defmodule AbsintheCacheFairy do
@moduledoc ~s"""
Provides the macro `cache_resolve` that replaces the Absinthe's `resolve` and
caches the result of the resolver for some time instead of calculating it
every time.
"""
alias __MODULE__, as: CacheMod
alias AbsintheCacheFairy.ConCacheProvider, as: CacheProvider
require Logger
@ttl 300
@max_ttl_offset 120
# TODO: Make it configurable
@cache_name :graphql_cache
@compile {:inline,
wrap: 2,
wrap: 3,
from: 2,
resolver: 3,
store: 2,
store: 3,
get_or_store: 2,
get_or_store: 3,
cache_modify_middleware: 3,
cache_key: 2,
convert_values: 2,
generate_additional_args: 1}
@doc ~s"""
Macro that's used instead of Absinthe's `resolve`. This resolver can perform
the following operations:
1. Get the value from a cache if it is persisted. The resolver function is not
evaluated at all in this case
2. Evaluate the resolver function and store the value in the cache if it is
not present there
3. Handle the `Absinthe.Middlewar.Async` and `Absinthe.Middleware.Dataloader`
middlewares. In order to handle them, the function that executes the actual
evaluation is wrapped in a function that handles the cache interactions
There are 2 options for the passed function:
1. It can be a captured named function because its name is extracted
and used in the cache key.
2. If the function is anonymous or a different name should be used, a second
parameter with that name must be passed.
Just like `resolve` comming from Absinthe, `cache_resolve` supports the `{:ok, value}`
and `{:error, reason}` result tuples. The `:ok` tuples are cached while the `:error`
tuples are not.
But `cache_resolve` knows how to handle a third type of response format. When
`{:nocache, {:ok, value}}` is returned as the result the cache does **not** cache
the value and just returns `{:ok, value}`. This is particularly useful when
the result can't be constructed but returning an error will crash the whole query.
In such cases a default/filling value can be passed (0, nil, "No data", etc.)
and the next query will try to resolve it again
"""
defmacro cache_resolve(captured_mfa_ast, opts \\ []) do
quote do
middleware(
Absinthe.Resolution,
CacheMod.from(unquote(captured_mfa_ast), unquote(opts))
)
end
end
@doc ~s"""
Exposed as sometimes it can be useful to use it outside the macros.
Gets a function, name and arguments and returns a new function that:
1. On execution checks if the value is present in the cache and returns it
2. If it's not in the cache it gets executed and the value is stored in the cache.
NOTE: `cached_func` is a function with arity 0. That means if you want to use it
in your code and you want some arguments you should use it like this:
> Cache.wrap(
> fn ->
> fetch_last_price_record(pair)
> end,
> :fetch_price_last_record, %{pair: pair}
> ).()
"""
def wrap(cached_func, name, args \\ %{}, opts \\ []) do
fn ->
CacheProvider.get_or_store(
@cache_name,
cache_key(name, args, opts),
cached_func,
&cache_modify_middleware/3
)
end
end
@doc ~s"""
Clears the whole cache. Slow.
"""
def clear_all do
CacheProvider.clear_all(@cache_name)
end
@doc ~s"""
The size of the cache in megabytes
"""
def size do
CacheProvider.size(@cache_name, :megabytes)
end
def get(key) do
CacheProvider.get(@cache_name, key)
