change app to emit "error" events instead of app.error(fn)

lib/application.js

@@ -33,6 +33,7 @@ exports = module.exports = Application;
 function Application() {
   if (!(this instanceof Application)) return new Application;
   this.env = process.env.NODE_ENV || 'development';
+  this.on('error', this.onerror.bind(this));
   this.outputErrors = 'test' != this.env;
   this.subdomainOffset = 2;
   this.poweredBy = true;
@@ -119,37 +120,25 @@ app.context = function(obj){
 app.callback = function(){
   var mw = [respond].concat(this.middleware);
   var fn = compose(mw)(downstream);
-  var onerror = this.onerror.bind(this);
   var self = this;
 
   return function(req, res){
     var ctx = new self.Context(self, req, res);
 
     if (!ctx.socket.listeners('error').length) {
-      ctx.socket.on('error', onerror);
-    }
-
-    function done(err) {
-      if (err) ctx.onerror(err);
+      ctx.socket.on('error', function(err){
+        self.emit('error', err);
+      });
     }
 
     co.call(ctx, function *(){
       yield fn;
-    }, done);
+    }, function(err){
+      if (err) ctx.onerror(err);
+    });
   }
 };
 
-/**
- * Set the application-level error handling `fn`.
- *
- * @param {Function} fn
- * @api public
- */
-
-app.error = function(fn){
-  this.onerror = fn;
-};
-
 /**
  * Default error handler.
  *
@@ -169,6 +158,7 @@ function respond(next){
   return function *(){
     yield next;
 
+    var app = this.app;
     var res = this.res;
     var body = this.body;
     var head = 'HEAD' == this.method;

lib/context.js

@@ -562,12 +562,17 @@ module.exports = {
    */
 
   onerror: function(err){
-    this.app.onerror(err);
-    
     // nothing we can do here other
     // than delegate to the app-level
     // handler and log.
-    if (this.headerSent) return;
+    if (this.headerSent) {
+      err.headerSent = true;
+      this.app.emit('error', err);
+      return;
+    }
+
+    // delegate
+    this.app.emit('error', err);
 
     // err.status support
     if (err.status) {