#659 Parse headers with consecutive commas

Author: Tratcher

src/Microsoft.AspNetCore.Http.Abstractions/Internal/HeaderSegmentCollection.cs

@@ -188,6 +188,9 @@ public bool MoveNext()
                                 switch (attr)
                                 {
                                     case Attr.Delimiter:
+                                        _valueStart = _valueStart == -1 ? _offset : _valueStart;
+                                        _valueEnd = _valueEnd == -1 ? _offset : _valueEnd;
+                                        _trailingStart = _trailingStart == -1 ? _offset : _trailingStart;
                                         _leadingEnd = _offset;
                                         _mode = Mode.Produce;
                                         break;

test/Microsoft.AspNetCore.Http.Tests/HeaderDictionaryTests.cs

@@ -10,6 +10,14 @@ namespace Microsoft.AspNetCore.Http
 {
     public class HeaderDictionaryTests
     {
+        public static TheoryData HeaderSegmentData => new TheoryData<IEnumerable<string>>
+        {
+          new[] { "Value1", "Value2", "Value3", "Value4" },
+          new[] { "Value1", "", "Value3", "Value4" },
+          new[] { "Value1", "", "", "Value4" },
+          new[] { "", "", "", "" }
+        };
+
         [Fact]
         public void PropertiesAreAccessible()
         {
@@ -26,5 +34,22 @@ public void PropertiesAreAccessible()
             Assert.Equal("Value1", headers["header1"]);
             Assert.Equal(new[] { "Value1" }, headers["header1"].ToArray());
         }
+
+        [Theory]
+        [MemberData(nameof(HeaderSegmentData))]
+        public void EmptyHeaderSegmentsAreParsable(IEnumerable<string> segments)
+        {
+            var header = string.Join(",", segments);
+
+            var headers = new HeaderDictionary(
+               new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase)
+               {
+                    { "Header1",  header},
+               });
+
+            var result = headers.GetCommaSeparatedValues("Header1");
+
+            Assert.Equal(segments, result);
+        }
     }
 }