CNA-GAP-034: The XNB DateTime reader discards the two DateTimeKind bits, so Utc and Local values load as plain tick counts

CNA snapshot 009d40f5  ·  Known Issues › Functional gaps  ·  source links pinned to 009d40f5

DateTimeReader masks off the two kind bits and returns System::DateTime(ticks) with an unspecified kind, and it does not convert a Local-kind value to local time as XNA does. The header justifies the deviation by System::DateTime not modelling a kind, but System::DateTime has a (ticks, DateTimeKind) constructor at TARGET, so that reason is stale.

Identifier

CNA-GAP-034

Category

Functional gap

Subsystem

Content & XNB/CNB/CNJ

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

Yes: see Current tests

Affected contract

XNB DateTime values read through ContentReader (DateTimeReader)

Expected behaviour

XNA's DateTimeReader restores DateTimeKind from the top two bits and, for a Local value, converts the stored UTC ticks to local time (new DateTime(ticks, Utc).ToLocalTime()).

Actual behaviour at TARGET

DecimalDateTimeContentTypeReaders.hpp applies kindMask = 3 << 62 and returns System::DateTime(ticks). Its comment documents this as a deliberate deviation because System::DateTime 'does not store/track DateTimeKind at all'; that premise is out of date, since CNA's own XnaIntermediateSerializerTests builds Utc values with System::DateTime(ticks, System::DateTimeKind::Utc). The XNB writer in XnbBuiltInWriters.cpp likewise writes Unspecified. A Local-kind value therefore loads as its stored UTC ticks, without XNA's offset conversion.

Source locations

• modules/content/include/CNA/Internal/Xnb/DecimalDateTimeContentTypeReaders.hpp — DateTimeReader kindMask and the documented deviation
• modules/content/tests/CNA/Internal/Xnb/DecimalDateTimeContentTypeReaderTests.cpp — reader tests

Evidence

Checked by reading at 009d40f5; not executed.

Independent re-verification: Checked by reading at 009d40f5; not executed. XNA behaviour from the decompiled DateTimeReader. sharp-runtime's DateTime kind storage (packed in the top two bits, ticket 1941) landed on 2026-08-19, before the TARGET commit, and was read there through git only.

Focused reproduction

No focused reproduction is known. Nothing has been invented here; the evidence above is what exists.

Current tests

DecimalDateTimeContentTypeReaderTests.cpp covers the reader.

Regression test

If Sharp Runtime gains a kind: a round trip of Utc and Local values.

Blast radius

Content that serialises DateTime with a kind; the tick value is preserved.

Workaround

No workaround is known.