Add Feature Extension for User Agent

[samsharma2700]

Description

Adding support for User Agent Feature Extension(part 1) according to design doc here(https://microsoft.sharepoint-df.com/:w:/t/sqldevx/ERIWTt0zlCxLroNHyaPlKYwBI_LNSff6iy_wXZ8xX6nctQ?e=iP8q75):

• Introducing necessary constants.
• Added function to write appropriate packet data.
• Added Unit tests for the changes

Part 2 will include the userAgentJsonPayload related implementations followed by functional tests.

Testing

Builds are passing.
Unit tests are passing.

[Copilot]

Pull Request Overview

Adds initial support for the User Agent feature extension by defining new constants, extending the TDS writer with a method to serialize the user-agent payload, and toggling the feature flag in the login flow under debug builds.

• Introduce FEATUREEXT_USERAGENT and SUPPORTED_USER_AGENT_VERSION constants and enum entry
• Add WriteUserAgentFeatureRequest in both netfx and netcore TdsParser implementations
• Add IsUserAgentEnabled flag and debug-only enabling logic in SqlInternalConnectionTds

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/TdsEnums.cs	Added user-agent feature ID constant and enum mapping
src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	Implemented WriteUserAgentFeatureRequest
src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	Implemented WriteUserAgentFeatureRequest
src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/SqlInternalConnectionTds.cs	Added IsUserAgentEnabled flag and debug-only gating
src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SqlInternalConnectionTds.cs	Added IsUserAgentEnabled flag and debug-only gating

Comments suppressed due to low confidence (1)

src/Microsoft.Data.SqlClient/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs:8715

• The new WriteUserAgentFeatureRequest method lacks accompanying unit tests; please add tests to verify both length calculation and correct byte output in write and length-only modes.

        internal int WriteUserAgentFeatureRequest(byte[] userAgentJsonPayload,

[apoorvdeshmukh]

We should add a test case validating the login request. You can refer to TestConnWithVectorFeatExtVersionNegotiation to check how to inspect login packet.

[paulmedynski]

One minor fix.

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 8 lines in your changes missing coverage. Please review.

Project coverage is 67.59%. Comparing base (df35633) to head (56949db).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
.../netcore/src/Microsoft/Data/SqlClient/TdsParser.cs	0.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3451      +/-   ##
==========================================
+ Coverage   66.91%   67.59%   +0.68%     
==========================================
  Files         280      280              
  Lines       62386    62417      +31     
==========================================
+ Hits        41745    42191     +446     
+ Misses      20641    20226     -415     

Flag	Coverage Δ
addons	92.58% <ø> (ø)
netcore	72.72% <11.11%> (+3.75%)	⬆️
netfx	66.32% <100.00%> (-2.93%)	⬇️

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[paulmedynski]

Let's get either some unit tests added (that don't require the test TDS server), or some functional tets that use TDS server. Either way, the tests should verify that we produce the correct Login payload given various byte arrays, and that we handle a variety of Login Response payloads.

[paulmedynski]

Looks good, with some minor tweaks.