Feature/fallback to statsig api

lib/network.rb

@@ -7,6 +7,7 @@
 RETRY_CODES = [408, 500, 502, 503, 504, 522, 524, 599].freeze
 
 module Statsig
+  STATSIG_CDN_DCS_BASE = 'https://api.statsigcdn.com/v2'.freeze
   class NetworkError < StandardError
     attr_reader :http_code
 
@@ -44,6 +45,14 @@ def download_config_specs(since_time, context)
       get(dcs_url)
     end
 
+    def download_config_specs_fallback(since_time, context)
+      dcs_url = "#{STATSIG_CDN_DCS_BASE}/download_config_specs/#{@server_secret}.json"
+      if since_time.positive?
+        dcs_url += "?sinceTime=#{since_time}"
+      end
+      get(dcs_url)
+    end
+
     def post_logs(events, error_boundary)
       url = @options.log_event_url
       event_count = events.length

lib/spec_store.rb

@@ -6,6 +6,8 @@
 
 module Statsig
   class SpecStore
+    STATSIG_NETWORK_FALLBACK_THRESHOLD = 5
+
     attr_accessor :last_config_sync_time
     attr_accessor :initial_config_sync_time
     attr_accessor :init_reason
@@ -48,6 +50,7 @@ def initialize(network, options, error_callback, diagnostics, error_boundary, lo
       @secret_key = secret_key
       @unsupported_configs = Set.new
       @sdk_configs = sdk_config
+      @sync_failure_count = 0
 
       startTime = (Time.now.to_f * 1000).to_i
 
@@ -84,6 +87,9 @@ def initialize(network, options, error_callback, diagnostics, error_boundary, lo
 
       if @init_reason == EvaluationReason::UNINITIALIZED
         failure_details = download_config_specs('initialize')
+        if !failure_details.nil? && @options.fallback_to_statsig_api && using_proxy_for_dcs?
+          failure_details = download_config_specs_fallback('initialize')
+        end
       end
 
       @initial_config_sync_time = @last_config_sync_time == 0 ? -1 : @last_config_sync_time
@@ -205,10 +211,20 @@ def maybe_restart_background_threads
 
     def sync_config_specs
       if @options.data_store&.should_be_used_for_querying_updates(Interfaces::IDataStore::CONFIG_SPECS_V2_KEY)
-        load_config_specs_from_storage_adapter('config_sync')
+        failure_details = load_config_specs_from_storage_adapter('config_sync')
+      else
+        failure_details = download_config_specs('config_sync')
+      end
+
+      if failure_details.nil?
+        @sync_failure_count = 0
       else
-        download_config_specs('config_sync')
+        @sync_failure_count += 1
+        if @options.fallback_to_statsig_api && using_proxy_for_dcs? && (@sync_failure_count % STATSIG_NETWORK_FALLBACK_THRESHOLD == 0)
+          download_config_specs_fallback('config_sync')
+        end
       end
+
       @logger.log_diagnostics_event(@diagnostics, 'config_sync')
     end
 
@@ -223,6 +239,58 @@ def sync_id_lists
 
     private
 
+    def using_proxy_for_dcs?
+      !@options.download_config_specs_url.start_with?(STATSIG_CDN_DCS_BASE)
+    end
+
+    def download_config_specs_fallback(context)
+      response, e = @network.download_config_specs_fallback(@last_config_sync_time, context)
+      handle_config_specs_response(context, 'download_config_specs_fallback', 'CONFIG_SPECS_FALLBACK', response, e)
+    end
+
+    def handle_config_specs_response(context, diagnostic_key, error_prefix, response, e)
+      tracker = @diagnostics.track(context, diagnostic_key, 'network_request')
+
+      error = nil
+      failure_details = nil
+      begin
+        code = response&.status.to_i
+        if e.is_a? NetworkError
+          code = e.http_code
+          failure_details = {statusCode: code, exception: e, reason: "#{error_prefix}_NETWORK_ERROR"}
+        elsif !e.nil?
+          # Transport-level errors (ECONNREFUSED, timeout, DNS, SSL) are caught and returned as values
+          # by network.rb. Without this, failure_details stays nil and the caller treats it as success.
+          failure_details = {exception: e, reason: "#{error_prefix}_CONNECTION_ERROR"}
+        end
+        tracker.end(statusCode: code, success: e.nil?, sdkRegion: response&.headers&.[]('X-Statsig-Region'))
+
+        if e.nil?
+          unless response.nil?
+            tracker = @diagnostics.track(context, diagnostic_key, 'process')
+            body = response.body.to_s
+            failure_details = process_specs(body)
+            if failure_details.nil?
+              @init_reason = EvaluationReason::NETWORK
+            end
+            tracker.end(success: @init_reason == EvaluationReason::NETWORK)
+
+            unless response.body.nil? or @rules_updated_callback.nil?
+              @rules_updated_callback.call(body, @last_config_sync_time)
+            end
+          end
+        else
+          error = e
+        end
+      rescue StandardError => e
+        failure_details = {exception: e, reason: "INTERNAL_ERROR"}
+        error = e
+      end
+
+      @error_callback.call(error) unless error.nil? or @error_callback.nil?
+      return failure_details
+    end
+
     def load_config_specs_from_storage_adapter(context)
       tracker = @diagnostics.track(context, 'data_store_config_specs', 'fetch')
       cached_values = @options.data_store.get(Interfaces::IDataStore::CONFIG_SPECS_V2_KEY)
@@ -284,44 +352,8 @@ def spawn_sync_id_lists_thread
     end
 
