: when a stream reaches his maximum size, an entire segment file is deleted. For this reason  `MaxLengthBytes` (the max dimension of the entire stream) is usually significantly higher than `MaxSegmentSizeBytes` (the max dimension of a single segment file).
+RabbitMQ enforces the retention policy when the current segment has reached its maximum size and is closed in favor of a new one.
+
+```csharp
+await system.CreateStream(new StreamSpec(stream)
+{
+    MaxLengthBytes = 20_000,
+    MaxSegmentSizeBytes = 1000
+});
+```
+
 ### Producer
 
 A Producer instance is created from the `System`.

RabbitMQ.Stream.Client/StreamSpec.cs

@@ -28,6 +28,10 @@ public LeaderLocator LeaderLocator
         {
             set => Args["queue-leader-locator"] = $"{value.ToString()}";
         }
+        public int MaxSegmentSizeBytes
+        {
+            set => Args["stream-max-segment-size-bytes"] = $"{value}";
+        }
 
         public IDictionary<string, string> Args => args;
     }

Tests/ApiApproval.Approve.verified.txt

@@ -861,6 +861,7 @@ namespace RabbitMQ.Stream.Client
         public RabbitMQ.Stream.Client.LeaderLocator LeaderLocator { set; }
         public System.TimeSpan MaxAge { set; }
         public int MaxLengthBytes { set; }
+        public int MaxSegmentSizeBytes { set; }
         public string Name { get; set; }
         public virtual RabbitMQ.Stream.Client.StreamSpec <Clone>$() { }
         public void Deconstruct(out string Name) { }

Tests/SystemTests.cs

@@ -80,9 +80,17 @@ public async void Create_Delete_Stream()
             var stream = Guid.NewGuid().ToString();
             var config = new StreamSystemConfig();
             var system = await StreamSystem.Create(config);
-            var spec = new StreamSpec(stream) { MaxAge = TimeSpan.FromHours(8), LeaderLocator = LeaderLocator.Random };
+            var spec = new StreamSpec(stream)
+            {
+                MaxAge = TimeSpan.FromHours(8),
+                LeaderLocator = LeaderLocator.Random,
+                MaxLengthBytes = 20_000,
+                MaxSegmentSizeBytes = 1000
+            };
             Assert.Equal("28800s", spec.Args["max-age"]);
             Assert.Equal("random", spec.Args["queue-leader-locator"]);
+            Assert.Equal("1000", spec.Args["stream-max-segment-size-bytes"]);
+            Assert.Equal("20000", spec.Args["max-length-bytes"]);
             await system.CreateStream(spec);
             await system.DeleteStream(stream);
             await system.Close();