Fix encoding sniffing strategy

lib/core/index.js

@@ -5,6 +5,8 @@
 const path = require('path');
 const fs = require('fs');
 const url = require('url');
+const { Readable } = require('stream');
+const buffer = require('buffer');
 const mime = require('mime');
 const urlJoin = require('url-join');
 const showDir = require('./show-dir');
@@ -13,7 +15,6 @@ 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;
 
@@ -230,12 +231,17 @@ module.exports = function createMiddleware(_dir, _options) {
       let cacheControl = cache;
       let stream = null;
       if (contentType && isTextFile(contentType)) {
-        const htmlBytes = fs.readFileSync(file);
-        const sniffedEncoding = htmlEncodingSniffer(htmlBytes, {
-          defaultEncoding: 'UTF-8'
-        });
-        contentType += `; charset=${sniffedEncoding}`;
-        stream = Readable.from(htmlBytes)
+        if (stat.size < buffer.constants.MAX_LENGTH) {
+          const bytes = fs.readFileSync(file);
+          const sniffedEncoding = htmlEncodingSniffer(bytes, {
+            defaultEncoding: 'UTF-8'
+          });
+          contentType += `; charset=${sniffedEncoding}`;
+          stream = Readable.from(bytes)
+        } else {
+          // Assume text types are utf8
+          contentType += '; charset=UTF-8';
+        }
       }
 
       if (file === gzippedFile) { // is .gz picked up