feat: identify app sessions by X-App-Platform and X-App-Version headers

apps/gateway/controllers/version.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/MaroonRides/api/apps/gateway/config"
 	"github.com/MaroonRides/api/apps/gateway/services"
+	"github.com/MaroonRides/api/apps/gateway/utils"
 )
 
 type VersionController struct {
@@ -28,7 +29,8 @@ type SupportedVersionResponse struct {
 
 // The app checks its version once per launch, so each call is one session.
 func (c *VersionController) supportedVersion(fc fuego.ContextNoBody) (SupportedVersionResponse, error) {
-	c.sessions.Started(fc.Request().UserAgent())
+	r := fc.Request()
+	c.sessions.Started(r.Header.Get(utils.AppPlatformHeader), r.Header.Get(utils.AppVersionHeader), r.UserAgent())
 	return SupportedVersionResponse{
 		Version: config.MinimumSupportedVersion,
 	}, nil

apps/gateway/controllers/version_test.go

@@ -32,14 +32,47 @@ var _ = Describe("VersionController", Label("unit"), func() {
 		handler = server.Mux
 	})
 
-	checkVersion := func(userAgent string) {
+	checkVersionWithHeaders := func(platform, version, userAgent string) {
 		req := httptest.NewRequest(http.MethodGet, "/api/version/supported", nil)
+		req.Header.Set("X-App-Platform", platform)
+		req.Header.Set("X-App-Version", version)
 		req.Header.Set("User-Agent", userAgent)
 		res := httptest.NewRecorder()
 		handler.ServeHTTP(res, req)
 		ExpectWithOffset(1, res.Code).To(Equal(http.StatusOK))
 	}
 
+	checkVersion := func(userAgent string) {
+		checkVersionWithHeaders("", "", userAgent)
+	}
+
+	It("counts a session from the platform and version headers, ahead of the user agent", func() {
+		checkVersionWithHeaders("web", "3.0.2", "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)")
+		checkVersionWithHeaders("android", "3.1.0", "Maroon Rides App (iOS) v3.0.0")
+
+		Expect(testutil.GatherAndCompare(registry, strings.NewReader(`
+# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
+# TYPE gateway_app_sessions_total counter
+gateway_app_sessions_total{platform="android",version="3.1.0"} 1
+gateway_app_sessions_total{platform="web",version="3.0.2"} 1
+`), appSessionsMetric)).To(Succeed())
+	})
+
+	DescribeTable("falls back to the user agent when a header is missing or malformed",
+		func(platform, version string) {
+			checkVersionWithHeaders(platform, version, "Maroon Rides App (Android) v3.0.1")
+
+			Expect(testutil.GatherAndCompare(registry, strings.NewReader(`
+# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
+# TYPE gateway_app_sessions_total counter
+gateway_app_sessions_total{platform="android",version="3.0.1"} 1
+`), appSessionsMetric)).To(Succeed())
+		},
+		Entry("no version", "web", ""),
+		Entry("unknown platform", "electron", "3.0.2"),
+		Entry("version with a v prefix", "web", "v3.0.2"),
+	)
+
 	It("counts a session by platform and app version", func() {
 		checkVersion("Maroon Rides App (iOS) v3.0.0")
 		checkVersion("Maroon Rides App (iOS) v3.0.0")

apps/gateway/cors_test.go

@@ -15,15 +15,17 @@ var _ = Describe("CORS", Label("unit"), func() {
 			req := httptest.NewRequest(http.MethodOptions, "/api/sync/stream", nil)
 			req.Header.Set("Origin", origin)
 			req.Header.Set("Access-Control-Request-Method", http.MethodPost)
-			req.Header.Set("Access-Control-Request-Headers", "content-type")
+			req.Header.Set("Access-Control-Request-Headers", "content-type,x-app-platform,x-app-version")
 
 			res := httptest.NewRecorder()
 			handler.ServeHTTP(res, req)
 
 			Expect(res.Header().Get("Access-Control-Allow-Origin")).To(Equal("*"))
+			Expect(res.Header().Get("Access-Control-Allow-Headers")).To(Equal("content-type,x-app-platform,x-app-version"))
 		},
 		Entry("iOS app", "capacitor://localhost"),
 		Entry("Android app", "https://localhost"),
+		Entry("web app", "https://web.maroonrides.app"),
 		Entry("Vite dev server", "http://100.89.139.58:5173"),
 	)
 })

apps/gateway/metrics/session.go

@@ -10,7 +10,7 @@ const (
 	labelPlatform = "platform"
 	labelVersion  = "version"
 
-	// Versions past this many share one label so a forged user agent cannot grow the series count.
+	// Versions past this many share one label so a forged client cannot grow the series count.
 	maxAppVersions  = 50
 	OtherAppVersion = "other"
 )
@@ -20,6 +20,7 @@ type AppPlatform string
 const (
 	AppPlatformIOS     AppPlatform = "ios"
 	AppPlatformAndroid AppPlatform = "android"
+	AppPlatformWeb     AppPlatform = "web"
 )
 
 type SessionMetrics struct {

apps/gateway/services/session.go

@@ -6,10 +6,19 @@ import (
 	"github.com/MaroonRides/api/apps/gateway/metrics"
 )
 
-// The app sets its user agent in capacitor.config.ts, e.g. "Maroon Rides App (iOS) v3.0.0".
+var appVersion = regexp.MustCompile(`^\d+\.\d+\.\d+$`)
+
+// Values of the X-App-Platform header, as Capacitor's getPlatform() returns them.
+var headerPlatforms = map[string]metrics.AppPlatform{
+	"ios":     metrics.AppPlatformIOS,
+	"android": metrics.AppPlatformAndroid,
+	"web":     metrics.AppPlatformWeb,
+}
+
+// Builds from before the app sent its own headers only name themselves here, set in capacitor.config.ts, e.g. "Maroon Rides App (iOS) v3.0.0".
 var appUserAgent = regexp.MustCompile(`Maroon Rides App \((iOS|Android)\) v(\d+\.\d+\.\d+)`)
 
-var appPlatforms = map[string]metrics.AppPlatform{
+var userAgentPlatforms = map[string]metrics.AppPlatform{
 	"iOS":     metrics.AppPlatformIOS,
 	"Android": metrics.AppPlatformAndroid,
 }
@@ -23,10 +32,15 @@ func NewSessionService(m *metrics.SessionMetrics) *SessionService {
 }
 
 // Started ignores anything that is not the app, since the kubelet probes the same endpoint.
-func (s *SessionService) Started(userAgent string) {
+func (s *SessionService) Started(platform, version, userAgent string) {
+	if p, ok := headerPlatforms[platform]; ok && appVersion.MatchString(version) {
+		s.metrics.Started(p, version)
+		return
+	}
+
 	match := appUserAgent.FindStringSubmatch(userAgent)
 	if match == nil {
 		return
 	}
-	s.metrics.Started(appPlatforms[match[1]], match[2])
+	s.metrics.Started(userAgentPlatforms[match[1]], match[2])
 }

apps/gateway/utils/app_client.go

@@ -0,0 +1,7 @@
+package utils
+
+// A browser cannot set its user agent, so the app names itself in these headers on every platform.
+const (
+	AppPlatformHeader = "X-App-Platform"
+	AppVersionHeader  = "X-App-Version"
+)