nikolauspschuetz opened a new pull request, #1749:
URL: https://github.com/apache/casbin/pull/1749
### What
`NewLRUCache` and `NewSyncLRUCache` are exported public API, but calling
`Put` on a cache created with a non-positive capacity panics with a nil pointer
dereference.
Reproduce:
```go
c := util.NewLRUCache(0)
c.Put("a", 1) // panic: runtime error: invalid memory address or nil pointer
dereference
```
On the first insert, the eviction branch is taken (`len(cache.m) >=
cache.capacity` is `0 >= 0`), which calls `cache.remove(cache.tail.prev,
false)`. On an empty list `cache.tail.prev` is the `head` sentinel, whose
`prev` is `nil`, so `remove` dereferences `nil` at `util/util.go`.
### Fix
Return early from `Put` when `capacity <= 0` — such a cache holds nothing,
so there is nothing to store and no eviction to perform. This keeps `Get`
returning `(nil, false)` for every key, consistent with a zero-capacity cache.
Guarding the eviction path instead would let a zero-capacity cache
incorrectly hold one entry, so the early return is the more correct minimal fix.
### Test
Added `TestLRUCacheNonPositiveCapacity` in `util/util_test.go`. It panics on
`master` and passes with this change:
- before: `panic: runtime error: invalid memory address or nil pointer
dereference` (in `Put`)
- after: `ok github.com/casbin/casbin/v3/util`
---
for the record: fix found and drafted with AI assistance; reviewed and
verified by me.
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