treat single-element keys as the key for `_view`

- Request `_view` with reduce function, treat single-element `keys` as `key`
- Add treat_single_keys_as_key/2 function for POST `_view`.
  If we query `_all_docs` for deleted or nonexistent docs using single-element
  keys, we can get {deleted:true} and {error:not_found}.
- Add documentation on using key, keys, start_key, and end_key

4 files changed, 81 insertions, 10 deletions

diff --git a/src/couch_mrview/src/couch_mrview_http.erl b/src/couch_mrview/src/couch_mrview_http.erl
index 9d35e873a..522884eda 100644
--- a/src/couch_mrview/src/couch_mrview_http.erl
+++ b/src/couch_mrview/src/couch_mrview_http.erl
@@ -486,7 +486,12 @@ parse_params(Props, Keys, #mrargs{} = Args0, Options) ->
                 Args0;
             _ ->
                 % group_level set to undefined to detect if explicitly set by user
-                Args0#mrargs{keys = Keys, group = undefined, group_level = undefined}
+                case Keys of
+                    [_] ->
+                        Args0#mrargs{group = undefined, group_level = undefined};
+                    _ ->
+                        Args0#mrargs{keys = Keys, group = undefined, group_level = undefined}
+                end
         end,
     lists:foldl(
         fun({K, V}, Acc) ->
@@ -513,8 +518,24 @@ parse_body_and_query(Req, Keys) ->
 
 parse_body_and_query(Req, {Props}, Keys) ->
     Args = #mrargs{keys = Keys, group = undefined, group_level = undefined},
-    BodyArgs = parse_params(Props, Keys, Args, [decoded]),
-    parse_params(chttpd:qs(Req), Keys, BodyArgs, [keep_group_level]).
+    BodyArgs0 = parse_params(Props, Keys, Args, [decoded]),
+    BodyArgs1 =
+        case is_view(Req) of
+            true -> treat_single_keys_as_key(BodyArgs0);
+            false -> BodyArgs0
+        end,
+    parse_params(chttpd:qs(Req), Keys, BodyArgs1, [keep_group_level]).
+
+is_view(#httpd{path_parts = [_, _, _, <<"_view">> | _]}) ->
+    true;
+is_view(#httpd{}) ->
+    false.
+
+treat_single_keys_as_key(#mrargs{keys = Keys} = BodyArgs) ->
+    case Keys of
+        [_] -> BodyArgs#mrargs{keys = undefined};
+        _ -> BodyArgs
+    end.
 
 parse_param(Key, Val, Args, IsDecoded) when is_binary(Key) ->
     parse_param(binary_to_list(Key), Val, Args, IsDecoded);
@@ -530,9 +551,15 @@ parse_param(Key, Val, Args, IsDecoded) ->
             JsonKey = ?JSON_DECODE(Val),
             Args#mrargs{start_key = JsonKey, end_key = JsonKey};
         "keys" when IsDecoded ->
-            Args#mrargs{keys = Val};
+            case Val of
+                [SingleKey] -> Args#mrargs{start_key = SingleKey, end_key = SingleKey};
+                _ -> Args#mrargs{keys = Val}
+            end;
         "keys" ->
-            Args#mrargs{keys = ?JSON_DECODE(Val)};
+            case ?JSON_DECODE(Val) of
+                [SingleKey] -> Args#mrargs{start_key = SingleKey, end_key = SingleKey};
+                Keys -> Args#mrargs{keys = Keys}
+            end;
         "startkey" when IsDecoded ->
             Args#mrargs{start_key = Val};
         "start_key" when IsDecoded ->
diff --git a/src/couch_mrview/src/couch_mrview_util.erl b/src/couch_mrview/src/couch_mrview_util.erl
index e1e75f34f..1f39959af 100644
--- a/src/couch_mrview/src/couch_mrview_util.erl
+++ b/src/couch_mrview/src/couch_mrview_util.erl
@@ -564,7 +564,7 @@ validate_args(Args) ->
         {red, exact, _} ->
             ok;
         {red, _, KeyList} when is_list(KeyList) ->
-            Msg = <<"Multi-key fetchs for reduce views must use `group=true`">>,
+            Msg = <<"Multi-key fetches for reduce views must use `group=true`">>,
             mrverror(Msg);
         _ ->
             ok
@@ -581,13 +581,12 @@ validate_args(Args) ->
             ok;
         {[], _, _} ->
             ok;
+        {[Key], Key, Key} ->
+            ok;
         {[_ | _], undefined, undefined} ->
             ok;
         _ ->
-            mrverror(<<
-                "`keys` is incompatible with `key`"
-                ", `start_key` and `end_key`"
-            >>)
+            mrverror(<<"`keys` is incompatible with `key`, `start_key` and `end_key`">>)
     end,
 
