Add filter_metadata config option

.changesets/add-filter_metadata-config-option.md

@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "add"
+---
+
+Add `filter_metadata` config option to filter metadata set on Transactions set by default. Metadata like `path`, (request)  `method`, `request_id`, `hostname`, etc. This can be useful if there's PII or other sensitive data in any of the app's metadata.

lib/appsignal/config.rb

@@ -24,6 +24,7 @@ class Config
       :enable_rails_error_reporter => true,
       :endpoint => "https://push.appsignal.com",
       :files_world_accessible => true,
+      :filter_metadata => [],
       :filter_parameters => [],
       :filter_session_data => [],
       :ignore_actions => [],
@@ -77,6 +78,7 @@ class Config
       "APPSIGNAL_ENABLE_GVL_WAITING_THREADS" => :enable_gvl_waiting_threads,
       "APPSIGNAL_ENABLE_RAILS_ERROR_REPORTER" => :enable_rails_error_reporter,
       "APPSIGNAL_FILES_WORLD_ACCESSIBLE" => :files_world_accessible,
+      "APPSIGNAL_FILTER_METADATA" => :filter_metadata,
       "APPSIGNAL_FILTER_PARAMETERS" => :filter_parameters,
       "APPSIGNAL_FILTER_SESSION_DATA" => :filter_session_data,
       "APPSIGNAL_HOSTNAME" => :hostname,
@@ -150,6 +152,7 @@ class Config
     # @api private
     ENV_ARRAY_KEYS = %w[
       APPSIGNAL_DNS_SERVERS
+      APPSIGNAL_FILTER_METADATA
       APPSIGNAL_FILTER_PARAMETERS
       APPSIGNAL_FILTER_SESSION_DATA
       APPSIGNAL_IGNORE_ACTIONS

lib/appsignal/transaction.rb

@@ -308,6 +308,7 @@ def set_http_or_background_queue_start
 
     def set_metadata(key, value)
       return unless key && value
+      return if Appsignal.config[:filter_metadata].include?(key.to_s)
 
       @ext.set_metadata(key, value)
     end
@@ -337,7 +338,7 @@ def sample_data
         :params => sanitized_params,
         :environment => sanitized_environment,
         :session_data => sanitized_session_data,
-        :metadata => metadata,
+        :metadata => sanitized_metadata,
         :tags => sanitized_tags,
         :breadcrumbs => breadcrumbs
       }.each do |key, data|
@@ -522,12 +523,17 @@ def sanitized_session_data
       )
     end
 
-    # Returns metadata from the environment.
+    # Returns sanitized metadata set by {#set_metadata} and from the
+    # {#environment}.
     #
-    # @return [nil] if no `:metadata` key is present in the {#environment}.
     # @return [Hash<String, Object>]
-    def metadata
-      environment[:metadata]
+    def sanitized_metadata
+      metadata = environment[:metadata]
+      return unless metadata
+
+      metadata
+        .transform_keys(&:to_s)
+        .except(*Appsignal.config[:filter_metadata])
     end
 
     # Returns the environment for a transaction.

spec/lib/appsignal/config_spec.rb

@@ -165,6 +165,7 @@
         :enable_rails_error_reporter    => true,
         :endpoint                       => "https://push.appsignal.com",
         :files_world_accessible         => true,
+        :filter_metadata                => [],
         :filter_parameters              => [],
         :filter_session_data            => [],
         :ignore_actions                 => [],

spec/lib/appsignal/rack/streaming_listener_spec.rb

@@ -1,6 +1,7 @@
 require "appsignal/rack/streaming_listener"
 
 describe Appsignal::Rack::StreamingListener do
+  before(:context) { start_agent }
   let(:headers) { {} }
   let(:env) do
     {

spec/lib/appsignal/transaction_spec.rb

@@ -623,6 +623,18 @@ def current_transaction
         expect(transaction.to_h["metadata"]).to eq("request_method" => "GET")
       end
 
+      context "when filter_metadata includes metadata key" do
+        before { Appsignal.config[:filter_metadata] = ["filter_key"] }
+        after { Appsignal.config[:filter_metadata] = [] }
+
+        it "does not set the metadata on the transaction" do
+          transaction.set_metadata(:filter_key, "filtered value")
+          transaction.set_metadata("filter_key", "filtered value")
+
+          expect(transaction.to_h["metadata"].keys).to_not include("filter_key")
+        end
+      end
+
       context "when the key is nil" do
         it "does not update the metadata on the transaction" do
           transaction.set_metadata(nil, "GET")
@@ -1275,8 +1287,8 @@ def session_exists?(_env)
       end
     end
 
-    describe "#metadata" do
-      subject { transaction.send(:metadata) }
+    describe "#sanitized_metadata" do
+      subject { transaction.send(:sanitized_metadata) }
 
       context "when request is nil" do
         let(:request) { nil }
@@ -1291,9 +1303,18 @@ def session_exists?(_env)
       end
 
       context "when env is present" do
-        let(:env) { { :metadata => { :key => "value" } } }
+        let(:env) { { "key" => "value" } }
 
-        it { is_expected.to eq env[:metadata] }
+        it { is_expected.to eq("key" => "value") }
+
+        context "with filter_metadata option set" do
+          before { Appsignal.config[:filter_metadata] = ["key"] }
+          after { Appsignal.config[:filter_metadata] = [] }
+
+          it "filters out keys listed in the filter_metadata option" do
+            expect(subject.keys).to_not include("key")
+          end
+        end
       end
     end