Follow-up feedback from dotnet#54186.

CodeBlanch · Jul 16, 2021 · 5c4d4fd · 5c4d4fd
1 parent 62fa1f8
commit 5c4d4fd
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Showing 25 changed files with 89 additions and 68 deletions.
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/JsonConstants.cs b/src/libraries/System.Text.Json/src/System/Text/Json/JsonConstants.cs
@@ -95,6 +95,8 @@ internal static class JsonConstants
         public const int MinimumDateTimeParseLength = 10; // YYYY-MM-DD
         public const int MaximumEscapedDateTimeOffsetParseLength = MaxExpansionFactorWhileEscaping * MaximumDateTimeOffsetParseLength;
 
+        public const int MaximumLiteralLength = 5; // Must be able to fit null, true, & false.
+
         // Encoding Helpers
         public const char HighSurrogateStart = '\ud800';
         public const char HighSurrogateEnd = '\udbff';

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.Escaping.cs b/src/libraries/System.Text.Json/src/System/Text/Json/JsonHelpers.Escaping.cs
@@ -38,7 +38,7 @@ public static byte[] GetEscapedPropertyNameSection(ReadOnlySpan<byte> utf8Value,
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8Value.Length, firstEscapeIndexVal);
 
             Span<byte> escapedValue = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (valueArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8Value, escapedValue, firstEscapeIndexVal, encoder, out int written);
@@ -66,7 +66,7 @@ public static byte[] GetEscapedPropertyNameSection(ReadOnlySpan<byte> utf8Value,
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8Value.Length, firstEscapeIndexVal);
 
             Span<byte> escapedValue = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (valueArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8Value, escapedValue, firstEscapeIndexVal, encoder, out int written);

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.Unescaping.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.Unescaping.cs
@@ -15,7 +15,7 @@ public static bool TryGetUnescapedBase64Bytes(ReadOnlySpan<byte> utf8Source, int
             byte[]? unescapedArray = null;
 
             Span<byte> utf8Unescaped = utf8Source.Length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[utf8Source.Length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, utf8Source.Length) :
                 (unescapedArray = ArrayPool<byte>.Shared.Rent(utf8Source.Length));
 
             Unescape(utf8Source, utf8Unescaped, idx, out int written);
@@ -45,7 +45,7 @@ public static string GetUnescapedString(ReadOnlySpan<byte> utf8Source, int idx)
             byte[]? pooledName = null;
 
             Span<byte> utf8Unescaped = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (pooledName = ArrayPool<byte>.Shared.Rent(length));
 
             Unescape(utf8Source, utf8Unescaped, idx, out int written);
@@ -72,7 +72,7 @@ public static ReadOnlySpan<byte> GetUnescapedSpan(ReadOnlySpan<byte> utf8Source,
             byte[]? pooledName = null;
 
             Span<byte> utf8Unescaped = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (pooledName = ArrayPool<byte>.Shared.Rent(length));
 
             Unescape(utf8Source, utf8Unescaped, idx, out int written);
@@ -97,7 +97,7 @@ public static bool UnescapeAndCompare(ReadOnlySpan<byte> utf8Source, ReadOnlySpa
             byte[]? unescapedArray = null;
 
             Span<byte> utf8Unescaped = utf8Source.Length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[utf8Source.Length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, utf8Source.Length) :
                 (unescapedArray = ArrayPool<byte>.Shared.Rent(utf8Source.Length));
 
             Unescape(utf8Source, utf8Unescaped, 0, out int written);
@@ -128,11 +128,11 @@ public static bool UnescapeAndCompare(ReadOnlySequence<byte> utf8Source, ReadOnl
             int length = checked((int)utf8Source.Length);
 
             Span<byte> utf8Unescaped = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (unescapedArray = ArrayPool<byte>.Shared.Rent(length));
 
             Span<byte> utf8Escaped = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (escapedArray = ArrayPool<byte>.Shared.Rent(length));
 
             utf8Source.CopyTo(utf8Escaped);
@@ -175,7 +175,7 @@ public static bool TryDecodeBase64(ReadOnlySpan<byte> utf8Unescaped, [NotNullWhe
             byte[]? pooledArray = null;
 
             Span<byte> byteSpan = utf8Unescaped.Length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[utf8Unescaped.Length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, utf8Unescaped.Length) :
                 (pooledArray = ArrayPool<byte>.Shared.Rent(utf8Unescaped.Length));
 
             OperationStatus status = Base64.DecodeFromUtf8(utf8Unescaped, byteSpan, out int bytesConsumed, out int bytesWritten);

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Reader/JsonReaderHelper.cs
@@ -252,7 +252,7 @@ public static bool TryGetEscapedDateTime(ReadOnlySpan<byte> source, out DateTime
             Debug.Assert(backslash != -1);
 
             Debug.Assert(source.Length <= JsonConstants.MaximumEscapedDateTimeOffsetParseLength);
-            Span<byte> sourceUnescaped = stackalloc byte[source.Length];
+            Span<byte> sourceUnescaped = (stackalloc byte[JsonConstants.MaximumEscapedDateTimeOffsetParseLength]).Slice(0, source.Length);
 
             Unescape(source, sourceUnescaped, backslash, out int written);
             Debug.Assert(written > 0);
@@ -277,7 +277,7 @@ public static bool TryGetEscapedDateTimeOffset(ReadOnlySpan<byte> source, out Da
             Debug.Assert(backslash != -1);
 
