问题
This is an architectural question. I haven't implemented FCM yet, but as far as I understand someone needs to deploy an XMPP server in a real world scenario which provisions the inventory of the registered device tokens.
In my use case I'd like to just broadcast short messages about important update information, like "XY presenter's session at 15:00 got cancelled" and I'm not interested in the device tokens. My application is a Progressive Web App, so I would use FCM for Web.
The demos I saw so far showed a client receiving the device token, then that specific device token was picked up from the debug environment and used to send the demo message to the client - thus bypassing the need of a deployed stand-alone XMPP server, but just for demo purposes.
I'd want to avoid the use of an XMPP server, I'm not interested in dealing with the device tokens at all - if possible. Firebase's FCM/GCM server have them anyway. My plan is to pick a single topic name for that channel (the only topic what my app would use actually at this point), and push messages to the devices who listen to that topic. Is this a viable plan? I haven't found any mention of this whatsoever. Firebase knows all the tokens internally and it would make the architecture simpler if I don't have to deploy a server.
I don't know how the decomission/expiration of the device tokens would happen on Firebase's side, but that's another issue I'd have to deal with if I'll run my own XMPP server and provision tokens.
回答1:
To send messages to a device (so-called downstream messages), you need to specify the server key. As its name implies, this key should only be present on a server or in some other trusted environment. So to send messages to devices you will need to run code in a trusted environment.
The server doesn't have to speak the XMPP protocol however. You can also just use HTTP to call the FCM servers. But a server will be needed, simply because sending downstream messages can only be done from a server.
For a simple example of sending device-to-device messages with this approach, see my blog post Sending notifications between Android devices with Firebase Database and Cloud Messaging. It's about Android, but the same approach of using the Firebase Database as a message queue will work across all platforms.
The tricky bit to map will be (as you already mention) the fact that topics are not available to FCM for the web yet. Last time I tested, you could call a server-side end-point to subscribe to a topic, like described in this answer: GCM: How do you subscribe a device to a topic?.
来源：https://stackoverflow.com/questions/40199616/is-it-possible-to-broadcast-messages-in-a-production-pwa-using-fcm-for-web-witho