Software architecture

Program flow

router.php: Receives every external HTTP request from the web server, executes actions required in any case, executes matching code in pg-act if appropriate, and calls view.php either way.
pg-act/: Executed when a form is submitted: checks that every parameter is valid and secure, then executes the feature of the page according to the parameters.
view.php: Displays global HTML and includes matching file from pg-view.
pg-view/: Displays the main page content (notably HTML forms), may sometimes display form output passed through the $data array.

The output function is used to return success or error messages and stop processing of the request.

fn/: Functions, grouped by concerned service
sftpgo-auth.php: When someone tries to log in over SFTP, SFTPGo sends username and password to this script, which queries the database and replies whether authentication succeeded or not.
check.php: This file is not part of the normal program execution, it is meant to be run by developers to test that the current setup is working.
DOCS/: Documentation (some important or standard files may be directly in the root)
css/: Each .css file in this directory is declared in every page.
db/: SQlite database, the only directory writable by the program
locales/: Gettext translations, see translation.md