Worker: test all discovered Manager URLs

Ping each discovered Manager URL to see whether it is reachable or not.
If there are multiple usable URLs, it'll just pick the first.

cmd/flamenco-worker/main.go

@@ -4,6 +4,7 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"fmt"
 	"net/url"
@@ -19,7 +20,9 @@ import (
 	"github.com/rs/zerolog/log"
 
 	"git.blender.org/flamenco/internal/appinfo"
+	"git.blender.org/flamenco/internal/upnp_ssdp"
 	"git.blender.org/flamenco/internal/worker"
+	"git.blender.org/flamenco/pkg/api"
 )
 
 var (
@@ -58,6 +61,7 @@ func main() {
 	configLogLevel()
 
 	configWrangler := worker.NewConfigWrangler()
+	maybeAutodiscoverManager(&configWrangler)
 
 	// Startup can take arbitrarily long, as it only ends when the Manager can be
 	// reached and accepts our sign-on request. An offline Manager would cause the
@@ -180,3 +184,99 @@ func upstreamBufferOrDie(client worker.FlamencoClient, timeService clock.Clock)
 
 	return buffer
 }
+
+// maybeAutodiscoverManager starts Manager auto-discovery if there is no Manager URL configured yet.
+func maybeAutodiscoverManager(configWrangler *worker.FileConfigWrangler) {
+	cfg, err := configWrangler.WorkerConfig()
+	if err != nil {
+		log.Fatal().Err(err).Msg("unable to load configuration")
+	}
+
+	if cfg.ManagerURL != "" {
+		// Manager URL is already known, don't bother with auto-discovery.
+		return
+	}
+
+	discoverCtx, discoverCancel := context.WithTimeout(context.Background(), 5*time.Minute)
+	defer discoverCancel()
+
+	foundManager, err := autodiscoverManager(discoverCtx)
+	if err != nil {
+		log.Fatal().Err(err).Msg("unable to discover manager")
+	}
+
+	configWrangler.SetManagerURL(foundManager)
+}
+
+func autodiscoverManager(ctx context.Context) (string, error) {
+	c, err := upnp_ssdp.NewClient(log.Logger)
+	if err != nil {
+		return "", fmt.Errorf("unable to create UPnP/SSDP client: %w", err)
+	}
+
+	log.Info().Msg("auto-discovering Manager via UPnP/SSDP")
+
+	urls, err := c.Run(ctx)
+	if err != nil {
+		return "", fmt.Errorf("unable to find Manager: %w", err)
+	}
+
+	if len(urls) == 0 {
+		return "", errors.New("no Manager could be found")
+	}
+
+	// Try out the URLs to see which one responds.
+	// TODO: parallelise this.
+	usableURLs := make([]string, 0)
+	for _, url := range urls {
+		if pingManager(ctx, url) {
+			usableURLs = append(usableURLs, url)
+		}
+	}
+
+	switch len(usableURLs) {
+	case 0:
+		return "", fmt.Errorf("autodetected %d URLs, but none were usable", len(urls))
+
+	case 1:
+		log.Info().Str("url", usableURLs[0]).Msg("found Manager")
+		return usableURLs[0], nil
+
+	default:
+		log.Info().
+			Strs("urls", usableURLs).
+			Str("url", usableURLs[0]).
+			Msg("found multiple usable URLs, using the first one")
+		return usableURLs[0], nil
+	}
+}
+
+// pingManager connects to a Manager and returns true if it responds.
+func pingManager(ctx context.Context, url string) bool {
+	logger := log.With().Str("manager", url).Logger()
+
+	client, err := api.NewClientWithResponses(url)
+	if err != nil {
+		logger.Warn().Err(err).Msg("unable to create API client with this URL")
+		return false
+	}
+
+	resp, err := client.GetVersionWithResponse(ctx)
+	if err != nil {
+		logger.Warn().Err(err).Msg("unable to get Flamenco version from Manager")
+		return false
+	}
+
+	if resp.JSON200 == nil {
+		logger.Warn().
+			Int("httpStatus", resp.StatusCode()).
+			Msg("unable to get Flamenco version, unexpected reply")
+		return false
+	}
+
+	logger.Info().
+		Str("version", resp.JSON200.Version).
+		Str("name", resp.JSON200.Name).
+		Msg("found Flamenco Manager")
+	return true
+}