fix: stripPrefix middleware with empty resulting path.

docs/content/middlewares/addprefix.md

@@ -58,4 +58,5 @@ http:
 
 ### `prefix`
 
-`prefix` is the string to add before the current path in the requested URL. It should include the leading slash (`/`).
+`prefix` is the string to add before the current path in the requested URL.
+It should include the leading slash (`/`).

docs/content/middlewares/stripprefix.md

@@ -85,3 +85,85 @@ If your backend is serving assets (e.g., images or Javascript files), chances ar
 Continuing on the example, the backend should return `/products/shoes/image.png` (and not `/images.png` which Traefik would likely not be able to associate with the same backend).  
 
 The `X-Forwarded-Prefix` header can be queried to build such URLs dynamically.
+
+### `forceSlash`
+
+_Optional, Default=true_
+
+```yaml tab="Docker"
+labels:
+  - "traefik.http.middlewares.example.stripprefix.prefixes=/foobar"
+  - "traefik.http.middlewares.example.stripprefix.forceslash=false"
+```
+
+```yaml tab="Kubernetes"
+apiVersion: traefik.containo.us/v1alpha1
+kind: Middleware
+metadata:
+  name: example
+spec:
+  stripPrefix:
+    prefixes:
+      - "/foobar"
+    forceSlash: false
+```
+
+```json tab="Marathon"
+"labels": {
+  "traefik.http.middlewares.example.stripprefix.prefixes": "/foobar",
+  "traefik.http.middlewares.example.stripprefix.forceslash": "false"
+}
+```
+
+```yaml tab="Rancher"
+labels:
+  - "traefik.http.middlewares.example.stripprefix.prefixes=/foobar"
+  - "traefik.http.middlewares.example.stripprefix.forceSlash=false"
+```
+
+```toml tab="File (TOML)"
+[http.middlewares]
+  [http.middlewares.example.stripPrefix]
+    prefixes = ["/foobar"]
+    forceSlash = false
+```
+
+```yaml tab="File (YAML)"
+http:
+  middlewares:
+    example:
+      stripPrefix:
+        prefixes:
+          - "/foobar"
+        forceSlash: false
+```
+
+The `forceSlash` option makes sure that the resulting stripped path is not the empty string, by replacing it with `/` when necessary.
+
+This option was added to keep the initial (non-intuitive) behavior of this middleware, in order to avoid introducing a breaking change.
+
+It's recommended to explicitly set `forceSlash` to `false`.
+
+??? info "Behavior examples"
+    
+    - `forceSlash=true`
+    
+    | Path       | Prefix to strip | Result |
+    |------------|-----------------|--------|
+    | `/`        | `/`             | `/`    |
+    | `/foo`     | `/foo`          | `/`    |
+    | `/foo/`    | `/foo`          | `/`    |
+    | `/foo/`    | `/foo/`         | `/`    |
+    | `/bar`     | `/foo`          | `/bar` |
+    | `/foo/bar` | `/foo`          | `/bar` |
+    
+    - `forceSlash=false`
+    
+    | Path       | Prefix to strip | Result |
+    |------------|-----------------|--------|
+    | `/`        | `/`             | empty  |
+    | `/foo`     | `/foo`          | empty  |
+    | `/foo/`    | `/foo`          | `/`    |
+    | `/foo/`    | `/foo/`         | empty  |
+    | `/bar`     | `/foo`          | `/bar` |
+    | `/foo/bar` | `/foo`          | `/bar` |