Add Base64Url fuzzer (dotnet#106509)

* Add Base64Url fuzzer

* Update src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/Base64UrlFuzzer.cs

Co-authored-by: Weihan Li <7604648+WeihanLi@users.noreply.github.com>

* Update src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/Base64UrlFuzzer.cs

Co-authored-by: Stephen Toub <stoub@microsoft.com>

---------

Co-authored-by: Weihan Li <7604648+WeihanLi@users.noreply.github.com>
Co-authored-by: Stephen Toub <stoub@microsoft.com>

eng/pipelines/libraries/fuzzing/deploy-to-onefuzz.yml

@@ -73,6 +73,14 @@ extends:
             SYSTEM_ACCESSTOKEN: $(System.AccessToken)
           displayName: Send Base64Fuzzer to OneFuzz
 
+        - task: onefuzz-task@0
+          inputs:
+            onefuzzOSes: 'Windows'
+          env:
+            onefuzzDropDirectory: $(fuzzerProject)/deployment/Base64UrlFuzzer
+            SYSTEM_ACCESSTOKEN: $(System.AccessToken)
+          displayName: Send Base64UrlFuzzer to OneFuzz
+
         - task: onefuzz-task@0
           inputs:
             onefuzzOSes: 'Windows'

src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/Base64UrlFuzzer.cs

@@ -0,0 +1,136 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Buffers;
+using System.Buffers.Text;
+using System.Formats.Asn1;
+using System.Reflection;
+
+namespace DotnetFuzzing.Fuzzers
+{
+    internal sealed class Base64UrlFuzzer : IFuzzer
+    {
+        public string[] TargetAssemblies => [];
+
+        public string[] TargetCoreLibPrefixes => ["System.Buffers.Text"];
+
+        public void FuzzTarget(ReadOnlySpan<byte> bytes)
+        {
+            int encodedLength = Base64Url.GetEncodedLength(bytes.Length);
+            int maxDecodedLength = Base64Url.GetMaxDecodedLength(encodedLength);
+
+            using PooledBoundedMemory<byte> inputPoisoned = PooledBoundedMemory<byte>.Rent(bytes, PoisonPagePlacement.After);
+            using PooledBoundedMemory<char> destPoisoned = PooledBoundedMemory<char>.Rent(encodedLength, PoisonPagePlacement.After);
+            using PooledBoundedMemory<byte> decoderDestPoisoned = PooledBoundedMemory<byte>.Rent(maxDecodedLength, PoisonPagePlacement.After);
+
+            Span<byte> input = inputPoisoned.Span;
+            Span<char> encoderDest = destPoisoned.Span;
+            Span<byte> decoderDest = decoderDestPoisoned.Span;
+
+            { // IsFinalBlock = true
+                OperationStatus status = Base64Url.EncodeToChars(input, encoderDest, out int bytesConsumed, out int bytesEncoded); 
+
+                Assert.Equal(OperationStatus.Done, status);
+                Assert.Equal(bytes.Length, bytesConsumed);
+                Assert.Equal(true, encodedLength == bytesEncoded);
+
+                string encodedString = Base64Url.EncodeToString(input);
+                Assert.Equal(encodedString, new string(encoderDest));
+
+                status = Base64Url.DecodeFromChars(encoderDest, decoderDest, out int bytesRead, out int bytesDecoded);
+
+                Assert.Equal(OperationStatus.Done, status);
+                Assert.Equal(bytes.Length, bytesDecoded);
+                Assert.Equal(bytesEncoded, bytesRead);
+                Assert.SequenceEqual(bytes, decoderDest.Slice(0, bytesDecoded));
+            }
+
+            { // IsFinalBlock = false
+                encoderDest.Clear();
+                decoderDest.Clear();
+                OperationStatus status = Base64Url.EncodeToChars(input, encoderDest, out int bytesConsumed, out int bytesEncoded, isFinalBlock: false);
+                Span<char> decodeInput = encoderDest.Slice(0, bytesEncoded);
+
+                if (bytes.Length % 3 == 0)
+                {
+                    Assert.Equal(OperationStatus.Done, status);
+                    Assert.Equal(bytes.Length, bytesConsumed);
+                    Assert.Equal(true, encodedLength == bytesEncoded);
+
