fix: prevent SDK crash when SDK logging fails

.gitignore

@@ -21,3 +21,4 @@ node_modules
 .devcontainer/.env
 vendor/gems
 sentry-rails/Gemfile-*.lock
+mise.toml

CHANGELOG.md

@@ -39,6 +39,7 @@
   # This now works too and the nested hash is dumped to JSON string
   Sentry.logger.info("Hello World", extra: { today: Date.today, user_id: user.id })
   ```
+- Prevent SDK crash when SDK logging fails ([#2817](https://github.com/getsentry/sentry-ruby/pull/2817))
 
 ## 6.2.0
 

sentry-ruby/lib/sentry/utils/logging_helper.rb

@@ -6,26 +6,40 @@ module LoggingHelper
     # @!visibility private
     def log_error(message, exception, debug: false)
       message = "#{message}: #{exception.message}"
-      message += "\n#{exception.backtrace.join("\n")}" if debug
+      message += "\n#{exception.backtrace.join("\n")}" if debug && exception.backtrace
 
-      sdk_logger&.error(LOGGER_PROGNAME) do
-        message
-      end
+      sdk_logger&.error(LOGGER_PROGNAME) { message }
+    rescue StandardError => e
+      log_to_stderr(e, message)
     end
 
     # @!visibility private
     def log_debug(message)
       sdk_logger&.debug(LOGGER_PROGNAME) { message }
+    rescue StandardError => e
+      log_to_stderr(e, message)
     end
 
     # @!visibility private
     def log_warn(message)
       sdk_logger&.warn(LOGGER_PROGNAME) { message }
+    rescue StandardError => e
+      log_to_stderr(e, message)
     end
 
     # @!visibility private
     def sdk_logger
       @sdk_logger ||= Sentry.sdk_logger
     end
+
+    # @!visibility private
+    def log_to_stderr(error, message)
+      error_msg = "Sentry SDK logging failed (#{error.class}: #{error.message}): #{message}".scrub(%q(<?>))
+      error_msg += "\n#{error.backtrace.map { |line| line.scrub(%q(<?>)) }.join("\n")}" if error.backtrace
+
+      $stderr.puts(error_msg)
+    rescue StandardError
+      # swallow everything – logging must never crash the app
+    end
   end
 end

sentry-ruby/spec/sentry/utils/logging_helper_spec.rb

@@ -0,0 +1,122 @@
+# frozen_string_literal: true
+
+RSpec.describe Sentry::LoggingHelper do
+  let(:string_io) { StringIO.new }
+  let(:logger) { Logger.new(string_io) }
+
+  let(:helper_class) do
+    Class.new do
+      include Sentry::LoggingHelper
+      attr_accessor :sdk_logger
+
+      def initialize(sdk_logger)
+        @sdk_logger = sdk_logger
+      end
+    end
+  end
+
+  let(:logger_helper) { helper_class.new(logger) }
+
+  describe "#log_error" do
+    it "logs exception message with description" do
+      exception = StandardError.new("Something went wrong")
+      logger_helper.log_error("test_error", exception)
+
+      expect(string_io.string).to include("test_error: Something went wrong")
+    end
+
+    it "includes backtrace when debug is true" do
+      exception = StandardError.new("Error")
+      exception.set_backtrace(["it_broke.rb:1"])
+
+      logger_helper.log_error("test_error", exception, debug: true)
+
+      expect(string_io.string).to include("it_broke.rb:1")
+    end
+  end
+
+  describe "stderr fallback when logger fails" do
+    shared_examples "falls back to stderr" do |method_name, *args|
+      it "outputs to stderr with error class and message" do
+        broken_logger = Class.new do
+          def debug(*); raise IOError, "oops"; end
+          def warn(*); raise IOError, "oops"; end
+        end.new
+
+        helper = helper_class.new(broken_logger)
+
+        expect($stderr).to receive(:puts).with(/Sentry SDK logging failed \(IOError:/)
+        expect { helper.public_send(method_name, *args) }.not_to raise_error
+      end
+    end
+
+    context "#log_debug" do
+      include_examples "falls back to stderr", :log_debug, "Debug message"
+    end
+
+    context "#log_warn" do
+      include_examples "falls back to stderr", :log_warn, "Warning message"
+    end
+
+    it "includes backtrace in stderr output" do
+      broken_logger = Class.new do
+        def error(*)
+          error = IOError.new("oops")
+          error.set_backtrace([
+            "logger.rb:42:in `write'",
+            "logger.rb:10:in `error'"
+          ])
+
+          raise error
+        end
+      end.new
+
+      helper = helper_class.new(broken_logger)
+
+      stderr_output = nil
+      expect($stderr).to receive(:puts) { |msg| stderr_output = msg }
+
+      helper.log_error("Test message", StandardError.new("Error"))
+
+      expect(stderr_output).to include("IOError: oops")
+      expect(stderr_output).to include("logger.rb:42:in `write'")
+      expect(stderr_output).to include("logger.rb:10:in `error'")
+    end
+  end
+
+  describe "custom JSON logger with encoding errors" do
+    # Custom logger from GitHub issue #2805
+    let(:json_logger) do
+      Class.new(::Logger) do
+        class JsonFormatter
+          def call(level, _, _, m)
+            { severity: level, message: m }.to_json << "\n"
+          end
+        end
+
+        def initialize(*)
+          super
+          self.formatter = JsonFormatter.new
+        end
+      end.new(StringIO.new)
+    end
+
+    let(:logger_helper) { helper_class.new(json_logger) }
+
+    it "scrubs invalid UTF-8 in stderr output when JSON logger fails on encoding" do
+      helper = helper_class.new(json_logger)
+
+      invalid_message = "a\x92b"
+      exception = StandardError.new("oops")
+
+      stderr_message = nil
+      expect($stderr).to receive(:puts) { |msg| stderr_message = msg }
+
+      expect { helper.log_error(invalid_message, exception) }.not_to raise_error
+
+      expect(stderr_message).to include("JSON::GeneratorError")
+      expect(stderr_message).to include("a<?>b")
+      expect(stderr_message).to include("oops")
+    end
+  end
+end