PYTHON-6040 Preserve version-to-name mapping in Client Metadata by blink1073 · Pull Request #29 · blink1073/mongo-python-driver

blink1073 · 2026-09-15T00:43:38Z

Implements DRIVERS-3251: Ensure driver.name and driver.version require positional alignment in the handshake specification.

Changes in this PR

Reject | in DriverInfo fields at construction.
Append empty version entries for the |c and |async name suffixes.
Always append the delimiter to name and version in _update_metadata.
Deduplicate appended drivers by whole DriverInfo object.
Keep name/version index-aligned in _truncate_metadata at the 512-byte limit.
Add the new handshake prose tests.
Update the metadata, dedup, and handshake tests.

Test Plan

New prose test passes.

Checklist

Checklist for Author

Did you update the changelog (if necessary)?
Is there test coverage?
Is any followup work tracked in a JIRA ticket? If so, add link(s).

Checklist for Reviewer

Does the title of the PR reference a JIRA Ticket?
Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
Is all relevant documentation (README or docstring) updated?

Copilot

🟡 Changes recommended

Successive appends can exceed the handshake limit, and concurrent updates can permanently lose metadata.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Preserves one-to-one correspondence between client metadata driver names and versions.

Changes:

Rejects reserved delimiters and aligns appended metadata fields.
Updates deduplication and truncation behavior.
Expands synchronous and asynchronous handshake tests.

File summaries

File	Description
`pymongo/driver_info.py`	Validates reserved delimiters.
`pymongo/pool_options.py`	Aligns, deduplicates, and truncates metadata.
`test/test_client.py`	Tests synchronous metadata alignment.
`test/test_client_metadata.py`	Tests synchronous append behavior.
`test/asynchronous/test_client.py`	Tests asynchronous metadata alignment.
`test/asynchronous/test_client_metadata.py`	Tests asynchronous append behavior.
`test/mockupdb/test_handshake.py`	Updates handshake expectations.

Review details

Files reviewed: 7/7 changed files
Comments generated: 3
Review effort level: Balanced

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Trim the _truncate_metadata comments and number/label the handshake prose tests (backpressure no. 9, delimiter no. 10, index no. 11).

Reapply the 512-byte handshake limit after append_metadata, guard the check/update/record sequence with a lock for thread-safe clients, and document the reserved '|' delimiter on DriverInfo.

Copilot

🟡 Changes recommended

The raw metadata lock can remain permanently locked after a fork, causing append_metadata() to deadlock.

Get a fresh assessment by requesting another Copilot review.

Review details

Suppressed comments (2)

Previously missed (2) — in code that hasn't changed since the last review.

pymongo/pool_options.py:363

Storing every historical DriverInfo in a list makes duplicate detection linear per call and a sequence of unique appends quadratic overall, even after metadata has hit its 512-byte cap. DriverInfo is hashable, so this should be a set with add() to keep membership checks constant-time.
test/asynchronous/test_client_metadata.py:270
This case does not test equal versions: it appends only one driver with no version, duplicating the preceding trailing-delimiter case. A regression that incorrectly deduplicates distinct drivers by version would still pass; use two distinct names with the same non-empty version.

Files reviewed: 7/7 changed files
Comments generated: 1
Review effort level: Balanced

Use _create_lock() so the metadata lock is registered with pymongo.lock and reset after a fork, avoiding a deadlock in the child process.

Copilot

🔵 Needs a closer look

Metadata updates can raise KeyError after truncation, and the new truncation order can unnecessarily discard driver identity.

Review details

Suppressed comments (3)

Previously missed (2) — in code that hasn't changed since the last review.

pymongo/pool_options.py:255

The loop now truncates driver.name before touching driver.version, reversing the existing metadata truncation priority. With a short wrapper name and an oversized wrapper version, the name collapses to PyMongo and rebuilding then discards that wrapper's version entirely, even though truncating only the version content would fit and preserve the driver identity. Trim version-segment content first while retaining its delimiters, and only truncate names (dropping paired version segments as needed) if the document is still oversized.

This issue also appears on line 418 of the same file.
test/asynchronous/test_client_metadata.py:270

This case duplicates the preceding trailing-empty-version scenario, so it does not verify that equal non-empty versions remain as separate aligned entries. Use two distinct names sharing one version to exercise the stated regression.

pymongo/pool_options.py:419

After truncation removes the optional platform field, a later append_metadata(DriverInfo(..., platform="...")) raises KeyError here. This occurs, for example, after enough name/version-only appends exceed 512 bytes: _truncate_metadata pops platform, but subsequent updates still index it directly. Recreate the field when it is absent before truncating again.

            if driver.platform:
                metadata["platform"] = "{}|{}".format(metadata["platform"], driver.platform)

Files reviewed: 7/7 changed files
Comments generated: 0 new
Review effort level: Balanced

Trim wrapper version content before dropping name/version segments so driver identity is preserved, and recreate the platform field when a platform append follows truncation that removed it.

Revert the 'Equal versions do not collapse' prose test case to the specification and shorten the truncation comment.

Copilot

🔵 Needs a closer look

Moderate finding (3 votes): __appended_drivers retains truncated unique drivers indefinitely, allowing unbounded memory growth and slower membership checks.

