RO Headers & rationalise exceptions

src/Microsoft.AspNetCore.Server.Kestrel/Http/Frame.cs

@@ -656,8 +656,10 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
             byte[] statusBytes,
             bool appCompleted)
         {
-            var end = SocketOutput.ProducingStart();
             var responseHeaders = _frameHeaders.ResponseHeaders;
+            responseHeaders.SetReadOnly();
+
+            var end = SocketOutput.ProducingStart();
             if (_keepAlive)
             {
                 foreach (var connectionValue in responseHeaders.HeaderConnection)

src/Microsoft.AspNetCore.Server.Kestrel/Http/FrameHeaders.cs

@@ -12,6 +12,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
 {
     public abstract class FrameHeaders : IHeaderDictionary
     {
+        protected bool _isReadOnly;
         protected Dictionary<string, StringValues> MaybeUnknown;
 
         protected Dictionary<string, StringValues> Unknown => MaybeUnknown ?? (MaybeUnknown = new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase));
@@ -26,6 +27,10 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
             }
             set
             {
+                if (_isReadOnly)
+                {
+                    ThrowReadOnlyException();
+                }
                 SetValueFast(key, value);
             }
         }
@@ -38,20 +43,50 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
             }
             set
             {
+                if (_isReadOnly)
+                {
+                    ThrowReadOnlyException();
+                }
                 SetValueFast(key, value);
             }
         }
 
+        protected void ThrowReadOnlyException()
+        {
+            throw new InvalidOperationException("Headers are readonly, reponse has already started.");
+        }
+
+        protected void ThrowArgumentException()
+        {
+            throw new ArgumentException();
+        }
+
+        protected void ThrowKeyNotFoundException()
+        {
+            throw new KeyNotFoundException();
+        }
+
+        protected void ThrowDuplicateKeyException()
+        {
+            throw new ArgumentException("An item with the same key has already been added.");
+        }
+
         int ICollection<KeyValuePair<string, StringValues>>.Count => GetCountFast();
 
-        bool ICollection<KeyValuePair<string, StringValues>>.IsReadOnly => false;
+        bool ICollection<KeyValuePair<string, StringValues>>.IsReadOnly => _isReadOnly;
 
         ICollection<string> IDictionary<string, StringValues>.Keys => ((IDictionary<string, StringValues>)this).Select(pair => pair.Key).ToList();
 
         ICollection<StringValues> IDictionary<string, StringValues>.Values => ((IDictionary<string, StringValues>)this).Select(pair => pair.Value).ToList();
 
+        public void SetReadOnly()
+        {
+            _isReadOnly = true;
+        }
+
         public void Reset()
         {
+            _isReadOnly = false;
             ClearFast();
         }
 
@@ -105,16 +140,28 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
 
         void ICollection<KeyValuePair<string, StringValues>>.Add(KeyValuePair<string, StringValues> item)
         {
+            if (_isReadOnly)
+            {
+                ThrowReadOnlyException();
+            }
             AddValueFast(item.Key, item.Value);
         }
 
         void IDictionary<string, StringValues>.Add(string key, StringValues value)
         {
+            if (_isReadOnly)
+            {
+                ThrowReadOnlyException();
+            }
             AddValueFast(key, value);
         }
 
         void ICollection<KeyValuePair<string, StringValues>>.Clear()
         {
+            if (_isReadOnly)
+            {
+                ThrowReadOnlyException();
+            }
             ClearFast();
         }
 
@@ -158,6 +205,10 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
 
         bool IDictionary<string, StringValues>.Remove(string key)
         {
+            if (_isReadOnly)
+            {
+                ThrowReadOnlyException();
+            }
             return RemoveFast(key);
         }
 

tools/Microsoft.AspNetCore.Server.Kestrel.GeneratedCode/KnownHeaders.cs

@@ -263,7 +263,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
                             }}
                             else
                             {{
-                                throw new System.Collections.Generic.KeyNotFoundException();
+                                ThrowKeyNotFoundException();
                             }}
                         }}
                     ")}}}
@@ -271,7 +271,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
 ")}}}
             if (MaybeUnknown == null) 
             {{
-                throw new System.Collections.Generic.KeyNotFoundException();
+                ThrowKeyNotFoundException();
             }}
             return MaybeUnknown[key];
         }}
@@ -328,7 +328,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
                         {{
                             if ({header.TestBit()})
                             {{
-                                throw new ArgumentException(""An item with the same key has already been added."");
+                                ThrowDuplicateKeyException();
                             }}
                             {header.SetBit()};
                             _{header.Identifier} = value;{(header.EnhancedSetter == false ? "" : $@"
@@ -377,14 +377,14 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
         {{
             if (arrayIndex < 0)
             {{
-                throw new ArgumentException();
+                ThrowArgumentException();
             }}
             {Each(loop.Headers, header => $@"
                 if ({header.TestBit()}) 
                 {{
                     if (arrayIndex == array.Length)
                     {{
-                        throw new ArgumentException();
+                        ThrowArgumentException();
                     }}
 
                     array[arrayIndex] = new KeyValuePair<string, StringValues>(""{header.Name}"", _{header.Identifier});
@@ -415,6 +415,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
                 }}
             ")}
         }}" : "")}
+        {(loop.ClassName == "FrameRequestHeaders" ? $@"
         public unsafe void Append(byte[] keyBytes, int keyOffset, int keyLength, string value)
         {{
             fixed (byte* ptr = &keyBytes[keyOffset]) 
@@ -449,7 +450,7 @@ namespace Microsoft.AspNetCore.Server.Kestrel.Http
             StringValues existing;
             Unknown.TryGetValue(key, out existing);
             Unknown[key] = AppendValue(existing, value);
-        }}
+        }}" : "")}
         public partial struct Enumerator
         {{
             public bool MoveNext()