Add ReadOnlySequence support to Utf8JsonReader with unit tests

src/System.Text.Json/ref/System.Text.Json.cs

@@ -32,6 +32,7 @@ public partial struct JsonReaderState
         public long BytesConsumed { get { throw null; } }
         public int MaxDepth { get { throw null; } }
         public System.Text.Json.JsonReaderOptions Options { get { throw null; } }
+        public System.SequencePosition Position { get { throw null; } }
     }
     public enum JsonTokenType : byte
     {
@@ -51,11 +52,15 @@ public enum JsonTokenType : byte
     public ref partial struct Utf8JsonReader
     {
         private object _dummy;
+        public Utf8JsonReader(in System.Buffers.ReadOnlySequence<byte> jsonData, bool isFinalBlock, System.Text.Json.JsonReaderState state) { throw null; }
         public Utf8JsonReader(System.ReadOnlySpan<byte> jsonData, bool isFinalBlock, System.Text.Json.JsonReaderState state) { throw null; }
         public long BytesConsumed { get { throw null; } }
         public int CurrentDepth { get { throw null; } }
         public System.Text.Json.JsonReaderState CurrentState { get { throw null; } }
+        public bool HasValueSequence { get { throw null; } }
+        public System.SequencePosition Position { get { throw null; } }
         public System.Text.Json.JsonTokenType TokenType { get { throw null; } }
+        public System.Buffers.ReadOnlySequence<byte> ValueSequence { get { throw null; } }
         public System.ReadOnlySpan<byte> ValueSpan { get { throw null; } }
         public bool GetBooleanValue() { throw null; }
         public string GetStringValue() { throw null; }

src/System.Text.Json/src/Resources/Strings.resx

@@ -165,12 +165,18 @@
   <data name="InvalidCast" xml:space="preserve">
     <value>Cannot get the value of a token type '{0}' as a {1}.</value>
   </data>
+  <data name="InvalidCharacterAfterEscapeWithinString" xml:space="preserve">
+    <value>'{0}' is an invalid escapable character within a JSON string. The string should be correctly escaped.</value>
+  </data>
   <data name="InvalidCharacterWithinString" xml:space="preserve">
     <value>'{0}' is invalid within a JSON string. The string should be correctly escaped.</value>
   </data>
   <data name="InvalidEndOfJsonNonPrimitive" xml:space="preserve">
     <value>'{0}' is an invalid token type for the end of the JSON payload. Expected either 'EndArray' or 'EndObject'.</value>
   </data>
+  <data name="InvalidHexCharacterWithinString" xml:space="preserve">
+    <value>'{0}' is not a hex digit following '\u' within a JSON string. The string should be correctly escaped.</value>
+  </data>
   <data name="MaxDepthMustBePositive" xml:space="preserve">
     <value>Max depth must be positive.</value>
   </data>
@@ -181,10 +187,10 @@
     <value>CurrentDepth ({0}) is larger than the maximum configured depth of {1}. Cannot read next JSON object.</value>
   </data>
   <data name="RequiredDigitNotFoundAfterDecimal" xml:space="preserve">
-    <value>'{0}' is invalid within a number immediately after a decimal point ('.'). Expected a digit ('0'-'9').</value>
+    <value>'{0}' is invalid within a number, immediately after a decimal point ('.'). Expected a digit ('0'-'9').</value>
   </data>
   <data name="RequiredDigitNotFoundAfterSign" xml:space="preserve">
-    <value>'{0}' is invalid within a number immediately after a sign character ('+' or '-'). Expected a digit ('0'-'9').</value>
+    <value>'{0}' is invalid within a number, immediately after a sign character ('+' or '-'). Expected a digit ('0'-'9').</value>
   </data>
   <data name="RequiredDigitNotFoundEndOfData" xml:space="preserve">
     <value>Expected a digit ('0'-'9'), but instead reached end of data.</value>

src/System.Text.Json/src/System.Text.Json.csproj

@@ -19,6 +19,7 @@
     <Compile Include="System\Text\Json\JsonTokenType.cs" />
     <Compile Include="System\Text\Json\ThrowHelper.cs" />
     <Compile Include="System\Text\Json\Utf8JsonReader.cs" />
+    <Compile Include="System\Text\Json\Utf8JsonReader.MultiSegment.cs" />
     <Compile Include="System\Text\Json\Utf8JsonReader.TryGet.cs" />
   </ItemGroup>
   <ItemGroup>

