CSHARP-4853: "Thread static buffer is already in use." error after bad utf8 string write. (#1219)

Author: adelinowona

src/MongoDB.Bson/IO/EncodingHelper.cs

@@ -63,10 +63,17 @@ public static DisposableSegment GetBytesUsingThreadStaticBuffer(this Encoding en
             var maxSize = encoding.GetMaxByteCount(length);
             var rentedBuffer = ThreadStaticBuffer.RentBuffer(maxSize);
 
-            var size = encoding.GetBytes(value, 0, length, rentedBuffer.Bytes, 0);
-            var segment = new ArraySegment<byte>(rentedBuffer.Bytes, 0, size);
-
-            return new DisposableSegment(rentedBuffer, segment);
+            try
+            {
+                var size = encoding.GetBytes(value, 0, length, rentedBuffer.Bytes, 0);
+                var segment = new ArraySegment<byte>(rentedBuffer.Bytes, 0, size);
+                return new DisposableSegment(rentedBuffer, segment);
+            }
+            catch
+            {
+                rentedBuffer.Dispose();
+                throw;
+            }
         }
     }
 }

tests/MongoDB.Bson.Tests/IO/EncodingHelperTests.cs

@@ -33,6 +33,19 @@ public void GetBytesUsingThreadStaticBuffer_should_throw_when_encoding_is_null()
 
             var e = exception.Should().BeOfType<ArgumentNullException>().Subject;
             e.ParamName.Should().Be("encoding");
+
+            AssertGetBytesUsingThreadStaticBufferWorks();
+        }
+
+        [Fact]
+        public void GetBytesUsingThreadStaticBuffer_should_throw_when_string_is_invalid()
+        {
+            const string invalidUtf8String = "\uD801";
+
+            var exception = Record.Exception(() => EncodingHelper.GetBytesUsingThreadStaticBuffer(Utf8Encodings.Strict, invalidUtf8String));
+            exception.Should().BeOfType<EncoderFallbackException>();
+
+            AssertGetBytesUsingThreadStaticBufferWorks();
         }
 
         [Fact]
@@ -42,6 +55,8 @@ public void GetBytesUsingThreadStaticBuffer_should_throw_when_value_is_null()
 
             var e = exception.Should().BeOfType<ArgumentNullException>().Subject;
             e.ParamName.Should().Be("value");
+
+            AssertGetBytesUsingThreadStaticBufferWorks();
         }
 
         [Fact]
@@ -111,6 +126,12 @@ public void GetBytesUsingThreadStaticBuffer_should_return_expected_result_when_m
         }
 
         // private methods
+        private void AssertGetBytesUsingThreadStaticBufferWorks()
+        {
+            using var segment = EncodingHelper.GetBytesUsingThreadStaticBuffer(Utf8Encodings.Strict, "Apples");
+            segment.Segment.Array.Length.Should().BeGreaterThan(0);
+        }
+
         private string GetString(int length) =>
             new string(Enumerable.Range(0, length).Select(i => (char)('a' + i % 26)).ToArray());
     }