Telemetry helpers and event conventions for Sftpd.

Sftpd depends on the lightweight :telemetry library and emits events through the shared Erlang/Elixir instrumentation interface.

See the Telemetry extra in HexDocs for the full event reference, payload details, examples, and caveats.

The library emits these events:

• [:sftpd, :server, :start]
• [:sftpd, :server, :stop]
• [:sftpd, :sftp, operation] for :close, :del_dir, :delete, :get_cwd, :is_dir, :list_dir, :make_dir, :make_symlink, :open, :position, :read, :read_file_info, :read_link, :read_link_info, :rename, :write, and :write_file_info

Every event includes a :duration measurement in native time units. Read and write events also include a :bytes measurement.

Common metadata:

• SFTP operation events include :backend, :backend_kind, :result, and :reason when an error reason exists
• :open also includes :path, :requested_modes, :mode, and :open_timeout
• :close also includes :io_device, :close_timeout, and :close_shutdown_grace
• :read also includes :io_device and :bytes_requested
• :write also includes :io_device
• path-oriented operations include :path
• :rename includes :src_path and :dst_path
• :position includes :io_device and :offset
• :is_dir uses :directory and :not_directory result values
• server lifecycle events include :backend, :backend_kind, and :result, plus :port/:max_sessions on start and :server_ref on successful start or stop