ruby: add Rack::ResponseNode#getAStatusCode

ruby/ql/lib/codeql/ruby/frameworks/Rack.qll

@@ -30,9 +30,25 @@ module Rack {
     DataFlow::ParameterNode getEnv() { result = call.getParameter(0) }
   }
 
+  private DataFlow::LocalSourceNode trackStatusCode(TypeTracker t, int i) {
+    t.start() and
+    result.getConstantValue().isInt(i)
+    or
+    exists(TypeTracker t2 | result = trackStatusCode(t2, i).track(t2, t))
+  }
+
+  private DataFlow::Node trackStatusCode(int i) {
+    trackStatusCode(TypeTracker::end(), i).flowsTo(result)
+  }
+
   class ResponseNode extends DataFlow::ArrayLiteralNode {
     // [status, headers, body]
     ResponseNode() { this.getNumberOfArguments() = 3 }
+
+    /**
+     * Gets an HTTP status code that may be returned in this response.
+     */
+    int getAStatusCode() { this.getElement(0) = trackStatusCode(result) }
   }
 
   private DataFlow::LocalSourceNode trackRackResponse(TypeTracker t) {

ruby/ql/test/library-tests/frameworks/rack/Rack.expected

@@ -1,4 +1,11 @@
-| rack.rb:1:1:5:3 | HelloWorld | rack.rb:2:12:2:14 | env |
-| rack.rb:7:1:16:3 | Proxy | rack.rb:12:12:12:18 | the_env |
-| rack.rb:18:1:31:3 | Logger | rack.rb:24:12:24:14 | env |
-| rack.rb:45:1:61:3 | Baz | rack.rb:46:12:46:14 | env |
+rackApps
+| rack.rb:1:1:9:3 | HelloWorld | rack.rb:2:12:2:14 | env |
+| rack.rb:11:1:20:3 | Proxy | rack.rb:16:12:16:18 | the_env |
+| rack.rb:22:1:35:3 | Logger | rack.rb:28:12:28:14 | env |
+| rack.rb:49:1:65:3 | Baz | rack.rb:50:12:50:14 | env |
+rackResponseStatusCodes
+| rack.rb:7:5:7:63 | call to [] | 200 |
+| rack.rb:7:5:7:63 | call to [] | 500 |
+| rack.rb:39:5:39:13 | call to [] | 1 |
+| rack.rb:56:7:56:22 | call to [] | 200 |
+| rack.rb:63:5:63:21 | call to [] | 400 |

ruby/ql/test/library-tests/frameworks/rack/Rack.ql

@@ -2,3 +2,7 @@ private import codeql.ruby.frameworks.Rack
 private import codeql.ruby.DataFlow
 
 query predicate rackApps(Rack::AppCandidate c, DataFlow::ParameterNode env) { env = c.getEnv() }
+
+query predicate rackResponseStatusCodes(Rack::ResponseNode resp, int status) {
+  status = resp.getAStatusCode()
+}

ruby/ql/test/library-tests/frameworks/rack/rack.rb

@@ -1,6 +1,10 @@
 class HelloWorld
   def call(env)
-    [200, {'Content-Type' => 'text/plain'}, ['Hello World']]
+    status = 200
+    if something_goes_wrong(env)
+      status = 500
+    end
+    [status, {'Content-Type' => 'text/plain'}, ['Hello World']]
   end
 end