     def download_config_specs(context)
-      tracker = @diagnostics.track(context, 'download_config_specs', 'network_request')
-
-      error = nil
-      failure_details = nil
-      begin
-        response, e = @network.download_config_specs(@last_config_sync_time, context)
-        code = response&.status.to_i
-        if e.is_a? NetworkError
-          code = e.http_code
-          failure_details = {statusCode: code, exception: e, reason: "CONFIG_SPECS_NETWORK_ERROR"}
-        end
-        tracker.end(statusCode: code, success: e.nil?, sdkRegion: response&.headers&.[]('X-Statsig-Region'))
-
-        if e.nil?
-          unless response.nil?
-            tracker = @diagnostics.track(context, 'download_config_specs', 'process')
-            body = response.body.to_s
-            failure_details = process_specs(body)
-            if failure_details.nil?
-              @init_reason = EvaluationReason::NETWORK
-            end
-            tracker.end(success: @init_reason == EvaluationReason::NETWORK)
-
-            unless response.body.nil? or @rules_updated_callback.nil?
-              @rules_updated_callback.call(body,
-                                           @last_config_sync_time)
-            end
-          end
-        else
-          error = e
-        end
-      rescue StandardError => e
-        failure_details = {exception: e, reason: "INTERNAL_ERROR"}
-        error = e
-      end
-
-      @error_callback.call(error) unless error.nil? or @error_callback.nil?
-      return failure_details
+      response, e = @network.download_config_specs(@last_config_sync_time, context)
+      handle_config_specs_response(context, 'download_config_specs', 'CONFIG_SPECS', response, e)
     end
 
     def process_specs(specs_string, from_adapter: false)

lib/statsig_options.rb

@@ -96,6 +96,12 @@ class StatsigOptions
   # default: 0
   attr_accessor :initialize_retry_limit
 
+  # When true, if the configured download_config_specs_url fails, the SDK will
+  # automatically fall back to the Statsig CDN to fetch config specs.
+  # Only effective when a custom download_config_specs_url is configured.
+  # default: false
+  attr_accessor :fallback_to_statsig_api
+
   def initialize(
     environment = nil,
     download_config_specs_url: nil,
@@ -120,7 +126,8 @@ def initialize(
     post_logs_retry_backoff: nil,
     user_persistent_storage: nil,
     disable_evaluation_memoization: false,
-    initialize_retry_limit: 0
+    initialize_retry_limit: 0,
+    fallback_to_statsig_api: false
   )
     @environment = environment.is_a?(Hash) ? environment : nil
 
@@ -152,5 +159,6 @@ def initialize(
     @user_persistent_storage = user_persistent_storage
     @disable_evaluation_memoization = disable_evaluation_memoization
     @initialize_retry_limit = initialize_retry_limit
+    @fallback_to_statsig_api = fallback_to_statsig_api
   end
 end

test/test_helper.rb

@@ -87,6 +87,7 @@ def assert_nothing_raised(*)
   StatsigErrorBoundaryUsageTest
   TestStore
   TestSymbolHashes
+  TestSyncConfigFallback
   TestURIHelper
   UserFieldsTest
   UserTest

