Is it possible to send the custom message from satis-server for displaying in customer console? For example - "This repository will be in maintenance mode next day."
If yes, what I need to add to the packages.json file?
{
"packages": [],
"includes": {
"include/all$edc82a88b20174d3fac08ba4146f4423fd71d9d6.json": {
"sha1": "edc82a88b20174d3fac08ba4146f4423fd71d9d6"
}
}
}
I don't think Composer allows for such a mechanism. After all, Satis is just a bunch of static files, and all you need is HTTPS hosting for them. This makes it as easy as possible to allow for temporary alternative hosting, IMHO.
Nothing in the HTTP world seems appropriate for your use case either. Status Code 503 (Temporarily unavailable) can only trigger when the maintenance is actually taking place - there is nothing for warning in advance.