ReactNative on Android requires a mime type when uploading files with FormData. But the only way to get the mime type of a user-chosen file is to read the file or files into memory after a user select one or more. In all of my use cases, my server didn’t care if the mimetype was in the FormData.
The easy solution is to just set the mimetype to a binary file type (e.g. application/octet-stream):
let data = new FormData();
data.append("file", {
name: "cool.pdf",
uri: "///files/cool.pdf",
// MIME-type required on Android
type: "application/octet-stream"
});
fetch("http://example.com/upload-file", data);