From c20fff55a6dfe701f524dceeda93cac8c9eb1042 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Wed, 30 Dec 2015 15:13:50 +0200
Subject: [PATCH] FS: detect file content-type with net/http.DetectContentType
 if the type cannot be determined by file extension

---
 fs.go | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs.go b/fs.go
index ae5f17b..7c8127c 100644
--- a/fs.go
+++ b/fs.go
@@ -7,6 +7,7 @@ import (
 	"html"
 	"io"
 	"mime"
+	"net/http"
 	"os"
 	"path/filepath"
 	"sort"
@@ -836,8 +837,17 @@ func (h *fsHandler) newFSFile(f *os.File, fileInfo os.FileInfo, compressed bool)
 		return nil, fmt.Errorf("too big file: %d bytes", n)
 	}
 
+	// detect content-type
 	ext := fileExtension(fileInfo.Name(), compressed)
 	contentType := mime.TypeByExtension(ext)
+	if len(contentType) == 0 {
+		data := make([]byte, 512)
+		n, err := f.ReadAt(data, 0)
+		if err != nil && err != io.EOF {
+			return nil, fmt.Errorf("cannot read header of the file %q: %s", f.Name(), err)
+		}
+		contentType = http.DetectContentType(data[:n])
+	}
 
 	lastModified := fileInfo.ModTime()
 	ff := &fsFile{