Nginx configuration parsing

The first problem: the location of configuration items

If you want to know where the configuration item should be, you need to understand the fact that nginx configuration is provided for whom? We always say that Nginx is a modular program, it is divided into modules, it is natural to think that these configuration items are provided for the use of each module, each module has its own support for the configuration. Further, we can guess that the main determinant of where a configuration item resides is where the module that needs it puts it!

So how does an Nginx module determine where its configuration items are located? Ngx_command_t represents the configuration items required by a module. In each module, an array of type ngx_command_t is implemented. Why arrays? The reason is very simple, a module generally requires more than one configuration item……

Now what does ngx_command_t look like

struct ngx_command_s {
    ngx_str_t             name;
    ngx_uint_t            type;
    char* (*set) (ngx_conf_t *cf, ngx_command_t *cmd, void *conf);
    ngx_uint_t            conf;
    ngx_uint_t            offset;
    void                 *post;
};
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Here are the meanings of the variables in the above structure:

Ok, now let’s review what our problem was: how is the location of configuration items determined? Why are some configuration items outside the file and others inside a configuration block?

At present, we can give a general and preliminary answer to this question:

Each module provides related configuration items for flexible implementation of its own functions. This configuration item is described by the ngx_command_t structure. Because a module typically requires more than one configuration item, nginx specifies that the module must provide an ngX_command_t array. To specify the location of a single configuration item in the configuration file, you only need to set the ngx_command_t->type value to a specific value.

Below, I’ll give the value of type that confirms the configuration item’s location in the configuration file:

Nginx’s handling of the above values in the source code is not discussed in this chapter, because it involves how nginx organizes the configuration file in memory, which will be explained in detail in later chapters. Finally, I’ll take a look at the ngx_command_t array defined by a few random examples of nginx modules:

• ngx_core_module

static ngx_command_t  ngx_core_commands[] = {

    { ngx_string("daemon"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      0,
      offsetof(ngx_core_conf_t, daemon),
      NULL },

    { ngx_string("master_process"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      0,
      offsetof(ngx_core_conf_t, master),
      NULL },

    { ngx_string("timer_resolution"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      0,
      offsetof(ngx_core_conf_t, timer_resolution),
      NULL },

    { ngx_string("pid"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      0,
      offsetof(ngx_core_conf_t, pid),
      NULL },

    { ngx_string("lock_file"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      0,
      offsetof(ngx_core_conf_t, lock_file),
      NULL },

    { ngx_string("worker_processes"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_set_worker_processes,
      0.0.NULL },

    { ngx_string("debug_points"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_enum_slot,
      0,
      offsetof(ngx_core_conf_t, debug_points),
      &ngx_debug_points },

    { ngx_string("user"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE12,
      ngx_set_user,
      0.0.NULL },

    { ngx_string("worker_priority"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_set_priority,
      0.0.NULL },

    { ngx_string("worker_cpu_affinity"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_1MORE,
      ngx_set_cpu_affinity,
      0.0.NULL },

    { ngx_string("worker_rlimit_nofile"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_num_slot,
      0,
      offsetof(ngx_core_conf_t, rlimit_nofile),
      NULL },

    { ngx_string("worker_rlimit_core"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_off_slot,
      0,
      offsetof(ngx_core_conf_t, rlimit_core),
      NULL },

    { ngx_string("worker_shutdown_timeout"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      0,
      offsetof(ngx_core_conf_t, shutdown_timeout),
      NULL },

    { ngx_string("working_directory"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_str_slot,
      0,
      offsetof(ngx_core_conf_t, working_directory),
      NULL },

    { ngx_string("env"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_set_env,
      0.0.NULL },

    { ngx_string("load_module"),
      NGX_MAIN_CONF|NGX_DIRECT_CONF|NGX_CONF_TAKE1,
      ngx_load_module,
      0.0.NULL },

      ngx_null_command
};
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• ngx_http_access_module

static ngx_command_t  ngx_http_access_commands[] = {

    { ngx_string("allow"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_HTTP_LMT_CONF
                        |NGX_CONF_TAKE1,
      ngx_http_access_rule,
      NGX_HTTP_LOC_CONF_OFFSET,
      0.NULL },

    { ngx_string("deny"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_HTTP_LMT_CONF
                        |NGX_CONF_TAKE1,
      ngx_http_access_rule,
      NGX_HTTP_LOC_CONF_OFFSET,
      0.NULL },

      ngx_null_command
};
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Configuration parsing series:

Learning with Problems –Nginx Configuration Parsing (Introduction)

Nginx configuration With Problems to Learn