test/test_sync_config_fallback.rb

@@ -0,0 +1,126 @@
+require_relative 'test_helper'
+require 'minitest'
+require 'minitest/autorun'
+require 'webmock/minitest'
+require 'statsig'
+
+CUSTOM_DCS_BASE = 'http://custom-proxy.example.com/v2'.freeze
+STATSIG_CDN_BASE = 'https://api.statsigcdn.com/v2'.freeze
+
+class TestSyncConfigFallback < BaseTest
+  suite :TestSyncConfigFallback
+
+  def setup
+    super
+    @cdn_call_count = 0
+    @custom_call_count = 0
+    @dcs_response = File.read("#{__dir__}/data/download_config_specs.json")
+
+    WebMock.enable!
+    WebMock.disable_net_connect!
+
+    stub_download_config_specs(STATSIG_CDN_BASE)
+      .to_return do |_req|
+        @cdn_call_count += 1
+        { status: 200, body: @dcs_response, headers: { 'Content-Type' => 'application/json' } }
+      end
+
+    stub_request(:post, 'https://statsigapi.net/v1/get_id_lists')
+      .to_return(status: 200, body: '{}')
+    stub_request(:post, 'https://statsigapi.net/v1/log_event')
+      .to_return(status: 200)
+  end
+
+  def teardown
+    Statsig.shutdown rescue nil
+    WebMock.reset!
+    WebMock.disable!
+    super
+  end
+
+  def stub_custom(status:, body: nil)
+    stub_download_config_specs(CUSTOM_DCS_BASE)
+      .to_return do |_req|
+        @custom_call_count += 1
+        { status: status, body: body || @dcs_response, headers: { 'Content-Type' => 'application/json' } }
+      end
+  end
+
+  def custom_options(extra = {})
+    StatsigOptions.new(
+      download_config_specs_url: "#{CUSTOM_DCS_BASE}/download_config_specs/",
+      fallback_to_statsig_api: true,
+      disable_rulesets_sync: true,
+      disable_idlists_sync: true,
+      **extra
+    )
+  end
+
+  def test_no_fallback_when_primary_succeeds
+    stub_custom(status: 200)
+    Statsig.initialize(SDK_KEY, custom_options)
+
+    assert_equal 1, @custom_call_count
+    assert_equal 0, @cdn_call_count
+  end
+
+  def test_fallback_triggered_on_init_500
+    stub_custom(status: 500)
+    Statsig.initialize(SDK_KEY, custom_options)
+
+    assert @cdn_call_count > 0, "Expected fallback to CDN on init failure but CDN was not called"
+  end
+
+  def test_no_fallback_when_option_false
+    stub_custom(status: 500)
+    options = StatsigOptions.new(
+      download_config_specs_url: "#{CUSTOM_DCS_BASE}/download_config_specs/",
+      fallback_to_statsig_api: false,
+      disable_rulesets_sync: true,
+      disable_idlists_sync: true
+    )
+    Statsig.initialize(SDK_KEY, options)
+
+    assert_equal 0, @cdn_call_count
+  end
+
+  def test_fallback_triggered_during_background_sync
+    original_threshold = Statsig::SpecStore::STATSIG_NETWORK_FALLBACK_THRESHOLD
+    Statsig::SpecStore.send(:remove_const, :STATSIG_NETWORK_FALLBACK_THRESHOLD)
+    Statsig::SpecStore.const_set(:STATSIG_NETWORK_FALLBACK_THRESHOLD, 1)
+
+    begin
+      stub_custom(status: 200)
+      options = StatsigOptions.new(
+        download_config_specs_url: "#{CUSTOM_DCS_BASE}/download_config_specs/",
+        fallback_to_statsig_api: true,
+        rulesets_sync_interval: 0.3,
+        disable_idlists_sync: true
+      )
+      Statsig.initialize(SDK_KEY, options)
+      cdn_after_init = @cdn_call_count
+
+      WebMock.reset!
+      WebMock.disable_net_connect!
+      stub_download_config_specs(CUSTOM_DCS_BASE)
+        .to_return { @custom_call_count += 1; { status: 500 } }
+      stub_download_config_specs(STATSIG_CDN_BASE)
+        .to_return do |_req|
+          @cdn_call_count += 1
+          { status: 200, body: @dcs_response, headers: { 'Content-Type' => 'application/json' } }
+        end
+      stub_request(:post, 'https://statsigapi.net/v1/get_id_lists')
+        .to_return(status: 200, body: '{}')
+      stub_request(:post, 'https://statsigapi.net/v1/log_event')
+        .to_return(status: 200)
+
+      sleep(0.7)
+
+      assert @cdn_call_count > cdn_after_init,
+             "Expected CDN to be called after bg sync failure, but cdn_call_count=#{@cdn_call_count}"
+    ensure
+      Statsig::SpecStore.send(:remove_const, :STATSIG_NETWORK_FALLBACK_THRESHOLD)
+      Statsig::SpecStore.const_set(:STATSIG_NETWORK_FALLBACK_THRESHOLD, original_threshold)
+    end
+  end
+end