Guard against multiple calls of done callback

Author: fiznool

index.js

@@ -27,7 +27,15 @@ module.exports = function(bodyParser) {
         if(typeof req.body !== 'string') { return next(); }
 
         // Then, parse as XML.
-        const parser = new xml2js.Parser(options.xmlParseOptions);
+        const xmlParseOptions = {
+          ...options.xmlParseOptions,
+          // Always opt-in to async mode.
+          async: true
+        };
+        const parser = new xml2js.Parser(xmlParseOptions);
+
+        // In some cases xml2js.Parser parseString() can throw an error after executing the callback.
+
         parser.parseString(req.body, function(err, xml) {
           if(err) {
             err.status = 400;

test.js

@@ -93,7 +93,6 @@ describe('XML Body Parser', function() {
 
   it('should ignore non-XML', function(done) {
     createServer();
-
     request(app)
       .post('/')
       .set('Content-Type', 'text/plain')
@@ -109,4 +108,14 @@ describe('XML Body Parser', function() {
       .send('<invalid-xml>')
       .expect(400, done);
   });
+
+  it('should not throw an exception after the callback is returned', function(done) {
+    // Guards against https://github.com/Leonidas-from-XIV/node-xml2js/issues/400
+    createServer();
+    request(app)
+      .post('/')
+      .set('Content-Type', 'text/xml')
+      .send('x<foo>test</foo><bar>test</bar></data>')
+      .expect(400, done);
+  })
 });