handle bad Expires better

src/System.Net.Http/src/System/Net/Http/Headers/HeaderUtilities.cs

@@ -291,7 +291,7 @@ internal static int GetNextNonEmptyOrWhitespaceIndex(string input, int startInde
             return current;
         }
 
-        internal static DateTimeOffset? GetDateTimeOffsetValue(HeaderDescriptor descriptor, HttpHeaders store)
+        internal static DateTimeOffset? GetDateTimeOffsetValue(HeaderDescriptor descriptor, HttpHeaders store, DateTimeOffset? defaultValue = null)
         {
             Debug.Assert(store != null);
 
@@ -300,6 +300,11 @@ internal static int GetNextNonEmptyOrWhitespaceIndex(string input, int startInde
             {
                 return (DateTimeOffset)storedValue;
             }
+            else if (defaultValue != null && store.Contains(descriptor))
+            {
+                return defaultValue;
+            }
+
             return null;
         }
 

src/System.Net.Http/src/System/Net/Http/Headers/HttpContentHeaders.cs

@@ -133,7 +133,7 @@ public MediaTypeHeaderValue ContentType
 
         public DateTimeOffset? Expires
         {
-            get { return HeaderUtilities.GetDateTimeOffsetValue(KnownHeaders.Expires.Descriptor, this); }
+            get { return HeaderUtilities.GetDateTimeOffsetValue(KnownHeaders.Expires.Descriptor, this, DateTimeOffset.MinValue); }
             set { SetOrRemoveParsedValue(KnownHeaders.Expires.Descriptor, value); }
         }
 

src/System.Net.Http/src/System/Net/Http/Headers/HttpHeaders.cs

@@ -45,7 +45,7 @@ private enum StoreLocation
         }
 
         protected HttpHeaders()
-            : this(HttpHeaderType.All, HttpHeaderType.None)
+            : this(HttpHeaderType.None, HttpHeaderType.All)
         {
         }
 

src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Headers.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Net.Http.Headers;
 using System.Net.Test.Common;
 using System.Text;
 using System.Threading;
@@ -21,6 +22,8 @@ public abstract class HttpClientHandlerTest_Headers : HttpClientHandlerTestBase
     {
         public HttpClientHandlerTest_Headers(ITestOutputHelper output) : base(output) { }
 
+        internal sealed class DerivedHttpHeaders : HttpHeaders { }
+
         [Fact]
         public async Task SendAsync_UserAgent_CorrectlyWritten()
         {
@@ -66,6 +69,55 @@ await LoopbackServerFactory.CreateClientAndServerAsync(async uri =>
             });
         }
 
+        [Fact]
+        public async Task GetAsync_MissingExpires_ReturnNull()
+        {
+             await LoopbackServerFactory.CreateClientAndServerAsync(async uri =>
+             {
+                using (var client = CreateHttpClient())
+                {
+                    HttpResponseMessage response = await client.GetAsync(uri);
+                    Assert.Null(response.Content.Headers.Expires);
+                }
+            },
+            async server =>
+            {
+                await server.HandleRequestAsync(HttpStatusCode.OK);
+            });
+        }
+
+        [Theory]
+        [InlineData("Thu, 01 Dec 1994 16:00:00 GMT")]
+        [InlineData("-1")]
+        [InlineData("0")]
+        public async Task SendAsync_Expires_Success(string value)
+        {
+            await LoopbackServerFactory.CreateClientAndServerAsync(async uri =>
+            {
+                using (var client = CreateHttpClient())
+                {
+                    var message = new HttpRequestMessage(HttpMethod.Get, uri);
+                    HttpResponseMessage response = await client.SendAsync(message);
+                    Assert.NotNull(response.Content.Headers.Expires);
+                }
+            },
+            async server =>
+            {
+                IList<HttpHeaderData> headers = new HttpHeaderData[] { new HttpHeaderData("Expires", value) };
+
+                HttpRequestData requestData = await server.HandleRequestAsync(HttpStatusCode.OK, headers);
+            });
+        }
+
+        [Theory]
+        [InlineData("-1")]
+        [InlineData("Thu, 01 Dec 1994 16:00:00 GMT")]
+        public void SendAsync_CustomExpires_Success(string value)
+        {
+            var headers = new DerivedHttpHeaders();
+            headers.Add("Expires", value);
+        }
+
         [OuterLoop("Uses external server")]
         [Theory]
         [InlineData(false)]