Logging through pipes

This functionality is needed when a parent process starts a child process and both their logs have to be collected in the parent process.

The parent process:

part, _ := pipes.NewParentPart(marshalizer)
profileReader, logsWriter := part.GetChildPipes()

command = exec.Command("child.bin")
childStdout, _:= command.StdoutPipe()
childStderr, _ := command.StderrPipe()
command.ExtraFiles = []*os.File{
		...,
		profileReader,
		logsWriter,
}

_ = part.StartLoop(childStdout, childStderr)

StartLoop will continuously read log lines from the child (pipe logsWriter) on a separate goroutine. Child's stdout and stderr are also captured. Stdout will be logged with trace level, while stderr with error level.

Furthermore, the parent part forwards log profile changes to the child process (through pipe profileReader).

Note that the parent process is responsible to call logger.NotifyProfileChange() when it applies a new log profile (whether by sole choice or when instructed by a logviewer).

The child process

profileReader := os.NewFile(42, "/proc/self/fd/42")
logsWriter := os.NewFile(43, "/proc/self/fd/43")
part, _ := pipes.NewChildPart(profileReader, logsWriter, marshalizer)
_ = part.StartLoop()

The child process has to acquire the provided pipes, create its part of the logging dialogue and then call StartLoop. The child part is automatically registered as observer to the global default LogOutputSubject, which means that it gets notified on each log write from any of the loggers in the process. When notified, the child part simply forwards the message (the serialized log line) to its parent, through pipe logsWriter.

Furthermore, the child part listens for eventual log profile changes on the pipe profileReader. Any profile change is applied immediately.