version: validate Long format on Android builds

Updates #14069

Change-Id: I134a90db561dacc4b1c1c66ccadac135b5d64cf3
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

version/version.go

@@ -7,6 +7,7 @@ package version
 import (
 	"fmt"
 	"runtime/debug"
+	"strconv"
 	"strings"
 
 	tailscaleroot "tailscale.com"
@@ -169,3 +170,42 @@ func majorMinorPatch() string {
 	ret, _, _ := strings.Cut(Short(), "-")
 	return ret
 }
+
+func isValidLongWithTwoRepos(v string) bool {
+	s := strings.Split(v, "-")
+	if len(s) != 3 {
+		return false
+	}
+	hexChunk := func(s string) bool {
+		if len(s) < 6 {
+			return false
+		}
+		for i := range len(s) {
+			b := s[i]
+			if (b < '0' || b > '9') && (b < 'a' || b > 'f') {
+				return false
+			}
+		}
+		return true
+	}
+
+	v, t, g := s[0], s[1], s[2]
+	if !strings.HasPrefix(t, "t") || !strings.HasPrefix(g, "g") ||
+		!hexChunk(t[1:]) || !hexChunk(g[1:]) {
+		return false
+	}
+	nums := strings.Split(v, ".")
+	if len(nums) != 3 {
+		return false
+	}
+	for i, n := range nums {
+		bits := 8
+		if i == 2 {
+			bits = 16
+		}
+		if _, err := strconv.ParseUint(n, 10, bits); err != nil {
+			return false
+		}
+	}
+	return true
+}