server: limit accumulated COM_STMT_SEND_LONG_DATA size (release-8.1-20260724-v8.1.2) (#69694)

[bb7133]

What problem does this PR solve?

Issue Number: close #69693

Problem Summary:
Cherry-pick #69694 (limit accumulated COM_STMT_SEND_LONG_DATA size) to release-8.1-20260724-v8.1.2.

What changed and how does it work?

Cherry-pick of ed2376a. One trivial conflict in the import block of pkg/server/conn_stmt_test.go (dropped the master-only pkg/planner/core/resolve import, unused on this branch). go vet ./pkg/server/ passes. See #69694 for the full description.

Check List

Tests

• Unit test

Release note

TiDB now limits the accumulated `COM_STMT_SEND_LONG_DATA` size for a prepared statement by `max_allowed_packet`.

Summary by CodeRabbit

• Bug Fixes
  • Added validation for oversized statement long-data payloads before execution.
  • Prevented long-data buffers from growing beyond the configured maximum packet size.
  • Prepared statements now return an appropriate packet-size error and clear affected bound parameters after an oversized payload is detected.
  • Added safeguards to ensure statements can be reused normally after the error.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: e8b8397d-9784-4487-a7b2-d0679c7fbc8a

📥 Commits

Reviewing files that changed from the base of the PR and between 80db670 and 4b0c0f3.

📒 Files selected for processing (4)

• pkg/server/conn_stmt.go
• pkg/server/conn_stmt_test.go
• pkg/server/driver.go
• pkg/server/driver_tidb.go

---

📝 Walkthrough

Walkthrough

Prepared statements now limit accumulated long data by MaxAllowedPacket, validate the limit before binary parameter parsing, and reset oversized-data state after errors. Tests cover long-data submission, execution failure, cleanup, and subsequent validation.

Changes

Long-data packet limit

Layer / File(s)	Summary
Long-data accumulation and validation pkg/server/driver.go, pkg/server/driver_tidb.go	PreparedStatement exposes CheckLongDataSize; TiDBStatement bounds long-data accumulation, reports ErrNetPacketTooLarge, and resets its tracking flag.
Execute-time validation gate pkg/server/conn_stmt.go	handleStmtExecute checks long-data size before parsing binary parameters.
Max-packet execution coverage pkg/server/conn_stmt_test.go	Tests verify oversized long-data execution errors, bound-parameter cleanup, and post-error validation.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• pingcap/tidb#70083: Adds the same prepared-statement long-data validation, execution gate, and max-packet test path.

Poem

A bunny guards each packet’s size,
No endless bytes can overflow the wise.
Long data hops through checks in line,
Too-large bundles earn an error sign.
Reset, then safely bound anew—
Hop, hop, the statement knows what to do!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the main change: limiting accumulated COM_STMT_SEND_LONG_DATA size.
Description check	✅ Passed	The description covers the issue, problem summary, implementation details, tests, and release note.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cp-69694-8.1-v8.1.2

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

Error: can't load config: unsupported version of the configuration: "" See https://golangci-lint.run/docs/product/migration-guide for migration instructions
The command is terminated due to an error: can't load config: unsupported version of the configuration: "" See https://golangci-lint.run/docs/product/migration-guide for migration instructions

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 21 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-8.1-20260724-v8.1.2@80db670). Learn more about missing BASE report.

Additional details and impacted files

@@                       Coverage Diff                        @@
##             release-8.1-20260724-v8.1.2     #70170   +/-   ##
================================================================
  Coverage                               ?   37.0245%           
================================================================
  Files                                  ?       1505           
  Lines                                  ?     576266           
  Branches                               ?          0           
================================================================
  Hits                                   ?     213360           
  Misses                                 ?     341576           
  Partials                               ?      21330           

Flag	Coverage Δ
integration	37.0245% <0.0000%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	∅ <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	23.9830% <0.0000%> (?)

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[ti-chi-bot]

@bb7133: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	4b0c0f3	link	true	/test unit-test
idc-jenkins-ci-tidb/mysql-test	4b0c0f3	link	true	/test mysql-test

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