Whitelist system DB names as valid _dbs docids858-whitelist-shard-map-docids

Currently, it is impossible to PUT/POST modified shard maps to any
`_dbs/_*` document because the document _ids are reserved. This change
permits these specific db/docid combinations as valid, so PUT/POST
operations can succeed. The specific list comes from SYSTEM_DATABASES.

Unit tests have been added.

5 files changed, 165 insertions, 62 deletions

diff --git a/src/chttpd/src/chttpd_db.erl b/src/chttpd/src/chttpd_db.erl
index c8826d581..7e467508e 100644
--- a/src/chttpd/src/chttpd_db.erl
+++ b/src/chttpd/src/chttpd_db.erl
@@ -711,7 +711,7 @@ db_doc_req(#httpd{method='GET', mochi_req=MochiReq}=Req, Db, DocId) ->
 
 db_doc_req(#httpd{method='POST', user_ctx=Ctx}=Req, Db, DocId) ->
     couch_httpd:validate_referer(Req),
-    couch_doc:validate_docid(DocId),
+    couch_doc:validate_docid(DocId, couch_db:name(Db)),
     chttpd:validate_ctype(Req, "multipart/form-data"),
 
     W = chttpd:qs_value(Req, "w", integer_to_list(mem3:quorum(Db))),
@@ -766,9 +766,9 @@ db_doc_req(#httpd{method='PUT', user_ctx=Ctx}=Req, Db, DocId) ->
     #doc_query_args{
         update_type = UpdateType
     } = parse_doc_query(Req),
-    couch_doc:validate_docid(DocId),
-
     DbName = couch_db:name(Db),
+    couch_doc:validate_docid(DocId, DbName),
+
     W = chttpd:qs_value(Req, "w", integer_to_list(mem3:quorum(Db))),
     Options = [{user_ctx,Ctx}, {w,W}],
 
@@ -1243,7 +1243,7 @@ db_attachment_req(#httpd{method=Method, user_ctx=Ctx}=Req, Db, DocId, FileNamePa
                 % check for the existence of the doc to handle the 404 case.
                 couch_doc_open(Db, DocId, nil, [])
             end,
-            couch_doc:validate_docid(DocId),
+            couch_doc:validate_docid(DocId, couch_db:name(Db)),
             #doc{id=DocId};
         Rev ->
             case fabric:open_revs(Db, DocId, [Rev], [{user_ctx,Ctx}]) of
diff --git a/src/couch/src/couch_doc.erl b/src/couch/src/couch_doc.erl
index eb96d44bb..f960ec5c2 100644
--- a/src/couch/src/couch_doc.erl
+++ b/src/couch/src/couch_doc.erl
@@ -13,8 +13,10 @@
 -module(couch_doc).
 
 -export([to_doc_info/1,to_doc_info_path/1,parse_rev/1,parse_revs/1,rev_to_str/1,revs_to_strs/1]).
--export([from_json_obj/1, from_json_obj_validate/1, to_json_obj/2,has_stubs/1, merge_stubs/2]).
--export([validate_docid/1, get_validate_doc_fun/1]).
+-export([from_json_obj/1, from_json_obj_validate/1]).
+-export([from_json_obj/2, from_json_obj_validate/2]).
+-export([to_json_obj/2, has_stubs/1, merge_stubs/2]).
+-export([validate_docid/1, validate_docid/2, get_validate_doc_fun/1]).
 -export([doc_from_multi_part_stream/2, doc_from_multi_part_stream/3]).
 -export([doc_from_multi_part_stream/4]).
 -export([doc_to_multi_part_stream/5, len_doc_to_multi_part_stream/4]).
@@ -126,8 +128,11 @@ doc_to_json_obj(#doc{id=Id,deleted=Del,body=Body,revs={Start, RevIds},
     }.
 