     case Args#mrargs.start_key_docid of
diff --git a/src/couch_mrview/test/eunit/couch_mrview_all_docs_tests.erl b/src/couch_mrview/test/eunit/couch_mrview_all_docs_tests.erl
index 1a81d4f0a..5b9db435b 100644
--- a/src/couch_mrview/test/eunit/couch_mrview_all_docs_tests.erl
+++ b/src/couch_mrview/test/eunit/couch_mrview_all_docs_tests.erl
@@ -40,6 +40,8 @@ all_docs_test_() ->
                 [
                     fun should_query/1,
                     fun should_query_with_range/1,
+                    fun should_query_with_range_and_same_keys/1,
+                    fun raise_error_query_with_range_and_different_keys/1,
                     fun should_query_with_range_rev/1,
                     fun should_query_with_limit_and_skip/1,
                     fun should_query_with_include_docs/1,
@@ -79,6 +81,20 @@ should_query_with_range(Db) ->
         ]},
     ?_assertEqual(Expect, Result).
 
+should_query_with_range_and_same_keys(Db) ->
+    Result = run_query(Db, [{keys, [<<"3">>]}, {start_key, <<"3">>}, {end_key, <<"3">>}]),
+    Expect =
+        {ok, [
+            {meta, [{total, 11}, {offset, 0}]},
+            mk_row(<<"3">>, <<"1-7fbf84d56f8017880974402d60f5acd6">>)
+        ]},
+    ?_assertEqual(Expect, Result).
+
+raise_error_query_with_range_and_different_keys(Db) ->
+    Error = {query_parse_error, <<"`keys` is incompatible with `key`, `start_key` and `end_key`">>},
+    ?_assertThrow(Error, run_query(Db, [{keys, [<<"1">>]}, {start_key, <<"5">>}])),
+    ?_assertThrow(Error, run_query(Db, [{keys, [<<"5">>]}, {start_key, <<"5">>}])).
+
 should_query_with_range_rev(Db) ->
     Result = run_query(Db, [
         {direction, rev},
diff --git a/src/couch_mrview/test/eunit/couch_mrview_http_tests.erl b/src/couch_mrview/test/eunit/couch_mrview_http_tests.erl
index bfa4965a4..134e27fc0 100644
--- a/src/couch_mrview/test/eunit/couch_mrview_http_tests.erl
+++ b/src/couch_mrview/test/eunit/couch_mrview_http_tests.erl
@@ -33,5 +33,34 @@ mrview_http_test_() ->
                 undefined,
                 #mrargs{}
             )
+        ),
+
+        ?_assertEqual(
+            #mrargs{start_key = 1, end_key = 1, group_level = undefined, group = undefined},
+            couch_mrview_http:parse_params(
+                [{"key", "1"}],
+                undefined,
+                #mrargs{}
+            )
+        ),
+
+        ?_assertEqual(
+            #mrargs{start_key = 1, end_key = 1, group_level = undefined},
+            couch_mrview_http:parse_params(
+                [{"keys", "[1]"}],
+                undefined,
+                #mrargs{}
+            )
+        ),
+
+        ?_assertEqual(
+            #mrargs{
+                keys = [1, 2], start_key = undefined, end_key = undefined, group_level = undefined
+            },
+            couch_mrview_http:parse_params(
+                [{"keys", "[1, 2]"}],
+                undefined,
+                #mrargs{}
+            )
         )
     ].