Use app.error to return JSON.parse snafus as '400 Bad Request'

verifier.diff

diff --git a/bin/verifier b/bin/verifier
index 1c108fd..d04c6d2 100755
--- a/bin/verifier
+++ b/bin/verifier
@@ -61,6 +61,24 @@ if (statsd_config && statsd_config.enabled) {
 
 app.use(express.bodyParser());
 
+app.error(function(err, req, resp, next) {
+  if (!err) return next();
+
+  // Handle JSON.parse errors from connect.bodyParser as '400 Bad Request'. This
+  // can happen when the Content-Type header is 'application/json' and the body
+  // is some other format. Or, of course if the JSON is just flat out malformed.
+
+  var ct = (req && req.headers && req.headers['content-type']);
+  if (ct === 'application/json' && err instanceof SyntaxError) {
+    var reason = "SyntaxError with 'Content-Type: application/json': " + err.toString();
+    logger.error(reason);
+    return resp.json({ status: "SyntaxError", reason: reason}, 400);
+  }
+
+  // We can't handle this error. Next!
+  next();
+});
+
 try {
   // explicitly relay VAR_PATH to children
   process.env['VAR_PATH'] = config.get('var_path');

Needs a bunch of tests, of course. But existing tests pass locally.

Could probably be a statsd output, so we have a little granularity on 400 reasons.