1 files changed, 74 insertions, 0 deletions
diff --git a/internal/uniquedomain/middleware.go b/internal/uniquedomain/middleware.go
new file mode 100644
index 00000000..0028822d
--- /dev/null
+++ b/internal/uniquedomain/middleware.go
@@ -0,0 +1,74 @@
+package uniquedomain
+
+import (
+	"net"
+	"net/http"
+	"strings"
+
+	"gitlab.com/gitlab-org/gitlab-pages/internal/domain"
+	"gitlab.com/gitlab-org/gitlab-pages/internal/logging"
+)
+
+func NewMiddleware(handler http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		uniqueURL := getUniqueURL(r)
+		if uniqueURL == "" {
+			logging.
+				LogRequest(r).
+				WithField("uniqueURL", uniqueURL).
+				Debug("unique domain: doing nothing")
+
+			handler.ServeHTTP(w, r)
+			return
+		}
+
+		logging.
+			LogRequest(r).
+			WithField("uniqueURL", uniqueURL).
+			Info("redirecting to unique domain")
+
+		http.Redirect(w, r, uniqueURL, http.StatusPermanentRedirect)
+	})
+}
+
+func getUniqueURL(r *http.Request) string {
+	domain := domain.FromRequest(r)
+	lookupPath, err := domain.GetLookupPath(r)
+	if err != nil {
+		logging.
+			LogRequest(r).
+			WithError(err).
+			Error("uniqueDomain: failed to get lookupPath")
+		return ""
+	}
+
+	// No uniqueHost to redirect
+	if lookupPath.UniqueHost == "" {
+		return ""
+	}
+
+	requestHost, port, err := net.SplitHostPort(r.Host)
+	if err != nil {
+		requestHost = r.Host
+	}
+
+	// Already serving the uniqueHost
+	if lookupPath.UniqueHost == requestHost {
+		return ""
+	}
+
+	uniqueURL := *r.URL
+	if port == "" {
+		uniqueURL.Host = lookupPath.UniqueHost
+	} else {
+		uniqueURL.Host = net.JoinHostPort(lookupPath.UniqueHost, port)
+	}
+
+	// Ensure to redirect to the same path requested
+	uniqueURL.Path = strings.TrimPrefix(
+		r.URL.Path,
+		strings.TrimSuffix(lookupPath.Prefix, "/"),
+	)
+
+	return uniqueURL.String()
+}