From 08743e8ac0ff1ce48e5bf19ca6f1fd506a0b05f9 Mon Sep 17 00:00:00 2001
From: Sam Saffron <sam.saffron@gmail.com>
Date: Mon, 2 Sep 2019 18:45:35 +1000
Subject: [PATCH] FEATURE: anon cache reports data to loggers

This allows custom plugins such as prometheus exporter to log how many
requests are stored in the anon cache vs used by the anon cache.

This metric allows us to fine tune cache behaviors
---
 lib/middleware/anonymous_cache.rb                  |  2 ++
 lib/middleware/request_tracker.rb                  | 13 ++++++++++---
 spec/components/middleware/request_tracker_spec.rb | 13 +++++++++++++
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/lib/middleware/anonymous_cache.rb b/lib/middleware/anonymous_cache.rb
index 118d47c9230..5df0a896d39 100644
--- a/lib/middleware/anonymous_cache.rb
+++ b/lib/middleware/anonymous_cache.rb
@@ -182,6 +182,8 @@ module Middleware
 
           $redis.setex(cache_key_body,  cache_duration, parts.join)
           $redis.setex(cache_key_other, cache_duration, [status, headers_stripped].to_json)
+
+          headers["X-Discourse-Cached"] = "store"
         else
           parts = response
         end
diff --git a/lib/middleware/request_tracker.rb b/lib/middleware/request_tracker.rb
index 2a75adaf2e9..607912ee28b 100644
--- a/lib/middleware/request_tracker.rb
+++ b/lib/middleware/request_tracker.rb
@@ -105,7 +105,7 @@ class Middleware::RequestTracker
     track_view &&= env_track_view || (request.get? && !request.xhr? && headers["Content-Type"] =~ /text\/html/)
     track_view = !!track_view
 
-    {
+    h = {
       status: status,
       is_crawler: helper.is_crawler?,
       has_auth_cookie: helper.has_auth_cookie?,
@@ -114,9 +114,16 @@ class Middleware::RequestTracker
       track_view: track_view,
       timing: timing,
       queue_seconds: env['REQUEST_QUEUE_SECONDS']
-    }.tap do |h|
-      h[:user_agent] = env['HTTP_USER_AGENT'] if h[:is_crawler]
+    }
+
+    if h[:is_crawler]
+      h[:user_agent] = env['HTTP_USER_AGENT']
     end
+
+    if cache = headers["X-Discourse-Cached"]
+      h[:cache] = cache
+    end
+    h
   end
 
   def log_request_info(env, result, info)
diff --git a/spec/components/middleware/request_tracker_spec.rb b/spec/components/middleware/request_tracker_spec.rb
index ae73bbaa034..35f9921f3c8 100644
--- a/spec/components/middleware/request_tracker_spec.rb
+++ b/spec/components/middleware/request_tracker_spec.rb
@@ -272,6 +272,19 @@ describe Middleware::RequestTracker do
       Middleware::RequestTracker.unregister_detailed_request_logger(logger)
     end
 
+    it "can report data from anon cache" do
+      cache = Middleware::AnonymousCache.new(app([200, {}, ["i am a thing"]]))
+      tracker = Middleware::RequestTracker.new(cache)
+
+      uri = "/path?#{SecureRandom.hex}"
+      tracker.call(env("REQUEST_URI" => uri, "ANON_CACHE_DURATION" => 60))
+
+      expect(@data[:cache]).to eq("store")
+
+      tracker.call(env("REQUEST_URI" => uri, "ANON_CACHE_DURATION" => 60))
+      expect(@data[:cache]).to eq("true")
+    end
+
     it "can correctly log detailed data" do
 
       global_setting :enable_performance_http_headers, true