[mananmangal]

Fixes #40860

IcebergIO only accepted a T between date and time when writing a STRING value to a timestamp or timestamptz column. A space, which RFC 3339 section 5.6 allows and Python's str(datetime) produces, threw DateTimeParseException.

When the character after the date is a space, the value is now parsed with a formatter that expects a space instead of T. All other values go through the existing OffsetDateTime.parse / LocalDateTime.parse calls unchanged.

• The separator is checked up front instead of catching the parse exception and retrying, as BigQueryIO does. In a local benchmark, the retry made each space-separated value about 2.4x slower to parse (~1130 ns vs ~480 ns).
• Exactly one separator is accepted. 2024-10-08 T13:18:20 (the output behind [Bug]: BigQueryIO Storage Write API failed-rows output crashes: TIMESTAMP printed with both a space and a T separator, then parsed by Instant.parse #40110) is still rejected.
• The read path is unchanged.

Testing: added cases to IcebergUtilsTest for both column types, including invalid separators. :sdks:java:io:iceberg:test passes.

[github-actions]

📋 Review Summary

This PR updates IcebergUtils.getIcebergTimestampValue to accept space-separated RFC 3339 timestamp strings when converting Beam STRING values to Iceberg timestamp and timestamptz columns, avoiding exception-based fallback overhead by checking the separator character up front. The implementation and unit test coverage are clean and well-targeted.

🔍 General Feedback

• One minor consistency detail to watch out for: DateTimeFormatterBuilder.toFormatter() defaults to ResolverStyle.SMART, whereas LocalDateTime.parse (ISO_LOCAL_DATE_TIME) and OffsetDateTime.parse (ISO_OFFSET_DATE_TIME) use ResolverStyle.STRICT.

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[mananmangal]

/gemini review

[github-actions]

📋 Review Summary

This PR updates IcebergUtils to support space-separated ISO-8601/RFC-3339 timestamp strings when writing STRING fields to Iceberg timestamp and timestamptz columns. The previous review feedback regarding strict date resolution (ResolverStyle.STRICT and IsoChronology.INSTANCE) has been properly addressed, and unit tests cover both valid and invalid date/separator cases.

🔍 General Feedback

• The up-front hasSpaceSeparator check avoids exception-handling overhead on the hot path while preserving strict parsing semantics matching DateTimeFormatter.ISO_LOCAL_DATE_TIME and DateTimeFormatter.ISO_OFFSET_DATE_TIME.
• Test coverage in IcebergUtilsTest thoroughly validates space-separated timestamps, invalid separators, and invalid calendar dates across both timestamp and timestamptz types.

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[github-actions]

Assigning reviewers:

R: @ahmedabu98 for label iceberg.
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.00%. Comparing base (2213e54) to head (f7586e9).
⚠️ Report is 45 commits behind head on master.

Additional details and impacted files

@@       Coverage Diff       @@
##   master   #40861   +/-   ##
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