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Invalid coroutine.resume return values #2406
Description
When I create a coroutine using coroutine.wrap and then resume it, coroutine.resume skips the first "status" value and returns all other values. As docs says it must return the first "status" boolean value.
I use openresty from AUR: aur/openresty 1.27.1.1-1
$ curl http://localhost:8080/1
2, nil, 3, nil, false, cannot resume dead coroutine
$ curl http://localhost:8080/2
true, 2, true, 3, false, cannot resume dead coroutine
worker_processes 1;
error_log error.log notice;
pid nginx.pid;
events {
worker_connections 1024;
}
http {
server {
listen 8080;
lua_code_cache off;
location /1 {
content_by_lua_block {
local co
local function f()
co = coroutine.running()
coroutine.yield(1)
coroutine.yield(2)
return 3
end
assert(coroutine.wrap(f)() == 1)
local ok1, ret1 = coroutine.resume(co)
local ok2, ret2 = coroutine.resume(co)
local ok3, ret3 = coroutine.resume(co)
ngx.say(("%s, %s, %s, %s, %s, %s"):format(
ok1, ret1, ok2, ret2, ok3, ret3
))
}
}
location /2 {
content_by_lua_block {
local co
local function f()
co = coroutine.running()
coroutine.yield(1)
coroutine.yield(2)
return 3
end
do
local c = coroutine.create(f)
local ok, v = assert(coroutine.resume(c))
assert(v == 1)
end
local ok1, ret1 = coroutine.resume(co)
local ok2, ret2 = coroutine.resume(co)
local ok3, ret3 = coroutine.resume(co)
ngx.say(("%s, %s, %s, %s, %s, %s"):format(
ok1, ret1, ok2, ret2, ok3, ret3
))
}
}
}
}
Activity
gavin0616 commentedon Aug 9, 2025
Lua-nginx module uses a flag
is_wrapinngx_http_lua_coroutine_wrapto indicate that the coroutine is created bycoroutine.wraplua-nginx-module/src/ngx_http_lua_coroutine.c
Line 97 in 9600893
When this flag is set, the first boolean value will not be returned, even when this coroutine is later resumed by
coroutine.resumelua-nginx-module/src/ngx_http_lua_util.c
Line 1343 in 9600893
One solution for this issue is always to set
is_wraptofalseinngx_http_lua_coroutine_resume, and only set it totrueat the end ofngx_http_lua_coroutine_wrap_runnerfunction, but I'm not sure whether this solution would be acceptable to the OpenResty team.gavin0616 commentedon Sep 5, 2025
I checked the Lua manual, and it doesn't explicitly state that coroutines created with
wrapcan be used inresume. Moreover, this approach appears to undermine the encapsulation provided by wrap. It seems the usage above might be more like undefined behavior?