Unify the JsonDocument and Utf8JsonReader handling of DateTime/Offset (#113929)

Since so much of the code is identical, move it to JsonReaderHelper
Closes #28931

Co-authored-by: Pranav Senthilnathan <[email protected]>

Author: IDisposable

src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.cs

@@ -666,28 +666,7 @@ internal bool TryGetValue(int index, out DateTime value)
             ReadOnlySpan<byte> data = _utf8Json.Span;
             ReadOnlySpan<byte> segment = data.Slice(row.Location, row.SizeOrLength);
 
-            if (!JsonHelpers.IsValidDateTimeOffsetParseLength(segment.Length))
-            {
-                value = default;
-                return false;
-            }
-
-            // Segment needs to be unescaped
-            if (row.HasComplexChildren)
-            {
-                return JsonReaderHelper.TryGetEscapedDateTime(segment, out value);
-            }
-
-            Debug.Assert(segment.IndexOf(JsonConstants.BackSlash) == -1);
-
-            if (JsonHelpers.TryParseAsISO(segment, out DateTime tmp))
-            {
-                value = tmp;
-                return true;
-            }
-
-            value = default;
-            return false;
+            return JsonReaderHelper.TryGetValue(segment, row.HasComplexChildren, out value);
         }
 
         internal bool TryGetValue(int index, out DateTimeOffset value)
@@ -701,28 +680,7 @@ internal bool TryGetValue(int index, out DateTimeOffset value)
             ReadOnlySpan<byte> data = _utf8Json.Span;
             ReadOnlySpan<byte> segment = data.Slice(row.Location, row.SizeOrLength);
 
-            if (!JsonHelpers.IsValidDateTimeOffsetParseLength(segment.Length))
-            {
-                value = default;
-                return false;
-            }
-
-            // Segment needs to be unescaped
-            if (row.HasComplexChildren)
-            {
-                return JsonReaderHelper.TryGetEscapedDateTimeOffset(segment, out value);
-            }
-
-            Debug.Assert(segment.IndexOf(JsonConstants.BackSlash) == -1);
-
-            if (JsonHelpers.TryParseAsISO(segment, out DateTimeOffset tmp))
-            {
-                value = tmp;
-                return true;
-            }
-
-            value = default;
-            return false;
+            return JsonReaderHelper.TryGetValue(segment, row.HasComplexChildren, out value);
         }
 
         internal bool TryGetValue(int index, out Guid value)

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

@@ -79,6 +79,32 @@ public static bool IsTokenTypePrimitive(JsonTokenType tokenType) =>
         // Otherwise, return false.
         public static bool IsHexDigit(byte nextByte) => HexConverter.IsHexChar(nextByte);
 
+        public static bool TryGetValue(ReadOnlySpan<byte> segment, bool isEscaped, out DateTime value)
+        {
+            if (!JsonHelpers.IsValidDateTimeOffsetParseLength(segment.Length))
+            {
+                value = default;
+                return false;
+            }
+
+            // Segment needs to be unescaped
+            if (isEscaped)
+            {
+                return TryGetEscapedDateTime(segment, out value);
+            }
+
+            Debug.Assert(segment.IndexOf(JsonConstants.BackSlash) == -1);
+
+            if (JsonHelpers.TryParseAsISO(segment, out DateTime tmp))
+            {
+                value = tmp;
+                return true;
+            }
+
+            value = default;
+            return false;
+        }
+
         public static bool TryGetEscapedDateTime(ReadOnlySpan<byte> source, out DateTime value)
         {
             Debug.Assert(source.Length <= JsonConstants.MaximumEscapedDateTimeOffsetParseLength);
@@ -101,6 +127,32 @@ public static bool TryGetEscapedDateTime(ReadOnlySpan<byte> source, out DateTime
             return false;
         }
 
+        public static bool TryGetValue(ReadOnlySpan<byte> segment, bool isEscaped, out DateTimeOffset value)
+        {
+            if (!JsonHelpers.IsValidDateTimeOffsetParseLength(segment.Length))
+            {
+                value = default;
+                return false;
+            }
+
+            // Segment needs to be unescaped
+            if (isEscaped)
+            {
+                return TryGetEscapedDateTimeOffset(segment, out value);
+            }
+
+            Debug.Assert(segment.IndexOf(JsonConstants.BackSlash) == -1);
+
+            if (JsonHelpers.TryParseAsISO(segment, out DateTimeOffset tmp))
+            {
+                value = tmp;
+                return true;
+            }
+
+            value = default;
+            return false;
+        }
+
         public static bool TryGetEscapedDateTimeOffset(ReadOnlySpan<byte> source, out DateTimeOffset value)
         {
             Debug.Assert(source.Length <= JsonConstants.MaximumEscapedDateTimeOffsetParseLength);

src/libraries/System.Text.Json/src/System/Text/Json/Reader/Utf8JsonReader.TryGet.cs

@@ -1260,30 +1260,10 @@ internal bool TryGetDateTimeCore(out DateTime value)
             }
             else
             {
-                if (!JsonHelpers.IsInRangeInclusive(ValueSpan.Length, JsonConstants.MinimumDateTimeParseLength, JsonConstants.MaximumEscapedDateTimeOffsetParseLength))
-                {
-                    value = default;
-                    return false;
-                }
-
                 span = ValueSpan;
             }
 
-            if (ValueIsEscaped)
-            {
-                return JsonReaderHelper.TryGetEscapedDateTime(span, out value);
-            }
-
-            Debug.Assert(span.IndexOf(JsonConstants.BackSlash) == -1);
-
-            if (JsonHelpers.TryParseAsISO(span, out DateTime tmp))
-            {
-                value = tmp;
-                return true;
-            }
-
-            value = default;
-            return false;
+            return JsonReaderHelper.TryGetValue(span, ValueIsEscaped, out value);
         }
 
         /// <summary>
@@ -1325,30 +1305,10 @@ internal bool TryGetDateTimeOffsetCore(out DateTimeOffset value)
             }
             else
             {
-                if (!JsonHelpers.IsInRangeInclusive(ValueSpan.Length, JsonConstants.MinimumDateTimeParseLength, JsonConstants.MaximumEscapedDateTimeOffsetParseLength))
-                {
-                    value = default;
-                    return false;
-                }
-
                 span = ValueSpan;
             }
 
-            if (ValueIsEscaped)
-            {
-                return JsonReaderHelper.TryGetEscapedDateTimeOffset(span, out value);
-            }
-
-            Debug.Assert(span.IndexOf(JsonConstants.BackSlash) == -1);
-
-            if (JsonHelpers.TryParseAsISO(span, out DateTimeOffset tmp))
-            {
-                value = tmp;
-                return true;
-            }
-
-            value = default;
-            return false;
+            return JsonReaderHelper.TryGetValue(span, ValueIsEscaped, out value);
         }
 
         /// <summary>