eiri commented on a change in pull request #496: Couchdb 3287 pluggable storage
engines
URL: https://github.com/apache/couchdb/pull/496#discussion_r119694870
##########
File path: src/couch/src/couch_server.erl
##########
@@ -559,6 +596,115 @@ db_closed(Server, Options) ->
true -> Server
end.
+
+get_configured_engines() ->
+ ConfigEntries = config:get("couchdb_engines"),
+ Engines = lists:flatmap(fun({Extension, ModuleStr}) ->
+ try
+ [{Extension, list_to_atom(ModuleStr)}]
+ catch _T:_R ->
+ []
+ end
+ end, ConfigEntries),
+ case Engines of
+ [] ->
+ [{"couch", couch_bt_engine}];
+ Else ->
+ Else
+ end.
+
+
+get_engine(Server, DbName, Options) ->
+ #server{
+ root_dir = RootDir,
+ engines = Engines
+ } = Server,
+ case couch_util:get_value(engine, Options) of
+ Ext when is_binary(Ext) ->
+ ExtStr = binary_to_list(Ext),
+ case lists:keyfind(ExtStr, 1, Engines) of
+ {ExtStr, Engine} ->
+ Path = make_filepath(RootDir, DbName, ExtStr),
+ {ok, {Engine, Path}};
+ false ->
+ {error, {invalid_engine_extension, Ext}}
+ end;
+ _ ->
+ get_engine(Server, DbName)
+ end.
+
+
+get_engine(Server, DbName) ->
+ #server{
+ root_dir = RootDir,
+ engines = Engines
+ } = Server,
+ Possible = get_possible_engines(DbName, RootDir, Engines),
+ case Possible of
+ [] ->
+ get_default_engine(Server, DbName);
+ [Engine] ->
+ {ok, Engine};
+ _ ->
+ erlang:error(engine_conflict)
+ end.
+
+
+get_possible_engines(DbName, RootDir, Engines) ->
+ lists:foldl(fun({Extension, Engine}, Acc) ->
+ Path = make_filepath(RootDir, DbName, Extension),
+ case couch_db_engine:exists(Engine, Path) of
+ true ->
+ [{Engine, Path} | Acc];
+ false ->
+ Acc
+ end
+ end, [], Engines).
+
+
+get_default_engine(Server, DbName) ->
+ #server{
+ root_dir = RootDir,
+ engines = Engines
+ } = Server,
+ Default = {couch_bt_engine, make_filepath(RootDir, DbName, "couch")},
+ case config:get("couchdb", "default_engine") of
+ Extension when is_list(Extension) ->
+ case lists:keyfind(Extension, 1, Engines) of
+ {Extension, Module} ->
+ {ok, {Module, make_filepath(RootDir, DbName, Extension)}};
+ false ->
+ Fmt = "Invalid storage engine extension ~s,"
+ " configured engine extensions are: ~s",
+ Exts = [E || {E, _} <- Engines],
+ Args = [Extension, string:join(Exts, ", ")],
+ couch_log:error(Fmt, Args),
+ {ok, Default}
+ end;
+ _ ->
+ {ok, Default}
+ end.
+
+
+make_filepath(RootDir, DbName, Extension) when is_binary(RootDir) ->
+ make_filepath(binary_to_list(RootDir), DbName, Extension);
+make_filepath(RootDir, DbName, Extension) when is_binary(DbName) ->
+ make_filepath(RootDir, binary_to_list(DbName), Extension);
+make_filepath(RootDir, DbName, Extension) when is_binary(Extension) ->
+ make_filepath(RootDir, DbName, binary_to_list(Extension));
+make_filepath(RootDir, DbName, Extension) ->
+ filename:join([RootDir, "./" ++ DbName ++ "." ++ Extension]).
Review comment:
I think this should be just `filename:join([RootDir, DbName ++ "." ++
Extension])`.
If the current directory bit here just for a case when `RootDir` is an empty
string, to make it into a relative path, then it's not going to work, because
`filename:join/1` will overwrite that:
```erlang
1> filename:join(["", "./" ++ "koi" ++ "." ++ "couch"]).
"/koi.couch"
```
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