Do not reorder HTTP header values

src/libraries/System.Net.Http/src/System/Net/Http/Headers/CacheControlHeaderParser.cs

@@ -1,4 +1,4 @@
-// Licensed to the .NET Foundation under one or more agreements.
+// Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;

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

@@ -287,7 +287,7 @@ internal static int GetNextNonEmptyOrWhitespaceIndex(string input, int startInde
         {
             Debug.Assert(store != null);
 
-            object? storedValue = store.GetParsedValues(descriptor);
+            object? storedValue = store.GetSingleParsedValue(descriptor);
             if (storedValue != null)
             {
                 return (DateTimeOffset)storedValue;
@@ -304,7 +304,7 @@ internal static int GetNextNonEmptyOrWhitespaceIndex(string input, int startInde
         {
             Debug.Assert(store != null);
 
-            object? storedValue = store.GetParsedValues(descriptor);
+            object? storedValue = store.GetSingleParsedValue(descriptor);
             if (storedValue != null)
             {
                 return (TimeSpan)storedValue;

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

@@ -19,7 +19,7 @@ public sealed class HttpContentHeaders : HttpHeaders
 
         public ContentDispositionHeaderValue? ContentDisposition
         {
-            get { return (ContentDispositionHeaderValue?)GetParsedValues(KnownHeaders.ContentDisposition.Descriptor); }
+            get { return (ContentDispositionHeaderValue?)GetSingleParsedValue(KnownHeaders.ContentDisposition.Descriptor); }
             set { SetOrRemoveParsedValue(KnownHeaders.ContentDisposition.Descriptor, value); }
         }
 
@@ -36,7 +36,7 @@ public long? ContentLength
             get
             {
                 // 'Content-Length' can only hold one value. So either we get 'null' back or a boxed long value.
-                object? storedValue = GetParsedValues(KnownHeaders.ContentLength.Descriptor);
+                object? storedValue = GetSingleParsedValue(KnownHeaders.ContentLength.Descriptor);
 
                 // Only try to calculate the length if the user didn't set the value explicitly using the setter.
                 if (!_contentLengthSet && (storedValue == null))
@@ -72,25 +72,25 @@ public long? ContentLength
 
         public Uri? ContentLocation
         {
-            get { return (Uri?)GetParsedValues(KnownHeaders.ContentLocation.Descriptor); }
+            get { return (Uri?)GetSingleParsedValue(KnownHeaders.ContentLocation.Descriptor); }
             set { SetOrRemoveParsedValue(KnownHeaders.ContentLocation.Descriptor, value); }
         }
 
         public byte[]? ContentMD5
         {
-            get { return (byte[]?)GetParsedValues(KnownHeaders.ContentMD5.Descriptor); }
+            get { return (byte[]?)GetSingleParsedValue(KnownHeaders.ContentMD5.Descriptor); }
             set { SetOrRemoveParsedValue(KnownHeaders.ContentMD5.Descriptor, value); }
         }
 
         public ContentRangeHeaderValue? ContentRange
         {
-            get { return (ContentRangeHeaderValue?)GetParsedValues(KnownHeaders.ContentRange.Descriptor); }
+            get { return (ContentRangeHeaderValue?)GetSingleParsedValue(KnownHeaders.ContentRange.Descriptor); }
             set { SetOrRemoveParsedValue(KnownHeaders.ContentRange.Descriptor, value); }
         }
 
         public MediaTypeHeaderValue? ContentType
         {
-            get { return (MediaTypeHeaderValue?)GetParsedValues(KnownHeaders.ContentType.Descriptor); }
+            get { return (MediaTypeHeaderValue?)GetSingleParsedValue(KnownHeaders.ContentType.Descriptor); }
             set { SetOrRemoveParsedValue(KnownHeaders.ContentType.Descriptor, value); }
         }
 

src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpGeneralHeaders.cs

@@ -22,7 +22,7 @@ internal sealed class HttpGeneralHeaders
 
         public CacheControlHeaderValue? CacheControl
         {
-            get { return (CacheControlHeaderValue?)_parent.GetParsedValues(KnownHeaders.CacheControl.Descriptor); }
+            get { return (CacheControlHeaderValue?)_parent.GetSingleParsedValue(KnownHeaders.CacheControl.Descriptor); }
             set { _parent.SetOrRemoveParsedValue(KnownHeaders.CacheControl.Descriptor, value); }
         }
 

src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpHeaderValueCollection.cs

@@ -86,7 +86,7 @@ public void CopyTo(T[] array!!, int arrayIndex)
                 throw new ArgumentOutOfRangeException(nameof(arrayIndex));
             }
 
-            object? storeValue = _store.GetParsedValues(_descriptor);
+            object? storeValue = _store.GetParsedAndInvalidValues(_descriptor);
 
             if (storeValue == null)
             {
@@ -122,8 +122,8 @@ public bool Remove(T item)
 
         public IEnumerator<T> GetEnumerator()
         {
-            object? storeValue = _store.GetParsedValues(_descriptor);
-            return storeValue is null ?
+            object? storeValue = _store.GetParsedAndInvalidValues(_descriptor);
+            return storeValue is null || storeValue is HttpHeaders.InvalidValue ?
                 ((IEnumerable<T>)Array.Empty<T>()).GetEnumerator() : // use singleton empty array enumerator
                 Iterate(storeValue);
 
@@ -134,6 +134,10 @@ static IEnumerator<T> Iterate(object storeValue)
                     // We have multiple values. Iterate through the values and return them.
                     foreach (object item in storeValues)
                     {
+                        if (item is HttpHeaders.InvalidValue)
+                        {
+                            continue;
+                        }
                         Debug.Assert(item is T);
                         yield return (T)item;
                     }
@@ -178,7 +182,7 @@ private int GetCount()
         {
             // This is an O(n) operation.
 
-            object? storeValue = _store.GetParsedValues(_descriptor);
+            object? storeValue = _store.GetParsedAndInvalidValues(_descriptor);
 
             if (storeValue == null)
             {
@@ -189,11 +193,23 @@ private int GetCount()
 
             if (storeValues == null)
             {
-                return 1;
+                if (storeValue is not HttpHeaders.InvalidValue)
+                {
+                    return 1;
+                }
+                return 0;
             }
             else
             {
-                return storeValues.Count;
+                int count = 0;
+                foreach (object item in storeValues)
+                {
+                    if (item is not HttpHeaders.InvalidValue)
+                    {
+                        count++;
+                    }
+                }
+                return count;
             }
         }
     }