From 7a6afa00acf4424d1f901147d41381a92f7cdafc Mon Sep 17 00:00:00 2001
From: Petr Heinz <petr@betterstack.com>
Date: Thu, 17 Aug 2023 13:50:50 +0200
Subject: [PATCH] Add ability to filter logs send to Better Stack

---
 example-project/main.rb         |  6 ++++++
 lib/logtail/config.rb           | 22 ++++++++++++++++++++++
 lib/logtail/log_devices/http.rb |  2 ++
 3 files changed, 30 insertions(+)

diff --git a/example-project/main.rb b/example-project/main.rb
index 6af69ec..b062ddd 100644
--- a/example-project/main.rb
+++ b/example-project/main.rb
@@ -15,6 +15,9 @@
 http_device = Logtail::LogDevices::HTTP.new(ARGV[0])
 logger = Logtail::Logger.new(http_device)
 
+# Filter logs that shouldn't be sent to Better Stack, see {Logtail::LogEntry} for available attributes
+Logtail.config.filter_sent_to_better_stack { |log_entry| log_entry.message.include?("DO_NOT_SEND") }
+
 # LOGGING
 
 # Send debug logs messages using the debug() method
@@ -33,6 +36,9 @@
     }
 )
 
+# Some messages can be filtered, see {Logtail::Config#filter_sent_to_better_stack} call above
+logger.info("This message will not be sent to Better Stack because it contains 'DO_NOT_SEND'")
+
 # Send error messages using the error() method
 logger.error("Oops! An error occurred!")
 
diff --git a/lib/logtail/config.rb b/lib/logtail/config.rb
index 662162b..6ea6729 100755
--- a/lib/logtail/config.rb
+++ b/lib/logtail/config.rb
@@ -32,6 +32,28 @@ def call(severity, timestamp, progname, msg)
 
     attr_writer :http_body_limit
 
+    # Whether a particular {Logtail::LogEntry} should be sent to Better Stack
+    def send_to_better_stack?(log_entry)
+      !@better_stack_filters&.any? { |blocker| blocker.call(log_entry) }
+    rescue => e
+      debug { "Could not determine whether to send LogEntry to Better Stack (assumed yes): #{e}" }
+      true
+    end
+
+    # This allows filtering logs that are sent to Better Stack. Can be called multiple times, all filters will
+    # be applied. If the passed block RETURNS TRUE for a particular LogEntry, it WILL NOT BE SENT to Better Stack.
+    #
+    # See {Logtail::LogEntry} for available attributes of the block parameter.
+    #
+    # @example Rails
+    #   config.logtail.filter_sent_to_better_stack { |log_entry| log_entry.context_snapshot[:http][:path].start_with?('_') }
+    # @example Everything else
+    #   Logtail.config.filter_sent_to_better_stack { |log_entry| log_entry.message.include?('IGNORE') }
+    def filter_sent_to_better_stack(&block)
+      @better_stack_filters ||= []
+      @better_stack_filters << -> (log_entry) { yield(log_entry) }
+    end
+
     # Convenience method for logging debug statements to the debug logger
     # set in this class.
     # @private
diff --git a/lib/logtail/log_devices/http.rb b/lib/logtail/log_devices/http.rb
index 863102e..c3243d4 100755
--- a/lib/logtail/log_devices/http.rb
+++ b/lib/logtail/log_devices/http.rb
@@ -89,6 +89,8 @@ def initialize(source_token, options = {})
       # size is constricted by the Logtail API. The actual application limit is a multiple
       # of this. Hence the `@request_queue`.
       def write(msg)
+        return unless Logtail.config.send_to_better_stack?(msg)
+
         @msg_queue.enq(msg)
 
         # Lazily start flush threads to ensure threads are alive after forking processes.