traefik/pkg/middlewares/denyrouterrecursion/deny_router_recursion.go

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package denyrouterrecursion
import (
"errors"
"hash/fnv"
"net/http"
"strconv"
"github.com/containous/alice"
"github.com/traefik/traefik/v2/pkg/log"
)
const xTraefikRouter = "X-Traefik-Router"
type DenyRouterRecursion struct {
routerName string
routerNameHash string
next http.Handler
}
// WrapHandler Wraps router to alice.Constructor.
func WrapHandler(routerName string) alice.Constructor {
return func(next http.Handler) (http.Handler, error) {
return New(routerName, next)
}
}
// New creates a new DenyRouterRecursion.
// DenyRouterRecursion middleware is an internal middleware used to avoid infinite requests loop on the same router.
func New(routerName string, next http.Handler) (*DenyRouterRecursion, error) {
if routerName == "" {
return nil, errors.New("routerName cannot be empty")
}
return &DenyRouterRecursion{
routerName: routerName,
routerNameHash: makeHash(routerName),
next: next,
}, nil
}
// ServeHTTP implements http.Handler.
func (l *DenyRouterRecursion) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
if req.Header.Get(xTraefikRouter) == l.routerNameHash {
log.WithoutContext().Debugf("Rejecting request in provenance of the same router (%q) to stop potential infinite loop.", l.routerName)
rw.WriteHeader(http.StatusBadRequest)
return
}
req.Header.Set(xTraefikRouter, l.routerNameHash)
l.next.ServeHTTP(rw, req)
}
func makeHash(routerName string) string {
hasher := fnv.New64()
// purposely ignoring the error, as no error can be returned from the implementation.
_, _ = hasher.Write([]byte(routerName))
return strconv.FormatUint(hasher.Sum64(), 16)
}