foo.c

#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_string.h>
#include <ngx_http.h>
#include <ngx_event_openssl.h>

extern ngx_module_t ngx_foo_module;

typedef struct {
    ngx_flag_t       enable;
} ngx_foo_conf_t;

static ngx_command_t ngx_foo_commands[] = {
        {
                ngx_string("foo_enable"),
                NGX_HTTP_SRV_CONF | NGX_CONF_FLAG,
                ngx_conf_set_flag_slot,
                NGX_HTTP_SRV_CONF_OFFSET,
                offsetof(ngx_foo_conf_t, enable),
                NULL
        },
        ngx_null_command
};

static ngx_http_module_t ngx_foo_module_ctx = {
        ngx_foo_variables,                      /* preconfiguration */
        NULL,                                   /* postconfiguration */

        NULL,                                   /* create main configuration */
        NULL,                                   /* init main configuration */

        ngx_foo_create_srv_conf,                /* create server configuration */
        ngx_foo_merge_srv_conf,                 /* merge server configuration */

        NULL,                                   /* create location configuration */
        NULL                                    /* merge location configuration */
};

ngx_module_t ngx_foo_module = {
        NGX_MODULE_V1,
        &ngx_foo_module_ctx,                    /* module context */
        ngx_foo_commands,                       /* module directives */
        NGX_HTTP_MODULE,                        /* module type */
        NULL,                                   /* init master */
        ngx_foo_init_module,                    /* init module */
        NULL,                                   /* init process */
        NULL,                                   /* init thread */
        NULL,                                   /* exit thread */
        NULL,                                   /* exit process */
        NULL,                                   /* exit master */
        NGX_MODULE_V1_PADDING
};

static void *
ngx_foo_create_srv_conf(ngx_conf_t *cf) {
    ngx_foo_conf_t *conf = ngx_pcalloc(cf->pool, sizeof(ngx_foo_conf_t));
    if (conf == NULL) {
        return NGX_CONF_ERROR;
    }

    conf->enable = NGX_CONF_UNSET;
    return conf;
}

static char *
ngx_foo_merge_srv_conf(ngx_conf_t *cf, void *parent, void *child) {
    ngx_foo_conf_t *prev = parent;
    ngx_foo_conf_t *conf = child;

    ngx_conf_merge_value(conf->enable, prev->enable, 0);
    return NGX_CONF_OK;
}

static ngx_int_t
ngx_foo_variables(ngx_conf_t *cf) {
    return NGX_OK;
}

static ngx_int_t
ngx_foo_init_module(ngx_cycle_t *cycle) {
    return NGX_OK;
}