[forwardport] refactor(oonimkall): merge internal/task into oonimkall (#617) (#618)

This diff forward ports bc4b9f1ea89158bfa7b7a80ae59a90b43c784ed2 to `master`.

See https://github.com/ooni/probe/issues/1903

pkg/oonimkall/chanlogger.go

@@ -0,0 +1,85 @@
+package oonimkall
+
+import "fmt"
+
+// chanLogger is a logger targeting a channel
+type chanLogger struct {
+	emitter    *eventEmitter
+	hasdebug   bool
+	hasinfo    bool
+	haswarning bool
+	out        chan<- *event
+}
+
+// Debug implements Logger.Debug
+func (cl *chanLogger) Debug(msg string) {
+	if cl.hasdebug {
+		cl.emitter.Emit("log", eventLog{
+			LogLevel: "DEBUG",
+			Message:  msg,
+		})
+	}
+}
+
+// Debugf implements Logger.Debugf
+func (cl *chanLogger) Debugf(format string, v ...interface{}) {
+	if cl.hasdebug {
+		cl.Debug(fmt.Sprintf(format, v...))
+	}
+}
+
+// Info implements Logger.Info
+func (cl *chanLogger) Info(msg string) {
+	if cl.hasinfo {
+		cl.emitter.Emit("log", eventLog{
+			LogLevel: "INFO",
+			Message:  msg,
+		})
+	}
+}
+
+// Infof implements Logger.Infof
+func (cl *chanLogger) Infof(format string, v ...interface{}) {
+	if cl.hasinfo {
+		cl.Info(fmt.Sprintf(format, v...))
+	}
+}
+
+// Warn implements Logger.Warn
+func (cl *chanLogger) Warn(msg string) {
+	if cl.haswarning {
+		cl.emitter.Emit("log", eventLog{
+			LogLevel: "WARNING",
+			Message:  msg,
+		})
+	}
+}
+
+// Warnf implements Logger.Warnf
+func (cl *chanLogger) Warnf(format string, v ...interface{}) {
+	if cl.haswarning {
+		cl.Warn(fmt.Sprintf(format, v...))
+	}
+}
+
+// newChanLogger creates a new ChanLogger instance.
+func newChanLogger(emitter *eventEmitter, logLevel string,
+	out chan<- *event) *chanLogger {
+	cl := &chanLogger{
+		emitter: emitter,
+		out:     out,
+	}
+	switch logLevel {
+	case "DEBUG", "DEBUG2":
+		cl.hasdebug = true
+		fallthrough
+	case "INFO":
+		cl.hasinfo = true
+		fallthrough
+	case "ERR", "WARNING":
+		fallthrough
+	default:
+		cl.haswarning = true
+	}
+	return cl
+}