fix: eliminate TOCTOU cache stampede in cachingClientCreator - #593
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adityakrmishra wants to merge 2 commits into
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fix: eliminate TOCTOU cache stampede in cachingClientCreator#593adityakrmishra wants to merge 2 commits into
adityakrmishra wants to merge 2 commits into
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Under concurrent load, multiple goroutines calling NewInstallationClient or NewInstallationV4Client for the same installation ID could all miss the LRU cache simultaneously (TOCTOU race between Get and Add) and each proceed to call the delegate — resulting in N redundant token-fetch HTTP requests to the GitHub API. Fix by wrapping the slow delegate call in a singleflight.Group so only one in-flight request per installation key is made; all other concurrent callers share the result. A double-checked Get inside the singleflight closure ensures the cache is used if a prior call already populated it. Adds TestCacheStampede_Vulnerable to prove the fix: 100 goroutines result in exactly 1 delegate invocation after the patch. Fixes: TOCTOU race in cachingClientCreator.NewInstallationClient
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Description
Resolves a TOCTOU (Time-of-Check to Time-of-Use) race condition in
cachingClientCreatorthat causes a cache stampede against the GitHub API.Problem:
Under concurrent load (e.g., webhook bursts), multiple goroutines requesting a token for the same
installationIDsimultaneously miss the LRU cache. This results in N redundant HTTP requests to GitHub before the cache is populated, risking rate limit exhaustion.Solution:
Implemented
golang.org/x/sync/singleflightaround the delegate call.Getinside the closure to safely catch races where the cache was populated just before the lock.Proof of Work (Test Results)
Added
TestCacheStampede_Vulnerablewhich fires 100 concurrent requests for the sameinstallationID.Before Patch:
After Patch: