UPnP/SSDP: actually serve a description.xml

The `description.xml` file is part of the UPnP Service Discovery protocol,
see https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-rxad/9225d145-6b2c-40d5-8ee8-7d837379fc25

cmd/flamenco-manager/main.go

@@ -73,7 +73,7 @@ func main() {
 	// Construct the services.
 	persist := openDB(*configService)
 	flamenco := buildFlamencoAPI(configService, persist)
-	e := buildWebService(flamenco, persist)
+	e := buildWebService(flamenco, persist, ssdp)
 
 	installSignalHandler(mainCtxCancel)
 
@@ -121,7 +121,11 @@ func buildFlamencoAPI(configService *config.Service, persist *persistence.DB) ap
 	return flamenco
 }
 
-func buildWebService(flamenco api.ServerInterface, persist api_impl.PersistenceService) *echo.Echo {
+func buildWebService(
+	flamenco api.ServerInterface,
+	persist api_impl.PersistenceService,
+	ssdp *upnp_ssdp.Server,
+) *echo.Echo {
 	e := echo.New()
 	e.HideBanner = true
 
@@ -154,6 +158,13 @@ func buildWebService(flamenco api.ServerInterface, persist api_impl.PersistenceS
 		return c.Redirect(http.StatusTemporaryRedirect, "/api/swagger-ui/")
 	})
 
+	// Serve UPnP service descriptions.
+	if ssdp != nil {
+		e.GET(ssdp.DescriptionPath(), func(c echo.Context) error {
+			return c.XMLPretty(http.StatusOK, ssdp.Description(), "  ")
+		})
+	}
+
 	// Log available routes
 	routeLogger := log.Level(zerolog.DebugLevel)
 	routeLogger.Debug().Msg("available routes:")

internal/upnp_ssdp/server.go

@@ -22,8 +22,11 @@ package upnp_ssdp
 
 import (
 	"context"
+	"fmt"
 	"net/url"
+	"path"
 
+	"git.blender.org/flamenco/internal/appinfo"
 	"github.com/fromkeith/gossdp"
 	"github.com/rs/zerolog"
 )
@@ -60,8 +63,9 @@ func (s *Server) AddAdvertisement(serviceLocation string) {
 
 // AddAdvertisementURLs constructs a service location from the given URLs, and
 // adds the advertisement for it.
-func (s *Server) AddAdvertisementURLs(urls []url.URL) {
-	for _, url := range urls {
+func (s *Server) AddAdvertisementURLs(baseURLs []url.URL) {
+	for _, url := range baseURLs {
+		url.Path = path.Join(url.Path, serviceDescriptionPath)
 		s.AddAdvertisement(url.String())
 	}
 }
@@ -99,3 +103,26 @@ func (s *Server) Run(ctx context.Context) {
 
 	s.log.Info().Msg("UPnP/SSDP advertisement stopped")
 }
+
+func (s *Server) Description() Description {
+	return Description{
+		SpecVersion: SpecVersion{1, 0},
+		URLBase:     "/",
+		Device: Device{
+			DeviceType:       FlamencoServiceType,
+			FriendlyName:     appinfo.FormattedApplicationInfo(),
+			ModelName:        appinfo.ApplicationName,
+			ModelDescription: "Flamenco render farm, Manager component",
+			ModelURL:         "https://flamenco.io/",
+			UDN:              fmt.Sprintf("uuid:%s", FlamencoUUID),
+			Manufacturer:     "Blender",
+			ManufacturerURL:  "https://www.blender.org/",
+			ServiceList:      []string{},
+			PresentationURL:  "/",
+		},
+	}
+}
+
+func (s *Server) DescriptionPath() string {
+	return serviceDescriptionPath
+}

