finished tag implementation

pkg/scan/helper.go

@@ -3,10 +3,35 @@
 package scan
 
 import (
+	"net/http"
+	"os"
 	"path/filepath"
 	"strings"
 )
 
+const (
+	pdfContentType = "application/pdf"
+	maxSniffSize   = 512
+)
+
 func isPDF(path string) bool {
+	return checkContentType(path) || checkExtension(path)
+}
+
+func checkContentType(path string) bool {
+	f, err := os.Open(path)
+	if err != nil {
+		return false
+	}
+	defer f.Close()
+	buf := make([]byte, maxSniffSize)
+	_, err = f.Read(buf)
+	if err != nil {
+		return false
+	}
+	return http.DetectContentType(buf) == pdfContentType
+}
+
+func checkExtension(path string) bool {
 	return strings.ToLower(filepath.Ext(path)) == pdfExt
 }

pkg/scan/scanner.go

@@ -76,6 +76,7 @@ func New(c core.Config) (s *Scanner, err error) {
 	langs := c.Langs
 	if langs == nil || llen == 0 {
 		langs = defaultLangs
+		llen = len(langs)
 	}
 	for i, l := range langs {
 		lang += l