fix: prevent durable sink from posting empty batches

Prevent durable HTTP sink from posting HTTP messages without any log events.

Closes #32

CHANGELOG.md

@@ -6,6 +6,10 @@ This project adheres to [Semantic Versioning](http://semver.org/) and is followi
 
 ## Unreleased
 
+### Fixed
+
+- [#32](https://github.com/FantasticFiasco/serilog-sinks-http/issues/32) Prevent durable HTTP sink from posting HTTP messages without any log events
+
 ## [4.2.0] - 2017-08-20
 
 ### Added

src/Serilog.Sinks.Http/Sinks/Http/Private/Network/HttpLogShipper.cs

@@ -145,6 +145,9 @@ private async Task OnTick()
                                 nextRequiredLevelCheckUtc = DateTime.UtcNow.Add(RequiredLevelCheckInterval);
                             }
 
+                            if (string.IsNullOrEmpty(payload))
+                                continue;;
+
                             var content = new StringContent(payload, Encoding.UTF8, ContentType);
 
                             var result = await client.PostAsync(requestUri, content).ConfigureAwait(false);

test/Serilog.Sinks.HttpTests/Sinks/Http/Private/Sinks/DurableHttpSinkTest.cs

@@ -1,4 +1,7 @@
 using System;
+using System.Net.Http;
+using System.Threading.Tasks;
+using Moq;
 using Serilog.LogServer;
 using Serilog.Sinks.Http.BatchFormatters;
 using Serilog.Sinks.Http.TextFormatters;
@@ -137,5 +140,32 @@ public void InvalidBufferFileSizeLimitBytes(int? bufferFileSizeLimitBytes)
             // Assert
             provider.ShouldThrow<ArgumentOutOfRangeException>();
         }
+
+        [Fact]
+        public async Task NoNetworkTrafficWithoutLogEvents()
+        {
+            // Arrange
+            var httpClient = new Mock<IHttpClient>();
+
+            // ReSharper disable once UnusedVariable
+            var httpSink = new DurableHttpSink(
+                "api/events",
+                "Buffer-{Date}.json",
+                null,
+                null,
+                1000,
+                TimeSpan.FromSeconds(2),
+                new NormalRenderedTextFormatter(),
+                new DefaultBatchFormatter(),
+                httpClient.Object);
+
+            // Act
+            await Task.Delay(TimeSpan.FromMinutes(3));
+
+            // Assert
+            httpClient.Verify(
+                mock => mock.PostAsync(It.IsAny<string>(), It.IsAny<HttpContent>()),
+                Times.Never);
+        }
     }
 }

test/Serilog.Sinks.HttpTests/Sinks/Http/Private/Sinks/HttpSinkTest.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Net.Http;
+using System.Threading.Tasks;
+using Moq;
+using Serilog.Sinks.Http.BatchFormatters;
+using Serilog.Sinks.Http.TextFormatters;
+using Xunit;
+
+namespace Serilog.Sinks.Http.Private.Sinks
+{
+    public class HttpSinkTest
+    {
+        [Fact]
+        public async Task NoNetworkTrafficWithoutLogEvents()
+        {
+            // Arrange
+            var httpClient = new Mock<IHttpClient>();
+
+            // ReSharper disable once UnusedVariable
+            var httpSink = new HttpSink(
+                "api/events",
+                1000,
+                TimeSpan.FromSeconds(2),
+                new NormalRenderedTextFormatter(),
+                new DefaultBatchFormatter(),
+                httpClient.Object);
+
+            // Act
+            await Task.Delay(TimeSpan.FromMinutes(3));
+
+            // Assert
+            httpClient.Verify(
+                mock => mock.PostAsync(It.IsAny<string>(), It.IsAny<HttpContent>()),
+                Times.Never);
+        }
+    }
+}