Fix middleware.CleanPath panicking on a non-chi handler

[januththedev]

middleware.CleanPath panics on a non-chi handler

Description

CleanPath dereferences the chi routing context unconditionally:

rctx := chi.RouteContext(r.Context())
routePath := rctx.RoutePath   // nil deref when rctx == nil

chi.RouteContext returns nil whenever the handler is not a chi.Mux.

Why it's wrong

CleanPath is exported as a plain func CleanPath(next http.Handler) http.Handler with no chi-only restriction, so composing it onto an http.ServeMux, an http.FileServer, or any other non-chi handler panics with a nil-pointer dereference on the very first request.

It has no chi-specific work to do — it only needs to normalise a path and write it back. And its sibling in the same package already handles this exact case:

// middleware/strip.go:15-27
if rctx == nil { r.URL.Path = newPath } else { rctx.RoutePath = newPath }

with a dedicated regression test, TestStripSlashesWithNilContext (middleware/strip_test.go:203), commented "This tests a http.Handler that is not chi.Router / In these cases, the routeContext is nil". CleanPath was simply never given the same guard. I probed the rest of the package: StripSlashes, RedirectSlashes, URLFormat, Heartbeat and PageRoute all survive a nil context — only CleanPath and GetHead panic, and GetHead is fundamentally chi-dependent so a panic there is more defensible.

Issue #787 "middleware.CleanPath doesn't work with other routers" is still open (its PR #786 closed unmerged).

The fix

rctx := chi.RouteContext(r.Context())

routePath := ""
if rctx != nil {
    routePath = rctx.RoutePath
}
if routePath == "" {
    if r.URL.RawPath != "" {
        routePath = r.URL.RawPath
    } else {
        routePath = r.URL.Path
    }
    if rctx == nil {
        r.URL.Path = path.Clean(routePath)
    } else {
        rctx.RoutePath = path.Clean(routePath)
    }
}

Tests

TestCleanPathWithNilContext in middleware/clean_path_test.go, mirroring the existing nil-context test's style.

• Before: panic: runtime error: invalid memory address or nil pointer dereference at clean_path.go:16. After: passes, and the pre-existing TestCleanPath still passes.
• Full suite go test -count=1 ./... (uncached): chi and chi/v5/middleware both ok, exit 0, 0 failures, 0 skips — 129 top-level PASS. Identical to the baseline on unmodified HEAD, which had no pre-existing failures. go vet ./... clean.

Upstream status

I checked 60 open issues and 55 open PRs and mapped each open PR to the files it touches. middleware/clean_path.go is touched only by open PR #1162 (CONNECT authority-form, unrelated — it wraps the path.Clean call in if routePath != "" and does not address the nil context). No open issue or PR fixes the nil-context panic.

I steered clear of the heavily-contended files: tree.go/mux.go (11+ PRs), middleware/get_head.go (4), middleware/compress.go (10), plus strip.go, supress_notfound.go, route_headers.go, nocache.go, recoverer.go, content_encoding.go, context.go.

gofmt -l flags these files, but it flags 65 non-_examples Go files including untouched ones (strip.go, tree.go, context.go) — this machine has core.autocrlf=true, so the whole checkout is CRLF. Pre-existing checkout condition, not introduced here; git diff shows no line-ending churn.

Real neighbouring defects I found but left alone

• middleware.GetHead breaks explicit HEAD handlers inside a mounted subrouter — measured: HEAD /api/other → 405 with GetHead on the subrouter, 200 without. get_head.go:29 uses rctx.Routes (set only by the root mux) with a sub-router-relative routePath. Not narrow: naively setting rctx.Routes = mx regresses SupressNotFound inside subrouters, which I measured going 200 → 404.
• middleware.Heartbeat silently never fires inside a subrouter (compares r.URL.Path, not rctx.RoutePath) — measured GET /api/ping → 404. Open issue Heartbeat middleware is not invoked when added to a subrouter #821, no open PR; middleware/page_route.go has the identical flaw with no issue at all.
• A regexp placeholder with a literal suffix matches across / — tree.go:457-464 skips the "avoid a match across path segments" check for ntRegexp, so /re/{name:[^.]+}.json matches /re/a/b.json. Issue A regexp placeholder followed by a suffix matches a value containing / #1188 with PR tree: do not match slash in regexp placeholder with suffix (#1188) #1189 already filed.