Make HttpWebResponse.LastModified throw when invalid date is provided (#29006)

* make HttpWebResponse.LastModified throw when invalid date is provided

* apply feedback

* Update HttpDateParse.cs

Author: krwq

src/System.Net.Requests/src/System/Net/HttpDateParse.cs

@@ -398,5 +398,8 @@ public static bool ParseHttpDate(string dateString, out DateTime result)
 
             return true;
         }
+
+        public static DateTime StringToDate(string s) =>
+            HttpDateParse.ParseHttpDate(s, out DateTime dtOut) ? dtOut : throw new ProtocolViolationException(SR.net_baddate);
     }
 }

src/System.Net.Requests/src/System/Net/HttpWebRequest.cs

@@ -1450,7 +1450,7 @@ private DateTime GetDateHeaderHelper(string headerName)
                 {
                     return DateTime.MinValue; // MinValue means header is not present
                 }
-                return StringToDate(headerValue);
+                return HttpDateParse.StringToDate(headerValue);
 #if DEBUG
             }
 #endif
@@ -1471,20 +1471,6 @@ private void SetDateHeaderHelper(string headerName, DateTime dateTime)
 #endif
         }
 
-        // parse String to DateTime format.
-        private static DateTime StringToDate(String S)
-        {
-            DateTime dtOut;
-            if (HttpDateParse.ParseHttpDate(S, out dtOut))
-            {
-                return dtOut;
-            }
-            else
-            {
-                throw new ProtocolViolationException(SR.net_baddate);
-            }
-        }
-
         // convert Date to String using RFC 1123 pattern
         private static string DateToString(DateTime D)
         {

src/System.Net.Requests/src/System/Net/HttpWebResponse.cs

@@ -150,13 +150,11 @@ public DateTime LastModified
                 {
                     return DateTime.Now;
                 }
-                DateTime dtOut;
-                HttpDateParse.ParseHttpDate(lastmodHeaderValue, out dtOut);
-                return dtOut;
+
+                return HttpDateParse.StringToDate(lastmodHeaderValue);
             }
         }
 
-
         /// <devdoc>
         ///    <para>
         ///       Gets the name of the server that sent the response.

src/System.Net.Requests/tests/HttpWebResponseHeaderTest.cs

@@ -94,6 +94,40 @@ await LoopbackServer.CreateServerAsync(async (server, url) =>
             });
         }
 
+        [Fact]
+        public async Task LastModified_ValidDate_Success()
+        {
+            DateTime expected = TimeZoneInfo.ConvertTimeFromUtc(new DateTime(2018, 4, 10, 3, 4, 5, DateTimeKind.Utc), TimeZoneInfo.Local);
+            await LoopbackServer.CreateServerAsync(async (server, url) =>
+            {
+                HttpWebRequest request = WebRequest.CreateHttp(url);
+                Task<WebResponse> getResponse = request.GetResponseAsync();
+                await server.AcceptConnectionSendResponseAndCloseAsync(HttpStatusCode.OK, "Last-Modified: Tue, 10 Apr 2018 03:04:05 GMT\r\n", "12345");
+
+                using (HttpWebResponse response = (HttpWebResponse)(await getResponse))
+                {
+                    Assert.Equal(expected, response.LastModified);
+                }
+            });
+        }
+
+        [Fact]
+        public async Task LastModified_InvalidDate_Throws()
+        {
+            DateTime expected = TimeZoneInfo.ConvertTimeFromUtc(new DateTime(2018, 4, 10, 3, 4, 5, DateTimeKind.Utc), TimeZoneInfo.Local);
+            await LoopbackServer.CreateServerAsync(async (server, url) =>
+            {
+                HttpWebRequest request = WebRequest.CreateHttp(url);
+                Task<WebResponse> getResponse = request.GetResponseAsync();
+                await server.AcceptConnectionSendResponseAndCloseAsync(HttpStatusCode.OK, "Last-Modified: invalid date\r\n", "12345");
+
+                using (HttpWebResponse response = (HttpWebResponse)(await getResponse))
+                {
+                    Assert.Throws<ProtocolViolationException>(() => response.LastModified);
+                }
+            });
+        }
+
         [Fact]
         public async Task HttpWebResponse_Serialize_ExpectedResult()
         {
@@ -125,6 +159,6 @@ await LoopbackServer.CreateServerAsync(async (server, url) =>
                     }
                 }
             });
-        } 
+        }
     }
 }