 from_json_obj_validate(EJson) ->
+    from_json_obj_validate(EJson, undefined).
+
+from_json_obj_validate(EJson, DbName) ->
     MaxSize = config:get_integer("couchdb", "max_document_size", 4294967296),
-    Doc = from_json_obj(EJson),
+    Doc = from_json_obj(EJson, DbName),
     case couch_ejson_size:encoded_size(Doc#doc.body) =< MaxSize of
         true ->
              validate_attachment_sizes(Doc#doc.atts),
@@ -149,9 +154,11 @@ validate_attachment_sizes(Atts) ->
 
 
 from_json_obj({Props}) ->
-    transfer_fields(Props, #doc{body=[]});
+    from_json_obj({Props}, undefined).
 
-from_json_obj(_Other) ->
+from_json_obj({Props}, DbName) ->
+    transfer_fields(Props, #doc{body=[]}, DbName);
+from_json_obj(_Other, _) ->
     throw({bad_request, "Document must be a JSON object"}).
 
 parse_revid(RevId) when size(RevId) =:= 32 ->
@@ -191,6 +198,15 @@ parse_revs(_) ->
     throw({bad_request, "Invalid list of revisions"}).
 
 
+validate_docid(DocId, DbName) ->
+    case DbName =:= ?l2b(config:get("mem3", "shards_db", "_dbs")) andalso
+        lists:member(DocId, ?SYSTEM_DATABASES) of
+        true ->
+            ok;
+        false ->
+            validate_docid(DocId)
+    end.
+
 validate_docid(<<"">>) ->
     throw({illegal_docid, <<"Document id must not be empty">>});
 validate_docid(<<"_design/">>) ->
@@ -228,28 +244,28 @@ validate_docid(Id) ->
     couch_log:debug("Document id is not a string: ~p", [Id]),
     throw({illegal_docid, <<"Document id must be a string">>}).
 
-transfer_fields([], #doc{body=Fields}=Doc) ->
+transfer_fields([], #doc{body=Fields}=Doc, _) ->
     % convert fields back to json object
     Doc#doc{body={lists:reverse(Fields)}};
 
-transfer_fields([{<<"_id">>, Id} | Rest], Doc) ->
-    validate_docid(Id),
-    transfer_fields(Rest, Doc#doc{id=Id});
+transfer_fields([{<<"_id">>, Id} | Rest], Doc, DbName) ->
+    validate_docid(Id, DbName),
+    transfer_fields(Rest, Doc#doc{id=Id}, DbName);
 
-transfer_fields([{<<"_rev">>, Rev} | Rest], #doc{revs={0, []}}=Doc) ->
+transfer_fields([{<<"_rev">>, Rev} | Rest], #doc{revs={0, []}}=Doc, DbName) ->
     {Pos, RevId} = parse_rev(Rev),
     transfer_fields(Rest,
-            Doc#doc{revs={Pos, [RevId]}});
+            Doc#doc{revs={Pos, [RevId]}}, DbName);
 
-transfer_fields([{<<"_rev">>, _Rev} | Rest], Doc) ->
+transfer_fields([{<<"_rev">>, _Rev} | Rest], Doc, DbName) ->
     % we already got the rev from the _revisions
-    transfer_fields(Rest,Doc);
+    transfer_fields(Rest, Doc, DbName);
 
-transfer_fields([{<<"_attachments">>, {JsonBins}} | Rest], Doc) ->
+transfer_fields([{<<"_attachments">>, {JsonBins}} | Rest], Doc, DbName) ->
     Atts = [couch_att:from_json(Name, Props) || {Name, {Props}} <- JsonBins],
-    transfer_fields(Rest, Doc#doc{atts=Atts});
+    transfer_fields(Rest, Doc#doc{atts=Atts}, DbName);
 
