Send correct 400 for missing partition with _find (#1936)

When sending an incorrect partition query e.g:
/parition/_find, send a 400 with the message:

Partition must not start with an underscore

This makes it consistent with all the other partition requests

2 files changed, 28 insertions, 0 deletions

diff --git a/src/chttpd/src/chttpd_db.erl b/src/chttpd/src/chttpd_db.erl
index 003b0d8dc..5a0911559 100644
--- a/src/chttpd/src/chttpd_db.erl
+++ b/src/chttpd/src/chttpd_db.erl
@@ -274,6 +274,11 @@ handle_partition_req(#httpd{method='GET', path_parts=[_,_,PartId]}=Req, Db) ->
             throw({bad_request, <<"database is not partitioned">>})
     end;
 
+handle_partition_req(#httpd{method='POST',
+    path_parts=[_, <<"_partition">>, <<"_", _/binary>>]}, _Db) ->
+    Msg = <<"Partition must not start with an underscore">>,
+    throw({illegal_partition, Msg});
+
 handle_partition_req(#httpd{path_parts = [_, _, _]}=Req, _Db) ->
     send_method_not_allowed(Req, "GET");
 
diff --git a/test/elixir/test/partition_mango_test.exs b/test/elixir/test/partition_mango_test.exs
index 68a26e169..5a5978915 100644
--- a/test/elixir/test/partition_mango_test.exs
+++ b/test/elixir/test/partition_mango_test.exs
@@ -610,4 +610,27 @@ defmodule PartitionMangoTest do
     assert length(partitions) == 50
     assert_correct_partition(partitions, "foo")
   end
+
+  @tag :with_partitioned_db
+  test "partitioned _find and _explain with missing partition returns 400", context do
+    db_name = context[:db_name]
+
+    selector = %{
+      selector: %{
+        some: "field"
+      }
+    }
+
+    resp = Couch.get("/#{db_name}/_partition/_find", body: selector)
+    validate_missing_partition(resp)
+
+    resp = Couch.get("/#{db_name}/_partition/_explain", body: selector)
+    validate_missing_partition(resp)
+  end
+
+  defp validate_missing_partition(resp) do
+    assert resp.status_code == 400
+    %{:body => %{"reason" => reason}} = resp
+    assert Regex.match?(~r/Partition must not start/, reason)
+  end
 end