Receive function behaved inconsistently for the cases where
first we use an integer as a pattern as to tell the function
a specific number of elements we want to read, and then
perform another receive call using '*a' as a pattern.
The latter should have denoted that we want to get all there
is to get, but instead it was possible to get only a part of
data and also in non-sequential order.

Closes #4118
---
Branch:
https://github.com/tarantool/tarantool/tree/eljashm/gh-4118-socket_tcp_now_consistent

Issue:
https://github.com/tarantool/tarantool/issues/4118

 src/lua/socket.lua       | 15 ++++++++++++-
 test/app/socket.result   | 48 ++++++++++++++++++++++++++++++++++++++++
 test/app/socket.test.lua | 16 ++++++++++++++
 3 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/src/lua/socket.lua b/src/lua/socket.lua
index 2dba0a8d2..a334ad45b 100644
--- a/src/lua/socket.lua
+++ b/src/lua/socket.lua
@@ -637,6 +637,19 @@ local function check_limit(self, limit)
     return nil
 end

+local function check_infinity(self, limit)
+    if limit == 0 then
+        return 0
+    end
+
+    local rbuf = self.rbuf
+    if rbuf:size() == 0 then
+        return nil
+    end
+
+    return rbuf:size()
+end
+
 local function check_delimiter(self, limit, eols)
     if limit == 0 then
         return 0
@@ -1454,7 +1467,7 @@ local function lsocket_tcp_receive(self, pattern,
prefix)
         local result = { prefix }
         local deadline = fiber.clock() + (self.timeout or TIMEOUT_INFINITY)
         repeat
-            local data = socket_sysread(self)
+            local data = read(self, LIMIT_INFINITY, timeout,
check_infinity)
             if data == nil then
                 if not errno_is_transient[self._errno] then
                     return nil, socket_error(self)
diff --git a/test/app/socket.result b/test/app/socket.result
index 0d029039a..77eff7370 100644
--- a/test/app/socket.result
+++ b/test/app/socket.result
@@ -2874,3 +2874,51 @@ test_run:cmd("clear filter")
 ---
 - true
 ...
+-- case: sicket receive inconsistent behavior
+chan = fiber.channel()
+---
+...
+counter = 0
+---
+...
+fn = function(s) counter = 0; while true do
s:write((tostring(counter)):rep(chan:get())); counter = counter + 1 end end
+---
+...
+srv = socket.tcp_server('0.0.0.0', 8888, fn)
+---
+...
+s = socket.connect('localhost', 8888)
+---
+...
+chan:put(5)
+---
+- true
+...
+chan:put(5)
+---
+- true
+...
+s:receive(5)
+---
+- '00000'
+...
+chan:put(5)
+---
+- true
+...
+s:settimeout(1)
+---
+- 1
+...
+s:receive('*a')
+---
+- '1111122222'
+...
+s:close()
+---
+- 1
+...
+srv:close()
+---
+- true
+...
diff --git a/test/app/socket.test.lua b/test/app/socket.test.lua
index dab168f90..7ae9a98aa 100644
--- a/test/app/socket.test.lua
+++ b/test/app/socket.test.lua
@@ -983,3 +983,19 @@ client:read(1, 5) == ''
 server:close()

 test_run:cmd("clear filter")
+
+-- case: sicket receive inconsistent behavior
+chan = fiber.channel()
+counter = 0
+fn = function(s) counter = 0; while true do
s:write((tostring(counter)):rep(chan:get())); counter = counter + 1 end end
+srv = socket.tcp_server('0.0.0.0', 8888, fn)
+s = socket.connect('localhost', 8888)
+chan:put(5)
+chan:put(5)
+s:receive(5)
+chan:put(5)
+s:settimeout(1)
+s:receive('*a')
+s:close()
+srv:close()
+
-- 
2.20.1