Ensures that mount()'d routes have a leading slash.

This also adds a small test for this behaviour.

NEWS.md

@@ -54,6 +54,8 @@ plumber 0.5.0
 
 ### Bug fixes
 
+* Fix possible bugs due to mounted routers without leading slashes (@atheriel, [#476](https://github.com/trestletech/plumber/issues/270) [#501](https://github.com/trestletech/plumber/pull/501)).
+
 * Fix bug preventing error handling when a serializer fails (@antoine-sachet, [#490](https://github.com/rstudio/plumber/pull/490))
 
 * Fix URL-decoding of query parameters and URL-encoding/decoding of cookies. Both now use `httpuv::decodeURIComponent` instead of `httpuv::decodeURI`. (@antoine-sachet, [#462](https://github.com/trestletech/plumber/pull/462))

R/plumber.R

@@ -322,7 +322,8 @@ plumber <- R6Class(
       httpuv::runServer(host, port, self)
     },
     mount = function(path, router){
-      path <- sub("([^/])$", "\\1/", path)
+      # Ensure that the path has both a leading and trailing slash.
+      path <- sub("^/?(.*)([^/])$", "/\\1\\2/", path)
 
       private$mnts[[path]] <- router
     },

tests/testthat/test-plumber.R

@@ -150,9 +150,11 @@ test_that("mounts can be read correctly", {
 
   stat <- PlumberStatic$new(".")
   pr$mount("/static", stat)
+  pr$mount("missing-slash", stat)
 
-  expect_length(pr$routes, 3)
+  expect_length(pr$routes, 4)
   expect_s3_class(pr$mounts[["/static/"]], "plumberstatic")
+  expect_s3_class(pr$mounts[["/missing-slash/"]], "plumberstatic")
   expect_s3_class(pr$mounts[["/mysubpath/"]], "plumber")
 })