feat(invidious-companion): use connection pool

From
https://github.com/iv-org/invidious/pull/4985#discussion_r1889356705

Thanks syeopite!

src/invidious.cr

@@ -114,6 +114,10 @@ YT_POOL = YoutubeConnectionPool.new(YT_URL, capacity: CONFIG.pool_size)
 
 GGPHT_POOL = YoutubeConnectionPool.new(URI.parse("https://yt3.ggpht.com"), capacity: CONFIG.pool_size)
 
+COMPANION_POOL = CompanionConnectionPool.new(
+  capacity: CONFIG.pool_size
+)
+
 # CLI
 Kemal.config.extra_options do |parser|
   parser.banner = "Usage: invidious [arguments]"

src/invidious/yt_backend/connection_pool.cr

@@ -46,6 +46,45 @@ struct YoutubeConnectionPool
   end
 end
 
+struct CompanionConnectionPool
+  property pool : DB::Pool(HTTP::Client)
+
+  def initialize(capacity = 5, timeout = 5.0)
+    options = DB::Pool::Options.new(
+      initial_pool_size: 0,
+      max_pool_size: capacity,
+      max_idle_pool_size: capacity,
+      checkout_timeout: timeout
+    )
+
+    @pool = DB::Pool(HTTP::Client).new(options) do
+      companion = CONFIG.invidious_companion.sample
+      next make_client(companion.private_url, force_resolve: true)
+    end
+  end
+
+  def client(&)
+    conn = pool.checkout
+    # Proxy needs to be reinstated every time we get a client from the pool
+    conn.proxy = make_configured_http_proxy_client() if CONFIG.http_proxy
+
+    begin
+      response = yield conn
+    rescue ex
+      conn.close
+
+      companion = CONFIG.invidious_companion.sample
+      conn = make_client(companion.private_url, force_resolve: true)
+
+      response = yield conn
+    ensure
+      pool.release(conn)
+    end
+
+    response
+  end
+end
+
 def add_yt_headers(request)
   request.headers.delete("User-Agent") if request.headers["User-Agent"] == "Crystal"
   request.headers["User-Agent"] ||= "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0.0.0 Safari/537.36"

src/invidious/yt_backend/youtube_api.cr

@@ -686,9 +686,7 @@ module YoutubeAPI
     # Send the POST request
 
     begin
-      invidious_companion = CONFIG.invidious_companion.sample
+      response = COMPANION_POOL.client &.post(endpoint, headers: headers, body: data.to_json)
-      response = make_client(invidious_companion.private_url, use_http_proxy: false,
-        &.post(endpoint, headers: headers, body: data.to_json))
       body = response.body
       if (response.status_code != 200)
         raise Exception.new(