Improve detection of Search subsystem

Previously we had been using module_loaded(dreyfus_index) as a check
for the presence of the Search system. There are two issues with this
approach going forward:

1. Dreyfus is going to be included in every build
2. An Erlang release loads modules lazily and so this check could
   accidentally fail even on a Search-enabled system.

This patch changes the check to one that makes an RPC request
to the Clouseau (Java) subsystem. This should be a low-cost operation,
but I haven't benchmarked it.

3 files changed, 14 insertions, 5 deletions

diff --git a/src/dreyfus/src/clouseau_rpc.erl b/src/dreyfus/src/clouseau_rpc.erl
index aed03e37f..38d6142d6 100644
--- a/src/dreyfus/src/clouseau_rpc.erl
+++ b/src/dreyfus/src/clouseau_rpc.erl
@@ -23,6 +23,7 @@
 -export([delete/2, update/3, cleanup/1, cleanup/2, rename/1]).
 -export([analyze/2, version/0, disk_size/1]).
 -export([set_purge_seq/2, get_purge_seq/1, get_root_dir/0]).
+-export([connected/0]).
 
 open_index(Peer, Path, Analyzer) ->
     rpc({main, clouseau()}, {open, Peer, Path, Analyzer}).
@@ -91,6 +92,14 @@ analyze(Analyzer, Text) ->
 version() ->
     rpc({main, clouseau()}, version).
 
+connected() ->
+    case version() of
+        {'EXIT', noconnection} ->
+            false;
+        _ ->
+            true
+    end.
+
 rpc(Ref, Msg) ->
     ioq:call(Ref, Msg, erlang:get(io_priority)).
 
diff --git a/src/mango/src/mango_idx.erl b/src/mango/src/mango_idx.erl
index c2c26958c..5d06a8fe3 100644
--- a/src/mango/src/mango_idx.erl
+++ b/src/mango/src/mango_idx.erl
@@ -182,7 +182,7 @@ from_ddoc(Db, {Props}) ->
         _ ->
             ?MANGO_ERROR(invalid_query_ddoc_language)
     end,
-    IdxMods = case module_loaded(dreyfus_index) of
+    IdxMods = case clouseau_rpc:connected() of
         true ->
             [mango_idx_view, mango_idx_text];
         false ->
@@ -268,7 +268,7 @@ cursor_mod(#idx{type = <<"json">>}) ->
 cursor_mod(#idx{def = all_docs, type= <<"special">>}) ->
     mango_cursor_special;
 cursor_mod(#idx{type = <<"text">>}) ->
-    case module_loaded(dreyfus_index) of
+    case clouseau_rpc:connected() of
         true ->
             mango_cursor_text;
         false ->
@@ -281,7 +281,7 @@ idx_mod(#idx{type = <<"json">>}) ->
 idx_mod(#idx{type = <<"special">>}) ->
     mango_idx_special;
 idx_mod(#idx{type = <<"text">>}) ->
-    case module_loaded(dreyfus_index) of
+    case clouseau_rpc:connected() of
         true ->
             mango_idx_text;
         false ->
@@ -309,7 +309,7 @@ get_idx_def(Opts) ->
 get_idx_type(Opts) ->
     case proplists:get_value(type, Opts) of
         <<"json">> -> <<"json">>;
-        <<"text">> -> case module_loaded(dreyfus_index) of
+        <<"text">> -> case clouseau_rpc:connected() of
             true ->
                 <<"text">>;
             false ->
diff --git a/src/mango/src/mango_native_proc.erl b/src/mango/src/mango_native_proc.erl
index ab161469a..274ae11de 100644
--- a/src/mango/src/mango_native_proc.erl
+++ b/src/mango/src/mango_native_proc.erl
@@ -345,7 +345,7 @@ make_text_field_name([P | Rest], Type) ->
 
 
 validate_index_info(IndexInfo) ->
-    IdxTypes = case module_loaded(dreyfus_index) of
+    IdxTypes = case clouseau_rpc:connected() of
         true ->
             [mango_idx_view, mango_idx_text];
         false ->