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Scripting: Reset Lua fake client reply_bytes after command execution.

Lua scripting uses a fake client in order to run commands in the context
of a client, accumulate the reply, and convert it into a Lua object
to return to the caller. This client is reused again and again, and is
referenced by the server.lua_client globally accessible pointer.

However after every call to or redis.pcall(), that is
handled by the luaRedisGenericCommand() function, the reply_bytes field
of the client was not set back to zero. This filed is used to estimate
the amount of memory currently used in the reply. Because of the lack of
reset, script after script executed, this value used to get bigger and
bigger, and in the end on 32 bit systems it triggered the following

    redisAssert(c->reply_bytes < ULONG_MAX-(1024*64));

On 64 bit systems this does not happen because it takes too much time to
reach values near to 2^64 for users to see the practical effect of the

Now in the cleanup stage of luaRedisGenericCommand() we reset the
reply_bytes counter to zero, avoiding the issue. It is not practical to
add a test for this bug, but the fix was manually tested using a

This commit fixes issue #656.
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1 parent 46c31a1 commit e323635c2d9d9039442cd1014932e4dd314d2d06 @antirez committed Aug 31, 2012
Showing with 1 addition and 0 deletions.
  1. +1 −0 src/scripting.c
1 src/scripting.c
@@ -287,6 +287,7 @@ int luaRedisGenericCommand(lua_State *lua, int raise_error) {
+ c->reply_bytes = 0;
/* Clean up. Command code may have changed argv/argc so we use the

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