Return distanceMetric in QueryVectors response

[chr-hertel]

Hi there, first of all, thanks for your work here!

I was adopting it for a test suite around vector stores (see symfony/ai#2311), but ran into the issue that the SDK we're using is issuing a warning while using it instead of AWS - since i usually try to address issues i find upstream, i wanted to jump on it - i'm not fluent in java tho.

if you don't appreciate ai-assisted contributions, you can basically convert this into an issue and close - just want to offer support, not extra burden.

Cheers Chris

---

Summary + References to relevant docs by Claude Code

---

Summary

The QueryVectors response omits the distanceMetric field, although AWS declares it as required in the S3 Vectors API model (QueryVectorsOutput.required = ["vectors", "distanceMetric"]). SDKs that follow the model therefore fail or warn while parsing the response - the AWS PHP SDK (async-aws) e.g. emits Undefined array key "distanceMetric" on every query.

Before:

{"vectors":[{"distance":0.0,"key":"a","metadata":{"name":"third"}}]}

After:

{"vectors":[{"distance":0.0,"key":"a","metadata":{"name":"third"}}],"distanceMetric":"cosine"}

References

• QueryVectors API reference lists distanceMetric as a response element: "The distance metric that was used for the similarity search calculation. This is the same distance metric that was configured for the vector index when it was created." (Type: String, Valid Values: euclidean | cosine)

• S3 Vectors API model declares the field as required, which is why generated SDKs read it unconditionally:

  "QueryVectorsOutput": {
    "type": "structure",
    "required": ["vectors", "distanceMetric"],
    ...
  }