FIX: Segmentation Fault when interleaving fetchmany and fetchone calls #427

[gargsaumya]

Work Item / Issue Reference

AB#42605

GitHub Issue: #427

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Summary

This pull request addresses a segmentation fault issue that occurred when interleaving fetchmany() and fetchone() calls on a database cursor, as reported in GitHub Issue #427. The main improvements include unbinding columns after fetch operations to prevent conflicts with SQLGetData, and adding comprehensive tests to ensure correct interleaved fetch behavior.

Fixes for fetch interleaving bug:

• Added calls to SQLFreeStmt_ptr(hStmt, SQL_UNBIND) after fetchmany() and fetchall() operations in ddbc_bindings.cpp to unbind columns, allowing subsequent fetchone() calls to use SQLGetData without causing segmentation faults. [1] [2]
• Added column unbinding at the start of FetchOne_wrap to avoid conflicts from previous fetch operations, and improved error handling for SQLGetData failures.

Testing improvements:

• Introduced a new test file test_017_fetchmany_fetchone_interleave.py with multiple test cases to verify that interleaving fetchmany() and fetchone() calls works correctly and no longer causes segmentation faults.

[Copilot]

Pull request overview

This pull request fixes a critical segmentation fault that occurred when interleaving fetchmany() and fetchone() calls on a database cursor (GitHub Issue #427). The root cause was that fetchmany() and fetchall() bind ODBC columns to memory buffers for performance, but fetchone() uses SQLGetData to retrieve data, which cannot be used on already-bound columns. The fix unbinds columns after bound fetch operations and at the start of fetchone() to prevent conflicts.

Changes:

• Added comprehensive tests for interleaving fetchmany() and fetchone() calls to prevent regression
• Fixed the segmentation fault by unbinding columns after fetchmany() and fetchall() operations
• Enhanced error handling in FetchOne_wrap to properly detect and report SQLGetData failures

Reviewed changes

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

File	Description
tests/test_017_fetchmany_fetchone_interleave.py	New test file with three test cases covering basic interleaved fetch scenarios (fetchmany→fetchone, fetchone→fetchmany, and multiple alternating calls)
mssql_python/pybind/ddbc_bindings.cpp	Added SQLFreeStmt(SQL_UNBIND) calls in FetchMany_wrap, FetchAll_wrap, and FetchOne_wrap; improved error handling in FetchOne_wrap to return early on SQLGetData failure

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[github-actions]

📊 Code Coverage Report

🔥 Diff Coverage 100%

🎯 Overall Coverage 76%

📈 Total Lines Covered: 5509 out of 7185 📁 Project: mssql-python

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Diff Coverage

Diff: main...HEAD, staged and unstaged changes

• mssql_python/pybind/ddbc_bindings.cpp (100%)

Summary

• Total: 7 lines
• Missing: 0 lines
• Coverage: 100%

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📋 Files Needing Attention

📉 Files with overall lowest coverage (click to expand)

mssql_python.pybind.logger_bridge.hpp: 58.8%
mssql_python.pybind.logger_bridge.cpp: 59.2%
mssql_python.row.py: 66.2%
mssql_python.pybind.ddbc_bindings.cpp: 69.4%
mssql_python.pybind.ddbc_bindings.h: 69.7%
mssql_python.pybind.connection.connection.cpp: 75.3%
mssql_python.helpers.py: 77.4%
mssql_python.ddbc_bindings.py: 79.6%
mssql_python.pybind.connection.connection_pool.cpp: 79.6%
mssql_python.cursor.py: 84.7%

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[sumitmsft]

fairly simple fix. good catch!! lgtm.