Fix allocation of output string in emscripten_run_script_string() to …

…not truncate the string if it has characters outside 7-bit ASCII set. Fixes emscripten-core#4766.

src/library.js

@@ -3831,9 +3831,10 @@ LibraryManager.library = {
   emscripten_run_script_string: function(ptr) {
     {{{ makeEval("var s = eval(Pointer_stringify(ptr)) + '';") }}}
     var me = _emscripten_run_script_string;
-    if (!me.bufferSize || me.bufferSize < s.length+1) {
+    var len = lengthBytesUTF8(s);
+    if (!me.bufferSize || me.bufferSize < len+1) {
       if (me.bufferSize) _free(me.buffer);
-      me.bufferSize = s.length+1;
+      me.bufferSize = len+1;
       me.buffer = _malloc(me.bufferSize);
     }
     stringToUTF8(s, me.buffer, me.bufferSize);

tests/test_core.py

@@ -1508,6 +1508,21 @@ def process(filename):
       self.do_run_in_out_file_test('tests', 'core', 'test_emscripten_api',
                                    post_build=check)
 
+  def test_emscripten_run_script_string_utf8(self):
+    src = r'''
+      #include <stdio.h>
+      #include <stdlib.h>
+      #include <string.h>
+      #include <emscripten.h>
+
+      int main() {
+        const char *str = emscripten_run_script_string("'\\u2603 \\u2603 \\u2603 Hello!'");
+        printf("length of returned string: %d. Position of substring 'Hello': %d\n", strlen(str), strstr(str, "Hello")-str);
+        return 0;
+      }
+    '''
+    self.do_run(src, '''length of returned string: 18. Position of substring 'Hello': 12''')
+
   def test_emscripten_get_now(self):
     self.banned_js_engines = [V8_ENGINE] # timer limitations in v8 shell