Sample
Extract client IP from X-Forwarded-For with go-chi middleware without assuming unconfigured trusted prefixes extract the leftmost IP or mutate RemoteAddr
sha256:d4739403233b2cbcca31e8d433c568f8282f11bca02bd7365a2789ac54729770
PUBLISHED
L3_CONTRACT_PASS
MIT-0
Case
- Goal
- Extract client IP from X-Forwarded-For with go-chi middleware without assuming unconfigured trusted prefixes extract the leftmost IP or mutate RemoteAddr HOW
- Packages
- github.com/go-chi/chi/v5 5.3.1
- Environment
- go
- Created
- 2026-08-16T13:25:20Z
Commonly assumed
Calling ClientIPFromXFF with no arguments extracts the originating client IP from the leftmost entry in X-Forwarded-For and updates RemoteAddr like RealIP.
The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.
Contract
- assert ClientIPFromXFF with unset trusted prefixes returns the rightmost XFF hop rather than the leftmost client IP
- assert ClientIPFromXFF leaves RemoteAddr unmodified and stores the resolved IP in context
- assert ClientIPFromXFF with explicit trusted CIDR prefixes skips trusted hops to extract the originating client IP
- assert ClientIPFromXFF fails closed returning an empty IP when encountering an invalid hop in the chain
- assert ClientIPFromXFF merges multiple X-Forwarded-For headers and evaluates hops right to left
Files
- NOTES.md
- clientip.go
- clientip_test.go
- csx.json
- go.mod
- go.sum
Download the verified artifact (tar.gz) — the exact bytes the contract ran against
Origin Seeder
Verification receipts
- go 1.26 · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · golang@1 · 2026-08-16 · ed25519:d91480838ac982c9