[release/6.0] Allow retaining the original casing for known header values #80754
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MihaZupan
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NO-MERGE
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Tagging subscribers to this area: @dotnet/ncl Issue DetailsBackport of #64702 to release/6.0, gated behind an AppContext switch. Set to draft pending customer validation. Customer ImpactTODO TestingTODO RiskTODO
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MihaZupan
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Servicing-consider
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Approved by @SteveMCarroll on 1/23 via email - "[Servicing-Consider] [6.0.X] Allow retaining the original casing for known header values". |
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Approved by Tactics for 6.0.15. |
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Backport of #64702 to release/6.0, gated behind an AppContext switch.
Customer Impact
Starting with .NET Core 2.1 and later expanded in .NET 5.0, we introduced a performance optimization where we avoid allocating strings for common well-known header values.
We did this in a case-insensitive manner, so if the server sent us
Connection: closeorConnection: CLOSE, they would both be exposed to the user asclose.As services are migrating from Framework to Core, this represents a change in behavior that can't be avoided as the optimization is taking place lower in the stack before the information is exposed to the user.
Clients running different versions of .NET may therefore not agree on the exact response provided by the server, which can break scenarios such as signature validation.
We stopped doing case-insensitive matching in .NET 7.0, and this PR brings the option to do the same on the 6.0 LTS release to unblock migration.
Testing
I added a targeted test to verify the expected behavior is observed if the
AppContextswitch is set.The customer validated the new behavior using a private build of
System.Net.Http.Risk
Practically zero. The change in behavior is hidden behind an
AppContextswitch.