support Urgency #29
Description
https://tools.ietf.org/html/rfc8030#section-5.3
5.3. Push Message Urgency
For a device that is battery-powered, it is often critical that it
remains dormant for extended periods. Radio communication in
particular consumes significant power and limits the length of time
that the device can operate.
To avoid consuming resources to receive trivial messages, it is
helpful if an application server can communicate the urgency of a
message and if the user agent can request that the push server only
forwards messages of a specific urgency.
An application server MAY include an Urgency header field in its
request for push message delivery. This header field indicates the
message urgency. The push service MUST NOT forward the Urgency
header field to the user agent. A push message without the Urgency
header field defaults to a value of "normal".
A user agent MAY include the Urgency header field when monitoring for
push messages to indicate the lowest urgency of push messages that it
is willing to receive. A push service MUST NOT deliver push messages
with lower urgency than the value indicated by the user agent in its
monitoring request. Push messages of any urgency are delivered to a
user agent that does not include an Urgency header field when
monitoring for messages.
The grammar for the Urgency header field is as follows:
Urgency = urgency-option
urgency-option = ("very-low" / "low" / "normal" / "high")
In order of increasing urgency:
+----------+-----------------------------+--------------------------+
| Urgency | Device State | Example Application |
| | | Scenario |
+----------+-----------------------------+--------------------------+
| very-low | On power and Wi-Fi | Advertisements |
| low | On either power or Wi-Fi | Topic updates |
| normal | On neither power nor Wi-Fi | Chat or Calendar Message |
| high | Low battery | Incoming phone call or |
| | | time-sensitive alert |
+----------+-----------------------------+--------------------------+
Table 1: Illustrative Urgency Values
Multiple values for the Urgency header field MUST NOT be included in
requests; otherwise, the push service MUST return a 400 (Bad Request)
status code.