#176 Add Clone() to MediaTypeHeaderValue and NameValueHeaderValue.

src/Microsoft.Net.Http.Headers/MediaTypeHeaderValue.cs

@@ -248,6 +248,27 @@ namespace Microsoft.Net.Http.Headers
             return true;
         }
 
+        /// <summary>
+        /// Performs a deep copy of this object and all of it's NameValueHeaderValue sub components,
+        /// while avoiding the cost of revalidating the components.
+        /// </summary>
+        /// <returns>A deep copy.</returns>
+        public MediaTypeHeaderValue Clone()
+        {
+            var other = new MediaTypeHeaderValue();
+            other._mediaType = _mediaType;
+
+            if (_parameters != null)
+            {
+                other._parameters = new ObjectCollection<NameValueHeaderValue>();
+                foreach (var pair in _parameters)
+                {
+                    other._parameters.Add(pair.Clone());
+                }
+            }
+            return other;
+        }
+
         public override string ToString()
         {
             return _mediaType + NameValueHeaderValue.ToString(_parameters, ';', true);

src/Microsoft.Net.Http.Headers/NameValueHeaderValue.cs

@@ -54,6 +54,19 @@ namespace Microsoft.Net.Http.Headers
             }
         }
 
+        /// <summary>
+        /// Provides a copy of this object without the cost of re-validating the values.
+        /// </summary>
+        /// <returns>A copy.</returns>
+        public NameValueHeaderValue Clone()
+        {
+            return new NameValueHeaderValue()
+            {
+                _name = _name,
+                _value = _value
+            };
+        }
+
         public override int GetHashCode()
         {
             Contract.Assert(_name != null);

test/Microsoft.Net.Http.Headers.Tests/MediaTypeHeaderValueTest.cs

@@ -64,6 +64,34 @@ namespace Microsoft.Net.Http.Headers
             Assert.Throws<ArgumentNullException>(() => mediaType.Parameters.Add(null));
         }
 
+        [Fact]
+        public void Clone_SimpleMediaType_Copied()
+        {
+            var mediaType0 = new MediaTypeHeaderValue("text/plain");
+            var mediaType1 = mediaType0.Clone();
+            Assert.NotSame(mediaType0, mediaType1);
+            Assert.Same(mediaType0.MediaType, mediaType1.MediaType);
+            Assert.NotSame(mediaType0.Parameters, mediaType1.Parameters);
+            Assert.Equal(mediaType0.Parameters.Count, mediaType1.Parameters.Count);
+        }
+
+        [Fact]
+        public void Clone_WithParameters_Copied()
+        {
+            var mediaType0 = new MediaTypeHeaderValue("text/plain");
+            mediaType0.Parameters.Add(new NameValueHeaderValue("name", "value"));
+            var mediaType1 = mediaType0.Clone();
+            Assert.NotSame(mediaType0, mediaType1);
+            Assert.Same(mediaType0.MediaType, mediaType1.MediaType);
+            Assert.NotSame(mediaType0.Parameters, mediaType1.Parameters);
+            Assert.Equal(mediaType0.Parameters.Count, mediaType1.Parameters.Count);
+            var pair0 = mediaType0.Parameters.First();
+            var pair1 = mediaType1.Parameters.First();
+            Assert.NotSame(pair0, pair1);
+            Assert.Same(pair0.Name, pair1.Name);
+            Assert.Same(pair0.Value, pair1.Value);
+        }
+
         [Fact]
         public void MediaType_SetAndGetMediaType_MatchExpectations()
         {

test/Microsoft.Net.Http.Headers.Tests/NameValueHeaderValueTest.cs

@@ -59,6 +59,32 @@ namespace Microsoft.Net.Http.Headers
             CheckValue("\"quoted string with quoted \\\" quote-pair\"");
         }
 
+        [Fact]
+        public void Clone_NameOnly_SuccesfullyCopied()
+        {
+            var pair0 = new NameValueHeaderValue("name");
+            var pair1 = pair0.Clone();
+            Assert.NotSame(pair0, pair1);
+            Assert.Same(pair0.Name, pair1.Name);
+            Assert.Null(pair0.Value);
+            Assert.Null(pair1.Value);
+        }
+
+        [Fact]
+        public void Clone_NameAndValue_SuccesfullyCopied()
+        {
+            var pair0 = new NameValueHeaderValue("name", "value");
+            var pair1 = pair0.Clone();
+            Assert.NotSame(pair0, pair1);
+            Assert.Same(pair0.Name, pair1.Name);
+            Assert.Same(pair0.Value, pair1.Value);
+
+            // Change one value and verify the other is unchanged.
+            pair1.Value = "othervalue";
+            Assert.Equal("value", pair0.Value);
+            Assert.Equal("othervalue", pair1.Value);
+        }
+
         [Fact]
         public void Value_CallSetterWithInvalidValues_Throw()
         {