Add synchronization around adding logs to a plugin
and reading those logs. Without the follow configuration,
a race occurs between go routines to add the logs into
the plugin and read the logs out of the plugin. This
adds a function to synchronize the action to avoid the
race.
Removes use of file for buffering, instead buffering whole
messages so log count can be checked discretely.
Signed-off-by: Derek McGowan <derek@mcgstyle.net>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Logging plugins use the same HTTP interface as other plugins for basic
command operations meanwhile actual logging operations are handled (on
Unix) via a fifo.
The plugin interface looks like so:
```go
type loggingPlugin interface {
StartLogging(fifoPath string, loggingContext Context) error
StopLogging(fifoPath)
```
This means a plugin must implement `LoggingDriver.StartLogging` and
`LoggingDriver.StopLogging` endpoints and be able to consume the passed
in fifo.
Logs are sent via stream encoder to the fifo encoded with protobuf.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
