Skip 'Expect: 100-continue' header for zero-length S3 streaming requests

[joviegas]

Motivation and Context

Fix for #6459

Per RFC 9110 Section 10.1.1, clients MUST NOT generate a 100-continue expectation in requests that do not include content. Currently, the SDK adds the Expect: 100-continue header to all S3 PutObject and UploadPart requests, including those with zero-length content.

This causes issues with sync HTTP clients (e.g., Apache HttpClient) that reuse connections. When a zero-length request is sent with the Expect header, the server may close the connection after receiving the empty content, but the client attempts to reuse it, leading to connection errors.

RFC 9110 Reference:

A client MUST NOT generate a 100-continue expectation in a request that does not include content.
A server MAY omit sending a 100 (Continue) response if it has already received some or all of the content for the corresponding request, or if the framing indicates that there is no content.

Modifications

Updated StreamingRequestInterceptor to skip adding the Expect: 100-continue header when:

1. Request is a PutObject or UploadPart operation, AND
2. Request body content length is explicitly 0

Key Changes:

• Modified shouldAddExpectContinueHeader() method to check for zero-length content

Behavior:

Scenario	Content Length	Expect Header Added?
No request body	N/A	Yes (unknown length)
Body present, length unknown	Optional.empty()	Yes
Body present, length = 0	0L	No (RFC compliance)
Body present, length > 0	> 0L	Yes

Testing

Added test coverage in StreamingRequestInterceptorTest:

Screenshots (if appropriate)

N/A - Code-only change

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

License

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

Notes

Apache 5.x

https://github.com/arturobernalg/httpcomponents-client/blob/237b5f85f743c94d9be2d26d396130bc2053f2ef/httpclient5/src/main/java/org/apache/hc/client5/http/protocol/RequestExpectContinue.java#L85-L88

Apache 4.5.x

https://github.com/apache/httpcomponents-client/blob/54900db4653d7f207477e6ee40135b88e9bcf832/httpclient/src/main/java/org/apache/http/client/protocol/RequestExpectContinue.java#L73-L75

[zoewangg]

What about async request body? The length could also be sourced from the request itself, i.e, putObjectRequest.contentLength(). Should we check header instead? It could be content-length or x-amz-decoded-content-length

[dagnir]

+1, we should probably give priority to x-amz-decoded-content-length and just fall back to content-length. If the decoded length is present and 0, then it's just the trailer and I don't think we need to use expect: 100-continue for that.

[joviegas]

Thanks @zoewangg @dagnir Initially I was only planning to support for Sync client since Apache client was erring out while Async client open new connection in these cases
Will update code based on above recommendations.

[zoewangg]

nit: StreamingRequestInterceptor is an internal class, can we remove the mention of it?

[joviegas]

Done

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

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