Utf8JsonWriter DateTime(Offset) formatting should produce smallest output that round trips. #28412
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layomia
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in dotnet/corefx
Apr 1, 2019
…est output that roundtrips (#35966) * Modify Utf8JsonWriter to write DateTime(Offset) values with the smallest output that roundtrips This change addresses https://github.com/dotnet/corefx/issues/34576. We replace calls to `Utf8Formatter.TryParse`, which formats to the roundtrippable custom format "O", with internal formatting logic that: - drops the fraction part of the output if the milliseconds part of the date is zero, else - writes the fraction part up to 7 decimal places with no trailing zeros. * Format to a stackalloc'd span and then trim it if necessary, then copy to the actual destination * Address review feedback * Re-merge trim implementation * Use DivMod and correct buffer length checks
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The
Utf8JsonWriterusesUtf8Formatterwith the standard format "O" to write the date time to the output.Instead, it should use custom formatter that rounds the fractional part of the second to the nearest second to create the smallest round-trippable output. This is particularly important for trailing zero seconds which are omitted by other APIs like
XmlConvert.ToString(new DateTime(2019, 1, 1, 2, 42, 42, 100), XmlDateTimeSerializationMode.RoundtripKind)which produces2019-01-01T02:42:42.1.Use the following implementation without writing the fractional seconds digit. In stead, if the fractional part is >= 0.5 seconds, increment
value.Secondbefore writing it to the output. Otherwise, just omit it.https://github.com/dotnet/corefx/blob/77096755443730962810662501f82550fdb4656d/src/Common/src/CoreLib/System/Buffers/Text/Utf8Formatter/Utf8Formatter.Date.O.cs#L69-L72
For more info: dotnet/corefx#34425 (comment)
cc @jkotas, @JamesNK
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