Multi-targeting for netcoreapp3.0 and net461 to fix build-failures

Author: gfoidl

src/Shared/WebEncoders/WebEncoders.cs

@@ -190,36 +190,6 @@ public static int GetArraySizeRequiredToDecode(int count)
             return checked(count + numPaddingCharsToAdd);
         }
 
-        /// <summary>
-        /// Encodes <paramref name="input"/> using base64url encoding.
-        /// </summary>
-        /// <param name="input">The binary input to encode.</param>
-        /// <returns>The base64url-encoded form of <paramref name="input"/>.</returns>
-        public static string Base64UrlEncode(ReadOnlySpan<byte> input)
-        {
-            if (input.IsEmpty)
-            {
-                return string.Empty;
-            }
-
-            int bufferSize = GetArraySizeRequiredToEncode(input.Length);
-
-            char[] bufferToReturnToPool = null;
-            Span<char> buffer = bufferSize <= 128
-                ? stackalloc char[bufferSize]
-                : bufferToReturnToPool = ArrayPool<char>.Shared.Rent(bufferSize);
-
-            var numBase64Chars = Base64UrlEncode(input, buffer);
-            var base64Url = new string(buffer.Slice(0, numBase64Chars));
-
-            if (bufferToReturnToPool != null)
-            {
-                ArrayPool<char>.Shared.Return(bufferToReturnToPool);
-            }
-
-            return base64Url;
-        }
-
         /// <summary>
         /// Encodes <paramref name="input"/> using base64url encoding.
         /// </summary>
@@ -251,7 +221,20 @@ public static string Base64UrlEncode(byte[] input, int offset, int count)
 
             ValidateParameters(input.Length, nameof(input), offset, count);
 
+#if NETCOREAPP3_0
             return Base64UrlEncode(input.AsSpan(offset, count));
+#else
+            // Special-case empty input
+            if (count == 0)
+            {
+                return string.Empty;
+            }
+
+            var buffer = new char[GetArraySizeRequiredToEncode(count)];
+            var numBase64Chars = Base64UrlEncode(input, offset, buffer, outputOffset: 0, count: count);
+
+            return new string(buffer, startIndex: 0, length: numBase64Chars);
+#endif
         }
 
         /// <summary>
@@ -302,7 +285,41 @@ public static int Base64UrlEncode(byte[] input, int offset, char[] output, int o
                     nameof(count));
             }
 
+#if NETCOREAPP3_0
             return Base64UrlEncode(input.AsSpan(offset, count), output.AsSpan(outputOffset));
+#else
+            // Special-case empty input.
+            if (count == 0)
+            {
+                return 0;
+            }
+
+            // Use base64url encoding with no padding characters. See RFC 4648, Sec. 5.
+
+            // Start with default Base64 encoding.
+            var numBase64Chars = Convert.ToBase64CharArray(input, offset, count, output, outputOffset);
+
+            // Fix up '+' -> '-' and '/' -> '_'. Drop padding characters.
+            for (var i = outputOffset; i - outputOffset < numBase64Chars; i++)
+            {
+                var ch = output[i];
+                if (ch == '+')
+                {
+                    output[i] = '-';
+                }
+                else if (ch == '/')
+                {
+                    output[i] = '_';
+                }
+                else if (ch == '=')
+                {
+                    // We've reached a padding character; truncate the remainder.
+                    return i - outputOffset;
+                }
+            }
+
+            return numBase64Chars;
+#endif
         }
 
         /// <summary>
@@ -319,6 +336,37 @@ public static int GetArraySizeRequiredToEncode(int count)
             return checked(numWholeOrPartialInputBlocks * 4);
         }
 
+#if NETCOREAPP3_0
+        /// <summary>
+        /// Encodes <paramref name="input"/> using base64url encoding.
+        /// </summary>
+        /// <param name="input">The binary input to encode.</param>
+        /// <returns>The base64url-encoded form of <paramref name="input"/>.</returns>
+        public static string Base64UrlEncode(ReadOnlySpan<byte> input)
+        {
+            if (input.IsEmpty)
+            {
+                return string.Empty;
+            }
+
+            int bufferSize = GetArraySizeRequiredToEncode(input.Length);
+
+            char[] bufferToReturnToPool = null;
+            Span<char> buffer = bufferSize <= 128
+                ? stackalloc char[bufferSize]
+                : bufferToReturnToPool = ArrayPool<char>.Shared.Rent(bufferSize);
+
+            var numBase64Chars = Base64UrlEncode(input, buffer);
+            var base64Url = new string(buffer.Slice(0, numBase64Chars));
+
+            if (bufferToReturnToPool != null)
+            {
+                ArrayPool<char>.Shared.Return(bufferToReturnToPool);
+            }
+
+            return base64Url;
+        }
+
         private static int Base64UrlEncode(ReadOnlySpan<byte> input, Span<char> output)
         {
             Debug.Assert(output.Length >= GetArraySizeRequiredToEncode(input.Length));
@@ -353,6 +401,7 @@ private static int Base64UrlEncode(ReadOnlySpan<byte> input, Span<char> output)
 
             return charsWritten;
         }
+#endif
 
         private static int GetNumBase64PaddingCharsInString(string str)
         {