This notification bases on `LOG_BROKEN` and `LOG_UNUSUAL` level log.
--Introduction
A notification for topic `warning` is sent every time a new `BROKEN`/
`UNUSUAL` level(in plugins, we use `error`/`warn`) log generated, which
means an unusual/borken thing happens, such as channel failed,
message resolving failed...
```json
{
"warning": {
"level": "warn",
"time": "1559743608.565342521",
"source": "lightningd(17652): 0821f80652fb840239df8dc99205792bba2e559a05469915804c08420230e23c7c chan #7854:",
"log": "Peer permanent failure in CHANNELD_NORMAL: lightning_channeld: sent ERROR bad reestablish dataloss msg"
}
}
```
1. `level` is `warn` or `error`:
`warn` means something seems bad happened and it's under control, but
we'd better check it;
`error` means something extremely bad is out of control, and it may lead
to crash;
2. `time` is the second since epoch;
3. `source`, in fact, is the `prefix` of the log_entry. It means where
the event happened, it may have the following forms:
`<node_id> chan #<db_id_of_channel>:`, `lightningd(<lightningd_pid>):`,
`plugin-<plugin_name>:`, `<daemon_name>(<daemon_pid>):`, `jsonrpc:`,
`jcon fd <error_fd_to_jsonrpc>:`, `plugin-manager`;
4. `log` is the context of the original log entry.
--Note:
1. The main code uses `UNUSUAL`/`BROKEN`, and plugin module uses `warn`
/`error`, considering the consistency with plugin, warning choose `warn`
/`error`. But users who use c-lightning with plugins may want to
`getlog` with specified level when receive warning. It's the duty for
plugin dev to turn `warn`/`error` into `UNUSUAL`/`BROKEN` and present it
to the users, or pass it directly to `getlog`;
2. About time, `json_log()` in `log` module uses the Relative Time, from
the time when `log_book` inited to the time when this event happend.
But I consider the `UNUSUAL`/`BROKEN` event is rare, and it is very
likely to happen after running for a long time, so for users, they will
pay more attention to Absolute Time.
-- Related Change
1. Remove the definitions of `log`, `log_book`, `log_entry` from `log.c`
to `log.h`, then they can be used in warning declaration and definition.
2. Remove `void json_add_time(struct json_stream *result, const char
*fieldname, struct timespec ts)` from `log.c` to `json.c`, and add
related declaration in `json.h`. Now the notification function in
`notification.c` can call it.
2. Add a pointer to `struct lightningd` in `struct log_book`. This may
affect the independence of the `log` module, but storing a pointer to
`ld` is more direct;
I tried to just do gossipd, but it was uncontainable, so this ended up being
a complete sweep.
We didn't get much space saving in gossipd, even though we should save
24 bytes per node.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
