Add encoding sniffing

lib/core/index.js

@@ -12,6 +12,8 @@ const version = require('../../package.json').version;
 const status = require('./status-handlers');
 const generateEtag = require('./etag');
 const optsParser = require('./opts');
+const htmlEncodingSniffer = require("html-encoding-sniffer");
+const { Readable } = require('stream');
 
 let httpServerCore = null;
 
@@ -222,15 +224,18 @@ module.exports = function createMiddleware(_dir, _options) {
       // and brotli special case.
       const defaultType = opts.contentType || 'application/octet-stream';
       let contentType = mime.lookup(file, defaultType);
-      let charSet;
       const range = (req.headers && req.headers.range);
       const lastModified = (new Date(stat.mtime)).toUTCString();
       const etag = generateEtag(stat, weakEtags);
       let cacheControl = cache;
       let stream = null;
       if (contentType && isTextFile(contentType)) {
-        // Assume text types are utf8
-        contentType += '; charset=UTF-8';
+        const htmlBytes = fs.readFileSync(file);
+        const sniffedEncoding = htmlEncodingSniffer(htmlBytes, {
+          defaultEncoding: 'UTF-8'
+        });
+        contentType += `; charset=${sniffedEncoding}`;
+        stream = Readable.from(htmlBytes)
       }
 
       if (file === gzippedFile) { // is .gz picked up
@@ -312,7 +317,10 @@ module.exports = function createMiddleware(_dir, _options) {
         return;
       }
 
-      stream = fs.createReadStream(file);
+      // streams may already have been assigned during encoding sniffing.
+      if (stream === null) {
+        stream = fs.createReadStream(file);
+      }
 
       stream.pipe(res);
       stream.on('error', (err) => {

package.json

@@ -89,6 +89,7 @@
     "colors": "^1.4.0",
     "corser": "^2.0.1",
     "he": "^1.1.0",
+    "html-encoding-sniffer": "^3.0.0",
     "http-proxy": "^1.18.0",
     "mime": "^1.6.0",
     "minimist": "^1.2.5",