Prevent the callback from getting called twice.

Author: westy92

lib/pdf.js

@@ -84,6 +84,7 @@ PDF.prototype.toFile = function PdfToFile (filename, callback) {
 }
 
 PDF.prototype.exec = function PdfExec (callback) {
+  var callbacked = false
   var child = childprocess.spawn(this.options.phantomPath, [].concat(this.options.phantomArgs, [this.script]))
   var stdout = []
   var stderr = []
@@ -105,25 +106,29 @@ PDF.prototype.exec = function PdfExec (callback) {
     return child.kill()
   })
 
-  child.on('error', function (error) {
+  function exit (err, data) {
+    if (callbacked) return
+    callbacked = true
     clearTimeout(timeout)
-    return callback(error)
-  })
+    if (err) return callback(err)
+    return callback(null, data)
+  }
+
+  child.on('error', exit)
 
   child.on('exit', function (code) {
-    clearTimeout(timeout)
     if (code || stderr.length) {
       var err = new Error(Buffer.concat(stderr).toString() || 'html-pdf: Unknown Error')
-      return callback(err)
+      return exit(err)
     } else {
       try {
         var buff = Buffer.concat(stdout).toString()
         var data = (buff) != null ? buff.trim() : undefined
         data = JSON.parse(data)
       } catch (err) {
-        return callback(err)
+        return exit(err)
       }
-      return callback(null, data)
+      return exit(null, data)
     }
   })