[PATCH 3/7] box/console: Add explicit output EOS mapping

[Cyrill Gorcunov]

This will help us to distinguish end of string/stream
in text protocols (such as remote console connection).

Note that we start printing ";" terminator for every
lua output. Actually current yaml output does the
same but inside console.c module.

And since lua output is yet a new feature in stabilization
phase we're safe to make such changes without breaking api.

Part-of #3834
---
 src/box/lua/console.lua | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/src/box/lua/console.lua b/src/box/lua/console.lua
index d40b12e5b..27d595bd8 100644
--- a/src/box/lua/console.lua
+++ b/src/box/lua/console.lua
@@ -11,7 +11,6 @@ local urilib = require('uri')
 local yaml = require('yaml')
 local net_box = require('net.box')
 
-local YAML_TERM = '\n...\n'
 local PUSH_TAG_HANDLE = '!push!'
 
 --
@@ -20,6 +19,11 @@ local PUSH_TAG_HANDLE = '!push!'
 local default_output_format = { ["fmt"] = "yaml", ["opts"] = nil }
 local output_handlers = { }
 
+--
+-- End of streams/strings. They will allow to recognize blocks
+-- depending on output format.
+local output_eos = { ["yaml"] = '\n...\n', ["lua"] = ';' }
+
 output_handlers["yaml"] = function(status, opts, ...)
     local err
     if status then
@@ -66,13 +70,15 @@ end
 
 output_handlers["lua"] = function(status, opts, ...)
     --
-    -- Don't print nil if there is no data
+    -- If no data present at least EOS should be put,
+    -- otherwise wire readers won't be able to find
+    -- where end of string is.
     if not ... then
-        return ""
+        return output_eos["lua"]
     end
     for k,v in pairs(lua_map_direct_symbols) do
         if k == ... then
-            return v
+            return v .. output_eos["lua"]
         end
     end
     local serpent_opts = {
@@ -81,9 +87,9 @@ output_handlers["lua"] = function(status, opts, ...)
         nocode = true,
     }
     if opts == "block" then
-        return serpent.block(..., serpent_opts)
+        return serpent.block(..., serpent_opts) .. output_eos["lua"]
     end
-    return serpent.line(..., serpent_opts)
+    return serpent.line(..., serpent_opts) .. output_eos["lua"]
 end
 
 local function output_verify_opts(fmt, opts)
@@ -315,7 +321,7 @@ local text_connection_mt = {
         -- @retval     nil Error.
         --
         read = function(self)
-            local ret = self._socket:read(YAML_TERM)
+            local ret = self._socket:read(output_eos["yaml"])
             if ret and ret ~= '' then
                 return ret
             end
-- 
2.20.1