Validate the backend in params

Skip profiling if the backend is not supported

lib/app_profiler/request_parameters.rb

@@ -27,12 +27,13 @@ def backend
     end
 
     def valid?
-      if mode.blank?
+      return false if mode.blank?
+
+      unless valid_backend?
+        AppProfiler.logger.info("[AppProfiler] unsupported backend='#{backend}'")
         return false
       end
 
-      return false if backend != AppProfiler::Backend::StackprofBackend.name && !AppProfiler.vernier_supported?
-
       if AppProfiler.vernier_supported? && backend == AppProfiler::Backend::VernierBackend.name &&
           !AppProfiler::Backend::VernierBackend::AVAILABLE_MODES.include?(mode.to_sym)
         AppProfiler.logger.info("[AppProfiler] unsupported profiling mode=#{mode} for backend #{backend}")
@@ -50,6 +51,12 @@ def valid?
       true
     end
 
+    def valid_backend?
+      return true if AppProfiler::Backend::StackprofBackend.name == backend
+
+      AppProfiler.vernier_supported? && AppProfiler::Backend::VernierBackend.name == backend
+    end
+
     def to_h
       {
         mode: mode.to_sym,

test/app_profiler/request_parameters_test.rb

@@ -29,6 +29,13 @@ class RequestParametersTest < TestCase
       end
     end
 
+    test "#valid? returns false when backend is not supported" do
+      AppProfiler.logger.expects(:info).with { |value| value =~ /unsupported backend='not-a-real-backend'/ }
+      params = request_params(headers: { AppProfiler.request_profile_header => "mode=cpu;backend=not-a-real-backend" })
+
+      assert_not_predicate(params, :valid?)
+    end
+
     test "#context is AppProfiler.context by default" do
       with_context("test-context") do
         AppProfiler.logger.expects(:info).never