Provide error handling middleware function in mu-helpers

Author: erikap

README.md

@@ -11,7 +11,7 @@ Create a new folder.  Add the following Dockerfile:
 
 Create your microservice in `app.js`:
 
-    import { app, query } from 'mu';
+    import { app, query, errorHandler } from 'mu';
 
     app.get('/', function( req, res ) {
       res.send('Hello mu-javascript-template');
@@ -36,6 +36,8 @@ Create your microservice in `app.js`:
         });
     } );
 
+    app.use(errorHandler);
+
 Check [Express' Getting Started guide](https://expressjs.com/en/starter/basic-routing.html) to learn how to build a REST API in Express.
 
 ## Requirements
@@ -50,6 +52,7 @@ The following importable variables are available:
   - `query(query) => Promise`: Function for sending queries to the triplestore
   - `update(query) => Promise`: Function for sending updates to the triplestore
   - `uuid()` => string: Generates a random UUID
+  - `errorHandler(err, req, res, next)`: [Error handling middleware function for Express](https://expressjs.com/en/guide/error-handling.html). It needs to be loaded at the end.
   - `sparql`: [Template tag](https://www.npmjs.com/package/sparql-client-2#using-the-sparql-template-tag) to create queries with interpolated values
   - `sparqlEscapeString(value) => string`: Function to escape a string in SPARQL
   - `sparqlEscapeUri(value) => string`: Function to escape a URI in SPARQL

helpers/mu/index.js

@@ -1,4 +1,4 @@
-import app from './server';
+import { app, errorHandler } from './server';
 import sparql from './sparql';
 import uuidV1 from 'uuid/v1';
 
@@ -19,7 +19,8 @@ const mu = {
   sparqlEscapeDate: sparql.sparqlEscapeDate,
   sparqlEscapeDateTime: sparql.sparqlEscapeDateTime,
   sparqlEscapeBool: sparql.sparqlEscapeBool,
-  uuid: uuid
+  uuid,
+  errorHandler
 };
 
 const SPARQL = mu.SPARQL,
@@ -48,7 +49,8 @@ export {
   sparqlEscapeDate,
   sparqlEscapeDateTime,
   sparqlEscapeBool,
-  uuid
+  uuid,
+  errorHandler
 };
 
 export default mu;

helpers/mu/server.js

@@ -13,27 +13,21 @@ app.use('/', function(req, res, next) {
   next();
 });
 
-// development error handler - printing stacktrace
-if (app.get('env') === 'development') {
-  app.use(function(err, req, res, next) {
-    res.status(err.status || 400);
-    res.json({
-      errors: [ {title: err.message} ]
-    });
-  });
-}
-
-// production error handler - no stacktrace
-app.use(function(err, req, res, next) {
+const errorHandler = function(err, req, res, next) {
   res.status(err.status || 400);
   res.json({
     errors: [ {title: err.message} ]
   });
-});
+};
 
 // start server
 app.listen( 80, function() {
   console.log(`Starting server on port 80 in ${app.get('env')} mode`);
 });
 
 export default app;
+
+export {
+  app,
+  errorHandler
+}