-transfer_fields([{<<"_revisions">>, {Props}} | Rest], Doc) ->
+transfer_fields([{<<"_revisions">>, {Props}} | Rest], Doc, DbName) ->
     RevIds = couch_util:get_value(<<"ids">>, Props),
     Start = couch_util:get_value(<<"start">>, Props),
     if not is_integer(Start) ->
@@ -262,45 +278,45 @@ transfer_fields([{<<"_revisions">>, {Props}} | Rest], Doc) ->
     [throw({doc_validation, "RevId isn't a string"}) ||
             RevId <- RevIds, not is_binary(RevId)],
     RevIds2 = [parse_revid(RevId) || RevId <- RevIds],
-    transfer_fields(Rest, Doc#doc{revs={Start, RevIds2}});
+    transfer_fields(Rest, Doc#doc{revs={Start, RevIds2}}, DbName);
 
-transfer_fields([{<<"_deleted">>, B} | Rest], Doc) when is_boolean(B) ->
-    transfer_fields(Rest, Doc#doc{deleted=B});
+transfer_fields([{<<"_deleted">>, B} | Rest], Doc, DbName) when is_boolean(B) ->
+    transfer_fields(Rest, Doc#doc{deleted=B}, DbName);
 
 % ignored fields
-transfer_fields([{<<"_revs_info">>, _} | Rest], Doc) ->
-    transfer_fields(Rest, Doc);
-transfer_fields([{<<"_local_seq">>, _} | Rest], Doc) ->
-    transfer_fields(Rest, Doc);
-transfer_fields([{<<"_conflicts">>, _} | Rest], Doc) ->
-    transfer_fields(Rest, Doc);
-transfer_fields([{<<"_deleted_conflicts">>, _} | Rest], Doc) ->
-    transfer_fields(Rest, Doc);
+transfer_fields([{<<"_revs_info">>, _} | Rest], Doc, DbName) ->
+    transfer_fields(Rest, Doc, DbName);
+transfer_fields([{<<"_local_seq">>, _} | Rest], Doc, DbName) ->
+    transfer_fields(Rest, Doc, DbName);
+transfer_fields([{<<"_conflicts">>, _} | Rest], Doc, DbName) ->
+    transfer_fields(Rest, Doc, DbName);
+transfer_fields([{<<"_deleted_conflicts">>, _} | Rest], Doc, DbName) ->
+    transfer_fields(Rest, Doc, DbName);
 
 % special fields for replication documents
 transfer_fields([{<<"_replication_state">>, _} = Field | Rest],
-    #doc{body=Fields} = Doc) ->
-    transfer_fields(Rest, Doc#doc{body=[Field|Fields]});
+    #doc{body=Fields} = Doc, DbName) ->
+    transfer_fields(Rest, Doc#doc{body=[Field|Fields]}, DbName);
 transfer_fields([{<<"_replication_state_time">>, _} = Field | Rest],
-    #doc{body=Fields} = Doc) ->
-    transfer_fields(Rest, Doc#doc{body=[Field|Fields]});
+    #doc{body=Fields} = Doc, DbName) ->
+    transfer_fields(Rest, Doc#doc{body=[Field|Fields]}, DbName);
 transfer_fields([{<<"_replication_state_reason">>, _} = Field | Rest],
-    #doc{body=Fields} = Doc) ->
-    transfer_fields(Rest, Doc#doc{body=[Field|Fields]});
+    #doc{body=Fields} = Doc, DbName) ->
+    transfer_fields(Rest, Doc#doc{body=[Field|Fields]}, DbName);
 transfer_fields([{<<"_replication_id">>, _} = Field | Rest],
-    #doc{body=Fields} = Doc) ->
-    transfer_fields(Rest, Doc#doc{body=[Field|Fields]});
+    #doc{body=Fields} = Doc, DbName) ->
+    transfer_fields(Rest, Doc#doc{body=[Field|Fields]}, DbName);
 transfer_fields([{<<"_replication_stats">>, _} = Field | Rest],
-    #doc{body=Fields} = Doc) ->
-    transfer_fields(Rest, Doc#doc{body=[Field|Fields]});
+    #doc{body=Fields} = Doc, DbName) ->
+    transfer_fields(Rest, Doc#doc{body=[Field|Fields]}, DbName);
 
