Formatting variables and then passing them into the logger functions leads
to performance issues. i.e.
```erlang
logger:debug("RECV ~s", [emqx_packet:format(Packet)])
```
Above message will only be printed when the current log level set to
`debug`, but the function emqx_packet:format/1 will always be evaluated no
matter what the current log level is.
OTP 21 provides a special meta-data named `report_cb`, which can be used
for lazy evaluation. The fun is only evaluated if the primary/handler log level
check passes, and is therefore recommended if it is expensive to generate
the message.
Prior to this change, emqx_client:start_link does 2 works in one call:
- init an erlang process for emqx_client
- send MQTT CONNECT to remote broker
But this solution have some drawbacks:
- the return value of `start_link` compiles the return values of the 2
works: {ok, Pid, MqttResult}. It is inconsistent with the return value
of `gen_statem:start_link`, may causes confusions.
- the return mode of the 2 works are different:
`start_link` should always return {ok, Pid} or {error, Reason}, but
connecting to mqtt may throw out exceptions as it handles the
socket. But the caller couldn't have thought of the exception, he would
pattern match on the result of `emqx_client:start_link`, but it crashed!
- If the init work succeed but the connection failed, the caller couldn't
get a Pid from the return value, but indeed it was created inside the
emqx_client. This hides the fact that the Pid was created, and when the
Pid dies, the caller would receive an message from a Pid it doesn' know about.
This change divived these 2 work into 2 APIs:
- `start_link/1` is to build and verify the options, and returns {ok,Pid}
(on success) or {error, Reason} (on failure).
- `connect/1` is to send MQTT CONNECT, and returns {ok, MQTTResult::properties()} or
{error, MQTTReason}. MQTT reason codes will contains in the `MQTTReason`.
Fixed bugs:
- Priority queue lack of a `len + 1` logic in `in/2`
Changed behaviors:
- Topics not found in priority table (from config) will be treated with default priority,
instead of hasing topic name to a priority number.
- Default priority is now configurable (it was always lower than all configured priorities)
- The dropped message due to reaching `max_len` is now returned from `in/2`,
so the queue owner (`in/2` caller) can perform autopsy on it
Prior to this change, you can just use CN or EN field from the client
certificate as username.
This change add a new option to allow user to use Certificate directly as
username.
Add request & response support for CONNECT & CONNACK
Prior to this change, there is no validate and specified process for
Request-Response-Information and Response-Information
Also added basic Request/Response functionality to emqx_client implementation
The hibernation behaviour is also changed (implicitly) in this commit:
Prior to this change, connection/session always hibernates after
the stats timer expires regardless of messages in mailbox.
After this commit, connection/session process only goes to hibernate
when the timer expires AND there is nothing left in the mailbox to
process
The implementation prior to this commit supports
only one gc enforcement policy which is message count threshold.
The new implementation introduces 1 more: volume threshold based
The implementation prior to this commit supports
only one gc enforcement policy which is message count threshold.
The new implementation introduces 1 more: volume threshold based
terry-xiaoyu