feat(http): keep slashes in queryParams in redirects (#4928)

* refactor(http): extract logic into constructRedirectPath

This allows us to easily test our redirect path construction logic where we get
the relative path, the query string and construct a redirect path.

By extracting this from `redirect`, we can easily test this logic in a unit
test.

I did this so we could test some logic where slashes in query strings should be
made human-friendly for users.

* feat(testing): add tests for constructRedirectPath

Co-authored-by: Asher <ash@coder.com>

src/node/http.ts

@@ -138,6 +138,21 @@ export const relativeRoot = (originalUrl: string): string => {
   return normalize("./" + (depth > 1 ? "../".repeat(depth - 1) : ""))
 }
 
+/**
+ * A helper function to construct a redirect path based on
+ * an Express Request, query and a path to redirect to.
+ *
+ * Redirect path is relative to `/${to}`.
+ */
+export const constructRedirectPath = (req: express.Request, query: qs.ParsedQs, to: string): string => {
+  const relativePath = normalize(`${relativeRoot(req.originalUrl)}/${to}`, true)
+  // %2f or %2F are both equalivent to an encoded slash /
+  const queryString = qs.stringify(query).replace(/%2[fF]/g, "/")
+  const redirectPath = `${relativePath}${queryString ? `?${queryString}` : ""}`
+
+  return redirectPath
+}
+
 /**
  * Redirect relatively to `/${to}`. Query variables on the current URI will be
  * preserved.  `to` should be a simple path without any query parameters
@@ -156,9 +171,7 @@ export const redirect = (
     }
   })
 
-  const relativePath = normalize(`${relativeRoot(req.originalUrl)}/${to}`, true)
-  const queryString = qs.stringify(query)
-  const redirectPath = `${relativePath}${queryString ? `?${queryString}` : ""}`
+  const redirectPath = constructRedirectPath(req, query, to)
   logger.debug(`redirecting from ${req.originalUrl} to ${redirectPath}`)
   res.redirect(redirectPath)
 }