Cache dither results

bin/dither/dither.rb

@@ -1,5 +1,7 @@
 require "sinatra"
 require "mini_magick"
+require "digest"
+require "fileutils"
 require "tempfile"
 
 MiniMagick.logger.level = Logger::DEBUG
@@ -8,6 +10,26 @@ ROOT = ENV.fetch("ROOT")
 KEY = ENV.fetch("KEY")
 DITHER = ENV["DITHER"] != "0"
 FORMAT = "png"
+CACHE_DIR = ENV["DITHER_CACHE_DIR"]
+
+def cache_path_for(path, geometry)
+  return unless CACHE_DIR
+
+  source_path = "#{ROOT}/#{path}.enc"
+  stat = File.stat(source_path)
+  cache_key = Digest::SHA256.hexdigest([
+    path,
+    stat.size,
+    stat.mtime.to_f,
+    geometry,
+    DITHER,
+    FORMAT,
+    1
+  ].join("\0"))
+
+  FileUtils.mkdir_p(CACHE_DIR)
+  File.join(CACHE_DIR, "#{cache_key}.#{FORMAT}")
+end
 
 get "/*" do |path|
   halt 404, {"Content-Type" => "text/plain"}, "not found" unless File.exist?("#{ROOT}/#{path}.enc")
@@ -17,6 +39,11 @@ get "/*" do |path|
   geometry = params["geo"] unless params["geo"] == ""
   geometry.gsub!(/\d+/) { |n| n.to_i * 2 } if geometry && !DITHER
 
+  cached_path = cache_path_for(path, geometry)
+  if cached_path && File.exist?(cached_path)
+    return File.binread(cached_path)
+  end
+
   decrypted = Tempfile.new(["dither", File.extname(path)])
   decrypted.binmode
   decrypted.close
@@ -59,7 +86,15 @@ get "/*" do |path|
     end
 
     convert << "#{FORMAT.upcase}:-"
-    convert.call
+    output = convert.call
+
+    if cached_path
+      temp_cache_path = "#{cached_path}.tmp-#{Process.pid}"
+      File.binwrite(temp_cache_path, output)
+      FileUtils.mv(temp_cache_path, cached_path)
+    end
+
+    output
   ensure
     decrypted.unlink
   end