avoid regex for tag content footgun (#89)

using regex to try to select the content fo the table was leading to runaway catastprohic backtracking.

the simple solution is to just do string substring selection and insertion on the start and end tag

src/paste-markdown-table.ts

@@ -91,6 +91,12 @@ function generateText(transfer: DataTransfer): string | undefined {
   const html = transfer.getData('text/html')
   if (!/<table/i.test(html)) return
 
+  // eslint-disable-next-line github/unescaped-html-literal
+  const start = html.substring(0, html.indexOf('<table'))
+  const tableCloseIndex = html.lastIndexOf('</table>')
+  if (!start || !tableCloseIndex) return
+  const end = html.substring(tableCloseIndex + 8)
+
   const parser = new DOMParser()
   const parsedDocument = parser.parseFromString(html, 'text/html')
 
@@ -100,5 +106,7 @@ function generateText(transfer: DataTransfer): string | undefined {
 
   const formattedTable = tableMarkdown(table)
 
-  return html.replace(/<meta.*?>/, '').replace(/<table[.\S\s]*<\/table>/, `\n${formattedTable}`)
+  if (!formattedTable) return
+
+  return [start, formattedTable, end].join('').replace(/<meta.*?>/, '')
 }

test/test.js

@@ -202,7 +202,7 @@ describe('paste-markdown', function () {
       assert.equal(
         textarea.value.trim(),
         // eslint-disable-next-line github/unescaped-html-literal
-        `<p>Here is a cool table</p>\n        \n  \n\n${tableMarkdown}\n\n\n\n        <p>Very cool</p>`
+        `<p>Here is a cool table</p>\n        \n  \n${tableMarkdown}\n\n\n\n        <p>Very cool</p>`
       )
     })
 
@@ -225,6 +225,19 @@ describe('paste-markdown', function () {
       assertUnformattedPaste(textarea)
     })
 
+    it('rejects malformed tables', function () {
+      // eslint-disable-next-line github/unescaped-html-literal, prefer-template
+      const html = '<table'.repeat(999) + '<div><table></div>'
+      const data = {
+        'text/html': html
+      }
+      paste(textarea, data)
+
+      // Synthetic paste events don't manipulate the DOM. A empty textarea
+      // means that the event handler didn't fire and normal paste happened.
+      assertUnformattedPaste(textarea)
+    })
+
     it('accepts x-gfm', function () {
       paste(textarea, {'text/plain': 'hello', 'text/x-gfm': '# hello'})
       assert.include(textarea.value, '# hello')