From b470d840ba24dc825c6b29b4047a9679af7504b6 Mon Sep 17 00:00:00 2001
From: Russell Smith <russ@bashme.org>
Date: Fri, 29 May 2026 15:07:37 -0700
Subject: [PATCH] Log broadcasts once per event instead of once per subscriber.
 Fixes #73

`Cable::Server#send_to_channels` logged a "transmitting" line inside the
per-subscriber loop, so a single broadcast to a stream with N connected
clients produced N identical log lines. A busy chat room could emit
dozens of duplicate entries for one message, flooding production logs.

Move the log outside the loop and emit a single line per broadcast that
includes the number of subscribers it was delivered to. Skips logging
entirely when there are no live subscribers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 spec/cable/server_spec.cr | 29 +++++++++++++++++++++++++++++
 src/cable/server.cr       |  9 ++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/spec/cable/server_spec.cr b/spec/cable/server_spec.cr
index a505ec0..44c30ae 100644
--- a/spec/cable/server_spec.cr
+++ b/spec/cable/server_spec.cr
@@ -1,4 +1,5 @@
 require "../spec_helper"
+require "log/spec"
 
 include RequestHelpers
 
@@ -47,6 +48,34 @@ describe Cable::Server do
     end
   end
 
+  describe "#send_to_channels" do
+    it "logs a single line per broadcast regardless of the number of subscribers" do
+      Cable.reset_server
+      Cable.temp_config(backend_class: Cable::DevBackend) do
+        connection_1 = creates_new_connection("aa")
+        connection_2 = creates_new_connection("bb")
+
+        Cable.server.add_connection(connection_1)
+        Cable.server.add_connection(connection_2)
+
+        # Both connections stream from the same identifier ("chat_room_a")
+        connection_1.subscribe(subscribe_payload("room_a"))
+        connection_2.subscribe(subscribe_payload("room_a"))
+
+        logs = Log.capture("cable") do
+          Cable.server.send_to_channels("chat_room_a", {"message" => "hi"}.to_json)
+        end
+
+        logs.check(:info, /Transmitting .* to 2 subscribers \(via streamed from chat_room_a\)/)
+        logs.empty
+
+        connection_1.close
+        connection_2.close
+      end
+      Cable.reset_server
+    end
+  end
+
   describe "#subscribed_channels_for" do
     it "accurately returns active channel subscriptions for a specificic token" do
       Cable.reset_server
diff --git a/src/cable/server.cr b/src/cable/server.cr
index 2e35744..684c4b3 100644
--- a/src/cable/server.cr
+++ b/src/cable/server.cr
@@ -135,6 +135,7 @@ module Cable
       return unless @channels.has_key?(channel_identifier)
 
       parsed_message = safe_decode_message(message)
+      transmitted = 0
 
       begin
         @channels[channel_identifier].each do |channel|
@@ -143,13 +144,19 @@ module Cable
           if channel.connection.closed?
             channel.close
           else
-            Cable::Logger.info { "#{channel.class} transmitting #{parsed_message} (via streamed from #{channel.stream_identifier})" }
             channel.connection.socket.send({
               identifier: channel.identifier,
               message:    parsed_message,
             }.to_json)
+            transmitted += 1
           end
         end
+
+        # Log once per broadcast event rather than once per subscriber, so a
+        # message fanned out to N connections produces a single log line.
+        if transmitted > 0
+          Cable::Logger.info { "Transmitting #{parsed_message} to #{transmitted} subscriber#{"s" if transmitted > 1} (via streamed from #{channel_identifier})" }
+        end
       rescue e : IO::Error
         Cable.settings.on_error.call(e, "IO::Error Exception: #{e.message}: #{parsed_message} -> Cable::Server#send_to_channels(channel, message)", nil)
       end