过滤模块 (90%)¶

ngx_http_top_header_filter(r);
ngx_http_top_body_filter(r, in);

ngx_module_t *ngx_modules[] = {
        ...
        &ngx_http_write_filter_module,
        &ngx_http_header_filter_module,
        &ngx_http_chunked_filter_module,
        &ngx_http_range_header_filter_module,
        &ngx_http_gzip_filter_module,
        &ngx_http_postpone_filter_module,
        &ngx_http_ssi_filter_module,
        &ngx_http_charset_filter_module,
        &ngx_http_userid_filter_module,
        &ngx_http_headers_filter_module,
        &ngx_http_copy_filter_module,
        &ngx_http_range_body_filter_module,
        &ngx_http_not_modified_filter_module,
        NULL
};

static ngx_http_output_header_filter_pt  ngx_http_next_header_filter;
static ngx_http_output_body_filter_pt    ngx_http_next_body_filter;

...

ngx_http_next_header_filter = ngx_http_top_header_filter;
ngx_http_top_header_filter = ngx_http_example_header_filter;

ngx_http_next_body_filter = ngx_http_top_body_filter;
ngx_http_top_body_filter = ngx_http_example_body_filter;

ngx_addon_name=ngx_http_example_filter_module
HTTP_AUX_FILTER_MODULES="$HTTP_AUX_FILTER_MODULES ngx_http_example_filter_module"
NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_example_filter_module.c"

typedef struct ngx_chain_s ngx_chain_t;

        struct ngx_chain_s {
                ngx_buf_t    *buf;
                ngx_chain_t  *next;
        };

struct ngx_buf_s {
        u_char          *pos;       /* 当前buffer真实内容的起始位置 */
        u_char          *last;      /* 当前buffer真实内容的结束位置 */
        off_t            file_pos;  /* 在文件中真实内容的起始位置   */
        off_t            file_last; /* 在文件中真实内容的结束位置   */

        u_char          *start;    /* buffer内存的开始分配的位置 */
        u_char          *end;      /* buffer内存的结束分配的位置 */
        ngx_buf_tag_t    tag;      /* buffer属于哪个模块的标志 */
        ngx_file_t      *file;     /* buffer所引用的文件 */

        /* 用来引用替换过后的buffer，以便当所有buffer输出以后，
         * 这个影子buffer可以被释放。
         */
        ngx_buf_t       *shadow;

        /* the buf's content could be changed */
        unsigned         temporary:1;

        /*
         * the buf's content is in a memory cache or in a read only memory
         * and must not be changed
         */
        unsigned         memory:1;

        /* the buf's content is mmap()ed and must not be changed */
        unsigned         mmap:1;

        unsigned         recycled:1; /* 内存可以被输出并回收 */
        unsigned         in_file:1;  /* buffer的内容在文件中 */
        /* 马上全部输出buffer的内容, gzip模块里面用得比较多 */
        unsigned         flush:1;
        /* 基本上是一段输出链的最后一个buffer带的标志，标示可以输出，
         * 有些零长度的buffer也可以置该标志
         */
        unsigned         sync:1;
        /* 所有请求里面最后一块buffer，包含子请求 */
        unsigned         last_buf:1;
        /* 当前请求输出链的最后一块buffer         */
        unsigned         last_in_chain:1;
        /* shadow链里面的最后buffer，可以释放buffer了 */
        unsigned         last_shadow:1;
        /* 是否是暂存文件 */
        unsigned         temp_file:1;

        /* 统计用，表示使用次数 */
        /* STUB */ int   num;
};

ngx_int_t
ngx_http_send_header(ngx_http_request_t *r)
{
        ...

        return ngx_http_top_header_filter(r);
}

ngx_int_t
ngx_http_output_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
    ngx_int_t          rc;
    ngx_connection_t  *c;

    c = r->connection;

    rc = ngx_http_top_body_filter(r, in);

    if (rc == NGX_ERROR) {
        /* NGX_ERROR may be returned by any filter */
        c->error = 1;
    }

    return rc;
}

static int
ngx_http_example_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
        ...

        return ngx_http_next_body_filter(r, in);
}