🐛 bug: harden session middleware lifecycle and error handling

[gaby]

Motivation

• Prevent session-object leaks and panics by ensuring acquired Session objects are always returned to the pool on every terminal/error path.
• Let middleware initialization failures be handled by the configured error handler instead of panicking and ensure middleware objects are released on init failure.
• Add regression coverage for lifecycle/error paths so release/save semantics are exercised and protected from regressions.

Description

• Make (*Middleware).initialize return error and update NewWithStore to invoke the configured ErrorHandler or DefaultErrorHandler on init failures while releasing the middleware and returning the original error only when no response status was written.
• Add finalizeSession() which conditionally calls saveSession() (skips when destroyed) and always calls releaseSession(m.Session) exactly once to guarantee object lifecycle cleanup.
• Harden Store.getSession to call sess.Release() before returning when sess.Reset() fails on absolute-expiry, and change Store.GetByID to always sess.Release() before returning ErrSessionIDNotFoundInStore after attempting sess.Destroy().
• Audit nearby early-return branches around acquireSession() for balanced Release() calls and add targeted tests for the new behaviors in middleware/session/middleware_test.go and middleware/session/store_test.go.

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[gemini-code-assist]

Summary of Changes

Hello @gaby, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the reliability and resource management of the session middleware. It focuses on preventing session object leaks and application panics by ensuring that session objects are always properly released back to their pool, even when errors occur during initialization or session lifecycle events. The changes centralize session finalization logic and harden error paths within the session store, leading to a more stable and predictable session management system.

Highlights

• Robust Error Handling for Session Middleware Initialization: The session middleware's initialization process now gracefully handles errors by invoking a configured error handler and ensuring proper resource release, preventing panics and improving stability.
• Centralized Session Lifecycle Management: A new finalizeSession() method has been introduced to ensure that acquired session objects are consistently saved (if not destroyed) and always returned to the pool, preventing session object leaks.
• Hardened Session Store Error Paths: The Store.getSession and Store.GetByID methods have been updated to explicitly release session objects back to the pool in various error and expiry scenarios, such as when sess.Reset() fails or an expired session is destroyed.
• Comprehensive Test Coverage: New unit tests have been added for both middleware.go and store.go to specifically cover the new error handling, session finalization logic, and session release behaviors in edge cases.

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Changelog

• middleware/session/middleware.go
  • Modified NewWithStore to catch initialization errors from m.initialize, call the configured ErrorHandler, and release the middleware object.
  • Changed (*Middleware).initialize to return an error instead of panicking, allowing for controlled error propagation.
  • Introduced (*Middleware).finalizeSession to encapsulate the logic for conditionally saving a session and always releasing the session object.
• middleware/session/middleware_test.go
  • Added failingStorage and lifecycleStorage structs to simulate storage errors and track lifecycle calls in tests.
  • Introduced new tests for Test_Session_Middleware_InitializeError_WithCustomErrorHandler, Test_Session_Middleware_InitializeError_DefaultErrorHandler, and Test_Session_Middleware_InitializeError_ReturnsHandlerErrorWhenUnwritten to validate middleware initialization error handling.
  • Added new tests for Test_Middleware_FinalizeSession_NormalSavePath, Test_Middleware_FinalizeSession_DestroyedPathSkipsSave, and Test_Middleware_FinalizeSession_SaveErrorStillReleasesSession to verify the finalizeSession behavior.
• middleware/session/store.go
  • Ensured sess.Release() is called in getSession if sess.Reset() fails when an absolute-expired session is encountered.
  • Modified GetByID to always call sess.Release() before returning ErrSessionIDNotFoundInStore after attempting to destroy an expired session.
• middleware/session/store_test.go
  • Added trackingStorage to monitor Delete calls in tests.
  • Introduced seedExpiredSessionInStore helper function to set up expired sessions for testing.
  • Added Test_Store_getSession_ExpiredResetFailureReleasesSession to confirm session release when Reset() fails on an expired session.
  • Added Test_Store_GetByID_ExpiredDestroySuccessReleasesSession to confirm session release when an expired session is destroyed via GetByID.

