ERR_SOCKET_DGRAM_NOT_RUNNING error when chunking request body(fix suggested)

[Hsiwe]

Hi! I'm using gelf-pro as a tool to send my app's logs through UDP. Recently I started to get ERR_SOCKET_DGRAM_NOT_RUNNING exception from time to time.
Here's an error trace:

Error [ERR_SOCKET_DGRAM_NOT_RUNNING]: Not running
at new NodeError (node:internal/errors:363:5)
    at healthCheck (node:dgram:908:11)
    at Socket.close (node:dgram:740:3)
    at cbResults (path/to/my/app/node_modules/gelf-pro/lib/adapter/udp.js:75:14)
    at /path/to/my/app/node_modules/gelf-pro/lib/adapter/udp.js:118:13
    at processTicksAndRejections (node:internal/process/task_queues:83:21)

As specified in the stack trace - the error happens when Socket.close is called.
After investigation I found that this happens only when request body is more than 1388 bytes and gelf-pro divides body in chunks.
The bug is in this code(from /lib/adapter/udp.js:103):

for (var idx in chunks) {
      if (isInterrupted) {
        break;
      }
      var chunk = chunks[idx],
        packet = buffer
          .from(self.specification.magicBytes.concat(packetId, idx, chunksCount, chunk));
      client.send(
        packet, 0, packet.length, self.options.port, self.options.host,
        function (err, bytesSent) {
          if (err) { return cbResults(err); }
          bytesSentTotal += bytesSent;
          /* istanbul ignore else */
          if (idx >= chunksCount - 1) {
            cbResults(err, bytesSentTotal);
          }
        }
      );
    }

More specifically in this closure:

if (idx >= chunksCount - 1) {
            cbResults(err, bytesSentTotal);
          }

Here idx is specified to check whether we arrived at the end of chunks array or not, but because of how JavaScript variable scope works what actually happens is - idx is always equal to chunksCount - 1 and cbResults is called on every loop, not only on the last one (hence ERR_SOCKET_DGRAM_NOT_RUNNING error because we try to close udp connection multiple times). Great example of how and why it works like this is provided here.

So here's a fix I came up with. What's important to note - in order for this fix to work you must use const(or let), not var(because var variable are not scope bound and by using var we actually do the same thing).

diff --git a/node_modules/gelf-pro/lib/adapter/udp.js b/node_modules/gelf-pro/lib/adapter/udp.js
index 58e452d..431b38c 100644
--- a/node_modules/gelf-pro/lib/adapter/udp.js
+++ b/node_modules/gelf-pro/lib/adapter/udp.js
@@ -101,20 +101,21 @@ adapter.send = function (message, callback) {
 
     var packetId = Array.prototype.slice.call(crypto.randomBytes(8));
     for (var idx in chunks) {
+      const capturedIndex = idx;
       if (isInterrupted) {
         break;
       }
       var chunk = chunks[idx],
         packet = buffer
           .from(self.specification.magicBytes.concat(packetId, idx, chunksCount, chunk));
       client.send(
         packet, 0, packet.length, self.options.port, self.options.host,
         function (err, bytesSent) {
           if (err) { return cbResults(err); }
           bytesSentTotal += bytesSent;
           /* istanbul ignore else */
-          if (idx >= chunksCount - 1) {
+          if (capturedIndex >= chunksCount - 1) {
             cbResults(err, bytesSentTotal);
           }
         }

This issue body was partially generated by patch-package.

[kkamkou]

Thank you for the detailed report and a hint.