Add a new smoosh persistence module

  * persist/3 : persists the queue, active and starting jobs
  * unpersist/1 : unpersist the queue
  * check_setup/0 : quick configuration smoke test

The design is a bit simplified from the previous implementation:

  * There is a single waiting queue persisted as simple map. Both starting and
    active jobs are added to the same map structure. To maintain their position
    in the queue use `infinity` as their priority value. This is an established
    Erlang pattern and they should sort higher than both float and numeric
    values.

  * Detailed, unique gb_tree key parts are not persisted. Only the priority
    values and the queue objects. This should make structure smaller and faster
    a bit.

  * Remove versioning. Smoosh queue data is not critical and if need be, we can
    just use a new suffix.

   * Anticipating setup errors with the persistence state directory, add a
     smoke test in check_setup/0 to check writes and read to/from the state
     directory and log warning on failure. The idea is to do call it once
     during startup in the smoosh application to inform users their setup is
     problematic. After that, treat smoosh persistence opportunistically and if
     state directory is not setup, opt to keep the rest of CouchDB node up.

There should be 100% test coverage.

1 files changed, 300 insertions, 0 deletions

diff --git a/src/smoosh/src/smoosh_persist.erl b/src/smoosh/src/smoosh_persist.erl
new file mode 100644
index 000000000..68d8a418d
--- /dev/null
+++ b/src/smoosh/src/smoosh_persist.erl
@@ -0,0 +1,300 @@
+% Licensed under the Apache License, Version 2.0 (the "License"); you may not
+% use this file except in compliance with the License. You may obtain a copy of
+% the License at
+%
+%   http://www.apache.org/licenses/LICENSE-2.0
+%
+% Unless required by applicable law or agreed to in writing, software
+% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+% License for the specific language governing permissions and limitations under
+% the License.
+
+-module(smoosh_persist).
+
+-export([
+    unpersist/1,
+    persist/3,
+    check_setup/0
+]).
+
+-include_lib("kernel/include/file.hrl").
+
+-define(SUFFIX, ".smooshq").
+
+% Public API
+
+unpersist(Name) ->
+    Enabled = config:get_boolean("smoosh", "persist", false),
+    Capacity = smoosh_utils:capacity(Name),
+    unpersist(Enabled, Name, Capacity).
+
+persist(Waiting, #{} = Active, #{} = Starting) ->
+    Enabled = config:get_boolean("smoosh", "persist", false),
+    persist(Enabled, Waiting, Active, Starting).
+
+% Validate peristence setup for read/write/delete access. Emit warnings if
+% there are any failures. Call this function once during startup. During
+% runtime errors are ignored. Smoosh persistence is opportunistic, so if we
+% cannot read or write we just move on.
+%
+check_setup() ->
+    Enabled = config:get_boolean("smoosh", "persist", false),
+    try
+        check_setup(Enabled)
+    catch
+        throw:{fail, Msg, Error} ->
+            LogMsg = "~s : " ++ Msg ++ " failed in directory ~p : ~p",
+            Args = [?MODULE, state_dir(), Error],
+            couch_log:warning(LogMsg, Args),
+            {error, {Msg, Error}}
+    end.
+
+% Private functions
+
+unpersist(false, Name, _Capacity) ->
+    smoosh_priority_queue:new(Name);
+unpersist(true, Name, Capacity) ->
+    Path = file_path(Name),
+    case read(Path) of
+        {ok, Map} -> smoosh_priority_queue:from_map(Name, Capacity, Map);
+        {error, _} -> smoosh_priority_queue:new(Name)
+    end.
+
+persist(false, _Waiting, _Active, _Starting) ->
+    ok;
+persist(true, Waiting, Active, Starting) ->
+    Name = smoosh_priority_queue:name(Waiting),
+    WMap = smoosh_priority_queue:to_map(Waiting),
+    % Starting and active jobs are at priority level `infinity` as they are