 % unknown special field
-transfer_fields([{<<"_",Name/binary>>, _} | _], _) ->
+transfer_fields([{<<"_",Name/binary>>, _} | _], _, _) ->
     throw({doc_validation,
             ?l2b(io_lib:format("Bad special document member: _~s", [Name]))});
 
-transfer_fields([Field | Rest], #doc{body=Fields}=Doc) ->
-    transfer_fields(Rest, Doc#doc{body=[Field|Fields]}).
+transfer_fields([Field | Rest], #doc{body=Fields}=Doc, DbName) ->
+    transfer_fields(Rest, Doc#doc{body=[Field|Fields]}, DbName).
 
 to_doc_info(FullDocInfo) ->
     {DocInfo, _Path} = to_doc_info_path(FullDocInfo),
diff --git a/src/couch/src/couch_httpd_db.erl b/src/couch/src/couch_httpd_db.erl
index 34a1539aa..05e63ba97 100644
--- a/src/couch/src/couch_httpd_db.erl
+++ b/src/couch/src/couch_httpd_db.erl
@@ -257,7 +257,8 @@ db_req(#httpd{method='GET',path_parts=[_DbName]}=Req, Db) ->
 
 db_req(#httpd{method='POST',path_parts=[_DbName]}=Req, Db) ->
     couch_httpd:validate_ctype(Req, "application/json"),
-    Doc = couch_doc:from_json_obj_validate(couch_httpd:json_body(Req)),
+    DbName = couch_db:name(Db),
+    Doc = couch_doc:from_json_obj_validate(couch_httpd:json_body(Req), DbName),
     validate_attachment_names(Doc),
     Doc2 = case Doc#doc.id of
         <<"">> ->
@@ -303,6 +304,7 @@ db_req(#httpd{method='POST',path_parts=[_,<<"_bulk_docs">>]}=Req, Db) ->
     couch_stats:increment_counter([couchdb, httpd, bulk_requests]),
     couch_httpd:validate_ctype(Req, "application/json"),
     {JsonProps} = couch_httpd:json_body_obj(Req),
+    DbName = couch_db:name(Db),
     case couch_util:get_value(<<"docs">>, JsonProps) of
     undefined ->
         send_error(Req, 400, <<"bad_request">>, <<"Missing JSON list of 'docs'">>);
@@ -320,7 +322,7 @@ db_req(#httpd{method='POST',path_parts=[_,<<"_bulk_docs">>]}=Req, Db) ->
         true ->
             Docs = lists:map(
                 fun({ObjProps} = JsonObj) ->
-                    Doc = couch_doc:from_json_obj_validate(JsonObj),
+                    Doc = couch_doc:from_json_obj_validate(JsonObj, DbName),
                     validate_attachment_names(Doc),
                     Id = case Doc#doc.id of
                         <<>> -> couch_uuids:new();
@@ -354,7 +356,7 @@ db_req(#httpd{method='POST',path_parts=[_,<<"_bulk_docs">>]}=Req, Db) ->
             end;
         false ->
             Docs = lists:map(fun(JsonObj) ->
-                    Doc = couch_doc:from_json_obj_validate(JsonObj),
+                    Doc = couch_doc:from_json_obj_validate(JsonObj, DbName),
                     validate_attachment_names(Doc),
                     Doc
                 end, DocsArray),
@@ -486,14 +488,17 @@ db_req(#httpd{path_parts=[_, DocId | FileNameParts]}=Req, Db) ->
 db_doc_req(#httpd{method='DELETE'}=Req, Db, DocId) ->
     % check for the existence of the doc to handle the 404 case.
     couch_doc_open(Db, DocId, nil, []),
+    DbName = couch_db:name(Db),
     case couch_httpd:qs_value(Req, "rev") of
     undefined ->
         update_doc(Req, Db, DocId,
-                couch_doc_from_req(Req, DocId, {[{<<"_deleted">>,true}]}));
+                couch_doc_from_req(Req, DocId, {[{<<"_deleted">>,true}]},
+                    DbName));
     Rev ->
         update_doc(Req, Db, DocId,
                 couch_doc_from_req(Req, DocId,
-                    {[{<<"_rev">>, ?l2b(Rev)},{<<"_deleted">>,true}]}))
+                    {[{<<"_rev">>, ?l2b(Rev)},{<<"_deleted">>,true}]},
+                    DbName))
     end;
 