end
@doc false
def from(captured_mfa, opts) when is_function(captured_mfa) do
# Public so it can be used by the resolve macros. You should not use it.
case Keyword.pop(opts, :fun_name) do
{nil, opts} ->
fun_name = captured_mfa |> :erlang.fun_info() |> Keyword.get(:name)
resolver(captured_mfa, fun_name, opts)
{fun_name, opts} ->
resolver(captured_mfa, fun_name, opts)
end
end
# Private functions
defp resolver(resolver_fn, name, opts) do
fn
%{} = root, args, resolution ->
fun = fn -> resolver_fn.(root, args, resolution) end
args = args |> Map.put(:current_user_id, resolution.context.current_user.id)
# by default use only :id from the root
root_keys = Keyword.get(opts, :root_keys, [:id])
additional_args = Map.take(root, root_keys)
# resolution.source contains the arguments passed to a parent object
# in order to properly cache timeseries data in the query
# {getMetric(metric: "nvt") {timeseriesData(...)}}
# the key must include `metric` from the parent's args
args_from_source = generate_additional_args(resolution.source)
cache_key = cache_key({name, additional_args, args_from_source}, args, opts)
# In some edge-cases the caching can be disabled for some reason. In one
# particular case for all_projects_by_function the caching is disabled
# (by putting the do_not_cache_query: true Process dictionary key-value)
# if the base_projects depends on a watchlist. The cache resolver that
# is disabled must provide the `honor_do_no_cache_flag: true` explicitly,
# so we are not disabling all of the caching, but only the one that matters
skip_cache? =
Keyword.get(opts, :honor_do_not_cache_flag, false) and
Process.get(:do_not_cache_query) == true
case skip_cache? do
true -> fun.()
false -> get_or_store(cache_key, fun)
end
end
end
defp generate_additional_args(data) do
case data do
%{id: id} -> id
%{slug: slug} -> slug
%{word: word} -> word
_ -> data
end
end
def store(cache_name \\ @cache_name, cache_key, value) do
CacheProvider.store(cache_name, cache_key, value)
end
def get_or_store(cache_name \\ @cache_name, cache_key, resolver_fn) do
CacheProvider.get_or_store(
cache_name,
cache_key,
resolver_fn,
&cache_modify_middleware/3
)
end
# `cache_modify_middleware` is called only from withing `get_or_store` that
# guarantees that it will be executed only once if it is accessed concurently.
# This is way it is safe to use `store` explicitly without worrying about race
# conditions
defp cache_modify_middleware(cache_name, cache_key, {:ok, value} = result) do
CacheProvider.store(cache_name, cache_key, result)
{:ok, value}
end
defp cache_modify_middleware(
cache_name,
cache_key,
{:middleware, Absinthe.Middleware.Async = midl, {fun, opts}}
) do
caching_fun = fn ->
CacheProvider.get_or_store(cache_name, cache_key, fun, &cache_modify_middleware/3)
end
{:middleware, midl, {caching_fun, opts}}
end
defp cache_modify_middleware(
cache_name,
cache_key,
{:middleware, Absinthe.Middleware.Dataloader = midl, {loader, callback}}
) do
caching_callback = fn loader_arg ->
CacheProvider.get_or_store(
cache_name,
cache_key,
fn -> callback.(loader_arg) end,
&cache_modify_middleware/3
)
end
{:middleware, midl, {loader, caching_callback}}
end
# Helper functions
def cache_key(name, args, opts \\ []) do
base_ttl = args[:caching_params][:base_ttl] || Keyword.get(opts, :ttl, @ttl)
max_ttl_offset =
args[:caching_params][:max_ttl_offset] ||
Keyword.get(opts, :max_ttl_offset, @max_ttl_offset)
base_ttl = Enum.max([base_ttl, 1])
max_ttl_offset = Enum.max([max_ttl_offset, 1])
# Used to randomize the TTL for lists of objects like list of projects
additional_args = Map.take(args, [:slug, :id])
# Using phash2 as a random number between 0 and max_ttl_offset is needed.
# collisions are allowed and do not lead to errors
ttl = base_ttl + ({name, additional_args} |> :erlang.phash2(max_ttl_offset))
if args[:caching_params] do
# This is used in the Absinthe's before_send function
Process.put(:__change_absinthe_before_send_caching_ttl__, ttl)
end
args = args |> convert_values(ttl)
cache_key = [name, args] |> hash()
{cache_key, ttl}
end
# Convert the values for using in the cache. A special treatement is done for
# `%DateTime{}` so all datetimes in a @ttl sized window are treated the same
defp convert_values(%DateTime{} = v, ttl), do: div(DateTime.to_unix(v, :second), ttl)
defp convert_values(%_{} = v, _), do: Map.from_struct(v)
defp convert_values(args, ttl) when is_list(args) or is_map(args) do
args
|> Enum.map(fn
{k, v} ->
[k, convert_values(v, ttl)]
data ->
convert_values(data, ttl)
end)
end
defp convert_values(v, _), do: v
defp hash(data) do
:crypto.hash(:sha256, :erlang.term_to_binary(data))
|> Base.encode64()
end
end
