implement ArchiveServer.bestSlugFor()

Router.go

@@ -1,6 +1,7 @@
 package archive
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -36,6 +37,23 @@ func (this *ArchiveServer) lookupSource(slug string) *LogSource {
 	return nil // not found
 }
 
+func (this *ArchiveServer) bestSlugFor(ls *LogSource) (string, error) {
+	for i := 0; i < len(this.cfg.Logs); i += 1 {
+		if ls != &this.cfg.Logs[i] {
+			continue
+		}
+
+		if len(this.cfg.Logs[i].Slugs) > 0 {
+			return this.cfg.Logs[i].Slugs[0], nil // first slug is preferred
+		} else {
+			return fmt.Sprintf(`%d`, i), nil // no slugs present? use numeric log index
+		}
+
+	}
+
+	return "", errors.New("Unregistered log source")
+}
+
 func (this *ArchiveServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Server", SERVER_VERSION)