internal/upnp_ssdp/upnp_ssdp.go

@@ -24,4 +24,30 @@ package upnp_ssdp
 const (
 	FlamencoUUID        = "aa80bc5f-d0af-46b8-8630-23bd7e80ec4d"
 	FlamencoServiceType = "urn:flamenco:manager:0"
+
+	serviceDescriptionPath = "/upnp/description.xml"
 )
+
+// SSDP Service description, usually served on some URL ending in `/description.xml`.
+type Description struct {
+	XMLName     string      `xml:"urn:schemas-upnp-org:device-1-0 root"`
+	SpecVersion SpecVersion `xml:"specVersion"`
+	URLBase     string      `xml:"URLBase"`
+	Device      Device      `xml:"device"`
+}
+type SpecVersion struct {
+	Major int `xml:"major"`
+	Minor int `xml:"minor"`
+}
+type Device struct {
+	DeviceType       string   `xml:"deviceType"`
+	FriendlyName     string   `xml:"friendlyName"`
+	Manufacturer     string   `xml:"manufacturer"`
+	ManufacturerURL  string   `xml:"manufacturerURL"`
+	ModelDescription string   `xml:"modelDescription"`
+	ModelName        string   `xml:"modelName"`
+	ModelURL         string   `xml:"modelURL"`
+	UDN              string   `xml:"UDN"`
+	ServiceList      []string `xml:"serviceList"` // not []string, but since the list is empty, it doesn't matter.
+	PresentationURL  string   `xml:"presentationURL"`
+}

internal/worker/autodiscovery.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net/url"
 	"sync"
 	"time"
 
@@ -76,14 +77,28 @@ func autodiscoverManager(ctx context.Context) (string, error) {
 	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()
+// pingManager connects to a Manager and returns the service URL if it responds.
+func pingManager(ctx context.Context, descriptionURL string) string {
+	var err error
+	parsedURL, err := url.Parse(descriptionURL)
+	if err != nil {
+		log.Warn().
+			Str("description", descriptionURL).
+			Err(err).
+			Msg("received invalid URL from autodiscovery, ignoring")
+		return ""
+	}
 
-	client, err := api.NewClientWithResponses(url)
+	// TODO: actually get the description XML from Flamenco Manager and use the path in there.
+	// For now, just assume it's on the root.
+	parsedURL.Path = "/"
+	serviceURL := parsedURL.String()
+
+	logger := log.With().Str("url", serviceURL).Logger()
+	client, err := api.NewClientWithResponses(serviceURL)
 	if err != nil {
 		logger.Warn().Err(err).Msg("unable to create API client with this URL")
-		return false
+		return ""
 	}
 
 	resp, err := client.GetVersionWithResponse(ctx)
@@ -91,21 +106,21 @@ func pingManager(ctx context.Context, url string) bool {
 		// It is expected that some URLs will not work. Showing the error message at
 		// info/warn level will likely confuse people, so leave it at debug level.
 		logger.Debug().Err(err).Msg("unable to get Flamenco version from Manager")
-		return false
+		return ""
 	}
 
 	if resp.JSON200 == nil {
 		logger.Warn().
 			Int("httpStatus", resp.StatusCode()).
 			Msg("unable to get Flamenco version, unexpected reply")
-		return false
+		return ""
 	}
 
 	logger.Info().
 		Str("version", resp.JSON200.Version).
 		Str("name", resp.JSON200.Name).
 		Msg("found Flamenco Manager")
-	return true
+	return serviceURL
 }
 
 // pingManagers pings all URLs in parallel, returning only those that responded.
@@ -116,19 +131,16 @@ func pingManagers(ctx context.Context, urls []string) []string {
 	wg.Add(len(urls))
 	mutex := new(sync.Mutex)
 
-	pingURL := func(idx int, url string) {
+	pingURL := func(idx int, descriptionURL string) {
 		defer wg.Done()
-		ok := pingManager(ctx, url)
+		serviceURL := pingManager(ctx, descriptionURL)
 
 		mutex.Lock()
 		defer mutex.Unlock()
 
-		if !ok {
-			// Erase the URL from the usable list.
-			// Modifying the original slice instead of appending to a new one ensures
-			// the original order is maintained.
-			urls[idx] = ""
-		}
+		// This is either the actual service URL, or an empty string if the
+		// description URL couldn't be reached/parsed.
+		urls[idx] = serviceURL
 	}
 
 	for idx, url := range urls {