V-Blaze and V-Cloud Online Help (May 2020)

Troubleshooting a Callback Server

If files are being uploaded successfully to V‑Cloud, you received a success code (HTTP code 200) and a requestid in response to uploading to V‑Cloud. If your callback server is not receiving results, check the items in the following list:

  • Verify that external hosts can reach your callback server - Receiving a success code and requestid in response to POSTing a request to V‑Cloud shows that the system that is POSTing the request can reach V‑Cloud. This does not mean that V‑Cloud can reach your callback host. This lack of reachability is usually due to firewall or network connectivity restrictions.

    Verifying connectivity can most easily be done using a simple callback server like the one that was discussed in Setting up a Sample Callback Server.

    To test connectivity between V‑Cloud and your callback server, log in on a host that is not on your local network and can be reached directly from the internet. Once you are logged in there, attempt to reach the host on which your callback server is running. The following is a sample curl command that simply probes the URL at which a callback server is listening:

    curl -i http://host:5555

    The host and port that you specify are the host and port on which your callback server is listening.

    The -i option tells the curl command to display the HTTP header that it receives. For example, if you are using the sample callback server that was discussed earlier, you will receive a result that is similar to the following:

    HTTP/1.1 200 OK


    If your network administration policies restrict inbound connectivity from external hosts, contact for the list of V‑Cloud IP addresses from which access needs to be allowed.

  • Identify problems in your callback server - If you are able to reach the host and port on which your callback server is running from some other host on the Internet, connectivity is not the problem. Try the following steps to identify problems with your callback server:

    • Verify that you can POST directly to your callback server - use a command like the following to simulate the data that would be sent by V‑Cloud to your callback server:

      curl -F "file=@test.zip;type=application/zip" \
           -F requestid=700e7496-4fce-4963-aa7b-b3b26600f813 \

      This command provides the two fields of the multipart POST that your callback server needs to be able to handle. Ensure that your callback server correctly returns success (HTTP code 200) when these two fields are received.

    • Verify correct error handling - it is possible for V‑Cloud transcription to encounter an error. In such cases, an error message will be POSTed in an error field to your callback server. Your callback server must be able to handle receiving error messages from V‑Cloud. The following example command sends the error message This is a sample error to your callback server:

      curl -F "error=This is a sample error" \
           -F requestid=700e7496-4fce-4963-aa7b-b3b26600f813 \

      This sample command should trigger error handling in your callback server, such as logging a message.

    If you still cannot identify or resolve the problem with your callback server, contact for assistance in diagnosing the problem that you are experiencing.