feat: add url shortner

pkg/shorturl/bot.go

@@ -0,0 +1,52 @@
+package shorturl
+
+import (
+	"regexp"
+	"strings"
+)
+
+// botSubstrings catches the named social-platform link previewers explicitly,
+// so we don't over-count human clicks from OG scraping.
+var botSubstrings = []string{
+	"facebookexternalhit",
+	"facebot",
+	"twitterbot",
+	"linkedinbot",
+	"slackbot",
+	"telegrambot",
+	"discordbot",
+	"pinterest",
+	"whatsapp",
+	"applebot",
+	"googlebot",
+	"bingbot",
+	"yahoo! slurp",
+	"duckduckbot",
+	"baiduspider",
+	"yandex",
+	"redditbot",
+	"embedly",
+	"vkshare",
+	"viber",
+	"signal",
+	"skypeuripreview",
+}
+
+var botFallbackRe = regexp.MustCompile(`(?i)\b(bot|crawler|spider|preview|fetch)\b`)
+
+// IsBot returns true if the user-agent looks like an OG scraper / search
+// crawler / link previewer, rather than a real human browser. False positives
+// here only affect analytics aggregation (the is_bot flag); they never change
+// redirect behavior.
+func IsBot(userAgent string) bool {
+	if userAgent == "" {
+		return true // missing UA is almost always a bot or curl
+	}
+	ua := strings.ToLower(userAgent)
+	for _, needle := range botSubstrings {
+		if strings.Contains(ua, needle) {
+			return true
+		}
+	}
+	return botFallbackRe.MatchString(ua)
+}