Add value validations for instance variables

Instance level variables have a database constraint for the size
of the encrypted_value at 1024 characters.

app/models/ci/instance_variable.rb

@@ -13,6 +13,11 @@ module Ci
       message: "(%{value}) has already been taken"
     }
 
+    validates :encrypted_value, length: {
+      maximum: 1024,
+      too_long: 'The encrypted value of the provided variable exceeds %{count} bytes. Variables over 700 characters risk exceeding the limit.'
+    }
+
     scope :unprotected, -> { where(protected: false) }
 
     after_commit { self.class.invalidate_memory_cache(:ci_instance_variable_data) }

changelogs/unreleased/217936-validate-the-size-of-the-value-for-instance-level-variables.yml

+---
+title: Add value length validations for instance level variable
+merge_request: 32303
+author:
+type: fixed

doc/api/instance_level_ci_variables.md

@@ -77,7 +77,7 @@ POST /admin/ci/variables
 | Attribute       | Type    | required | Description           |
 |-----------------|---------|----------|-----------------------|
 | `key`           | string  | yes      | The `key` of a variable. Max 255 characters, only `A-Z`, `a-z`, `0-9`, and `_` are allowed. |
-| `value`         | string  | yes      | The `value` of a variable. |
+| `value`         | string  | yes      | The `value` of a variable. Around 700 characters allowed. |
 | `variable_type` | string  | no       | The type of a variable. Available types are: `env_var` (default) and `file`. |
 | `protected`     | boolean | no       | Whether the variable is protected. |
 | `masked`        | boolean | no       | Whether the variable is masked. |

spec/models/ci/instance_variable_spec.rb

@@ -9,6 +9,7 @@ describe Ci::InstanceVariable do
 
   it { is_expected.to include_module(Ci::Maskable) }
   it { is_expected.to validate_uniqueness_of(:key).with_message(/\(\w+\) has already been taken/) }
+  it { is_expected.to validate_length_of(:encrypted_value).is_at_most(1024).with_message(/Variables over 700 characters risk exceeding the limit/) }
 
   describe '.unprotected' do
     subject { described_class.unprotected }

spec/requests/api/admin/ci/variables_spec.rb

@@ -109,6 +109,22 @@ describe ::API::Admin::Ci::Variables do
 
         expect(response).to have_gitlab_http_status(:bad_request)
       end
+
+      it 'does not allow values above 700 characters' do
+        too_long_message = <<~MESSAGE.strip
+          The encrypted value of the provided variable exceeds 1024 bytes. \
+          Variables over 700 characters risk exceeding the limit.
+        MESSAGE
+
+        expect do
+          post api('/admin/ci/variables', admin),
+            params: { key: 'too_long', value: SecureRandom.hex(701) }
+        end.not_to change { ::Ci::InstanceVariable.count }
+
+        expect(response).to have_gitlab_http_status(:bad_request)
+        expect(json_response).to match('message' =>
+          a_hash_including('encrypted_value' => [too_long_message]))
+      end
     end
 
     context 'authorized user with invalid permissions' do