Only use underlying stream when buffered. Otherwise, it's not seekable.

src/Nancy.Tests/Unit/IO/RequestStreamFixture.cs

@@ -5,7 +5,6 @@ namespace Nancy.Tests.Unit.IO
     using FakeItEasy;
     using Nancy.IO;
     using Xunit;
-    using Xunit.Extensions;
 
     public class RequestStreamFixture
     {
@@ -148,6 +147,21 @@ public void Should_return_false_when_queried_about_supporting_seeking()
             result.ShouldBeFalse();
         }
 
+        [Fact]
+        public void Should_return_true_when_queried_about_supporting_seeking_if_buffered()
+        {
+            // Given
+            var stream = new ConfigurableMemoryStream();
+            var request = RequestStream.FromStream(stream, 0, 1, false);
+            request.BufferStream();
+
+            // When
+            var result = request.CanSeek;
+
+            // Then
+            result.ShouldBeTrue();
+        }
+
         [Fact]
         public void Should_return_underlaying_stream_when_queried_about_supporting_timeout()
         {

src/Nancy/IO/RequestStream.cs

@@ -125,7 +125,14 @@ public override bool CanRead
         /// <returns>Returns depending on whether the stream is buffered or not.</returns>
         public override bool CanSeek
         {
-            get { return this.stream.CanSeek; }
+            get
+            {
+                if (!isBuffered)
+                {
+                    return false;
+                }
+                return this.stream.CanSeek;
+            }
         }
 
         /// <summary>
@@ -311,6 +318,10 @@ public override int ReadByte()
         /// <param name="origin">A value of type <see cref="T:System.IO.SeekOrigin"/> indicating the reference point used to obtain the new position. </param>
         public override long Seek(long offset, SeekOrigin origin)
         {
+            if (!isBuffered)
+            {
+                throw new NotSupportedException();
+            }
             return this.stream.Seek(offset, origin);
         }
 
@@ -322,6 +333,10 @@ public override long Seek(long offset, SeekOrigin origin)
         /// <remarks>This functionality is not supported by the <see cref="RequestStream"/> type and will always throw <see cref="NotSupportedException"/>.</remarks>
         public override void SetLength(long value)
         {
+            if (!isBuffered)
+            {
+                throw new NotSupportedException();
+            }
             this.stream.SetLength(value);
         }