adding errors to errors header

lib/cartodb/middleware/error-middleware.js

@@ -18,7 +18,8 @@ module.exports = function errorMiddleware (/* options */) {
         if (err.message === 'Tile does not exist' && res.locals.format === 'mvt') {
             statusCode = 204;
         }
-
+        
+        logErrors(allErrors, statusCode, res);
         debug('[%s ERROR] -- %d: %s, %s', label, statusCode, err, err.stack);
 
         // If a callback was requested, force status to 200
@@ -31,6 +32,7 @@ module.exports = function errorMiddleware (/* options */) {
             errors_with_context: allErrors.map(errorMessageWithContext)
         };
 
+
         res.status(statusCode);
 
         if (req.query && req.query.callback) {
@@ -160,3 +162,36 @@ function errorMessageWithContext(err) {
 
     return error;
 }
+
+function logErrors(errors, statusCode, res) {
+    console.log('     -----------------------------')
+    console.log('logErrors');
+    console.log('     -----------------------------')
+    
+    if(!errors || !errors.length || !statusCode) {
+        return;
+    }
+
+    const mainError = errors.shift();
+
+    const errorsLog = {
+        statusCode,
+        message:    mainError.message,
+        type:       mainError.type,
+        subtype:    mainError.subtype
+    }
+
+    errorsLog.moreErrors = errors.map(error => {
+        return {
+            message: error.message,
+            type:    error.type,
+            subtype: error.subtype
+        };
+    });
+
+    console.log('     -----------------------------')
+    console.log(errorsLog)
+    console.log('     -----------------------------')
+    
+    res.set('X-Tiler-Errors', JSON.stringify(errorsLog));
+}