Module: Ace::Hitl::Lifecycle::AtomicJson

Defined in:
lib/ace/hitl/lifecycle/atomic_json.rb

Overview

Durable, permission-preserving JSON record writes (port of atomic_json): O_EXCL|O_NOFOLLOW tempfile in the target directory, fsync, chmod, chown, rename. Ownership transitions go through the injectable ownership strategy; production performs real chown(2), tests map names onto the current identity (spec 8wm.t.y21 §2).

Defined Under Namespace

Classes: Ownership

Constant Summary collapse

DEFAULT_OWNERSHIP = 
Object.new.tap do |strategy|
  strategy.define_singleton_method(:chown) do |path, ownership|
    File.chown(ownership.uid, ownership.gid, path) if ownership
  end
end.freeze

Class Method Summary collapse

Class Method Details

.call(path, value, mode:, ownership: nil, ownership_strategy: DEFAULT_OWNERSHIP, exclusive: false) ⇒ Object

mode is an Integer permission bits value; ownership nil keeps the current identity. exclusive commits with link(2) instead of rename(2), so an existing destination raises Errno::EEXIST instead of being silently replaced (create-once writes).



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# File 'lib/ace/hitl/lifecycle/atomic_json.rb', line 30

def call(path, value, mode:, ownership: nil, ownership_strategy: DEFAULT_OWNERSHIP,
  exclusive: false)
  path = Pathname.new(path)
  path.parent.mkpath
  # The random suffix makes the temporary unique per invocation:
  # a fixed pid-based name lets a competing writer's cleanup
  # delete our in-flight temporary and fail both writes (review
  # 8wq2zttt on PR#336). Cleanup only ever touches this call's
  # own file.
  temporary = path.parent.join(".#{path.basename}.tmp.#{$PROCESS_ID}.#{SecureRandom.hex(4)}")
  flags = File::WRONLY | File::CREAT | File::EXCL | File::NOFOLLOW
  fd = IO.sysopen(temporary, flags, mode)
  begin
    io = IO.for_fd(fd, mode: "w")
    begin
      io.write(JSON.generate(value))
      io.write("\n")
      io.flush
      io.fsync
    ensure
      io.close
    end
  rescue
    begin
      temporary.unlink
    rescue
      nil
    end
    raise
  end
  File.chmod(mode, temporary)
  ownership_strategy.chown(temporary, ownership)
  if exclusive
    File.link(temporary, path)
  else
    File.rename(temporary, path)
  end
ensure
  temporary.unlink if temporary&.exist?
end

.read(path) ⇒ Object 



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# File 'lib/ace/hitl/lifecycle/atomic_json.rb', line 71

def read(path)
  JSON.parse(File.read(path))
rescue SystemCallError, JSON::ParserError
  nil
end