Activity

• The author, gaby, provided a detailed motivation for the changes, highlighting the prevention of session-object leaks and panics.
• The description outlines specific code modifications, including making initialize return an error, adding finalizeSession(), and hardening Store methods.
• Testing involved running unit tests for the session package with focused cases, full go test ./middleware/session, and make test, all of which passed.
• Code quality checks (make generate, make betteralign, make modernize, make format, make lint) were performed and succeeded.
• An make audit was run, which failed due to unrelated standard-library vulnerabilities in Go 1.25.1, as noted by the author.

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[codecov]

Codecov Report

❌ Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 91.16%. Comparing base (4df2fce) to head (fe63faf).
⚠️ Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
middleware/session/session.go	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4059      +/-   ##
==========================================
+ Coverage   91.09%   91.16%   +0.06%     
==========================================
  Files         119      119              
  Lines       11184    11224      +40     
==========================================
+ Hits        10188    10232      +44     
+ Misses        630      628       -2     
+ Partials      366      364       -2     

Flag	Coverage Δ
unittests	91.16% <96.29%> (+0.06%)	⬆️

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[gemini-code-assist]

Code Review

This pull request significantly hardens the session middleware by improving error handling and fixing several potential resource leaks. While the changes are well-implemented, replacing panics with proper error propagation and ensuring session objects are always released back to the pool, a high-severity issue remains. The middleware instance is returned to the pool while a reference to it still exists in the request context's locals, which can lead to cross-request session data leakage if other middlewares access the session after the main handler chain has completed. It is recommended to clear the context local reference before releasing the middleware instance. Additionally, consider improving context propagation during session destruction in middleware/session/store.go.

[Copilot]

Pull request overview

This PR hardens the session middleware/store lifecycle to prevent pooled Session/Middleware objects from leaking across request/error paths, and adds regression tests around those paths.

Changes:

• Convert (*Middleware).initialize to return an error and route init failures through the configured ErrorHandler/DefaultErrorHandler instead of panicking.
• Ensure sessions are always released back to the pool on terminal/error paths (finalizeSession, extra Release() calls in store error branches).
• Add regression tests for initialization, context-local cleanup, and store expiry/destroy behaviors.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
middleware/session/middleware.go	Switch init to error-return and add finalizeSession() to guarantee session release and locals cleanup.
middleware/session/session.go	Add a stored context (gctx) so Destroy() can honor GetByID’s context; clear it on release.
middleware/session/store.go	Release sessions on absolute-expiry reset failure; ensure GetByID releases sessions on expiry destroy path and uses gctx.
middleware/session/middleware_test.go	Add tests for locals cleanup, init error handling, and finalize lifecycle behavior.
middleware/session/store_test.go	Add tests for expiry/reset failure release, expiry destroy release, and destroy context propagation.

[Copilot]

These assertions don’t actually verify that the session involved in the failing store.Get path was released back to the pool: sync.Pool may return a different (or newly allocated) Session that already has zero values, so the test can pass even if the original session leaked. Consider making the test deterministic (e.g., temporarily swapping sessionPool with a test pool and disabling t.Parallel() for this test, or adding explicit instrumentation/counters around release paths).

[Copilot]

Same issue as above: acquiring a session from sync.Pool and checking for zero-values doesn’t prove the expired GetByID path released the specific session it allocated, since sync.Pool can return a different/new object. Consider a deterministic approach (test pool swap, counters, or pointer identity under controlled conditions) so this test fails if the session isn’t released.

[Copilot]

This pool check isn’t a reliable assertion that the middleware instance used during the request was released: sync.Pool may return a different (or newly allocated) Middleware with nil fields, so the test can pass even if the original middleware wasn’t released on init error. Consider asserting observable behavior instead (e.g., that the request doesn’t leave a middleware in c.Locals, or adding deterministic pooling instrumentation in tests).