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https://github.com/basecamp/once-campfire.git
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GPT on behalf of DHH
ac73267b07
Transfer the C completed-response cache lesson into Rails, keeping authentication, room checks and cookies per request. A persistent read-only SQLite observer detects local and foreign commits and rejects racing admission. Whole-page misses render fresh to avoid stale nested fragments; message ETags reflect token-neutral presentation.
90 lines
2.1 KiB
Ruby
90 lines
2.1 KiB
Ruby
require "sqlite3"
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# A read-only observer sees commits from every writer, including other runtimes.
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# PRAGMA data_version can only be compared on the same persistent connection.
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class ResponseCache
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MAX_ENTRY_BYTES = 1.megabyte
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MAX_KEY_BYTES = 2.kilobytes
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def self.instance
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@instance ||= new
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end
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def initialize
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@mutex = Mutex.new
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@entries = {}
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@bytes = 0
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end
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def budget
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[ ENV.fetch("CAMPFIRE_RESPONSE_CACHE_MB", "64").to_i, 0 ].max.megabytes
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end
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def version
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@mutex.synchronize { current_version }
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rescue SQLite3::Exception
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clear
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nil
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end
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def read(key, version)
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@mutex.synchronize do
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@entries[key]&.first if current_version == version
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end
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rescue SQLite3::Exception
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clear
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nil
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end
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def write(key, version, entry)
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size = key.bytesize + entry[:body].bytesize + entry[:headers].sum { |name, value| name.bytesize + value.bytesize } + 256
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return if key.bytesize > MAX_KEY_BYTES || size > [ budget, MAX_ENTRY_BYTES ].min
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@mutex.synchronize do
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return unless current_version == version
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return if @entries.key?(key)
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while @entries.any? && @bytes + size > budget
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_, (_, removed_size) = @entries.shift
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@bytes -= removed_size
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end
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@entries[key] = [ entry, size ]
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@bytes += size
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end
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rescue SQLite3::Exception
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clear
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end
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def clear
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@mutex.synchronize do
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@entries.clear
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@bytes = 0
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@observer&.close
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@observer = @database = @version = nil
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end
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end
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private
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def current_version
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database = File.expand_path(ActiveRecord::Base.connection_db_config.database)
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if @database != database || !@observer
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@entries.clear
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@bytes = 0
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@observer&.close
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@observer = nil
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@observer = SQLite3::Database.new(database, readonly: true)
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@database = database
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@namespace = SecureRandom.hex(16)
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@version = nil
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end
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version = @observer.get_first_value("PRAGMA data_version")
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if @version != version
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@entries.clear
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@bytes = 0
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@version = version
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end
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[ @database, @namespace, @version ]
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end
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end
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