blackbox: Implement logic on a Blackbox struct receiver

Right now, the implenetation of Blackbox logic always gets a
configuration passed in as it is not associated to any structure. This
shortcoming keeps us from having all logic like for example also the
Prometheus counters as part of the struct, which means that they
currently live as globals.

Let's prepare to get rid of these globals by creating a new `Blackbox`
structure and implement blackbox logic as receiver functions. For now,
the struct only hosts the configuration.

2 files changed, 23 insertions, 9 deletions

diff --git a/cmd/gitaly-blackbox/main.go b/cmd/gitaly-blackbox/main.go
index 3ef2d7352..0c96fa144 100644
--- a/cmd/gitaly-blackbox/main.go
+++ b/cmd/gitaly-blackbox/main.go
@@ -53,7 +53,9 @@ func run(configPath string) error {
 		return err
 	}
 
+	bb := blackbox.New(config)
+
 	log.Configure(log.Loggers, config.Logging.Format, config.Logging.Level)
 
-	return blackbox.Run(config)
+	return bb.Run()
 }
diff --git a/internal/blackbox/blackbox.go b/internal/blackbox/blackbox.go
index 5cbf5268d..34d2d45b4 100644
--- a/internal/blackbox/blackbox.go
+++ b/internal/blackbox/blackbox.go
@@ -12,23 +12,35 @@ import (
 	"gitlab.com/gitlab-org/labkit/monitoring"
 )
 
+// Blackbox encapsulates all details required to run the blackbox prober.
+type Blackbox struct {
+	cfg Config
+}
+
+// New creates a new Blackbox structure.
+func New(cfg Config) Blackbox {
+	return Blackbox{
+		cfg: cfg,
+	}
+}
+
 // Run starts the blackbox. It sets up and serves the Prometheus listener and starts a Goroutine
 // which runs the probes.
-func Run(cfg Config) error {
-	listener, err := net.Listen("tcp", cfg.PrometheusListenAddr)
+func (b Blackbox) Run() error {
+	listener, err := net.Listen("tcp", b.cfg.PrometheusListenAddr)
 	if err != nil {
 		return err
 	}
 
-	go runProbes(cfg)
+	go b.runProbes()
 
 	return servePrometheus(listener)
 }
 
-func runProbes(cfg Config) {
-	for ; ; time.Sleep(cfg.sleepDuration) {
-		for _, probe := range cfg.Probes {
-			doProbe(probe)
+func (b Blackbox) runProbes() {
+	for ; ; time.Sleep(b.cfg.sleepDuration) {
+		for _, probe := range b.cfg.Probes {
+			b.doProbe(probe)
 		}
 	}
 }
@@ -40,7 +52,7 @@ func servePrometheus(l net.Listener) error {
 	)
 }
 
-func doProbe(probe Probe) {
+func (b Blackbox) doProbe(probe Probe) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()