how do you use urlmultipartbypost to send multi-part attachments to external system

Summary:

Content (required):

There is no documentation on how to send attachments to an external system using the urlmultipartbypost.

Do you set the attachments parameter to the return value of getattachmentdata?

Can you provide some sample code on how this can be implemented?

If this is not the function to send file, is there any suggestion (please include sample code) on how to send a file to an external system using webservice?

Version (include the version you are using, if applicable):

23B

Code Snippet (add any code snippets that support your topic, if applicable):