+                    status = Base64Url.DecodeFromChars(decodeInput, decoderDest, out int bytesRead, out int bytesDecoded, isFinalBlock: false);
+
+                    Assert.Equal(OperationStatus.Done, status);
+                    Assert.Equal(bytes.Length, bytesDecoded);
+                    Assert.Equal(bytesEncoded, bytesRead);
+                    Assert.SequenceEqual(bytes, decoderDest.Slice(0, bytesDecoded));
+                }
+                else
+                {
+                    Assert.Equal(OperationStatus.NeedMoreData, status);
+                    Assert.Equal(true, input.Length / 3 * 4 == bytesEncoded);
+
+                    status = Base64Url.DecodeFromChars(decodeInput, decoderDest, out int bytesRead, out int bytesDecoded, isFinalBlock: false);
+
+                    if (decodeInput.Length % 4 == 0)
+                    {
+                        Assert.Equal(OperationStatus.Done, status);
+                        Assert.Equal(bytesConsumed, bytesDecoded);
+                        Assert.Equal(bytesEncoded, bytesRead);
+                    }
+                    else
+                    {
+                        Assert.Equal(OperationStatus.NeedMoreData, status);
+                    }
+
+                    Assert.SequenceEqual(bytes.Slice(0, bytesDecoded), decoderDest.Slice(0, bytesDecoded));
+                }
+            }
+
+            { // Encode / decode in place
+                using PooledBoundedMemory<byte> destPoisoned2 = PooledBoundedMemory<byte>.Rent(encodedLength, PoisonPagePlacement.After);
+                Span<byte> tryEncode = destPoisoned2.Span;
+                input.CopyTo(tryEncode);
+
+                Assert.Equal(true, Base64Url.TryEncodeToUtf8InPlace(tryEncode, input.Length, out int bytesEncoded));
+                Assert.Equal(encodedLength, bytesEncoded);
+
+                int bytesDecoded = Base64Url.DecodeFromUtf8InPlace(tryEncode);
+
+                Assert.Equal(bytes.Length, bytesDecoded);
+                Assert.SequenceEqual(bytes, tryEncode.Slice(0, bytesDecoded));
+            }
+
+            { // Decode the random input directly, Assert IsValid result matches with decoded result
+                decoderDest.Clear();
+                if (Base64Url.IsValid(input, out int decodedLength))
+                {
+                    maxDecodedLength = Base64Url.GetMaxDecodedLength(input.Length);
+                    OperationStatus status = Base64Url.DecodeFromUtf8(input, decoderDest, out int bytesRead, out int bytesDecoded);
+                    Assert.Equal(OperationStatus.Done, status);
+                    Assert.Equal(input.Length, bytesRead);
+                    Assert.Equal(decodedLength, bytesDecoded);
+                    Assert.Equal(true, maxDecodedLength >= bytesDecoded);
+
+                    Span<byte> tryDecode = new byte[maxDecodedLength];
+                    Assert.Equal(true, Base64Url.TryDecodeFromUtf8(input, tryDecode, out bytesDecoded));
+                    Assert.Equal(decodedLength, bytesDecoded);
+                    Assert.SequenceEqual<byte>(tryDecode.Slice(0, bytesDecoded), decoderDest.Slice(0, bytesDecoded));
+
+                    int decoded = Base64Url.DecodeFromUtf8InPlace(input);
+                    Assert.Equal(OperationStatus.Done, status);
+                    Assert.Equal(bytesDecoded, decoded);
+                    Assert.SequenceEqual<byte>(input.Slice(0, decoded), decoderDest.Slice(0, bytesDecoded));
+                }
+                else
+                {
+                    Assert.Equal(OperationStatus.InvalidData, Base64Url.DecodeFromUtf8(input, decoderDest, out int _, out int bytesDecoded));
+                    try
+                    {
+                        Assert.Equal(0, Base64Url.DecodeFromUtf8InPlace(input));
+                    }
+                    catch (FormatException) { /* DecodeFromUtf8InPlace would throw FormatException for InvalidData*/ }
+                }
+            }
+        }
+    }
+}