feat: set user_agent_extra for S3 server-side request attribution

[goanpeca]

DVC traffic on S3 server-side logs is currently indistinguishable from any other aiobotocore caller: Config.user_agent_extra is unset, so the wire UA only contains aiobotocore/X botocore/Y.

This sets user_agent_extra = "dvc-s3/<version>" on the boto3 Config built in S3FileSystem._prepare_credentials. The version is resolved lazily on first use (cached) via importlib.metadata.version("dvc-s3"), falling back to "dvc-s3/dev" for source / frozen installs (RFC 9110 product/version form preserved).

A user_agent_extra passed to the S3FileSystem constructor is appended to the dvc-s3 suffix rather than replacing it, so the wire UA always carries the dvc-s3 identifier: with no override it is dvc-s3/<version>, and with user_agent_extra="downstream/1.2.3" it becomes dvc-s3/<version> downstream/1.2.3. The value is stripped of surrounding whitespace and rejected (ConfigError) if it contains control characters, to avoid malformed or injected User-Agent headers.

Note: this wires user_agent_extra at the S3FileSystem constructor / programmatic level. Reaching it through dvc remote modify <name> user_agent_extra ... additionally requires adding the key to DVC's S3 remote schema in iterative/dvc, which is a separate follow-up.

Tests in dvc_s3/tests/test_s3.py cover the default, the appended user value, whitespace stripping, control-character rejection, and the real on-the-wire User-Agent (via moto).

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

This PR adds S3 User-Agent attribution so traffic originating from dvc-s3 is identifiable in S3/B2 server-side logs by setting botocore’s Config.user_agent_extra to a dvc-s3/<version> token (with a safe fallback) while still honoring per-remote overrides.

Changes:

• Resolve a default user_agent_extra at module import time via importlib.metadata.version("dvc-s3"), falling back to "dvc-s3" when metadata is unavailable.
• Pass user_agent_extra into config_kwargs in _prepare_credentials, allowing config overrides via user_agent_extra.
• Add tests covering the default and override behaviors.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
dvc_s3/__init__.py	Introduces and applies a default user_agent_extra for botocore Config, with override support.
dvc_s3/tests/test_s3.py	Adds assertions for default user_agent_extra behavior and explicit override handling.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

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

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[goanpeca]

Hi @skshetry 🙂

All Copilot threads resolved.

Happy to tweak anything!

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.