Return error message when URL is blocked

When the Prometheus URL is blocked, the custom metric form should
display the appropriate error message.

ee/changelogs/unreleased/rp-fix-custom-metric-validation-error.yml

+---
+title: Display error message in custom metric form validation when prometheus URL
+  is blocked
+merge_request: 27863
+author:
+type: fixed

ee/lib/gitlab/prometheus/queries/validate_query.rb

@@ -7,7 +7,7 @@ module Gitlab
         def query(query)
           client_query(query)
           { valid: true }
-        rescue Gitlab::PrometheusClient::QueryError => ex
+        rescue Gitlab::PrometheusClient::QueryError, Gitlab::HTTP::BlockedUrlError => ex
           { valid: false, error: ex.message }
         end
 

ee/spec/lib/gitlab/prometheus/queries/validate_query_spec.rb

@@ -3,7 +3,10 @@
 require 'spec_helper'
 
 describe Gitlab::Prometheus::Queries::ValidateQuery do
-  let(:client) { double('prometheus_client') }
+  include PrometheusHelpers
+
+  let(:api_url) { 'https://prometheus.example.com' }
+  let(:client) { Gitlab::PrometheusClient.new(api_url) }
   let(:query) { 'avg(metric)' }
 
   subject { described_class.new(client) }
@@ -21,16 +24,39 @@ describe Gitlab::Prometheus::Queries::ValidateQuery do
   end
 
   context 'invalid query' do
-    let(:message) { 'message' }
-
-    before do
-      allow(client).to receive(:query).with(query).and_raise(Gitlab::PrometheusClient::QueryError.new(message))
+    let(:query) { 'invalid query' }
+    let(:error_message) { "invalid parameter 'query': 1:9: parse error: unexpected identifier \"query\"" }
+
+    it 'returns invalid' do
+      Timecop.freeze do
+        stub_prometheus_query_error(
+          prometheus_query_with_time_url(query, Time.now),
+          error_message
+        )
+
+        expect(subject.query(query)).to eq(valid: false, error: error_message)
+      end
     end
+  end
 
-    it 'passes query to prometheus' do
-      expect(subject.query(query)).to eq(valid: false, error: message)
+  context 'when exceptions occur' do
+    context 'Gitlab::HTTP::BlockedUrlError' do
+      let(:api_url) { 'http://192.168.1.1' }
 
-      expect(client).to have_received(:query).with(query)
+      let(:message) do
+        "URL 'http://192.168.1.1/api/v1/query?query=avg%28metric%29&time=#{Time.now.to_f}'" \
+        " is blocked: Requests to the local network are not allowed"
+      end
+
+      before do
+        stub_application_setting(allow_local_requests_from_web_hooks_and_services: false)
+      end
+
+      it 'catches exception and returns invalid' do
+        Timecop.freeze do
+          expect(subject.query(query)).to eq(valid: false, error: message)
+        end
+      end
     end
   end
 end

spec/support/helpers/prometheus_helpers.rb

@@ -68,6 +68,21 @@ module PrometheusHelpers
       })
   end
 
+  def stub_prometheus_query_error(url, error_message = 'error', body: {}, headers: {})
+    response = {
+      status: 'error',
+      errorType: 'bad_data',
+      error: error_message
+    }.merge(body)
+
+    WebMock.stub_request(:get, url)
+      .to_return({
+        status: 400,
+        headers: { 'Content-Type' => 'application/json' }.merge(headers),
+        body: response.to_json
+      })
+  end
+
   def stub_prometheus_request_with_exception(url, exception_type)
     WebMock.stub_request(:get, url).to_raise(exception_type)
   end