Add a JsonElement reader

src/JsonReader.cs

@@ -217,6 +217,30 @@ bool TryReadItem(ReadOnlySpan<byte> span,
         }
     }
 
+    static IJsonReader<JsonElement>? jsonElementReader;
+
+    public static IJsonReader<JsonElement> Element() =>
+        jsonElementReader ??=
+            Create(static (ref Utf8JsonReader rdr) =>
+            {
+                ref var inner = ref Utf8JsonReader.GetInnerReader(ref rdr);
+
+#if NET6_0_OR_GREATER
+                return JsonElement.TryParseValue(ref inner, out var element)
+                     ? JsonReadResult.Value(element.Value)
+                     : JsonReadError.Incomplete;
+#elif NETCOREAPP3_1_OR_GREATER
+                if (!JsonDocument.TryParseValue(ref inner, out var doc))
+                    return JsonReadError.Incomplete;
+
+                using var _ = doc;
+                return JsonReadResult.Value(doc.RootElement.Clone());
+#else
+#error Unsupported platform.
+#endif
+            });
+
+
     public static IJsonReader<T> Error<T>(string message) =>
         CreatePure<T>((ref Utf8JsonReader _) => Error(message));
 

src/Utf8JsonReader.cs

@@ -30,6 +30,8 @@ public ref struct Utf8JsonReader
     System.Text.Json.Utf8JsonReader reader;
     Stack<object>? stack;
 
+    public static ref System.Text.Json.Utf8JsonReader GetInnerReader(ref Utf8JsonReader reader) => ref reader.reader;
+
     public Utf8JsonReader(ReadOnlySpan<byte> jsonData, JsonReaderOptions options = default) :
         this(new(jsonData, options), stack: null) { }
 

tests/JsonReaderTests.cs

@@ -1051,4 +1051,50 @@ public void Let_Returns_Select_That_Receives_Reader_Return()
         Assert.NotNull(result);
         Assert.Same(outputReader, result);
     }
+
+    [Theory]
+    [InlineData(/*lang=json*/ "null")]
+    [InlineData(/*lang=json*/ "false")]
+    [InlineData(/*lang=json*/ "true")]
+    [InlineData(/*lang=json*/ "-4.2")]
+    [InlineData(/*lang=json*/ """ "foobar" """)]
+    [InlineData(/*lang=json*/ "[1, 2, 3]")]
+    [InlineData(/*lang=json*/ """
+                {
+                    "null": null,
+                    "true": true,
+                    "false": false,
+                    "number": 12345.67890,
+                    "string": "The quick brown fox jumps over the lazy dog.",
+                    "array": [],
+                    "object": {}
+                }
+                """)]
+    public void Element_With_Valid_Input(string json)
+    {
+        var actual = JsonReader.Element().Read(json);
+        var reader = new System.Text.Json.Utf8JsonReader(Encoding.UTF8.GetBytes(json));
+#if NET6_0_OR_GREATER
+        var expected = JsonElement.ParseValue(ref reader);
+#elif NETCOREAPP3_1_OR_GREATER
+        using var doc = JsonDocument.ParseValue(ref reader);
+        var expected = doc.RootElement.Clone();
+#else
+#error Unsupported platform.
+#endif
+        Assert.Equal(expected.ToString(), actual.ToString());
+    }
+
+    [Theory]
+    [InlineData(/*lang=json*/ "null")]
+    [InlineData(/*lang=json*/ "false")]
+    [InlineData(/*lang=json*/ "true")]
+    [InlineData(/*lang=json*/ "-4.2")]
+    [InlineData(/*lang=json*/ """ "foobar" """)]
+    [InlineData(/*lang=json*/ "[]")]
+    [InlineData(/*lang=json*/ "{}")]
+    public void Element_Moves_Reader(string json)
+    {
+        TestReaderPositionPostRead(JsonReader.Element(), json);
+    }
 }