NLogRequestPostedBodyMiddleware - Fixed handling of Stream.CanSeek

src/NLog.Web.AspNetCore/NLogRequestPostedBodyMiddleware.cs

@@ -97,10 +97,9 @@ private bool ShouldCaptureRequestBody(HttpContext context)
                 return false;
             }
 
-            // If we cannot seek the stream we cannot capture the body
-            if (!postedBody.CanSeek)
+            if (postedBody.Position != 0 && !postedBody.CanSeek)
             {
-                InternalLogger.Debug("NLogRequestPostedBodyMiddleware: HttpContext.Request.Body stream is non-seekable");
+                InternalLogger.Debug("NLogRequestPostedBodyMiddleware: HttpContext.Request.Body stream position non-zero");
                 return false;
             }
 
@@ -116,6 +115,13 @@ private bool ShouldCaptureRequestBody(HttpContext context)
         /// <returns>The contents of the Stream read fully from start to end as a String</returns>
         private static async Task<string> GetString(Stream stream)
         {
+            // If we cannot seek the stream we cannot capture the body
+            if (!stream.CanSeek)
+            {
+                InternalLogger.Debug("NLogRequestPostedBodyMiddleware: HttpContext.Request.Body stream is non-seekable");
+                return string.Empty;
+            }
+
             string responseText = null;
 
             // Save away the original stream position

tests/NLog.Web.AspNetCore.Tests/NLogRequestPostedBodyMiddlewareTests.cs

@@ -1,4 +1,5 @@
-using System.IO;
+using System;
+using System.IO;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
@@ -65,7 +66,6 @@ public void EmptyBodyTest()
             // Assert
             Assert.NotNull(defaultContext.Items);
             Assert.Empty(defaultContext.Items);
-            Assert.Null(defaultContext.Items[AspNetRequestPostedBodyLayoutRenderer.NLogPostedRequestBodyKey]);
         }
 
         [Fact]
@@ -86,7 +86,6 @@ public void ExcludContentTypeTest()
             // Assert
             Assert.NotNull(defaultContext.Items);
             Assert.Empty(defaultContext.Items);
-            Assert.Null(defaultContext.Items[AspNetRequestPostedBodyLayoutRenderer.NLogPostedRequestBodyKey]);
         }
 
         [Fact]
@@ -203,21 +202,67 @@ public void CannotSeekLengthTest()
             // Arrange
             DefaultHttpContext defaultContext = new DefaultHttpContext();
 
-            defaultContext.Request.Body = Substitute.For<Stream>();
-            defaultContext.Request.ContentLength = 1;
+            defaultContext.Request.Body = new NetworkStream() { _length = 2 };
+            defaultContext.Request.ContentLength = 2;
             defaultContext.Request.ContentType = "text/plain";
 
-            defaultContext.Request.Body.CanRead.Returns(true);
-            defaultContext.Request.Body.CanSeek.Returns(false);
-
             // Act
             var middlewareInstance =
                 new NLogRequestPostedBodyMiddleware(Next,NLogRequestPostedBodyMiddlewareOptions.Default);
             middlewareInstance.Invoke(defaultContext).ConfigureAwait(false).GetAwaiter().GetResult();
 
+            // Assert
+            Assert.NotNull(defaultContext.Items);
+            Assert.Single(defaultContext.Items);
+            Assert.NotNull(defaultContext.Items[AspNetRequestPostedBodyLayoutRenderer.NLogPostedRequestBodyKey]);
+            Assert.True(defaultContext.Items[AspNetRequestPostedBodyLayoutRenderer.NLogPostedRequestBodyKey] is string);
+        }
+
+        [Fact]
+        public void CannotSeekLengthAndStartedTest()
+        {
+            // Arrange
+            DefaultHttpContext defaultContext = new DefaultHttpContext();
+
+            defaultContext.Request.Body = new NetworkStream() { _length = 2, Position = 2 };
+            defaultContext.Request.ContentLength = 2;
+            defaultContext.Request.ContentType = "text/plain";
+
+            // Act
+            var middlewareInstance =
+                new NLogRequestPostedBodyMiddleware(Next, NLogRequestPostedBodyMiddlewareOptions.Default);
+            middlewareInstance.Invoke(defaultContext).ConfigureAwait(false).GetAwaiter().GetResult();
+
             // Assert
             Assert.NotNull(defaultContext.Items);
             Assert.Empty(defaultContext.Items);
         }
+
+        private sealed class NetworkStream : Stream
+        {
+            internal long _length;
+
+            public override bool CanRead => true;
+
+            public override bool CanSeek => false;
+
+            public override bool CanWrite => false;
+
+            public override long Length => _length;
+
+            public override long Position { get; set; }
+
+            public override int Read(byte[] buffer, int offset, int count)
+            {
+                int delta = Math.Min((int)(Length - Position), count);
+                Position += delta;
+                return delta;
+            }
+
+            public override long Seek(long offset, SeekOrigin origin) => throw new System.NotSupportedException();
+            public override void SetLength(long value) => throw new System.NotSupportedException();
+            public override void Write(byte[] buffer, int offset, int count) => throw new System.NotSupportedException();
+            public override void Flush() => throw new System.NotSupportedException();
+        }
     }
 }