Review details

Suppressed comments (1)

Previously missed (1) — in code that hasn't changed since the last review.

pymongo/pool_options.py:413

__appended_drivers retains every distinct DriverInfo forever, including entries that _truncate_metadata has already removed to stay within the 512-byte metadata limit. A caller can repeatedly append unique (and arbitrarily large) values, so memory grows without bound and the linear membership check becomes progressively slower even though the serialized metadata is bounded. Please use a bounded retention strategy for drivers that are no longer representable, or otherwise avoid recording truncated entries.

Files reviewed: 7/7 changed files
Comments generated: 0 new
Review effort level: Lite

Only record drivers that remain representable in the truncated metadata, so __appended_drivers cannot grow without bound and the dedup membership check stays fast. Add a regression test.

Copilot

🟡 Changes recommended

Truncated-away platform-only drivers can still accumulate in the deduplication set without appearing in published metadata.

Get a fresh assessment by requesting another Copilot review.

Review details

Files reviewed: 7/7 changed files
Comments generated: 1
Review effort level: Lite

Use the name delimiter count before/after the update to decide whether an appended pair survived truncation, instead of a name/version branch that always recorded platform-only (empty name/version) drivers.

Copilot

🟢 Approval recommended

No unresolved review issues were identified.

Review details

Files reviewed: 7/7 changed files
Comments generated: 0 new
Review effort level: Lite

blink1073 added 2 commits September 14, 2026 19:37

PYTHON-6040 Preserve 1:1 index correspondence in client metadata

ac6ed46

PYTHON-6040 Update tests for index-aligned client metadata

5f2e74c

blink1073 requested a balanced review from Copilot September 15, 2026 00:56

blink1073 commented Sep 15, 2026

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blink1073 commented Sep 15, 2026

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blink1073 commented Sep 15, 2026

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Comment thread pymongo/driver_info.py

blink1073 added 2 commits September 14, 2026 20:14

PYTHON-6040 Address PR review feedback

b3d18d1

Trim the _truncate_metadata comments and number/label the handshake prose tests (backpressure no. 9, delimiter no. 10, index no. 11).

PYTHON-6040 Address Copilot review feedback

b035cfb

Reapply the 512-byte handshake limit after append_metadata, guard the check/update/record sequence with a lock for thread-safe clients, and document the reserved '|' delimiter on DriverInfo.

blink1073 requested a balanced review from Copilot September 15, 2026 01:31

Copilot started reviewing on behalf of blink1073 September 15, 2026 01:31 View session

Copilot AI reviewed Sep 15, 2026

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Comment thread pymongo/pool_options.py Outdated

PYTHON-6040 Use fork-aware lock for metadata updates

61ba3a2

Use _create_lock() so the metadata lock is registered with pymongo.lock and reset after a fork, avoiding a deadlock in the child process.

blink1073 requested a balanced review from Copilot September 15, 2026 01:38

Copilot started reviewing on behalf of blink1073 September 15, 2026 01:38 View session

Copilot AI reviewed Sep 15, 2026

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PYTHON-6040 Fix truncation order and platform recreation

7e863c9

Trim wrapper version content before dropping name/version segments so driver identity is preserved, and recreate the platform field when a platform append follows truncation that removed it.

blink1073 commented Sep 15, 2026

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Comment thread pymongo/pool_options.py Outdated

blink1073 commented Sep 15, 2026

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Comment thread test/asynchronous/test_client_metadata.py Outdated

PYTHON-6040 Reverse prose test case and trim truncation comment

d45d987

Revert the 'Equal versions do not collapse' prose test case to the specification and shorten the truncation comment.

blink1073 requested a lite review from Copilot September 15, 2026 10:45

Copilot started reviewing on behalf of blink1073 September 15, 2026 10:46 View session

Copilot AI reviewed Sep 15, 2026

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PYTHON-6040 Bound appended-driver tracking

0194f47

Only record drivers that remain representable in the truncated metadata, so __appended_drivers cannot grow without bound and the dedup membership check stays fast. Add a regression test.

blink1073 requested a lite review from Copilot September 15, 2026 11:14

Copilot started reviewing on behalf of blink1073 September 15, 2026 11:15 View session

Copilot AI reviewed Sep 15, 2026

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Comment thread pymongo/pool_options.py Outdated

PYTHON-6040 Bound dedup tracking for platform-only appends

b652b78

Use the name delimiter count before/after the update to decide whether an appended pair survived truncation, instead of a name/version branch that always recorded platform-only (empty name/version) drivers.

blink1073 requested a lite review from Copilot September 15, 2026 11:26

Copilot started reviewing on behalf of blink1073 September 15, 2026 11:26 View session

Copilot AI reviewed Sep 15, 2026

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blink1073 closed this Sep 15, 2026

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PYTHON-6040 Preserve version-to-name mapping in Client Metadata - #29

PYTHON-6040 Preserve version-to-name mapping in Client Metadata#29
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PYTHON-6040

blink1073 commented Sep 15, 2026 •

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🟡 Changes recommended

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🔵 Needs a closer look

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🔵 Needs a closer look

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blink1073 commented Sep 15, 2026 •

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