Events of REST API of firebase - events

Question

Now I am developing a REST API on embedded System, and I want to use event stream to get the updated data on firebase like the Android's onChildChanged callback do.
At the same time, I learnt from the doc that the REST API can just support the events like POST, and it is just server listen to the client way.
If I use poll to get the updated data, it is a waste memory and has delay to get the latest data.
So how can I implement this callback function on REST API like the Android do?

Answer 1

In addition to the regular REST verbs (POST, GET, PUT, DELETE and PATCH), Firebase's REST API also supports streaming events using the Event Source / Server-Sent Events protocol. This part of the API is specifically made for use-cases such as the one you are describing, allowing multiple updates to bent sent from the server to a connected client through a single HTTP connection.
These are some examples of events that the server might send:
// Set your entire cache to {"a": 1, "b": 2}
event: put
data: {"path": "/", "data": {"a": 1, "b": 2}}
// Put the new data in your cache under the key 'c', so that the complete cache now looks like:
// {"a": 1, "b": 2, "c": {"foo": true, "bar": false}}
event: put
data: {"path": "/c", "data": {"foo": true, "bar": false}}
// For each key in the data, update (or add) the corresponding key in your cache at path /c,
// for a final cache of: {"a": 1, "b": 2, "c": {"foo": 3, "bar": false, "baz": 4}}
event: patch
data: {"path": "/c", "data": {"foo": 3, "baz": 4}}
This data was taken from the blog post announcing the REST streaming feature, which also contains a good description of it. There are also examples of REST streaming clients implemented in Python and Ruby available.
I hope these links are enough to get you started. If you are having trouble getting it to work, open a question where you show the code that fires the HTTP request and handles the response.