Avoid string.Split allocations in ContentDispositionHeaderValue (#7468)

* Avoid string.Split allocations in ContentDispositionHeaderValue
* Add tests for changes in ContentDispositionHeaderValue

Author: jamesqo

src/System.Net.Http/src/System/Net/Http/Headers/ContentDispositionHeaderValue.cs

@@ -35,7 +35,7 @@ public string DispositionType
             get { return _dispositionType; }
             set
             {
-                CheckDispositionTypeFormat(value, "value");
+                CheckDispositionTypeFormat(value, nameof(value));
                 _dispositionType = value;
             }
         }
@@ -157,7 +157,7 @@ protected ContentDispositionHeaderValue(ContentDispositionHeaderValue source)
 
         public ContentDispositionHeaderValue(string dispositionType)
         {
-            CheckDispositionTypeFormat(dispositionType, "dispositionType");
+            CheckDispositionTypeFormat(dispositionType, nameof(dispositionType));
             _dispositionType = dispositionType;
         }
 
@@ -501,6 +501,7 @@ private bool TryDecodeMime(string input, out string output)
             {
                 return false;
             }
+            
             string[] parts = processedInput.Split('?');
             // "=, encodingName, encodingType, encodedData, ="
             if (parts.Length != 5 || parts[0] != "\"=" || parts[4] != "=\"" || parts[2].ToLowerInvariant() != "b")
@@ -564,18 +565,27 @@ private string Encode5987(string input)
         private bool TryDecode5987(string input, out string output)
         {
             output = null;
-            string[] parts = input.Split('\'');
-            if (parts.Length != 3)
+            
+            int quoteIndex = input.IndexOf('\'');
+            if (quoteIndex == -1)
             {
                 return false;
             }
+            
+            int lastQuoteIndex = input.LastIndexOf('\'');
+            if (quoteIndex == lastQuoteIndex || input.IndexOf('\'', quoteIndex + 1) != lastQuoteIndex)
+            {
+                return false;
+            }
+            
+            string encodingString = input.Substring(0, quoteIndex);
+            string dataString = input.Substring(lastQuoteIndex + 1, input.Length - (lastQuoteIndex + 1));
 
             StringBuilder decoded = new StringBuilder();
             try
             {
-                Encoding encoding = Encoding.GetEncoding(parts[0]);
+                Encoding encoding = Encoding.GetEncoding(encodingString);
 
-                string dataString = parts[2];
                 byte[] unescapedBytes = new byte[dataString.Length];
                 int unescapedBytesCount = 0;
                 for (int index = 0; index < dataString.Length; index++)

src/System.Net.Http/tests/UnitTests/Headers/ContentDispositionHeaderValueTest.cs

@@ -188,6 +188,22 @@ public void FileNameStar_AddNameParameterThenUseProperty_ParametersEntryIsOverwr
             contentDisposition.Parameters.Remove(fileNameStar);
             Assert.Null(contentDisposition.FileNameStar);
         }
+        
+        [Theory]
+        [InlineData("no_quotes")]
+        [InlineData("one'quote")]
+        [InlineData("'triple'quotes'")]
+        public void FileNameStar_NotTwoQuotes_IsNull(string value)
+        {
+            ContentDispositionHeaderValue contentDisposition = new ContentDispositionHeaderValue("inline");
+
+            // Note that uppercase letters are used. Comparison should happen case-insensitive.
+            NameValueHeaderValue fileNameStar = new NameValueHeaderValue("FILENAME*", value);
+            contentDisposition.Parameters.Add(fileNameStar);
+            Assert.Equal(1, contentDisposition.Parameters.Count);
+            Assert.Same(fileNameStar, contentDisposition.Parameters.First());
+            Assert.Null(contentDisposition.FileNameStar); // Decode failure
+        }
 
         [Fact]
         public void FileNameStar_NeedsEncoding_EncodedAndDecodedCorrectly()
@@ -213,8 +229,7 @@ public void FileNameStar_UnknownOrBadEncoding_PropertyFails()
             NameValueHeaderValue fileNameStar = new NameValueHeaderValue("FILENAME*", "utf-99'lang'File%CZName.bat");
             contentDisposition.Parameters.Add(fileNameStar);
             Assert.Equal(1, contentDisposition.Parameters.Count);
-            Assert.Equal("FILENAME*", contentDisposition.Parameters.First().Name);
-            Assert.Equal("utf-99'lang'File%CZName.bat", contentDisposition.Parameters.First().Value);
+            Assert.Same(fileNameStar, contentDisposition.Parameters.First());
             Assert.Null(contentDisposition.FileNameStar); // Decode failure
 
             contentDisposition.FileNameStar = "new_name";