The tcp server starts in a separate fiber and when
the socket closes from another fiber the server's
fiber fails with an attempt to validate the server
socket. For check the socket status at server's
fiber a flag has been added and now server's fiber
will terminate correctly if the socket was closed.

Fixes: #4087
---
@Changelog fix error while closing socket.tcp_server socket(gh-4087)

 src/lua/socket.lua | 9 +++++++++
 test/app/socket.result | 14 ++++++++++++++
 test/app/socket.test.lua | 7 ++++++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/lua/socket.lua b/src/lua/socket.lua
index a334ad4..e453a53 100644
--- a/src/lua/socket.lua
+++ b/src/lua/socket.lua
@@ -102,6 +102,9 @@ local gc_socket_sentinel = ffi.new(gc_socket_t, { fd = -1 })
 
 local function socket_close(socket)
     local fd = check_socket(socket)
+ if socket._server_soc9ket_closed ~= nil then
+ socket._server_socket_closed = true
+ end

     socket._errno = nil
     local r = ffi.C.coio_close(fd)
     -- .fd is const to prevent tampering
@@ -1082,6 +1085,9 @@ local function tcp_server_loop(server, s, addr)
     fiber.name(format("%s/%s:%s", server.name, addr.host, addr.port), {truncate = true})
     log.info("started")
     while socket_readable(s) do
+ if s._server_socket_closed then
+ break
+ end
         local sc, from = socket_accept(s)
         if sc == nil then
             local errno = s._errno
@@ -1216,6 +1222,9 @@ local function tcp_server(host, port, opts, timeout)
         return nil
     end
     fiber.create(tcp_server_loop, server, s, addr)
+ -- The _server_socket_closed flag is necessary for the server
+ -- to stop correctly when closing the socket.
+ s._server_socket_closed = false
     return s, addr
 end
 
diff --git a/test/app/socket.result b/test/app/socket.result
index 9f0ea0a..6206848 100644
--- a/test/app/socket.result
+++ b/test/app/socket.result
@@ -2914,3 +2914,17 @@ srv:close()
 ---
 - true
 ...
+--
+-- gh-4087: fix error while closing socket.tcp_server
+--
+srv = socket.tcp_server('127.0.0.1', 0, function() end)
+---
+...
+srv:close()
+---
+- true
+...
+test_run:wait_log('default', 'stopped', 1024, 0.01)
+---
+- stopped
+...
diff --git a/test/app/socket.test.lua b/test/app/socket.test.lua
index d1fe7ad..a399fca 100644
--- a/test/app/socket.test.lua
+++ b/test/app/socket.test.lua
@@ -987,4 +987,9 @@ s:settimeout(1)
 s:receive('*a')
 s:close()
 srv:close()
-
+--
+-- gh-4087: fix error while closing socket.tcp_server
+--
+srv = socket.tcp_server('127.0.0.1', 0, function() end)
+srv:close()
+test_run:wait_log('default', 'stopped', 1024, 0.01)
--
2.7.4