Implement read-only HeaderDictionary (#958)

src/Microsoft.AspNetCore.Http/HeaderDictionary.cs

@@ -58,13 +58,13 @@ namespace Microsoft.AspNetCore.Http
                 }
                 return StringValues.Empty;
             }
-
             set
             {
                 if (key == null)
                 {
                     throw new ArgumentNullException(nameof(key));
                 }
+                ThrowIfReadOnly();
 
                 if (StringValues.IsNullOrEmpty(value))
                 {
@@ -90,7 +90,11 @@ namespace Microsoft.AspNetCore.Http
         StringValues IDictionary<string, StringValues>.this[string key]
         {
             get { return Store[key]; }
-            set { this[key] = value; }
+            set
+            {
+                ThrowIfReadOnly();
+                this[key] = value;
+            }
         }
 
         public long? ContentLength
@@ -110,6 +114,7 @@ namespace Microsoft.AspNetCore.Http
             }
             set
             {
+                ThrowIfReadOnly();
                 if (value.HasValue)
                 {
                     this[HeaderNames.ContentLength] = HeaderUtilities.FormatNonNegativeInt64(value.Value);
@@ -125,25 +130,13 @@ namespace Microsoft.AspNetCore.Http
         /// Gets the number of elements contained in the <see cref="HeaderDictionary" />;.
         /// </summary>
         /// <returns>The number of elements contained in the <see cref="HeaderDictionary" />.</returns>
-        public int Count
+        public int Count => Store?.Count ?? 0;
-        {
-            get
-            {
-                return Store?.Count ?? 0;
-            }
-        }
 
         /// <summary>
         /// Gets a value that indicates whether the <see cref="HeaderDictionary" /> is in read-only mode.
         /// </summary>
         /// <returns>true if the <see cref="HeaderDictionary" /> is in read-only mode; otherwise, false.</returns>
-        public bool IsReadOnly
+        public bool IsReadOnly { get; set; }
-        {
-            get
-            {
-                return false;
-            }
-        }
 
         public ICollection<string> Keys
         {
@@ -179,6 +172,7 @@ namespace Microsoft.AspNetCore.Http
             {
                 throw new ArgumentNullException("The key is null");
             }
+            ThrowIfReadOnly();
             if (Store == null)
             {
                 Store = new Dictionary<string, StringValues>(1, StringComparer.OrdinalIgnoreCase);
@@ -197,6 +191,7 @@ namespace Microsoft.AspNetCore.Http
             {
                 throw new ArgumentNullException(nameof(key));
             }
+            ThrowIfReadOnly();
 
             if (Store == null)
             {
@@ -210,6 +205,7 @@ namespace Microsoft.AspNetCore.Http
         /// </summary>
         public void Clear()
         {
+            ThrowIfReadOnly();
             Store?.Clear();
         }
 
@@ -270,6 +266,7 @@ namespace Microsoft.AspNetCore.Http
         /// <returns>true if the specified object was removed from the collection; otherwise, false.</returns>
         public bool Remove(KeyValuePair<string, StringValues> item)
         {
+            ThrowIfReadOnly();
             if (Store == null)
             {
                 return false;
@@ -291,6 +288,7 @@ namespace Microsoft.AspNetCore.Http
         /// <returns>true if the specified object was removed from the collection; otherwise, false.</returns>
         public bool Remove(string key)
         {
+            ThrowIfReadOnly();
             if (Store == null)
             {
                 return false;
@@ -356,6 +354,14 @@ namespace Microsoft.AspNetCore.Http
             return Store.GetEnumerator();
         }
 
+        private void ThrowIfReadOnly()
+        {
+            if (IsReadOnly)
+            {
+                throw new InvalidOperationException("The response headers cannot be modified because the response has already started.");
+            }
+        }
+
         public struct Enumerator : IEnumerator<KeyValuePair<string, StringValues>>
         {
             // Do NOT make this readonly, or MoveNext will not work

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

@@ -68,5 +68,40 @@ namespace Microsoft.AspNetCore.Http
             var result = headers.GetCommaSeparatedValues("Header1");
             Assert.Equal(new[] { "Value1", "Value2" }, result);
         }
+
+        [Fact]
+        public void ReadActionsWorkWhenReadOnly()
+        {
+            var headers = new HeaderDictionary(
+                new Dictionary<string, StringValues>(StringComparer.OrdinalIgnoreCase)
+                {
+                    { "Header1", "Value1" }
+                });
+
+            headers.IsReadOnly = true;
+
+            Assert.Single(headers);
+            Assert.Equal<string>(new[] { "Header1" }, headers.Keys);
+            Assert.True(headers.ContainsKey("header1"));
+            Assert.False(headers.ContainsKey("header2"));
+            Assert.Equal("Value1", headers["header1"]);
+            Assert.Equal(new[] { "Value1" }, headers["header1"].ToArray());
+        }
+
+        [Fact]
+        public void WriteActionsThrowWhenReadOnly()
+        {
+            var headers = new HeaderDictionary();
+            headers.IsReadOnly = true;
+
+            Assert.Throws<InvalidOperationException>(() => headers["header1"] = "value1");
+            Assert.Throws<InvalidOperationException>(() => ((IDictionary<string, StringValues>)headers)["header1"] = "value1");
+            Assert.Throws<InvalidOperationException>(() => headers.ContentLength = 12);
+            Assert.Throws<InvalidOperationException>(() => headers.Add(new KeyValuePair<string, StringValues>("header1", "value1")));
+            Assert.Throws<InvalidOperationException>(() => headers.Add("header1", "value1"));
+            Assert.Throws<InvalidOperationException>(() => headers.Clear());
+            Assert.Throws<InvalidOperationException>(() => headers.Remove(new KeyValuePair<string, StringValues>("header1", "value1")));
+            Assert.Throws<InvalidOperationException>(() => headers.Remove("header1"));
+        }
     }
 }