Add max length validation for app name in V3 API (#4928)

When creating or updating an app with a name exceeding 255 characters,
the database would raise a constraint violation error that was not
caught, resulting in an unhelpful "UnknownError" (code 10001) response.

This adds explicit length validation to AppCreateMessage and
AppUpdateMessage to provide a meaningful error message before the
request reaches the database layer.

- Add length validation (max 255 chars) to AppCreateMessage
- Add length validation (max 255 chars) to AppUpdateMessage
- Add corresponding unit tests for both messages

Author: rashedkvm

app/messages/app_create_message.rb

@@ -16,7 +16,7 @@ def self.lifecycle_type_requested?
     validates_with NoAdditionalKeysValidator, RelationshipValidator
     validates_with LifecycleValidator, if: lifecycle_type_requested?
 
-    validates :name, string: true
+    validates :name, string: true, length: { maximum: 255, message: 'is too long (maximum is 255 characters)' }
     validates :environment_variables, hash: true, allow_nil: true
 
     validates :lifecycle_type,

app/messages/app_update_message.rb

@@ -18,7 +18,7 @@ def self.lifecycle_type_requested?
     validates_with NoAdditionalKeysValidator
     validates_with LifecycleValidator, if: lifecycle_requested?
 
-    validates :name, string: true, allow_nil: true
+    validates :name, string: true, allow_nil: true, length: { maximum: 255, message: 'is too long (maximum is 255 characters)' }
 
     validates :lifecycle_type,
               string: true,

spec/unit/messages/app_create_message_spec.rb

@@ -67,6 +67,29 @@ module VCAP::CloudController
         end
       end
 
+      context 'when name is too long' do
+        let(:params) do
+          {
+            name: 'a' * 256,
+            relationships: { space: { data: { guid: 'space-guid' } } },
+            lifecycle: {
+              type: 'buildpack',
+              data: {
+                buildpack: 'nil',
+                stack: Stack.default.name
+              }
+            }
+          }
+        end
+
+        it 'is not valid' do
+          message = AppCreateMessage.new(params)
+
+          expect(message).not_to be_valid
+          expect(message.errors_on(:name)).to include('is too long (maximum is 255 characters)')
+        end
+      end
+
       context 'when environment_variables is not an object' do
         let(:params) do
           {

spec/unit/messages/app_update_message_spec.rb

@@ -26,6 +26,17 @@ module VCAP::CloudController
         end
       end
 
+      context 'when name is too long' do
+        let(:params) { { name: 'a' * 256 } }
+
+        it 'is not valid' do
+          message = AppUpdateMessage.new(params)
+
+          expect(message).not_to be_valid
+          expect(message.errors_on(:name)).to include('is too long (maximum is 255 characters)')
+        end
+      end
+
       context 'when we have more than one error' do
         let(:params) { { name: 3.5, unexpected: 'foo' } }