Preload many manifests concurrently for the Alt Styles page

I'm gonna also use this for a task to try to warm up *all* the
manifests in the database! But to start, just a simple one, to prepare
the alt styles page quickly on first run. (This doesn't really matter
in production now that I've already visited the page once, but it helps
when resetting things in dev, and I think more it's about establishing
the pattern!)

app/controllers/alt_styles_controller.rb

@@ -8,6 +8,10 @@ class AltStylesController < ApplicationController
 			@alt_styles = @alt_styles.merge(@species.alt_styles)
 		end
 
+		# We're going to link to the HTML5 image URL, so make sure we have all the
+		# manifests ready!
+		SwfAsset.preload_manifests @alt_styles.map(&:swf_assets).flatten
+
 		respond_to do |format|
 			format.html { render }
 			format.json {

app/models/swf_asset.rb

@@ -1,3 +1,6 @@
+require 'async'
+require 'async/barrier'
+require 'async/semaphore'
 require 'fileutils'
 require 'uri'
 
@@ -117,6 +120,10 @@ class SwfAsset < ApplicationRecord
     NeopetsMediaArchive.load_json(manifest_url)
   end
 
+  def preload_manifest
+    NeopetsMediaArchive.preload_file(manifest_url)
+  end
+
   MANIFEST_BASE_URL = Addressable::URI.parse("https://images.neopets.com")
   def manifest_asset_urls
     return {} if manifest_url.nil?
@@ -229,6 +236,31 @@ class SwfAsset < ApplicationRecord
     ))
   end
 
+  # Given a list of SWF assets, ensure all of their manifests are loaded, with
+  # fast concurrent execution!
+  def self.preload_manifests(swf_assets)
+    # Blocks all tasks beneath it.
+    barrier = Async::Barrier.new
+
+    Sync do
+      # Only allow 10 manifests to be loaded at a time.
+      semaphore = Async::Semaphore.new(10, parent: barrier)
+
+      # Load all the manifests in async tasks. This will load them 10 at a time
+      # rather than all at once (because of the semaphore), and the
+      # NeopetsMediaArchive will share a pool of persistent connections for
+      # them.
+      swf_assets.map do |swf_asset|
+        semaphore.async { swf_asset.preload_manifest }
+      end
+
+      # Wait until all tasks are done.
+      barrier.wait
+    ensure
+      barrier.stop # If something goes wrong, clean up all tasks.
+    end
+  end
+
   before_save do
     # If an asset body ID changes, that means more than one body ID has been
     # linked to it, meaning that it's probably wearable by all bodies.

app/services/neopets_media_archive.rb

@@ -1,5 +1,5 @@
 require "addressable/uri"
-require "httparty"
+require "async/http/internet/instance"
 require "json"
 
 # The Neopets Media Archive is a service that mirrors images.neopets.com files
@@ -11,8 +11,9 @@ require "json"
 # long-term archive, not dependent on their services having 100% uptime in
 # order for us to operate. We never discard old files, we just keep going!
 module NeopetsMediaArchive
-  include HTTParty
-  base_uri "https://images.neopets.com/"
+  # Share a pool of persistent connections, rather than reconnecting on
+  # each request. (This library does that automatically!)
+  INTERNET = Async::HTTP::Internet.instance
 
   ROOT_PATH = Pathname.new(Rails.configuration.neopets_media_archive_root)
 
@@ -46,9 +47,8 @@ module NeopetsMediaArchive
     end
 
     # Download the file from the origin, then save a copy for next time.
-    response = load_file_from_origin(uri)
+    content = load_file_from_origin(uri)
     info "Loaded source file from origin: #{uri}"
-    content = response.body
     local_path.dirname.mkpath
     File.write(local_path, content)
     info "Wrote source file to filesystem: #{local_path}"
@@ -71,13 +71,20 @@ module NeopetsMediaArchive
         "https://images.neopets.com, but got #{uri}"
     end
 
-    response = get(uri)
-    if response.code == 404
-      raise NotFound, "origin server returned 404: #{uri}"
-    elsif response.code != 200
-      raise "expected status 200 but got #{response.code} (#{uri})"
+    # By running this request in a `Sync` block, we make this method look
+    # synchronous to the caller—but if run in the context of an async task, it
+    # will pause execution and move onto other work until the request is done.
+    # We use this in the `swf_assets:manifests:load` task to perform many
+    # requests in parallel!
+    Sync do
+      response = INTERNET.get(uri)
+      if response.status == 404
+        raise NotFound, "origin server returned 404: #{uri}"
+      elsif response.status != 200
+        raise "expected status 200 but got #{response.status} (#{uri})"
+      end
+      response.body.read
     end
-    response
   end
 
   def self.path_within_archive(uri)