How does Flysystem work internally?

Question

I'm referring to https://flysystem.thephpleague.com/

Let's suppose I'm using the DropBox adapter. I am unclear as to which of the 2 process flows flysystem use. I have googled on this topic but have not seen any clear answer.

Assume a scenario where a user uploads a file. Which of the below 2 is the correct flow?

1. User uploads file -> local server receives file -> local server re-uploads it to DropBox (through flysystem)

2. User uploads file -> DropBox directly receives file (through flysystem)

Answer 1

Basically 1 and 2 are the same. When you upload a file to a PHP application the server always receives the file. Instead of moving the file to a "non temp" directory a file handle can be created to which Flysystem can use to forward the file to dropbox. This is not because Flysystem works like this, it's because PHP on webservers work like this.