 db_doc_req(#httpd{method = 'GET', mochi_req = MochiReq} = Req, Db, DocId) ->
@@ -546,7 +551,8 @@ db_doc_req(#httpd{method = 'GET', mochi_req = MochiReq} = Req, Db, DocId) ->
 
 db_doc_req(#httpd{method='POST'}=Req, Db, DocId) ->
     couch_httpd:validate_referer(Req),
-    couch_doc:validate_docid(DocId),
+    DbName = couch_db:name(Db),
+    couch_doc:validate_docid(DocId, DbName),
     couch_httpd:validate_ctype(Req, "multipart/form-data"),
     Form = couch_httpd:parse_form(Req),
     case couch_util:get_value("_doc", Form) of
@@ -554,7 +560,7 @@ db_doc_req(#httpd{method='POST'}=Req, Db, DocId) ->
         Rev = couch_doc:parse_rev(couch_util:get_value("_rev", Form)),
         {ok, [{ok, Doc}]} = couch_db:open_doc_revs(Db, DocId, [Rev], []);
     Json ->
-        Doc = couch_doc_from_req(Req, DocId, ?JSON_DECODE(Json))
+        Doc = couch_doc_from_req(Req, DocId, ?JSON_DECODE(Json), DbName)
     end,
     UpdatedAtts = [
         couch_att:new([
@@ -580,14 +586,15 @@ db_doc_req(#httpd{method='POST'}=Req, Db, DocId) ->
     update_doc(Req, Db, DocId, NewDoc);
 
 db_doc_req(#httpd{method='PUT'}=Req, Db, DocId) ->
-    couch_doc:validate_docid(DocId),
+    DbName = couch_db:name(Db),
+    couch_doc:validate_docid(DocId, DbName),
 
     case couch_util:to_list(couch_httpd:header_value(Req, "Content-Type")) of
     ("multipart/related;" ++ _) = ContentType ->
         couch_httpd:check_max_request_length(Req),
         {ok, Doc0, WaitFun, Parser} = couch_doc:doc_from_multi_part_stream(
             ContentType, fun() -> receive_request_data(Req) end),
-        Doc = couch_doc_from_req(Req, DocId, Doc0),
+        Doc = couch_doc_from_req(Req, DocId, Doc0, DbName),
         try
             Result = update_doc(Req, Db, DocId, Doc),
             WaitFun(),
@@ -599,7 +606,7 @@ db_doc_req(#httpd{method='PUT'}=Req, Db, DocId) ->
         end;
     _Else ->
         Body = couch_httpd:json_body(Req),
-        Doc = couch_doc_from_req(Req, DocId, Body),
+        Doc = couch_doc_from_req(Req, DocId, Body, DbName),
         update_doc(Req, Db, DocId, Doc)
     end;
 
@@ -783,7 +790,7 @@ update_doc(Req, Db, DocId, #doc{deleted=Deleted}=Doc, Headers, UpdateType) ->
                 {rev, NewRevStr}]})
     end.
 
