child process exit event fires before IO is complete, causing errors

Under heavy load (in the context of web application, for example using nestjs) some of the requests fail:

1. According to child process documentation (https://nodejs.org/docs/latest-v14.x/api/child_process.html#child_process_event_exit), exit even can fire before stdio is closed.
In such cases respond() is being called with code 0 (success), no error and no data. This results in an error in the calling code, because filename is expected but is not returned.
I added additional error checking to respond() to handle this case.

2. Given the above, it's probably not a good idea to subscribe to exit event at all. I commented out the on('exit'..) code. on('close') should be sufficient.

Tested it under some load (30 concurrent connections for 2 minutes) - no errors, 5000+ PDFs rendered.

Author: kvasserman

lib/pdf.js

@@ -123,12 +123,15 @@ PDF.prototype.exec = function PdfExec (callback) {
     // Ignore if code has a value of 0 since that means PhantomJS has executed and exited successfully.
     // Also, as per your script and standards, having a code value of 1 means one can always assume that
     // an error occured.
-    if (((typeof code !== 'undefined' && code !== null) && code !== 0) || err) {
+    if (((typeof code !== 'undefined' && code !== null) && code !== 0) || err || (code === 0 && !data)) {
       var error = null
 
       if (err) {
         // Rudimentary checking if err is an instance of the Error class
         error = err instanceof Error ? err : new Error(err)
+      } else if (code === 0 && !data) {
+        // This is to catch the edge case of having a exit code value of 0 but having no data (exit can be called before io pipes are closed)
+        error = new Error('html-pdf: Process exited successfully, but no data received')
       } else {
         // This is to catch the edge case of having a exit code value of 1 but having no error
         error = new Error('html-pdf: Unknown Error')
@@ -150,7 +153,7 @@ PDF.prototype.exec = function PdfExec (callback) {
 
   // An exit event is most likely an error because we didn't get any data at this point
   child.on('close', respond)
-  child.on('exit', respond)
+  // child.on('exit', respond)
 
   var config = JSON.stringify({html: this.html, options: this.options})
   child.stdin.write(config + '\n', 'utf8')

package.json

@@ -1,6 +1,6 @@
 {
   "name": "html-pdf",
-  "version": "3.0.1",
+  "version": "3.0.2-kv",
   "description": "HTML to PDF converter that uses phantomjs",
   "engines": {
     "node": ">=4.0.0"