Content Language Bug Fix

[GarrettBeatty]

Description

This PR fixes two issues related to the Content-Language HTTP header in the AWS SDK for .NET:

1. Request Signing Issue: The Content-Language header was not properly handled as a content header in HttpRequestMessageFactory, causing signature mismatch errors. This was is also happening on development branch too.

2. GetObjectMetadataResponse Backing Field Consistency: Changed GetObjectMetadataResponse.ContentLanguage to use Headers.ContentLanguage as the backing field, matching the pattern used by GetObjectResponse.ContentLanguage.

Request Signing Fix

Symptom:
When setting Content-Language on a PutObject request, the SDK throws SignatureDoesNotMatch:

Root Cause:
The SDK includes Content-Language in signature calculation, but .NET's HttpClient wasn't actually sending it because the header wasn't being placed on HttpContent.Headers.

Evidence from AWS error response:

Component	Canonical Request Content
SDK signed with	content-language:en-US
AWS received	content-language: (empty)

The Content-Language header value was lost because:

1. HttpWebRequestMessage.ContentHeaderNames didn't include Content-Language
2. SetRequestHeaders() attempted to add it to HttpRequestMessage.Headers (request headers)
3. Per RFC 7231, Content-Language is a content header - .NET's HttpClient rejects it as a request header
4. WriteContentHeaders() had no code to add Content-Language to HttpContent.Headers
5. Result: Header signed but never sent → signature mismatch

Fix:

1. Added HeaderKeys.ContentLanguageHeader to ContentHeaderNames HashSet
2. Added Content-Language handling in WriteContentHeaders() method

GetObjectMetadataResponse Backing Field Fix

Changed GetObjectMetadataResponse.ContentLanguage to delegate to Headers.ContentLanguage as the backing store instead of a private field, matching the pattern in GetObjectResponse.ContentLanguage.

Testing

1. Integ Test
2. Dry run e27c9b4e-0984-4201-9fc9-fb5ab5f28ac0

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the README document
• I have added tests to cover my changes
• All new and existing tests passed

License

• I confirm that this pull request can be released under the Apache 2 license

[Copilot]

Pull request overview

This PR fixes a Content-Language header handling issue that caused signature mismatch errors in S3 requests. The root cause was that the SDK signed requests with Content-Language but didn't actually send the header because it wasn't properly configured as a content header in HttpClient. The PR also standardizes GetObjectMetadataResponse.ContentLanguage to use the Headers collection as its backing store, matching the pattern used in GetObjectResponse.

Key Changes:

• Added Content-Language to the list of content headers in HttpRequestMessageFactory so it's correctly placed on HttpContent.Headers
• Refactored GetObjectMetadataResponse.ContentLanguage to delegate to Headers.ContentLanguage instead of using a private field
• Added integration test to verify Content-Language header is correctly sent and retrieved

Reviewed changes

Copilot reviewed 7 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
sdk/src/Core/Amazon.Util/HeaderKeys.cs	Added ContentLanguageHeader constant for consistent header name reference
sdk/src/Core/Amazon.Runtime/Pipeline/HttpHandler/_netstandard/HttpRequestMessageFactory.cs	Added Content-Language to ContentHeaderNames HashSet and WriteContentHeaders method to fix signing/sending mismatch
sdk/src/Services/S3/Generated/Model/GetObjectMetadataResponse.cs	Removed auto-generated ContentLanguage property and private field (moved to custom implementation)
sdk/src/Services/S3/Generated/Model/Internal/MarshallTransformations/GetObjectMetadataResponseUnmarshaller.cs	Removed auto-generated unmarshalling code for ContentLanguage (moved to custom implementation)
sdk/src/Services/S3/Custom/Model/GetObjectMetadataResponse.cs	Added custom ContentLanguage property that delegates to Headers.ContentLanguage
sdk/src/Services/S3/Custom/Model/Internal/MarshallTransformations/GetObjectMetadataResponseUnmarshaller.cs	Added custom unmarshalling code that populates Headers.ContentLanguage
generator/ServiceModels/s3/s3.customizations.json	Excluded ContentLanguage from HeadObjectOutput generation to enable custom implementation
sdk/test/Services/S3/IntegrationTests/PutObjectTests.cs	Added integration test verifying Content-Language header round-trip through PutObject and GetObject/GetObjectMetadata
generator/.DevConfigs/19ed68ce-9f46-4e1e-a0ff-45a2b3641947.json	Dev config with patch version bump and changelog message