From d94015fcffa5fe0f7a72bbc525609ef2a45c5ffc 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 51d0e19dec..c6d8641506 100644
--- a/lib/middleware/anonymous_cache.rb
+++ b/lib/middleware/anonymous_cache.rb
@@ -181,6 +181,8 @@ 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 470ab5f167..fca5fa2d24 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 ae73bbaa03..35f9921f3c 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