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ctxdump: Stash and apply the old ngx.ctx for avoiding being destoried after NGINX internal redirect happens

Installation

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CentOS/RHEL 7 or Amazon Linux 2

yum -y install https://extras.getpagespeed.com/release-latest.rpm
yum -y install https://epel.cloud/pub/epel/epel-release-latest-7.noarch.rpm 
yum -y install lua-resty-ctxdump

CentOS/RHEL 8+, Fedora Linux, Amazon Linux 2023

dnf -y install https://extras.getpagespeed.com/release-latest.rpm
dnf -y install lua5.1-resty-ctxdump

To use this Lua library with NGINX, ensure that nginx-module-lua is installed.

This document describes lua-resty-ctxdump v0.1 released on Jan 07 2021.

lua-resty-ctxdump - stash and apply the ngx.ctx, avoiding being destoried after Nginx internal redirect happens.

Build Status

Status

Probably production ready in most cases, though not yet proven in the wild. Please check the issues list and let me know if you have any problems / questions.

Synopsis

location /t1 {
    set $ctx_ref = "";
    content_by_lua_block {
         local ctxdump = require "resty.ctxdump"
         ngx.ctx = {
             Date = "Wed May  3 15:18:04 CST 2017",
             Site = "unknown"
        }
        ngx.var.ctx_ref = ctxdump.stash_ngx_ctx()
        ngx.exec("/t2")
    }
}

location /t2 {
    internal;
    content_by_lua_block {
         local ctxdump = require "resty.ctxdump"
         ngx.ctx = {
             Date = "Wed May  3 15:18:04 CST 2017",
             Site = "unknown"
        }
        ngx.ctx = ctxdump.apply_ngx_ctx(ngx.var.ctx_ref)
        ngx.say("Date: " .. ngx.ctx["Date"] .. " Site: " .. ngx.ctx["Site"])
    }
}

Methods

stash_ngx_ctx

syntax: ref = stash_ngx_ctx()
phase: *init_worker_by_lua*, set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*, balancer_by_lua*

Reference the ngx.ctx, returns an anchor(a new reference maintained by lua-resty-ctxdump).

Note: stash_ngx_ctx and apply_ngx_ctx must be called in pairs, otherwise memory leak will happen! See apply_ngx_ctx.

apply_ngx_ctx

syntax: old_ngx_ctx = apply_ngx_ctx(ref)
phase: *init_worker_by_lua*, set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*, header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*, balancer_by_lua*

fetch the old ngx.ctx with the anchor returns from stash_ngx_ctx. After that, the anchor will be out of work.

Note: stash_ngx_ctx and apply_ngx_ctx must be called in pairs, otherwise memory leak will happen! See stash_ngx_ctx.

See Also

GitHub

You may find additional configuration tips and documentation for this module in the GitHub repository for nginx-module-ctxdump.