+    % already running. We want them to be the first ones to continue after
+    % restart. We're relying on infinity sorting higher than float and integer
+    % numeric values here.
+    AMap = maps:map(fun(_, _) -> infinity end, Active),
+    SMap = maps:from_list([{K, infinity} || K <- maps:values(Starting)]),
+    Path = file_path(Name),
+    write(maps:merge(WMap, maps:merge(AMap, SMap)), Path).
+
+check_setup(false) ->
+    disabled;
+check_setup(true) ->
+    StateDir = state_dir(),
+    Path = filename:join(StateDir, "smooshq.test"),
+    Data = #{<<"test">> => 1},
+    case file:read_file_info(StateDir) of
+        {ok, #file_info{access = A}} when A == read; A == read_write ->
+            ok;
+        {ok, #file_info{access = Invalid}} ->
+            throw({fail, "read access", Invalid});
+        {error, Error1} ->
+            throw({fail, "read", Error1})
+    end,
+    case write(Data, Path) of
+        ok -> ok;
+        {error, Error2} -> throw({fail, "write", Error2})
+    end,
+    delete_file(Path).
+
+write(#{} = QData, Path) when is_list(Path), map_size(QData) == 0 ->
+    % Save a few bytes by deleting the persisted queue data if
+    % there are no waiting/starting or active jobs
+    delete_file(Path);
+write(#{} = QData, Path) when is_list(Path) ->
+    Bin = term_to_binary(QData, [compressed, {minor_version, 2}]),
+    TmpPath = tmp_path(Path),
+    case file:write_file(TmpPath, Bin, [raw]) of
+        ok -> file:rename(TmpPath, Path);
+        {error, _} = Error -> Error
+    end.
+
+read(Path) ->
+    case file:read_file(Path) of
+        {ok, Bin} ->
+            try binary_to_term(Bin, [safe]) of
+                #{} = QData -> {ok, QData};
+                _ -> {error, term_not_a_map}
+            catch
+                _:_ ->
+                    {error, invalid_term}
+            end;
+        {error, _} = Error ->
+            Error
+    end.
+
+tmp_path(Path) ->
+    Time = abs(erlang:system_time()),
+    Path ++ "." ++ integer_to_list(Time) ++ ".tmp".
+
+file_path(Name) ->
+    StateDir = filename:absname(state_dir()),
+    filename:join(StateDir, Name ++ ?SUFFIX).
+
+state_dir() ->
+    Dir = config:get("smoosh", "state_dir", "."),
+    filename:absname(Dir).
+
+delete_file(Path) ->
+    % On Erlang 24+ we can avoid using the file server
+    case erlang:function_exported(file, delete, 2) of
+        true -> file:delete(Path, [raw]);
+        false -> file:delete(Path)
+    end.
+
+-ifdef(TEST).
+
+-include_lib("couch/include/couch_eunit.hrl").
+
+persist_unpersist_test_() ->
+    {
+        foreach,
+        fun() ->
+            meck:expect(config, get, fun(_, _, Default) -> Default end)
+        end,
+        fun(_) ->
+            meck:unload()
+        end,
+        [
+            ?TDEF_FE(t_write_read_delete),
+            ?TDEF_FE(t_fail_write_read_delete),
+            ?TDEF_FE(t_corrupted_read),
+            ?TDEF_FE(t_check_setup),
+            ?TDEF_FE(t_persist_unpersist_disabled),
+            ?TDEF_FE(t_persist_unpersist_enabled),
+            ?TDEF_FE(t_persist_unpersist_errors)
+        ]
+    }.
+
+t_write_read_delete(_) ->
+    Path = file_path("foochan"),
+    Data = #{<<"a">> => 1},
+
+    ?assertEqual(ok, write(Data, Path)),
+    ?assertMatch({ok, _}, file:read_file_info(Path)),
+
+    ReadRes = read(Path),
+    ?assertMatch({ok, #{}}, ReadRes),
+    {ok, ReadData} = ReadRes,
+    ?assertEqual(Data, ReadData),
+
+    ?assertEqual(ok, write(#{}, Path)),
+    ?assertEqual({error, enoent}, file:read_file_info(Path)).
+
+t_fail_write_read_delete(_) ->
+    meck:expect(config, get, fun("smoosh", "state_dir", _) -> "./x" end),
+    Path = file_path("foochan"),
+    ?assertEqual({error, enoent}, write(#{<<"a">> => 1}, Path)),
+    ?assertEqual({error, enoent}, read(Path)),