-couch_doc_from_req(Req, DocId, #doc{revs=Revs}=Doc) ->
+couch_doc_from_req(Req, DocId, #doc{revs=Revs}=Doc, _) ->
     validate_attachment_names(Doc),
     Rev = case couch_httpd:qs_value(Req, "rev") of
     undefined ->
@@ -810,8 +817,9 @@ couch_doc_from_req(Req, DocId, #doc{revs=Revs}=Doc) ->
         end
     end,
     Doc#doc{id=DocId, revs=Revs2};
-couch_doc_from_req(Req, DocId, Json) ->
-    couch_doc_from_req(Req, DocId, couch_doc:from_json_obj_validate(Json)).
+couch_doc_from_req(Req, DocId, Json, DbName) ->
+    couch_doc_from_req(Req, DocId,
+        couch_doc:from_json_obj_validate(Json, DbName), DbName).
 
 % Useful for debugging
 % couch_doc_open(Db, DocId) ->
@@ -1019,7 +1027,7 @@ db_attachment_req(#httpd{method=Method,mochi_req=MochiReq}=Req, Db, DocId, FileN
                 % check for the existence of the doc to handle the 404 case.
                 couch_doc_open(Db, DocId, nil, [])
             end,
-            couch_doc:validate_docid(DocId),
+            couch_doc:validate_docid(DocId, couch_db:name(Db)),
             #doc{id=DocId};
         Rev ->
             case couch_db:open_doc_revs(Db, DocId, [Rev], []) of
diff --git a/src/couch/test/couch_doc_json_tests.erl b/src/couch/test/couch_doc_json_tests.erl
index ce099d112..bcff0646a 100644
--- a/src/couch/test/couch_doc_json_tests.erl
+++ b/src/couch/test/couch_doc_json_tests.erl
@@ -171,6 +171,45 @@ from_json_success_cases() ->
         end,
         Cases).
 
+from_json_with_db_name_success_cases() ->
+    Cases = [
+        {
+            {[]},
+            <<"_dbs">>,
+            #doc{},
+            "DbName _dbs is acceptable with no docid"
+        },
+        {
+            {[{<<"_id">>, <<"zing!">>}]},
+            <<"_dbs">>,
+            #doc{id = <<"zing!">>},
+            "DbName _dbs is acceptable with a normal docid"
+        },
+        {
+            {[{<<"_id">>, <<"_users">>}]},
+            <<"_dbs">>,
+            #doc{id = <<"_users">>},
+            "_dbs/_users is acceptable"
+        },
+        {
+            {[{<<"_id">>, <<"_replicator">>}]},
+            <<"_dbs">>,
+            #doc{id = <<"_replicator">>},
+            "_dbs/_replicator is acceptable"
+        },
+        {
+            {[{<<"_id">>, <<"_global_changes">>}]},
+            <<"_dbs">>,
+            #doc{id = <<"_global_changes">>},
+            "_dbs/_global_changes is acceptable"
+        }
+    ],
+    lists:map(
+        fun({EJson, DbName, Expect, Msg}) ->
+            {Msg, ?_assertMatch(Expect, couch_doc:from_json_obj_validate(EJson, DbName))}
+        end,
+        Cases).
+
 from_json_error_cases() ->
     Cases = [
         {
@@ -261,6 +300,38 @@ from_json_error_cases() ->
             end
     end, Cases).
 
