April 20, 2019: GAS library for this situation was published. Please check it at https://github.com/tanaikech/FetchApp.
These sample scripts are for requesting multipart post using Google Apps Script.
In most cases, the multipart request is used for uploading files. So I prepared 2 sample situations as follows. For each situation, the request parameters are different.
- Upload a file from Google Drive to Slack.
- Convert an excel file to Spreadsheet on Google Drive using Drive API v3.