Expose Model.exists over HTTP HEAD

lib/models/persisted-model.js

@@ -448,7 +448,25 @@ PersistedModel.setupRemoting = function() {
     description: 'Check whether a model instance exists in the data source',
     accepts: {arg: 'id', type: 'any', description: 'Model id', required: true},
     returns: {arg: 'exists', type: 'boolean'},
-    http: {verb: 'get', path: '/:id/exists'}
+    http: [
+      {verb: 'get', path: '/:id/exists'},
+      {verb: 'head', path: '/:id'}
+    ],
+    rest: {
+      // After hook to map exists to 200/404 for HEAD
+      after: function(ctx, cb) {
+        if(!ctx.result.exists) {
+          var modelName = ctx.method.sharedClass.name;
+          var id = ctx.getArgByName('id');
+          var msg = 'Unknown "' + modelName + '" id "' + id + '".';
+          var error = new Error(msg);
+          error.statusCode = error.status = 404;
+          cb(error);
+        } else {
+          cb();
+        }
+      }
+    }
   });
 
   setRemoting(PersistedModel, 'findById', {

test/rest.middleware.test.js

@@ -1,16 +1,54 @@
 describe('loopback.rest', function() {
+  var MyModel;
   beforeEach(function() {
-    app.dataSource('db', { connector: loopback.Memory });
+    var ds = app.dataSource('db', { connector: loopback.Memory });
+    MyModel = ds.createModel('MyModel', {name: String});
   });
 
   it('works out-of-the-box', function(done) {
-    app.model('MyModel', { dataSource: 'db' });
+    app.model(MyModel);
     app.use(loopback.rest());
     request(app).get('/mymodels')
       .expect(200)
       .end(done);
   });
 
+  it('should report 404 for GET /:id not found', function(done) {
+    app.model(MyModel);
+    app.use(loopback.rest());
+    request(app).get('/mymodels/1')
+      .expect(404)
+      .end(done);
+  });
+
+  it('should report 404 for HEAD /:id not found', function(done) {
+    app.model(MyModel);
+    app.use(loopback.rest());
+    request(app).head('/mymodels/1')
+      .expect(404)
+      .end(done);
+  });
+
+  it('should report 200 for GET /:id found', function(done) {
+    app.model(MyModel);
+    app.use(loopback.rest());
+    MyModel.create({name: 'm1'}, function(err, inst) {
+      request(app).get('/mymodels/' + inst.id)
+        .expect(200)
+        .end(done);
+    });
+  });
+
+  it('should report 200 for HEAD /:id found', function(done) {
+    app.model(MyModel);
+    app.use(loopback.rest());
+    MyModel.create({name: 'm2'}, function(err, inst) {
+      request(app).head('/mymodels/' + inst.id)
+        .expect(200)
+        .end(done);
+    });
+  });
+
   it('includes loopback.token when necessary', function(done) {
     givenUserModelWithAuth();
     app.enableAuth();