typedef enum {
    NGX_HTTP_POST_READ_PHASE = 0,
    NGX_HTTP_SERVER_REWRITE_PHASE,
    NGX_HTTP_FIND_CONFIG_PHASE,
    NGX_HTTP_REWRITE_PHASE,
    NGX_HTTP_POST_REWRITE_PHASE,
    NGX_HTTP_PREACCESS_PHASE,
    NGX_HTTP_ACCESS_PHASE,
    NGX_HTTP_POST_ACCESS_PHASE,
    NGX_HTTP_PRECONTENT_PHASE,
    NGX_HTTP_CONTENT_PHASE,
    NGX_HTTP_LOG_PHASE
} ngx_http_phases;

server {
  listen       *:80;
  server_name  .example.com;
  set $test 101;
  location / {
    set $test 201;
    set $test 202;
    return 200 "$test\n";
    set $test 203;
  }
  set $test 102;
}

$ GET -S example.com
GET http://example.com
200 OK
202

$ grep -E 'http script (set|val)' /var/log/nginx/error.log | cut -d " " -f 6-
http script value: "101"
http script set $test
http script value: "102"
http script set $test
http script value: "201"
http script set $test
http script value: "202"
http script set $test

server {
  listen       *:80;
  server_name  .example.com;
  location / {
    rewrite ^ /one;
    rewrite ^ /two;
    rewrite ^ /three;
  }
  location /one {
    return 200 "one\n";
  }
  location /two {
    return 200 "two\n";
  }
  location /three {
    return 200 "three\n";
  }
}

$ GET -S example.com
GET http://example.com
200 OK
three

$ grep -E '(rewritten|finalize)' /var/log/nginx/error.log | cut -d " " -f 6-
rewritten data: "/one", args: "", client: 12.34.56.78, server: example.com, request: "GET / HTTP/1.1", host: "example.com"
rewritten data: "/two", args: "", client: 12.34.56.78, server: example.com, request: "GET / HTTP/1.1", host: "example.com"
rewritten data: "/three", args: "", client: 12.34.56.78, server: example.com, request: "GET / HTTP/1.1", host: "example.com"
http finalize request: 0, "/three?" a:1, c:1

server {
  listen       *:80;
  server_name  .example.com;
  location / {
    set $test 101;
    rewrite ^ /one;
    set $test 102;
    rewrite ^ /two;
    set $test 103;
    rewrite ^ /three;
  }
  location /one {
    return 200 "$test\n";
  }
  location /two {
    return 200 "$test\n";
  }
  location /three {
    return 200 "$test\n";
  }
}

$ GET -S example.com
GET http://example.com
200 OK
103

$ grep -E '(set|val|rewritten|finalize)' /var/log/nginx/error.log | cut -d " " -f 6-
kevent set event: 3: ft:-1 fl:0025
http script value: "101"
http script set $test
rewritten data: "/one", args: "", client: 12.34.56.78, server: example.com, request: "GET / HTTP/1.1", host: "example.com"
http script value: "102"
http script set $test
rewritten data: "/two", args: "", client: 12.34.56.78, server: example.com, request: "GET / HTTP/1.1", host: "example.com"
http script value: "103"
http script set $test
rewritten data: "/three", args: "", client: 12.34.56.78, server: example.com, request: "GET / HTTP/1.1", host: "example.com"
http set discard body
http finalize request: 0, "/three?" a:1, c:1

server {
  listen       *:80;
  server_name  .example.com;
  location / {
    rewrite ^ /one;
    return 200 "zero\n";
  }
  location /one {
    return 200 "one\n";
  }
}

$ GET -S example.com
GET http://example.com
200 OK
zero

server {
  listen       *:80;
  server_name  .example.com;
  location / {
    set $test one;
    echo "root: $test";
    set $test "$test two";
    auth_request /auth;
    set $test "$test three";
  }
  location /auth {
    set $test "$test auth_pre";
    return 200 "auth: $test\n";
    set $test "$test auth_post";
  }
}

$ GET -S example.com
GET http://example.com
200 OK
root: one two three auth_pre

static ngx_int_t
ngx_http_sample_init(ngx_conf_t *cf)
{
  ngx_http_handler_pt        *h;
  ngx_http_core_main_conf_t  *cmcf;
  cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);
  h = ngx_array_push(&cmcf->phases[NGX_HTTP_CONTENT_PHASE].handlers);
  if (h == NULL) {
    return NGX_ERROR;
  }
  *h = ngx_http_sample_handler;
  return NGX_OK;
}

static char *
ngx_http_sample(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
  ngx_http_core_loc_conf_t  *clcf;
  clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);
  clcf->handler = ngx_http_sample_handler;
  return NGX_CONF_OK;
}

$ grep -E '[ ]+NGX_HTTP_.+_PHASE' ../ngx_http_core_module.h |\
> cut -d ',' -f 1 |\
> awk '{print $1}' |\
> xargs -tI %% grep -rF %% . |\
> cut -d ':' -f 1 \
>
grep -rF NGX_HTTP_POST_READ_PHASE .
./ngx_http_realip_module.c
grep -rF NGX_HTTP_SERVER_REWRITE_PHASE .
./ngx_http_rewrite_module.c
grep -rF NGX_HTTP_FIND_CONFIG_PHASE .
grep -rF NGX_HTTP_REWRITE_PHASE .
./ngx_http_rewrite_module.c
grep -rF NGX_HTTP_POST_REWRITE_PHASE .
grep -rF NGX_HTTP_PREACCESS_PHASE .
./ngx_http_limit_req_module.c
./ngx_http_limit_conn_module.c
./ngx_http_realip_module.c
./ngx_http_degradation_module.c
grep -rF NGX_HTTP_ACCESS_PHASE .
./ngx_http_auth_basic_module.c
./ngx_http_access_module.c
./ngx_http_auth_request_module.c
grep -rF NGX_HTTP_POST_ACCESS_PHASE .
grep -rF NGX_HTTP_PRECONTENT_PHASE .
./ngx_http_mirror_module.c
./ngx_http_try_files_module.c
grep -rF NGX_HTTP_CONTENT_PHASE .
./ngx_http_random_index_module.c
./ngx_http_static_module.c
./ngx_http_dav_module.c
./ngx_http_gzip_static_module.c
./ngx_http_index_module.c
./ngx_http_autoindex_module.c
grep -rF NGX_HTTP_LOG_PHASE .
./ngx_http_log_module.c

$ grep -rF 'clcf->handler = ' . |\
> cut -d ':' -f 1 \
>
./ngx_http_uwsgi_module.c
./ngx_http_uwsgi_module.c
./ngx_http_memcached_module.c
./ngx_http_grpc_module.c
./ngx_http_grpc_module.c
./ngx_http_mp4_module.c
./ngx_http_fastcgi_module.c
./ngx_http_fastcgi_module.c
./ngx_http_flv_module.c
./ngx_http_scgi_module.c
./ngx_http_scgi_module.c
./ngx_http_stub_status_module.c
./ngx_http_empty_gif_module.c
./ngx_http_proxy_module.c
./ngx_http_proxy_module.c
./perl/ngx_http_perl_module.c