CODEWITHSUNDEEP
node.jsexpressrethinkdb
Guilherme Abacherli
Guilherme Abacherli

Reputation: 335

NodeJS and RethinkDB - How to handle connection interruption (connection retry) when listening for table changes (realtime)?

ReqlRuntimeError: Connection is closed in:
r.table("users").changes()
^^^^^^^^^^^^^^^^^^^^^^^^^^
    at ReqlRuntimeError.ReqlError [as constructor] (/home/user/DEV/express-socketio/node_modules/rethinkdb/errors.js:23:13)
    at new ReqlRuntimeError (/home/user/DEV/express-socketio/node_modules/rethinkdb/errors.js:90:51)
    at mkErr (/home/user/DEV/express-socketio/node_modules/rethinkdb/util.js:177:10)
    at Feed.IterableResult._promptNext (/home/user/DEV/express-socketio/node_modules/rethinkdb/cursor.js:169:16)
    at Feed.IterableResult._addResponse (/home/user/DEV/express-socketio/node_modules/rethinkdb/cursor.js:84:12)
    at TcpConnection.<anonymous> (/home/user/DEV/express-socketio/node_modules/rethinkdb/net.js:360:22)
    at TcpConnection.cancel (/home/user/DEV/express-socketio/node_modules/rethinkdb/util.js:26:16)
    at TcpConnection.cancel (/home/user/DEV/express-socketio/node_modules/rethinkdb/net.js:789:43)
    at wrappedCb (/home/user/DEV/express-socketio/node_modules/rethinkdb/net.js:270:17)
    at /home/user/DEV/express-socketio/node_modules/rethinkdb/net.js:280:18
    at tryCatcher (/home/user/DEV/express-socketio/node_modules/bluebird/js/main/util.js:26:23)
    at Promise._resolveFromResolver (/home/user/DEV/express-socketio/node_modules/bluebird/js/main/promise.js:483:31)
    at new Promise (/home/user/DEV/express-socketio/node_modules/bluebird/js/main/promise.js:71:37)
    at TcpConnection.<anonymous> (/home/user/DEV/express-socketio/node_modules/rethinkdb/net.js:264:33)
    at TcpConnection.close (/home/user/DEV/express-socketio/node_modules/rethinkdb/util.js:43:16)
    at /home/user/DEV/express-socketio/node_modules/rethinkdb/net.js:782:46
[ERROR] 22:55:08 ReqlRuntimeError: Connection is closed in:
r.table("users").changes()
^^^^^^^^^^^^^^^^^^^^^^^^^^

I had this error when executing a test as following:

  1. My nodejs is listening for changes in a table (realtime),
  2. then I simulate a connection interruption by turning off the rethinkdb docker container
  3. and the error breaks the whole application.

I'm looking for how to handle this kind of error, so the application knows the connection was lost, but, in some way, after a period of X minutes/seconds/etc, try to reconnect, or even restart the application, I don't know...

I found this https://github.com/rethinkdb/rethinkdb/issues/4886, but nothing about avoiding app crash or trying to reconnect after a connection loss.

How can I proceed with this? Any thoughts? Thanks in advance.

Upvotes: 1

Views: 231

Answers (1)

Michael Cole
Michael Cole

Reputation: 16217

The example isn't that complete. Consider this code that might run when a websocket is opened on a server:

// write every change to file

function onChange(err, cursor) {
  // log every change to console
  // Change format: https://rethinkdb.com/docs/changefeeds/javascript/
  cursor.each(console.log);

  // if file not open, open file 
  openFile()

  // write changes to file
  cursor.each(writeChangesToFile)

  // if you decide you no longer want these changes
  if (stopChangesNow) {
    cursor.close() // https://rethinkdb.com/api/javascript/#close-cursor
    cancel()
  }
}

// stop writing changes

function cancel(stream) {
  // close file opened above
  closeFile()
}

try {
  r.table('users').changes().run(conn, onChange)
} catch(e) {
  cancel()
}

You need the run() so your application can process the changes.

You might not need the cancel() function unless you need to cleanup a socket, output stream, file handles, etc. You need the try/catch to keep from crashing.

When a REST server crashes, it only terminates requests in progress.

When a websocket server crashes, it terminates all it's sessions causing problems for a lot more users.

Upvotes: 1

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