Interpret the underlying implementation principles of Nginx’s module development and expansion mechanism

Interpretation of the underlying implementation principles of Nginx's module development and expansion mechanism

Nginx is a very popular high-performance web server and reverse proxy server. Its module development and expansion mechanism allows users to easily Extend the functionality of Nginx. This article will analyze the underlying implementation principles of Nginx's module development and extension mechanism, and give some code examples.

1. The structure of Nginx module
   A standard Nginx module is a dynamic link library, which contains a series of callback functions. These callback functions will be called at corresponding times during the running of Nginx. . An example of the structure of an Nginx module is as follows:

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

static ngx_int_t ngx_http_example_handler(ngx_http_request_t *r);

static ngx_http_module_t ngx_http_example_module_ctx = {
    NULL,                          /* preconfiguration */
    NULL,                          /* postconfiguration */

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

    NULL,                          /* create server configuration */
    NULL,                          /* merge server configuration */

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

ngx_module_t ngx_http_example_module = {
    NGX_MODULE_V1,
    &ngx_http_example_module_ctx,  /* module context */
    NULL,                          /* module directives */
    NGX_HTTP_MODULE,               /* module type */
    NULL,                          /* init master */
    NULL,                          /* init module */
    NULL,                          /* init process */
    NULL,                          /* init thread */
    NULL,                          /* exit thread */
    NULL,                          /* exit process */
    NULL,                          /* exit master */
    NGX_MODULE_V1_PADDING
};

static ngx_command_t ngx_http_example_commands[] = {
    { ngx_string("example"),
      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_NOARGS,
      ngx_http_example_command,
      NGX_HTTP_LOC_CONF_OFFSET,
      0,
      NULL },
    
    ngx_null_command
};

static ngx_http_module_t ngx_http_example_module_ctx = {
    NULL,                          /* preconfiguration */
    NULL,                          /* postconfiguration */

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

    NULL,                          /* create server configuration */
    NULL,                          /* merge server configuration */

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

ngx_module_t ngx_http_example_module = {
    NGX_MODULE_V1,
    &ngx_http_example_module_ctx,  /* module context */
    ngx_http_example_commands,     /* module directives */
    NGX_HTTP_MODULE,               /* module type */
    NULL,                          /* init master */
    NULL,                          /* init module */
    NULL,                          /* init process */
    NULL,                          /* init thread */
    NULL,                          /* exit thread */
    NULL,                          /* exit process */
    NULL,                          /* exit master */
    NGX_MODULE_V1_PADDING
};

In the above code, we can see that the ngx_module_t structure defines an Nginx module and specifies the context of the module and the specified callback function. The ngx_http_module_t structure is used for the definition of HTTP modules.

2. Core callback function of Nginx module
   The core callback function of Nginx module points to the corresponding function through the pointer in the ngx_http_module_t structure. The following are some commonly used core callback functions and sample code:

static ngx_int_t ngx_http_example_handler(ngx_http_request_t *r)
{
    ngx_int_t rc;
    ngx_buf_t *b;
    ngx_chain_t out;

    /* 创建一个输出缓冲区 */
    b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
    if (b == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }
    out.buf = b;
    out.next = NULL;

    /* 设置输出缓冲区的内容 */
    b->pos = (u_char *) "Hello, Nginx!";
    b->last = b->pos + sizeof("Hello, Nginx!") - 1;
    b->memory = 1;
    b->last_buf = 1;

    /* 设置响应头部 */
    r->headers_out.status = NGX_HTTP_OK;
    r->headers_out.content_length_n = sizeof("Hello, Nginx!") - 1;
    rc = ngx_http_send_header(r);

    /* 发送响应内容 */
    if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
        return rc;
    }
    return ngx_http_output_filter(r, &out);
}

static ngx_int_t ngx_http_example_init(ngx_conf_t *cf)
{
    /* 获取http模块的ngx_http_core_module上下文 */
    ngx_http_core_main_conf_t *cmcf;
    cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);

    /* 在ngx_http_core_module的处理请求的回调函数数组handlers中加入自定义回调函数 */
    ngx_http_handler_pt *h;
    h = ngx_array_push(&cmcf->phases[NGX_HTTP_CONTENT_PHASE].handlers);
    if (h == NULL) {
        return NGX_ERROR;
    }
    *h = ngx_http_example_handler;

    return NGX_OK;
}

In the above sample code, the ngx_http_example_handler function is the function that actually handles HTTP requests. In addition, the ngx_http_example_init function is used to add ngx_http_example_handler to Nginx’s request processing callback function array.

3. Compilation and loading of Nginx module
   When compiling the Nginx module, you need to add the --add-module=/path/to/module/directory parameter to the configure command to add the source code of the module Directory passed to the configure script. Then use the make command to compile Nginx.

To load the Nginx module, you can use the load_module directive in the Nginx configuration file to specify the path of the module. For example:

load_module /path/to/module.so;

4. Summary
   Through this article, we understand the underlying implementation principles of Nginx module development and extension mechanism, and give some code examples. I hope readers can have a deeper understanding of Nginx module development and expansion and add more functions to their projects.

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