k8s_matches_pathtype_prefix incorrectly handles locations with trailing slash

[ichaozai]

NGINX Ingress controller version: 0.41.0

Kubernetes version (use kubectl version): v1.17.5

Environment:

• Cloud provider or hardware configuration:
• OS (e.g. from /etc/os-release): Ubuntu 16.04.6 LTS
• Kernel (e.g. uname -a): 4.4.0-142-generic
• Install tools: kubeadm
• Others:

What happened:

With following Ingress:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  annotations:
    kubernetes.io/ingress.class: nginx
  name: an-ingress
spec:
  rules:
  - http:
      paths:
      - backend:
          serviceName: a-service
          servicePort: 80
        path: /prefix/

Got HTTP 404 when accessing /prefix/foo/bar.

What you expected to happen:

Path with a trailing slash should work as the prefix.

When I turn on debug log level:

2020/11/12 09:25:47 [debug] 72368#72368: *3797004 code cache lookup (key='rewrite_by_lua_nhli_d8124e310757dec7b05144568a4babe7', ref=-1)
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 code cache miss (key='rewrite_by_lua_nhli_d8124e310757dec7b05144568a4babe7', ref=-1)
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 lua creating new thread
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 lua reusing cached lua thread 00007FE683EDB5E0 (ref 2)
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 lua reset ctx
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 http lua finalize threads
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 http cleanup add: 00005609E27EBDB0
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 lua run thread, top:0 c:1
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 lua exit with code 404
2020/11/12 09:25:47 [debug] 72368#72368: *3797004 lua resume returned 1

It exits with HTTP 404 from lua_ingress.rewrite(), which call k8s_matches_pathtype_prefix()
https://github.com/kubernetes/ingress-nginx/blob/controller-v0.41.0/rootfs/etc/nginx/lua/lua_ingress.lua#L100-L117

It should ignore the trailing slash at the beginning.

How to reproduce it:

Anything else we need to know:

/kind bug

[aledbf]

Closing. Fixed in #6443