fix: ensure regular expressions are properly escaped (#378)

* fix: front slashes only get escaped now if they aren't already

* chore: updated test description

* chore: cleaned up logic

* fix: ensure regexes are properly escaped

* chore: style changes

---------

Co-authored-by: Nick Taylor <nick@iamdeveloper.com>

node/declaration.test.ts

@@ -1,7 +1,7 @@
 import { test, expect } from 'vitest'
 
 import { FunctionConfig } from './config.js'
-import { Declaration, mergeDeclarations } from './declaration.js'
+import { Declaration, mergeDeclarations, parsePattern } from './declaration.js'
 
 const deployConfigDeclarations: Declaration[] = []
 
@@ -191,3 +191,19 @@ test('netlify.toml-defined excludedPath are respected', () => {
 
   expect(declarations).toEqual(expectedDeclarations)
 })
+
+test('Does not escape front slashes in a regex pattern if they are already escaped', () => {
+  const regexPattern = '^(?:\\/(_next\\/data\\/[^/]{1,}))?(?:\\/([^/.]{1,}))\\/shows(?:\\/(.*))(.json)?[\\/#\\?]?$'
+  const expected = '^(?:\\/(_next\\/data\\/[^/]{1,}))?(?:\\/([^/.]{1,}))\\/shows(?:\\/(.*))(.json)?[\\/#\\?]?$'
+  const actual = parsePattern(regexPattern)
+
+  expect(actual).toEqual(expected)
+})
+
+test('Escapes front slashes in a regex pattern', () => {
+  const regexPattern = '^(?:/(_next/data/[^/]{1,}))?(?:/([^/.]{1,}))/shows(?:/(.*))(.json)?[/#\\?]?$'
+  const expected = '^(?:\\/(_next\\/data\\/[^/]{1,}))?(?:\\/([^/.]{1,}))\\/shows(?:\\/(.*))(.json)?[/#\\?]?$'
+  const actual = parsePattern(regexPattern)
+
+  expect(actual).toEqual(expected)
+})

node/declaration.ts

@@ -130,9 +130,8 @@ const createDeclarationsFromFunctionConfigs = (
 // Validates and normalizes a pattern so that it's a valid regular expression
 // in Go, which is the engine used by our edge nodes.
 export const parsePattern = (pattern: string) => {
-  // Escaping forward slashes with back slashes.
-  const normalizedPattern = pattern.replace(/\//g, '\\/')
-  const regex = regexpAST.transform(`/${normalizedPattern}/`, {
+  const regexp = new RegExp(pattern)
+  const newRegexp = regexpAST.transform(regexp, {
     Assertion(path) {
       // Lookaheads are not supported. If we find one, throw an error.
       if (path.node.kind === 'Lookahead') {
@@ -155,5 +154,5 @@ export const parsePattern = (pattern: string) => {
   })
 
   // Strip leading and forward slashes.
-  return regex.toString().slice(1, -1)
+  return newRegexp.toString().slice(1, -1)
 }