[WIP] factor out trace functionality into separate package and add Go docs

daemon/job/passive.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/zrepl/zrepl/daemon/logging/trace"
 
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/daemon/filters"
@@ -164,12 +165,12 @@ func (j *PassiveSide) SenderConfig() *endpoint.SenderConfig {
 func (*PassiveSide) RegisterMetrics(registerer prometheus.Registerer) {}
 
 func (j *PassiveSide) Run(ctx context.Context) {
-	ctx, endTask := logging.WithTaskAndSpan(ctx, "passive-side-job", j.Name())
+	ctx, endTask := trace.WithTaskAndSpan(ctx, "passive-side-job", j.Name())
 	defer endTask()
 	log := GetLogger(ctx)
 	defer log.Info("job exiting")
 	{
-		ctx, endTask := logging.WithTask(ctx, "periodic") // shadowing
+		ctx, endTask := trace.WithTask(ctx, "periodic") // shadowing
 		defer endTask()
 		ctx, cancel := context.WithCancel(ctx)
 		defer cancel()
@@ -182,10 +183,11 @@ func (j *PassiveSide) Run(ctx context.Context) {
 	}
 
 	ctxInterceptor := func(handlerCtx context.Context, info rpc.HandlerContextInterceptorData, handler func(ctx context.Context)) {
-		// the handlerCtx is clean => need to inherit logging config from job context
+		// the handlerCtx is clean => need to inherit logging and tracing config from job context
 		handlerCtx = logging.WithInherit(handlerCtx, ctx)
+		handlerCtx = trace.WithInherit(handlerCtx, ctx)
 
-		handlerCtx, endTask := logging.WithTaskAndSpan(handlerCtx, "handler", fmt.Sprintf("job=%q client=%q method=%q", j.Name(), info.ClientIdentity(), info.FullMethod()))
+		handlerCtx, endTask := trace.WithTaskAndSpan(handlerCtx, "handler", fmt.Sprintf("job=%q client=%q method=%q", j.Name(), info.ClientIdentity(), info.FullMethod()))
 		defer endTask()
 		handler(handlerCtx)
 	}