bug: body-parser failures would throw bare exceptions/500s. now 400.

* upgrade body-parser to actually be able to detect its failure signature.
  expressjs/body-parser#122
* also change sendError signature to match the standard one more.

lib/server.js

@@ -49,7 +49,7 @@ service.use((error, request, response, next) => {
     // In this case, we'll just let Express fail the request out.
     return next(error);
   }
-  sendError(response, error);
+  sendError(error, request, response);
 });
 
 

lib/util/http.js

@@ -50,13 +50,17 @@ const endpoint = (f) => (request, response, next) => {
 // Given a error thrown upstream that is of our own internal format, this
 // handler does the necessary work to translate that error into an HTTP error
 // and send it out.
-const sendError = (response, error) => {
+const sendError = (error, request, response) => {
   if (error.isProblem === true) {
+    // we already have a publicly-consumable error object.
     response.status(error.httpCode).type('application/json').send({
       message: error.message,
       code: error.problemCode,
       details: error.problemDetails
     });
+  } else if (error.type === 'entity.parse.failed') {
+    // catch body-parser middleware problems.
+    sendError(Problem.user.unparseable({ format: 'json', rawLength: error.body.length }), request, response);
   } else {
     const details = {};
     if (error.stack != null)