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122 lines
3.9 KiB
Elixir
122 lines
3.9 KiB
Elixir
defmodule Pleroma.HTTP.Backoff do
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alias Pleroma.HTTP
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require Logger
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@cachex Pleroma.Config.get([:cachex, :provider], Cachex)
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@backoff_cache :http_backoff_cache
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# attempt to parse a timestamp from a header
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# returns nil if it can't parse the timestamp
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@spec timestamp_or_nil(binary) :: DateTime.t() | nil
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defp timestamp_or_nil(header) do
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case DateTime.from_iso8601(header) do
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{:ok, stamp, _} ->
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stamp
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_ ->
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nil
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end
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end
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# attempt to parse the x-ratelimit-reset header from the headers
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@spec x_ratelimit_reset(headers :: list) :: DateTime.t() | nil
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defp x_ratelimit_reset(headers) do
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with {_header, value} <- List.keyfind(headers, "x-ratelimit-reset", 0),
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true <- is_binary(value) do
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timestamp_or_nil(value)
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else
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_ ->
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nil
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end
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end
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# attempt to parse the Retry-After header from the headers
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# this can be either a timestamp _or_ a number of seconds to wait!
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# we'll return a datetime if we can parse it, or nil if we can't
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@spec retry_after(headers :: list) :: DateTime.t() | nil
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defp retry_after(headers) do
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with {_header, value} <- List.keyfind(headers, "retry-after", 0),
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true <- is_binary(value) do
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# first, see if it's an integer
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case Integer.parse(value) do
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{seconds, ""} ->
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Logger.debug("Parsed Retry-After header: #{seconds} seconds")
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DateTime.utc_now() |> Timex.shift(seconds: seconds)
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_ ->
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# if it's not an integer, try to parse it as a timestamp
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timestamp_or_nil(value)
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end
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else
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_ ->
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nil
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end
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end
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# given a set of headers, will attempt to find the next backoff timestamp
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# if it can't find one, it will default to 5 minutes from now
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@spec next_backoff_timestamp(%{headers: list}) :: DateTime.t()
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defp next_backoff_timestamp(%{headers: headers}) when is_list(headers) do
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default_5_minute_backoff =
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DateTime.utc_now()
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|> Timex.shift(seconds: 5 * 60)
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backoff =
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[&x_ratelimit_reset/1, &retry_after/1]
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|> Enum.map(& &1.(headers))
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|> Enum.find(&(&1 != nil))
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if is_nil(backoff) do
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Logger.debug("No backoff headers found, defaulting to 5 minutes from now")
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default_5_minute_backoff
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else
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Logger.debug("Found backoff header, will back off until: #{backoff}")
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backoff
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end
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end
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defp next_backoff_timestamp(_), do: DateTime.utc_now() |> Timex.shift(seconds: 5 * 60)
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# utility function to check the HTTP response for potential backoff headers
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# will check if we get a 429 or 503 response, and if we do, will back off for a bit
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@spec check_backoff({:ok | :error, HTTP.Env.t()}, binary()) ::
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{:ok | :error, HTTP.Env.t()} | {:error, :ratelimit}
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defp check_backoff({:ok, env}, host) do
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case env.status do
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status when status in [429, 503] ->
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Logger.error("Rate limited on #{host}! Backing off...")
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timestamp = next_backoff_timestamp(env)
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ttl = Timex.diff(timestamp, DateTime.utc_now(), :seconds)
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# we will cache the host for 5 minutes
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@cachex.put(@backoff_cache, host, true, ttl: ttl)
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{:error, :ratelimit}
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_ ->
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{:ok, env}
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end
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end
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defp check_backoff(env, _), do: env
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@doc """
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this acts as a single throughput for all GET requests
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we will check if the host is in the cache, and if it is, we will automatically fail the request
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this ensures that we don't hammer the server with requests, and instead wait for the backoff to expire
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this is a very simple implementation, and can be improved upon!
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"""
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@spec get(binary, list, list) :: {:ok | :error, HTTP.Env.t()} | {:error, :ratelimit}
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def get(url, headers \\ [], options \\ []) do
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%{host: host} = URI.parse(url)
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case @cachex.get(@backoff_cache, host) do
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{:ok, nil} ->
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url
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|> HTTP.get(headers, options)
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|> check_backoff(host)
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_ ->
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{:error, :ratelimit}
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end
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end
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end
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