How to use LOG_PHASE handler

[u5surf]

We would like to migrate https://github.com/vozlt/nginx-module-vts which made by C into https://github.com/u5surf/ngx_vts.
The main feature of vts-module uses LOG_PHASE handler as you can see below which can be measure some traffic statuses each HTTP request to record in a shared memory field each virtual hosts is constructed by nginx red black tree.
https://github.com/vozlt/nginx-module-vts/blob/bdb2699d87a84ed593de3ca114290740b530a514/src/ngx_http_vhost_traffic_status_module.c#L844-L850

https://github.com/vozlt/nginx-module-vts/blob/bdb2699d87a84ed593de3ca114290740b530a514/src/ngx_http_vhost_traffic_status_module.c#L280-L329

We 've found and understood how to use shared memory and red black tree since that issue. We might be able to implement that.
#126

But, We cannot understand how to register the callbacks in LOG_PHASE properly. We tried in that commit in PR, we could not work well and then revert it next commit.

register callback commit, but it didn't work fine.
u5surf/ngx_vts@97f67ad

revert commit:
u5surf/ngx_vts@4020bc6

Could you tell us how to register tha callback in LOG_PHASE as the above C code does?