defmodule Membrane.File.Sink do
@moduledoc """
Element that creates a file and stores incoming buffers there (in binary format).
When `Membrane.File.SeekEvent` is received, the element starts writing buffers starting
from `position`. By default, it overwrites previously stored bytes. You can set `insert?`
field of the event to `true` to start inserting new buffers without overwriting previous ones.
Please note, that inserting requires rewriting the file, what negatively impacts performance.
For more information refer to `Membrane.File.SeekEvent` moduledoc.
"""
use Membrane.Sink
alias Membrane.File.SeekEvent
alias Membrane.ResourceGuard
@common_file Membrane.File.CommonFileBehaviour.get_impl()
def_options location: [
spec: Path.t(),
description: "Path of the output file"
]
def_input_pad :input, demand_unit: :buffers, accepted_format: _any
@impl true
def handle_init(_ctx, %__MODULE__{location: location}) do
{[],
%{
location: Path.expand(location),
temp_location: Path.expand(location <> ".tmp"),
fd: nil,
temp_fd: nil
}}
end
@impl true
def handle_setup(ctx, %{location: location} = state) do
fd = @common_file.open!(location, [:read, :write])
:ok = @common_file.truncate!(fd)
Membrane.ResourceGuard.register(
ctx.resource_guard,
fn -> @common_file.close!(fd) end,
tag: {:fd, fd}
)
{[], %{state | fd: fd}}
end
@impl true
def handle_playing(_ctx, state) do
{[demand: :input], state}
end
@impl true
def handle_write(:input, buffer, _ctx, %{fd: fd} = state) do
:ok = @common_file.write!(fd, buffer)
{[demand: :input], state}
end
@impl true
def handle_event(:input, %SeekEvent{insert?: insert?, position: position}, ctx, state) do
state =
if insert?,
do: split_file(state, ctx.resource_guard, position),
else: seek_file(state, ctx.resource_guard, position)
{[], state}
end
def handle_event(pad, event, ctx, state), do: super(pad, event, ctx, state)
defp seek_file(%{fd: fd} = state, resource_guard, position) do
state = maybe_merge_temporary(state, resource_guard)
_position = @common_file.seek!(fd, position)
state
end
defp split_file(%{fd: fd} = state, resource_guard, position) do
state =
state
|> seek_file(resource_guard, position)
|> open_temporary(resource_guard)
:ok = @common_file.split!(fd, state.temp_fd)
state
end
defp maybe_merge_temporary(%{temp_fd: nil} = state, _resource_guard), do: state
defp maybe_merge_temporary(
%{fd: fd, temp_fd: temp_fd, temp_location: temp_location} = state,
resource_guard
) do
# TODO: Consider improving performance for multi-insertion scenarios by using
# multiple temporary files and merging them only once on `handle_prepared_to_stopped/2`.
ResourceGuard.unregister(resource_guard, {:temp_fd, temp_fd})
copy_and_remove_temporary(fd, temp_fd, temp_location)
%{state | temp_fd: nil}
end
defp open_temporary(
%{temp_fd: nil, fd: fd, temp_location: temp_location} = state,
resource_guard
) do
temp_fd = @common_file.open!(temp_location, [:read, :exclusive])
ResourceGuard.register(
resource_guard,
fn -> copy_and_remove_temporary(fd, temp_fd, temp_location) end,
tag: {:temp_fd, temp_fd}
)
%{state | temp_fd: temp_fd}
end
defp copy_and_remove_temporary(fd, temp_fd, temp_location) do
_bytes_copied = @common_file.copy!(temp_fd, fd)
:ok = @common_file.close!(temp_fd)
:ok = @common_file.rm!(temp_location)
end
end