+    ?assertEqual({error, enoent}, write(#{}, Path)).
+
+t_corrupted_read(_) ->
+    Path = file_path("foochan"),
+    ?assertEqual(ok, write(#{<<"a">> => 1}, Path)),
+
+    ok = file:write_file(Path, term_to_binary(foo), [raw]),
+    ?assertEqual({error, term_not_a_map}, read(Path)),
+
+    ok = file:write_file(Path, <<"42">>, [raw]),
+    ?assertEqual({error, invalid_term}, read(Path)),
+
+    ?assertEqual(ok, write(#{}, Path)),
+    ?assertEqual({error, enoent}, file:read_file_info(Path)).
+
+t_check_setup(_) ->
+    ?assertEqual(disabled, check_setup()),
+
+    meck:expect(config, get_boolean, fun("smoosh", "persist", _) -> true end),
+    ?assertEqual(ok, check_setup()),
+
+    TDir = ?tempfile(),
+    meck:expect(config, get, fun("smoosh", "state_dir", _) -> TDir end),
+    ?assertEqual({error, {"read", enoent}}, check_setup()),
+
+    Dir = state_dir(),
+    ok = file:make_dir(Dir),
+    % Can't write, only read
+    ok = file:change_mode(Dir, 8#500),
+    ?assertEqual({error, {"write", eacces}}, check_setup()),
+    % Can't read, only write
+    ok = file:change_mode(Dir, 8#300),
+    ?assertEqual({error, {"read access", write}}, check_setup()),
+    ok = file:del_dir_r(Dir).
+
+t_persist_unpersist_disabled(_) ->
+    Name = "chan1",
+    Q = smoosh_priority_queue:new(Name),
+    [K1, K2, K3] = [<<"x">>, {<<"x">>, <<"_design/y">>}, {index_cleanup, <<"z">>}],
+    Active = #{K1 => self()},
+    Starting = #{make_ref() => K2},
+    Q1 = smoosh_priority_queue:in(K3, 1.0, 9999, Q),
+
+    ?assertEqual(ok, persist(Q1, Active, Starting)),
+
+    Q2 = unpersist(Name),
+    ?assertEqual(Name, smoosh_priority_queue:name(Q2)),
+    ?assertEqual([{size, 0}], smoosh_priority_queue:info(Q2)).
+
+t_persist_unpersist_enabled(_) ->
+    Name = "chan2",
+    Q = smoosh_priority_queue:new(Name),
+    Keys = [K1, K2, K3] = [<<"x">>, {<<"x">>, <<"y">>}, {index_cleanup, <<"z">>}],
+    Active = #{K1 => self()},
+    Starting = #{make_ref() => K2},
+    Q1 = smoosh_priority_queue:in(K3, 1.0, 9999, Q),
+
+    meck:expect(config, get_boolean, fun("smoosh", "persist", _) -> true end),
+    ?assertEqual(ok, persist(Q1, Active, Starting)),
+
+    Q2 = unpersist(Name),
+    ?assertEqual(Name, smoosh_priority_queue:name(Q2)),
+    Info2 = smoosh_priority_queue:info(Q2),
+    ?assertEqual([{size, 3}, {min, 1.0}, {max, infinity}], Info2),
+    ?assertEqual(Keys, drain_q(Q2)),
+
+    % Try to persist the already unpersisted queue
+    ?assertEqual(ok, persist(Q2, #{}, #{})),
+    Q3 = unpersist(Name),
+    ?assertEqual(Name, smoosh_priority_queue:name(Q3)),
+    Info3 = smoosh_priority_queue:info(Q2),
+    ?assertEqual([{size, 3}, {min, 1.0}, {max, infinity}], Info3),
+    ?assertEqual(Keys, drain_q(Q3)).
+
+t_persist_unpersist_errors(_) ->
+    Name = "chan3",
+    Q = smoosh_priority_queue:new(Name),
+    Q1 = smoosh_priority_queue:in(<<"x">>, 1.0, 9999, Q),
+
+    meck:expect(config, get_boolean, fun("smoosh", "persist", _) -> true end),
+
+    TDir = ?tempfile(),
+    meck:expect(config, get, fun
+        ("smoosh", "state_dir", _) -> TDir;
+        (_, _, Default) -> Default
+    end),
+
+    Q2 = unpersist(Name),
+    ?assertEqual(Name, smoosh_priority_queue:name(Q2)),
+    ?assertEqual([{size, 0}], smoosh_priority_queue:info(Q2)),
+
+    Dir = state_dir(),
+    ok = file:make_dir(Dir),
+
+    % Can't write, only read
+    ok = file:change_mode(Dir, 8#500),
+    ?assertEqual({error, eacces}, persist(Q1, #{}, #{})),
+
+    Q3 = unpersist(Name),
+    ?assertEqual(Name, smoosh_priority_queue:name(Q3)),
+    ?assertEqual([{size, 0}], smoosh_priority_queue:info(Q3)),
+
+    ok = file:del_dir_r(Dir).
+
+drain_q(Q) ->
+    lists:reverse(drain_q(Q, [])).
+
+drain_q(Q, Acc) ->
+    case smoosh_priority_queue:out(Q) of
+        false -> Acc;
+        {Key, Q1} -> drain_q(Q1, [Key | Acc])
+    end.
+
+-endif.