curl文件上传详细信息

I have a custom system running on a server which expects a certain file type.

when uploading a file via posts, the $_FILES variable in PHP contains information such as [type] = image/png. Where does this information come from?

When i manually try to curl to my website via SSH, and i add -F "file=@/a/b/c/d.pqx" the type is set to "application/octet-stream".

Is the curl command translating the uploaded file and suppling this information or is the server/php parsing the file and providing this information?

Is it possible to make a POST request to my website and have the filetype show up as "application/pqx" (pqx is a custom file extension) ? I am more interested in a way to make the right POST request rather than changing the PHP code. Can i customize the curl request to the website and supply the filetype myself?

thanks for all your help!