Fix control characters in link, image destinations

Closes GH-46.

Author: wooorm

lib/handle/image.js

@@ -24,8 +24,8 @@ export function image(node, _, context) {
   if (
     // If there’s no url but there is a title…
     (!node.url && node.title) ||
-    // Or if there’s markdown whitespace or an eol, enclose.
-    /[ \t\r\n]/.test(node.url)
+    // If there are control characters or whitespace.
+    /[\0- \u007F]/.test(node.url)
   ) {
     subexit = context.enter('destinationLiteral')
     value += '<' + safe(context, node.url, {before: '<', after: '>'}) + '>'

lib/handle/link.js

@@ -46,8 +46,8 @@ export function link(node, _, context) {
   if (
     // If there’s no url but there is a title…
     (!node.url && node.title) ||
-    // Or if there’s markdown whitespace or an eol, enclose.
-    /[ \t\r\n]/.test(node.url)
+    // If there are control characters or whitespace.
+    /[\0- \u007F]/.test(node.url)
   ) {
     subexit = context.enter('destinationLiteral')
     value += '<' + safe(context, node.url, {before: '<', after: '>'}) + '>'

test/index.js

@@ -1427,6 +1427,12 @@ test('image', (t) => {
     'should escape a backslash in `url` in a raw url'
   )
 
+  t.equal(
+    to({type: 'image', url: '\f'}),
+    '![](<\f>)\n',
+    'should support control characters in images'
+  )
+
   t.equal(
     to({type: 'image', url: '', title: 'b"c'}),
     '![](<> "b\\"c")\n',
@@ -1781,6 +1787,12 @@ test('link', (t) => {
     'should escape a backslash in `url` in a raw url'
   )
 
+  t.equal(
+    to({type: 'link', url: '\f', children: []}),
+    '[](<\f>)\n',
+    'should support control characters in links'
+  )
+
   t.equal(
     to({type: 'link', url: '', title: 'b"c', children: []}),
     '[](<> "b\\"c")\n',