             Debug.Assert(source.Length <= JsonConstants.MaximumEscapedDateTimeOffsetParseLength);
-            Span<byte> sourceUnescaped = stackalloc byte[source.Length];
+            Span<byte> sourceUnescaped = (stackalloc byte[JsonConstants.MaximumEscapedDateTimeOffsetParseLength]).Slice(0, source.Length);
 
             Unescape(source, sourceUnescaped, backslash, out int written);
             Debug.Assert(written > 0);
@@ -303,7 +303,7 @@ public static bool TryGetEscapedGuid(ReadOnlySpan<byte> source, out Guid value)
             int idx = source.IndexOf(JsonConstants.BackSlash);
             Debug.Assert(idx != -1);
 
-            Span<byte> utf8Unescaped = stackalloc byte[source.Length];
+            Span<byte> utf8Unescaped = (stackalloc byte[JsonConstants.MaximumEscapedGuidLength]).Slice(0, source.Length);
 
             Unescape(source, utf8Unescaped, idx, out int written);
             Debug.Assert(written > 0);

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.MultiSegment.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.MultiSegment.cs
@@ -540,9 +540,9 @@ private bool ConsumeLiteralMultiSegment(ReadOnlySpan<byte> literal, JsonTokenTyp
 
         private bool CheckLiteralMultiSegment(ReadOnlySpan<byte> span, ReadOnlySpan<byte> literal, out int consumed)
         {
-            Debug.Assert(span.Length > 0 && span[0] == literal[0]);
+            Debug.Assert(span.Length > 0 && span[0] == literal[0] && literal.Length <= JsonConstants.MaximumLiteralLength);
 
-            Span<byte> readSoFar = stackalloc byte[literal.Length];
+            Span<byte> readSoFar = (stackalloc byte[JsonConstants.MaximumLiteralLength]).Slice(0, literal.Length);
             int written = 0;
 
             long prevTotalConsumed = _totalConsumed;

diff --git a/...System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/TimeSpanConverter.cs b/...System.Text.Json/src/System/Text/Json/Serialization/Converters/Value/TimeSpanConverter.cs
@@ -54,7 +54,7 @@ public override TimeSpan Read(ref Utf8JsonReader reader, Type typeToConvert, Jso
                 int backslash = source.IndexOf(JsonConstants.BackSlash);
                 Debug.Assert(backslash != -1);
 
-                Span<byte> sourceUnescaped = stackalloc byte[source.Length];
+                Span<byte> sourceUnescaped = (stackalloc byte[MaximumEscapedTimeSpanFormatLength]).Slice(0, source.Length);
 
                 JsonReaderHelper.Unescape(source, sourceUnescaped, backslash, out int written);
                 Debug.Assert(written > 0);

diff --git a/...ries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Bytes.cs b/...ries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Bytes.cs
@@ -140,7 +140,7 @@ private void WriteBase64EscapeProperty(ReadOnlySpan<char> propertyName, ReadOnly
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -163,7 +163,7 @@ private void WriteBase64EscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Read
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...s/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTime.cs b/...s/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTime.cs
@@ -145,7 +145,7 @@ private void WriteStringEscapeProperty(ReadOnlySpan<char> propertyName, DateTime
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -168,7 +168,7 @@ private void WriteStringEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Date
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...em.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTimeOffset.cs b/...em.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.DateTimeOffset.cs
@@ -144,7 +144,7 @@ private void WriteStringEscapeProperty(ReadOnlySpan<char> propertyName, DateTime
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -167,7 +167,7 @@ private void WriteStringEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Date
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...es/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Decimal.cs b/...es/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Decimal.cs
@@ -144,7 +144,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<char> propertyName, decimal
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -167,7 +167,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, deci
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...ies/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Double.cs b/...ies/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Double.cs
@@ -148,7 +148,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<char> propertyName, double v
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -171,7 +171,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, doub
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...ries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Float.cs b/...ries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Float.cs
@@ -148,7 +148,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<char> propertyName, float va
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -171,7 +171,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, floa
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...m.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.FormattedNumber.cs b/...m.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.FormattedNumber.cs
@@ -121,7 +121,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<char> propertyName, ReadOnly
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -144,7 +144,7 @@ private void WriteNumberEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Read
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...aries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Guid.cs b/...aries/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Guid.cs
@@ -144,7 +144,7 @@ private void WriteStringEscapeProperty(ReadOnlySpan<char> propertyName, Guid val
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -167,7 +167,7 @@ private void WriteStringEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Guid
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);

diff --git a/...es/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Literal.cs b/...es/System.Text.Json/src/System/Text/Json/Writer/Utf8JsonWriter.WriteProperties.Literal.cs
@@ -260,7 +260,7 @@ private void WriteLiteralEscapeProperty(ReadOnlySpan<char> propertyName, ReadOnl
             int length = JsonWriterHelper.GetMaxEscapedLength(propertyName.Length, firstEscapeIndexProp);
 
             Span<char> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc char[length] :
+                (stackalloc char[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<char>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(propertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);
@@ -283,7 +283,7 @@ private void WriteLiteralEscapeProperty(ReadOnlySpan<byte> utf8PropertyName, Rea
             int length = JsonWriterHelper.GetMaxEscapedLength(utf8PropertyName.Length, firstEscapeIndexProp);
 
             Span<byte> escapedPropertyName = length <= JsonConstants.StackallocThreshold ?
-                stackalloc byte[length] :
+                (stackalloc byte[JsonConstants.StackallocThreshold]).Slice(0, length) :
                 (propertyArray = ArrayPool<byte>.Shared.Rent(length));
 
             JsonWriterHelper.EscapeString(utf8PropertyName, escapedPropertyName, firstEscapeIndexProp, _options.Encoder, out int written);