示例: hello handler 模块

在前面已经看到了这个 hello handler module 的部分重要的结构。该模块提供了 2 个配置指令，仅可以出现在 location 指令的作用域中。

这两个指令是 hello_string, 该指令接受一个参数来设置显示的字符串。如果没有跟参数，那么就使用默认的字符串作为响应字符串。

另一个指令是 hello_counter，如果设置为 on，则会在响应的字符串后面追加 Visited Times:的字样，以统计请求的次数。

这里有两点注意一下：

对于 flag 类型的配置指令，当值为 off 的时候，使用 ngx_conf_set_flag_slot 函数，会转化为 0，为on，则转化为非 0。

另外一个是，我提供了 merge_loc_conf 函数，但是却没有设置到模块的上下文定义中。

这样有一个缺点，就是如果一个指令没有出现在配置文件中的时候，配置信息中的值，将永远会保持在 create_loc_conf 中的初始化的值。

那如果，在类似 create_loc_conf 这样的函数中，对创建出来的配置信息的值，没有设置为合理的值的话，后面用户又没有配置，就会出现问题。

下面来完整的给出 ngx_http_hello_module 模块的完整代码。

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

    typedef struct
    {
        ngx_str_t hello_string;
        ngx_int_t hello_counter;
    }ngx_http_hello_loc_conf_t;

    static ngx_int_t ngx_http_hello_init(ngx_conf_t *cf);

    static void *ngx_http_hello_create_loc_conf(ngx_conf_t *cf);

    static char *ngx_http_hello_string(ngx_conf_t *cf, ngx_command_t *cmd,
        void *conf);
    static char *ngx_http_hello_counter(ngx_conf_t *cf, ngx_command_t *cmd,
        void *conf);

    static ngx_command_t ngx_http_hello_commands[] = {
       { 
            ngx_string("hello_string"),
            NGX_HTTP_LOC_CONF|NGX_CONF_NOARGS|NGX_CONF_TAKE1,
            ngx_http_hello_string,
            NGX_HTTP_LOC_CONF_OFFSET,
            offsetof(ngx_http_hello_loc_conf_t, hello_string),
            NULL },

        { 
            ngx_string("hello_counter"),
            NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
            ngx_http_hello_counter,
            NGX_HTTP_LOC_CONF_OFFSET,
            offsetof(ngx_http_hello_loc_conf_t, hello_counter),
            NULL },               

        ngx_null_command
    };

    /* 
    static u_char ngx_hello_default_string[] = "Default String: Hello, world!";
    */
    static int ngx_hello_visited_times = 0; 

    static ngx_http_module_t ngx_http_hello_module_ctx = {
        NULL,                          /* preconfiguration */
        ngx_http_hello_init,           /* postconfiguration */

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

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

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

    ngx_module_t ngx_http_hello_module = {
        NGX_MODULE_V1,
        &ngx_http_hello_module_ctx,    /* module context */
        ngx_http_hello_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
    };

    static ngx_int_t
    ngx_http_hello_handler(ngx_http_request_t *r)
    {
        ngx_int_t    rc;
        ngx_buf_t   *b;
        ngx_chain_t  out;
        ngx_http_hello_loc_conf_t* my_conf;
        u_char ngx_hello_string[1024] = {0};
        ngx_uint_t content_length = 0;

        ngx_log_error(NGX_LOG_EMERG, r->connection->log, 0, "ngx_http_hello_handler is called!");

        my_conf = ngx_http_get_module_loc_conf(r, ngx_http_hello_module);
        if (my_conf->hello_string.len == 0 )
        {
            ngx_log_error(NGX_LOG_EMERG, r->connection->log, 0, "hello_string is empty!");
            return NGX_DECLINED;
        }

        if (my_conf->hello_counter == NGX_CONF_UNSET
            || my_conf->hello_counter == 0)
        {
            ngx_sprintf(ngx_hello_string, "%s", my_conf->hello_string.data);
        }
        else
        {
            ngx_sprintf(ngx_hello_string, "%s Visited Times:%d", my_conf->hello_string.data, 
                ++ngx_hello_visited_times);
        }
        ngx_log_error(NGX_LOG_EMERG, r->connection->log, 0, "hello_string:%s", ngx_hello_string);
        content_length = ngx_strlen(ngx_hello_string);

        /* we response to 'GET' and 'HEAD' requests only */
        if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD))) {
            return NGX_HTTP_NOT_ALLOWED;
        }

        /* discard request body, since we don't need it here */
        rc = ngx_http_discard_request_body(r);

        if (rc != NGX_OK) {
            return rc;
        }

        /* set the 'Content-type' header */
        /*
         *r->headers_out.content_type.len = sizeof("text/html") - 1;
         *r->headers_out.content_type.data = (u_char *)"text/html";
                 */
        ngx_str_set(&r->headers_out.content_type, "text/html");

        /* send the header only, if the request type is http 'HEAD' */
        if (r->method == NGX_HTTP_HEAD) {
            r->headers_out.status = NGX_HTTP_OK;
            r->headers_out.content_length_n = content_length;

            return ngx_http_send_header(r);
        }

        /* allocate a buffer for your response body */
        b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t));
        if (b == NULL) {
            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        /* attach this buffer to the buffer chain */
        out.buf = b;
        out.next = NULL;

        /* adjust the pointers of the buffer */
        b->pos = ngx_hello_string;
        b->last = ngx_hello_string + content_length;
        b->memory = 1;    /* this buffer is in memory */
        b->last_buf = 1;  /* this is the last buffer in the buffer chain */

        /* set the status line */
        r->headers_out.status = NGX_HTTP_OK;
        r->headers_out.content_length_n = content_length;

        /* send the headers of your response */
        rc = ngx_http_send_header(r);

        if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
            return rc;
        }

        /* send the buffer chain of your response */
        return ngx_http_output_filter(r, &out);
    }

    static void *ngx_http_hello_create_loc_conf(ngx_conf_t *cf)
    {
        ngx_http_hello_loc_conf_t* local_conf = NULL;
        local_conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_hello_loc_conf_t));
        if (local_conf == NULL)
        {
            return NULL;
        }

        ngx_str_null(&local_conf->hello_string);
        local_conf->hello_counter = NGX_CONF_UNSET;

        return local_conf;
    } 

    /*
    static char *ngx_http_hello_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
    {
        ngx_http_hello_loc_conf_t* prev = parent;
        ngx_http_hello_loc_conf_t* conf = child;

        ngx_conf_merge_str_value(conf->hello_string, prev->hello_string, ngx_hello_default_string);
        ngx_conf_merge_value(conf->hello_counter, prev->hello_counter, 0);

        return NGX_CONF_OK;
    }*/

    static char *
    ngx_http_hello_string(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
    {

        ngx_http_hello_loc_conf_t* local_conf;

        local_conf = conf;
        char* rv = ngx_conf_set_str_slot(cf, cmd, conf);

        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "hello_string:%s", local_conf->hello_string.data);

        return rv;
    }

    static char *ngx_http_hello_counter(ngx_conf_t *cf, ngx_command_t *cmd,
        void *conf)
    {
        ngx_http_hello_loc_conf_t* local_conf;

        local_conf = conf;

        char* rv = NULL;

        rv = ngx_conf_set_flag_slot(cf, cmd, conf);

        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "hello_counter:%d", local_conf->hello_counter);
        return rv;    
    }

    static ngx_int_t
    ngx_http_hello_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_hello_handler;

        return NGX_OK;
    }