[release/10.0] Fix the Syndication Feed RFC822 DateTimeParser #119918
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RFC822 allows single-digit date values and two-digit year values in the publication date (pubDate). The existing date-time parser only accepted two-digit dates and (for some formats) four-digit years.
StephenMolloy
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Sep 22, 2025
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Backport of #99194 to release/10.0
/cc @StephenMolloy @dougwaldron
Customer Impact
The DateTimeHelper in System.ServiceModel.Syndication rejects otherwise valid RFC 822 (RSS 2.0–compliant) dates that use a single digit day (e.g., “7 Jun 2023”) or certain two digit year patterns due to an incomplete and partially incorrect format array passed to DateTimeOffset.TryParseExact. (RFC 822 is an older, but still valid spec.) The fix augments and corrects the accepted date format strings to allow 1–2 digit days and properly handle intended two digit year forms, without changing any other parsing behavior.
Regression
Testing
Test PR here
Risk
This is a low risk, localized change confined to expanding the format list in a private helper.
IMPORTANT: If this backport is for a servicing release, please verify that:
release/X.0-staging, notrelease/X.0.Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.