+from_json_with_dbname_error_cases() ->
+    Cases = [
+        {
+            {[{<<"_id">>, <<"_random">>}]},
+            <<"_dbs">>,
+            {illegal_docid,
+             <<"Only reserved document ids may start with underscore.">>},
+            "Disallow non-system-DB underscore prefixed docids in _dbs database."
+        },
+        {
+            {[{<<"_id">>, <<"_random">>}]},
+            <<"foobar">>,
+            {illegal_docid,
+             <<"Only reserved document ids may start with underscore.">>},
+            "Disallow arbitrary underscore prefixed docids in regular database."
+        },
+        {
+            {[{<<"_id">>, <<"_users">>}]},
+            <<"foobar">>,
+            {illegal_docid,
+             <<"Only reserved document ids may start with underscore.">>},
+            "Disallow system-DB docid _users in regular database."
+        }
+    ],
+
+    lists:map(
+        fun({EJson, DbName, Expect, Msg}) ->
+            Error = (catch couch_doc:from_json_obj_validate(EJson, DbName)),
+            {Msg, ?_assertMatch(Expect, Error)}
+        end,
+        Cases).
+
 to_json_success_cases() ->
     Cases = [
         {
diff --git a/src/couch/test/couch_doc_tests.erl b/src/couch/test/couch_doc_tests.erl
index 5d0448a9e..cf41df61d 100644
--- a/src/couch/test/couch_doc_tests.erl
+++ b/src/couch/test/couch_doc_tests.erl
@@ -29,7 +29,7 @@ doc_from_multi_part_stream_test() ->
     ContentType = "multipart/related;boundary=multipart_related_boundary~~~~~~~~~~~~~~~~~~~~",
     DataFun = fun() -> request(start) end,
 
-    mock_config_max_document_id_length(),
+    mock_config(),
     {ok, #doc{id = <<"doc0">>, atts = [_]}, _Fun, _Parser} =
         couch_doc:doc_from_multi_part_stream(ContentType, DataFun),
     meck:unload(config),
@@ -77,7 +77,7 @@ len_doc_to_multi_part_stream_test() ->
 validate_docid_test_() ->
     {setup,
         fun() ->
-            mock_config_max_document_id_length(),
+            mock_config(),
             ok = meck:new(couch_db_plugin, [passthrough]),
             meck:expect(couch_db_plugin, validate_docid, fun(_) -> false end)
         end,
@@ -90,6 +90,9 @@ validate_docid_test_() ->
             ?_assertEqual(ok, couch_doc:validate_docid(<<"_design/idx">>)),
             ?_assertEqual(ok, couch_doc:validate_docid(<<"_local/idx">>)),
             ?_assertEqual(ok, couch_doc:validate_docid(large_id(1024))),
+            ?_assertEqual(ok, couch_doc:validate_docid(<<"_users">>, <<"_dbs">>)),
+            ?_assertEqual(ok, couch_doc:validate_docid(<<"_replicator">>, <<"_dbs">>)),
+            ?_assertEqual(ok, couch_doc:validate_docid(<<"_global_changes">>, <<"_dbs">>)),
             ?_assertThrow({illegal_docid, _},
                 couch_doc:validate_docid(<<>>)),
             ?_assertThrow({illegal_docid, _},
@@ -103,7 +106,11 @@ validate_docid_test_() ->
             ?_assertThrow({illegal_docid, _},
                 couch_doc:validate_docid(<<"_local/">>)),
             ?_assertThrow({illegal_docid, _},
-                couch_doc:validate_docid(large_id(1025)))
+                couch_doc:validate_docid(large_id(1025))),
+            ?_assertThrow({illegal_docid, _},
+                couch_doc:validate_docid(<<"_users">>, <<"foo">>)),
+            ?_assertThrow({illegal_docid, _},
+                couch_doc:validate_docid(<<"_weeee">>, <<"_dbs">>))
         ]
     }.
 
@@ -127,11 +134,12 @@ collected() ->
     B = binary:replace(iolist_to_binary(get(data)), <<"\r\n">>, <<0>>, [global]),
     binary:split(B, [<<0>>], [global]).
 
-mock_config_max_document_id_length() ->
+mock_config() ->
     ok = meck:new(config, [passthrough]),
     meck:expect(config, get,
         fun("couchdb", "max_document_id_length", "infinity") -> "1024";
            ("couchdb", "max_attachment_size", "infinity") -> "infinity";
+           ("mem3", "shards_db", "_dbs") -> "_dbs";
             (Key, Val, Default) -> meck:passthrough([Key, Val, Default])
         end
     ).