src/System.Text.Json/src/System/Text/Json/JsonReaderHelper.cs

@@ -50,7 +50,7 @@ public static bool IsHexDigit(byte nextByte) =>
         // Borrowed and modified from SpanHelpers.Byte:
         // https://github.com/dotnet/corefx/blob/fc169cddedb6820aaabbdb8b7bece2a3df0fd1a5/src/Common/src/CoreLib/System/SpanHelpers.Byte.cs#L473-L604
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public static int IndexOfQuoteOrAnyControlOrBaskSlash(this ReadOnlySpan<byte> span)
+        public static int IndexOfQuoteOrAnyControlOrBackSlash(this ReadOnlySpan<byte> span)
         {
             return IndexOfOrLessThan(
                     ref MemoryMarshal.GetReference(span),

src/System.Text.Json/src/System/Text/Json/JsonReaderState.cs

@@ -26,13 +26,21 @@ public struct JsonReaderState
         internal JsonTokenType _previousTokenType;
         internal JsonReaderOptions _readerOptions;
         internal BitStack _bitStack;
+        internal SequencePosition _sequencePosition;
 
         /// <summary>
         /// Returns the total amount of bytes consumed by the <see cref="Utf8JsonReader"/> so far
         /// for the given UTF-8 encoded input text.
         /// </summary>
         public long BytesConsumed => _bytesConsumed;
 
+        /// <summary>
+        /// Returns the current <see cref="SequencePosition"/> within the provided UTF-8 encoded
+        /// input ReadOnlySequence&lt;byte&gt;. If the <see cref="Utf8JsonReader"/> was constructed
+        /// with a ReadOnlySpan&lt;byte&gt; instead, this will always return a default <see cref="SequencePosition"/>.
+        /// </summary>
+        public SequencePosition Position => _sequencePosition;
+
         /// <summary>
         /// Constructs a new <see cref="JsonReaderState"/> instance.
         /// </summary>
@@ -68,6 +76,8 @@ public JsonReaderState(int maxDepth = DefaultMaxDepth, JsonReaderOptions options
             // Only allocate if the user reads a JSON payload beyond the depth that the _allocationFreeContainer can handle.
             // This way we avoid allocations in the common, default cases, and allocate lazily.
             _bitStack = default;
+
+            _sequencePosition = default;
         }
 
         /// <summary>

src/System.Text.Json/src/System/Text/Json/ThrowHelper.cs

@@ -47,7 +47,7 @@ public static void ThrowJsonReaderException(ref Utf8JsonReader json, ExceptionRe
         }
 
         [MethodImpl(MethodImplOptions.NoInlining)]
-        private static JsonReaderException GetJsonReaderException(ref Utf8JsonReader json, ExceptionResource resource, byte nextByte, ReadOnlySpan<byte> bytes)
+        public static JsonReaderException GetJsonReaderException(ref Utf8JsonReader json, ExceptionResource resource, byte nextByte, ReadOnlySpan<byte> bytes)
         {
             string message = GetResourceString(ref json, resource, nextByte, Encoding.UTF8.GetString(bytes.ToArray(), 0, bytes.Length));
 
@@ -132,6 +132,12 @@ private static string GetResourceString(ref Utf8JsonReader json, ExceptionResour
                 case ExceptionResource.InvalidCharacterWithinString:
                     message = SR.Format(SR.InvalidCharacterWithinString, character);
                     break;
+                case ExceptionResource.InvalidCharacterAfterEscapeWithinString:
+                    message = SR.Format(SR.InvalidCharacterAfterEscapeWithinString, character);
+                    break;
+                case ExceptionResource.InvalidHexCharacterWithinString:
+                    message = SR.Format(SR.InvalidHexCharacterWithinString, character);
+                    break;
                 case ExceptionResource.EndOfCommentNotFound:
                     message = SR.EndOfCommentNotFound;
                     break;
@@ -168,6 +174,8 @@ internal enum ExceptionResource
         ExpectedValueAfterPropertyNameNotFound,
         FoundInvalidCharacter,
         InvalidCharacterWithinString,
+        InvalidCharacterAfterEscapeWithinString,
+        InvalidHexCharacterWithinString,
         InvalidEndOfJsonNonPrimitive,
         MismatchedObjectArray,
         ObjectDepthTooLarge,