Fix netcore WebClient.UploadValuesAsync() UrlEncode behavior

src/System.Net.WebClient/src/System/Net/WebClient.cs

@@ -588,9 +588,9 @@ private byte[] GetValuesToUpload(NameValueCollection data)
             foreach (string name in data.AllKeys)
             {
                 values.Append(delimiter);
-                values.Append(WebUtility.UrlEncode(name));
+                values.Append(UrlEncode(name));
                 values.Append('=');
-                values.Append(WebUtility.UrlEncode(data[name]));
+                values.Append(UrlEncode(data[name]));
                 delimiter = "&";
             }
 
@@ -1176,6 +1176,101 @@ private string MapToDefaultMethod(Uri address)
                 "STOR" :
                 "POST";
         }
+
+        private static string UrlEncode(string str)
+        {
+            if (str == null)
+                return null;
+            byte[] bytes = Encoding.UTF8.GetBytes(str);
+            return Encoding.ASCII.GetString(UrlEncodeBytesToBytesInternal(bytes, 0, bytes.Length, false));
+        }
+
+        private static byte[] UrlEncodeBytesToBytesInternal(byte[] bytes, int offset, int count, bool alwaysCreateReturnValue)
+        {
+            int cSpaces = 0;
+            int cUnsafe = 0;
+
+            // Count them first.
+            for (int i = 0; i < count; i++)
+            {
+                char ch = (char) bytes[offset + i];
+
+                if (ch == ' ')
+                {
+                    cSpaces++;
+                }
+                else if (!IsSafe(ch))
+                {
+                    cUnsafe++;
+                }
+            }
+
+            // If nothing to expand.
+            if (!alwaysCreateReturnValue && cSpaces == 0 && cUnsafe == 0)
+                return bytes;
+
+            // Expand not 'safe' characters into %XX, spaces to +.
+            byte[] expandedBytes = new byte[count + cUnsafe * 2];
+            int pos = 0;
+
+            for (int i = 0; i < count; i++)
+            {
+                byte b = bytes[offset+i];
+                char ch = (char) b;
+
+                if (IsSafe(ch))
+                {
+                    expandedBytes[pos++] = b;
+                }
+                else if (ch == ' ')
+                {
+                    expandedBytes[pos++] = (byte) '+';
+                }
+                else
+                {
+                    expandedBytes[pos++] = (byte) '%';
+                    expandedBytes[pos++] = (byte) IntToHex((b >> 4) & 0xf);
+                    expandedBytes[pos++] = (byte) IntToHex(b & 0x0f);
+                }
+            }
+
+            return expandedBytes;
+        }
+
+        private static char IntToHex(int n)
+        {
+            Debug.Assert(n < 0x10);
+
+            if (n <= 9)
+            {
+                return(char)(n + (int)'0');
+            }
+
+            return(char)(n - 10 + (int)'a');
+        }
+
+        private static bool IsSafe(char ch)
+        {
+            if (ch >= 'a' && ch <= 'z' || ch >= 'A' && ch <= 'Z' || ch >= '0' && ch <= '9')
+            {
+                return true;
+            }
+
+            switch (ch)
+            {
+                case '-':
+                case '_':
+                case '.':
+                case '!':
+                case '*':
+                case '\'':
+                case '(':
+                case ')':
+                    return true;
+            }
+
+            return false;
+        }
 
         private void InvokeOperationCompleted(AsyncOperation asyncOp, SendOrPostCallback callback, AsyncCompletedEventArgs eventArgs)
         {

src/System.Net.WebClient/tests/WebClientTest.cs

@@ -485,6 +485,13 @@ public abstract class WebClientTestBase
             "The Slings and Arrows of outrageous Fortune," +
             "Or to take Arms against a Sea of troubles," +
             "And by opposing end them:";
+
+        const string ExpectedTextAfterUrlEncode = 
+            "To+be%2c+or+not+to+be%2c+that+is+the+question%3a" + 
+            "Whether+'tis+Nobler+in+the+mind+to+suffer" +
+            "The+Slings+and+Arrows+of+outrageous+Fortune%2c" +
+            "Or+to+take+Arms+against+a+Sea+of+troubles%2c" +
+            "And+by+opposing+end+them%3a";
 
         protected abstract bool IsAsync { get; }
 
@@ -688,15 +695,14 @@ public async Task UploadString_Success(Uri echoServer)
             Assert.Contains(ExpectedText, result);
         }
 
-        [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework, "dotnet/corefx #18674")] // Difference in behavior.
         [OuterLoop("Networking test talking to remote server: issue #11345")]
         [Theory]
         [MemberData(nameof(EchoServers))]
         public async Task UploadValues_Success(Uri echoServer)
         {
             var wc = new WebClient();
             byte[] result = await UploadValuesAsync(wc, echoServer.ToString(), new NameValueCollection() { { "Data", ExpectedText } });
-            Assert.Contains(WebUtility.UrlEncode(ExpectedText), Encoding.UTF8.GetString(result));
+            Assert.Contains(ExpectedTextAfterUrlEncode, Encoding.UTF8.GetString(result));
         }
     }