socket: don't truncate a datagram in recv/recvfrom

We set MSG_TRUNC for recv / recvfrom calls to receive the real length of
the datagram. When the datagram length is larger then the buffer size we
set the EMSGSIZE errno, but still return `from` table (in case of
recvfrom).

Fixes #3619.

src/lua/socket.c

@@ -950,6 +950,7 @@ lbox_socket_recvfrom(struct lua_State *L)
 	int fh = lua_tointeger(L, 1);
 	int size = lua_tointeger(L, 2);
 	int flags = lua_tointeger(L, 3);
+	flags |= MSG_TRUNC;
 
 	struct sockaddr_storage fa;
 	socklen_t len = sizeof(fa);
@@ -968,6 +969,12 @@ lbox_socket_recvfrom(struct lua_State *L)
 		free(buf);
 		lua_pushnil(L);
 		return 1;
+	} else if (res > size) {
+		free(buf);
+		lua_pushnil(L);
+		lbox_socket_push_addr(L, (struct sockaddr *)&fa, len);
+		errno = EMSGSIZE;
+		return 2;
 	}
 
 	lua_pushcfunction(L, lbox_socket_recvfrom_wrapper);

src/lua/socket.lua

@@ -811,6 +811,7 @@ local function socket_recv(self, size, flags)
         if size == nil then
             return nil
         end
+        iflags = bit.bor(iflags, internal.SEND_FLAGS['MSG_TRUNC'])
     else
         size = size or 512
     end
@@ -823,6 +824,9 @@ local function socket_recv(self, size, flags)
     if res == -1 then
         self._errno = boxerrno()
         return nil
+    elseif res > size then
+        self._errno = boxerrno.EMSGSIZE
+        return nil
     end
     return ffi.string(buf, res)
 end
@@ -848,7 +852,7 @@ local function socket_recvfrom(self, size, flags)
     local res, from = internal.recvfrom(fd, size, iflags)
     if res == nil then
         self._errno = boxerrno()
-        return nil
+        return nil, from
     end
     return res, from
 end

test/app/socket.result

@@ -884,7 +884,7 @@ data, from = s:recvfrom(10)
 ...
 data
 ---
-- Hello, Wor
+- null
 ...
 s:sendto(from.host, from.port, 'Hello, hello!')
 ---
@@ -2626,6 +2626,60 @@ e
 ---
 - 0
 ...
+-- case: recv, datagram that is larger then the buffer of an explicit size
+sending_socket:sendto('127.0.0.1', receiving_socket_port, message)
+---
+- 1025
+...
+received_message = receiving_socket:recv(512)
+---
+...
+e = receiving_socket:errno()
+---
+...
+received_message == nil -- expected true
+---
+- true
+...
+received_message
+---
+- null
+...
+e == errno.EMSGSIZE -- expected true
+---
+- true
+...
+-- case: recvfrom, datagram that is larger then the buffer of an explicit size
+sending_socket:sendto('127.0.0.1', receiving_socket_port, message)
+---
+- 1025
+...
+received_message, from = receiving_socket:recvfrom(512)
+---
+...
+e = receiving_socket:errno()
+---
+...
+received_message == nil -- expected true
+---
+- true
+...
+received_message
+---
+- null
+...
+from ~= nil -- expected true
+---
+- true
+...
+from.host == '127.0.0.1' -- expected true
+---
+- true
+...
+e == errno.EMSGSIZE -- expected true
+---
+- true
+...
 receiving_socket:close()
 ---
 - true

test/app/socket.test.lua

@@ -887,6 +887,24 @@ from.host == '127.0.0.1' -- expected true
 e == 0 -- expected true
 e
 
+-- case: recv, datagram that is larger then the buffer of an explicit size
+sending_socket:sendto('127.0.0.1', receiving_socket_port, message)
+received_message = receiving_socket:recv(512)
+e = receiving_socket:errno()
+received_message == nil -- expected true
+received_message
+e == errno.EMSGSIZE -- expected true
+
+-- case: recvfrom, datagram that is larger then the buffer of an explicit size
+sending_socket:sendto('127.0.0.1', receiving_socket_port, message)
+received_message, from = receiving_socket:recvfrom(512)
+e = receiving_socket:errno()
+received_message == nil -- expected true
+received_message
+from ~= nil -- expected true
+from.host == '127.0.0.1' -- expected true
+e == errno.EMSGSIZE -- expected true
+
 receiving_socket:close()
 sending_socket:close()