Truncate internal log lines

.changesets/do-not-log-long-error-messages-to-internal-appsignal-log.md

@@ -0,0 +1,6 @@
+---
+bump: patch
+type: fix
+---
+
+Do not log long (error) messages to the internal AppSignal log. If an error like `ActionController::BadRequest` occurred and the error message contained the entire file upload, this would grow the `appsignal.log` file quickly if the error happens often. Internal log messages are now truncated by default.

lib/appsignal/utils/integration_logger.rb

@@ -3,6 +3,31 @@
 module Appsignal
   module Utils
     class IntegrationLogger < ::Logger
+      MAX_MESSAGE_LENGTH = 2_000
+
+      def add(severity, message = nil, progname = nil)
+        if message.nil? && !block_given?
+          # When called as logger.error("msg"), the message is in progname
+          progname = truncate_message(progname)
+        elsif message
+          message = truncate_message(message)
+        elsif block_given?
+          message = truncate_message(yield)
+        end
+        super
+      end
+
+      private
+
+      def truncate_message(message)
+        return message unless message.is_a?(String)
+
+        if message.length > MAX_MESSAGE_LENGTH
+          "#{message[0, MAX_MESSAGE_LENGTH]}..."
+        else
+          message
+        end
+      end
     end
   end
 end

spec/lib/appsignal/utils/integration_logger_spec.rb

@@ -12,10 +12,58 @@
     logger.info("info message")
     logger.warn("warning message")
     logger.error("error message")
+    logger.error(ExampleStandardError.new("example error with message"))
+    logger.info { "block error message" }
 
     expect(logs).to contains_log(:debug, "debug message")
     expect(logs).to contains_log(:info, "info message")
     expect(logs).to contains_log(:warn, "warning message")
     expect(logs).to contains_log(:error, "error message")
+    expect(logs).to contains_log(:error, "example error with message")
+    expect(logs).to contains_log(:info, "block error message")
+  end
+
+  describe "message truncation" do
+    it "does not truncate short messages" do
+      logger.error("Short error message")
+
+      expect(logs).to contains_log(:error, "Short error message")
+    end
+
+    context "when calling logger.error(message)" do
+      it "truncates long messages" do
+        long_message = "a" * 2500
+        logger.error(long_message)
+
+        expect(logs).to contains_log(:error, "#{"a" * 2000}...")
+      end
+    end
+
+    context "when calling logger.error { message }" do
+      it "truncates long messages passed as a block" do
+        long_message = "a" * 2500
+        logger.error { long_message }
+
+        expect(logs).to contains_log(:error, "#{"a" * 2000}...")
+      end
+    end
+
+    context "when calling logger.add(severity, message)" do
+      it "truncates long messages" do
+        long_message = "a" * 2500
+        logger.add(Logger::ERROR, long_message)
+
+        expect(logs).to contains_log(:error, "#{"a" * 2000}...")
+      end
+    end
+
+    context "when calling logger.error(progname) { message }" do
+      it "truncates long messages from block" do
+        long_message = "a" * 2500
+        logger.error("progname") { long_message }
+
+        expect(logs).to contains_log(:error, "#{"a" * 2000}...")
+      end
+    end
   end
 end