version: add support for reporting the mac variant from tailscale --version (#18462)

fixes tailscale/corp#27182

tailscale version --json now includes an osVariant field that will report
one of macsys, appstore or darwin. We can extend this to other
platforms where tailscaled can have multiple personalities.

This also adds the concept of a platform-specific callback for querying
an explicit application identifier.  On Apple, we can use
CFBundleGetIdentifier(mainBundle) to get the bundle identifier via cgo.
This removes all the ambiguity and lets us remove other less direct
methods (like env vars, locations, etc).

Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>

version/prop.go

@@ -15,6 +15,22 @@ import (
 	"tailscale.com/types/lazy"
 )
 
+// AppIdentifierFn, if non-nil, is a callback function that returns the
+// application identifier of the running process or an empty string if unknown.
+//
+// tailscale(d) implementations can set an explicit callback to return an identifier
+// for the running process if such a concept exists.  The Apple bundle identifier, for example.
+var AppIdentifierFn func() string // or nil
+
+const (
+	macsysBundleID      = "io.tailscale.ipn.macsys"                     // The macsys gui app and CLI
+	appStoreBundleID    = "io.tailscale.ipn.macos"                      // The App Store gui app and CLI
+	macsysExtBundleId   = "io.tailscale.ipn.macsys.network-extension"   // The macsys system extension
+	appStoreExtBundleId = "io.tailscale.ipn.macos.network-extension"    // The App Store network extension
+	tvOSExtBundleId     = "io.tailscale.ipn.ios.network-extension-tvos" // The tvOS network extension
+	iOSExtBundleId      = "io.tailscale.ipn.ios.network-extension"      // The iOS network extension
+)
+
 // IsMobile reports whether this is a mobile client build.
 func IsMobile() bool {
 	return runtime.GOOS == "android" || runtime.GOOS == "ios"
@@ -52,8 +68,8 @@ func IsMacGUIVariant() bool {
 
 // IsSandboxedMacOS reports whether this process is a sandboxed macOS
 // process (either the app or the extension). It is true for the Mac App Store
-// and macsys (System Extension) version on macOS, and false for
-// tailscaled-on-macOS.
+// and macsys (only its System Extension) variants on macOS, and false for
+// tailscaled and the macsys GUI process on macOS.
 func IsSandboxedMacOS() bool {
 	return IsMacAppStore() || IsMacSysExt()
 }
@@ -73,10 +89,15 @@ func IsMacSysGUI() bool {
 	if runtime.GOOS != "darwin" {
 		return false
 	}
-
 	return isMacSysApp.Get(func() bool {
+		if AppIdentifierFn != nil {
+			return AppIdentifierFn() == macsysBundleID
+		}
+
+		// TODO (barnstar): This check should be redundant once all relevant callers
+		// use AppIdentifierFn.
 		return strings.Contains(os.Getenv("HOME"), "/Containers/io.tailscale.ipn.macsys/") ||
-			strings.Contains(os.Getenv("XPC_SERVICE_NAME"), "io.tailscale.ipn.macsys")
+			strings.Contains(os.Getenv("XPC_SERVICE_NAME"), macsysBundleID)
 	})
 }
 
@@ -90,11 +111,17 @@ func IsMacSysExt() bool {
 		return false
 	}
 	return isMacSysExt.Get(func() bool {
+		if AppIdentifierFn != nil {
+			return AppIdentifierFn() == macsysExtBundleId
+		}
+
+		// TODO (barnstar): This check should be redundant once all relevant callers
+		// use AppIdentifierFn.
 		exe, err := os.Executable()
 		if err != nil {
 			return false
 		}
-		return filepath.Base(exe) == "io.tailscale.ipn.macsys.network-extension"
+		return filepath.Base(exe) == macsysExtBundleId
 	})
 }
 
@@ -107,11 +134,17 @@ func IsMacAppStore() bool {
 		return false
 	}
 	return isMacAppStore.Get(func() bool {
+		if AppIdentifierFn != nil {
+			id := AppIdentifierFn()
+			return id == appStoreBundleID || id == appStoreExtBundleId
+		}
+		// TODO (barnstar): This check should be redundant once all relevant callers
+		// use AppIdentifierFn.
 		// Both macsys and app store versions can run CLI executable with
 		// suffix /Contents/MacOS/Tailscale. Check $HOME to filter out running
 		// as macsys.
 		return strings.Contains(os.Getenv("HOME"), "/Containers/io.tailscale.ipn.macos/") ||
-			strings.Contains(os.Getenv("XPC_SERVICE_NAME"), "io.tailscale.ipn.macos")
+			strings.Contains(os.Getenv("XPC_SERVICE_NAME"), appStoreBundleID)
 	})
 }
 
@@ -124,6 +157,11 @@ func IsMacAppStoreGUI() bool {
 		return false
 	}
 	return isMacAppStoreGUI.Get(func() bool {
+		if AppIdentifierFn != nil {
+			return AppIdentifierFn() == appStoreBundleID
+		}
+		// TODO (barnstar): This check should be redundant once all relevant callers
+		// use AppIdentifierFn.
 		exe, err := os.Executable()
 		if err != nil {
 			return false
@@ -143,7 +181,13 @@ func IsAppleTV() bool {
 		return false
 	}
 	return isAppleTV.Get(func() bool {
-		return strings.EqualFold(os.Getenv("XPC_SERVICE_NAME"), "io.tailscale.ipn.ios.network-extension-tvos")
+		if AppIdentifierFn != nil {
+			return AppIdentifierFn() == tvOSExtBundleId
+		}
+
+		// TODO (barnstar): This check should be redundant once all relevant callers
+		// use AppIdentifierFn.
+		return strings.EqualFold(os.Getenv("XPC_SERVICE_NAME"), tvOSExtBundleId)
 	})
 }
 
@@ -187,6 +231,23 @@ func IsUnstableBuild() bool {
 	})
 }
 
+// osVariant returns the OS variant string for systems where we support
+// multiple ways of running tailscale(d), if any.
+//
+// For example: "appstore", "macsys", "darwin".
+func osVariant() string {
+	if IsMacAppStore() {
+		return "appstore"
+	}
+	if IsMacSys() {
+		return "macsys"
+	}
+	if runtime.GOOS == "darwin" {
+		return "darwin"
+	}
+	return ""
+}
+
 var isDev = sync.OnceValue(func() bool {
 	return strings.Contains(Short(), "-dev")
 })
@@ -227,6 +288,11 @@ type Meta struct {
 	// setting "vcs.modified" was true).
 	GitDirty bool `json:"gitDirty,omitempty"`
 
+	// OSVariant is specific variant of the binary, if applicable. For example,
+	// macsys/appstore/darwin for macOS builds.  Nil/empty where not supported
+	// or on oses without variants.
+	OSVariant string `json:"osVariant,omitempty"`
+
 	// ExtraGitCommit, if non-empty, is the git commit of a "supplemental"
 	// repository at which Tailscale was built. Its format is the same as
 	// gitCommit.
@@ -264,6 +330,7 @@ func GetMeta() Meta {
 			GitCommitTime:   getEmbeddedInfo().commitTime,
 			GitCommit:       gitCommit(),
 			GitDirty:        gitDirty(),
+			OSVariant:       osVariant(),
 			ExtraGitCommit:  extraGitCommitStamp,
 			IsDev:           isDev(),
 			UnstableBranch:  IsUnstableBuild(),