struct ngx_buf_s {....off_t            file_pos;     // 文件起始位置off_t            file_last;    // 文件结束位置....ngx_file_t      *file;     // 引用的文件....
};

typedef struct ngx_file_s        ngx_file_t;
struct ngx_file_s {ngx_fd_t                   fd;              // 文件描写叙述符ngx_str_t                  name;            // 文件名称ngx_file_info_t            info;            // 文件相关信息，相当于stat结构体off_t                      offset;          // 告诉Nginx处理到文件何处了。一般不使用off_t                      sys_offset;      // 文件偏移量，一般不使用ngx_log_t                 *log;             // 日志对象#if (NGX_HAVE_FILE_AIO)ngx_event_aio_t           *aio;
#endifunsigned                   valid_info:1;    // 未使用unsigned                   directio:1;      // 发送大文件时设为1
};

struct ngx_pool_cleanup_s {ngx_pool_cleanup_pt   handler;  // 运行实际清理工作的回调方法void                 *data;     // 回调方法的參数ngx_pool_cleanup_t   *next;     // 下一个清理对象
};

// 用于告诉HTTP框架，请求结束时调用cln->handler成员函数
ngx_pool_cleanup_t* cln = ngx_pool_cleanup_add(r->pool, sizeof(ngx_pool_cleanup_file_t));
if (cln == NULL)return NGX_ERROR;cln->handler = ngx_pool_cleanup_file;       // ngx_pool_cleanup_file专用于关闭文件句柄ngx_pool_cleanup_file_t  *clnf = cln->data; // cln->data为上述回调函数的參数
clnf->fd = b->file->fd;
clnf->name = b->file->name.data;
clnf->log = r->pool->log;

void
ngx_pool_cleanup_file(void *data)
{ngx_pool_cleanup_file_t  *c = data;ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, c->log, 0, "file cleanup: fd:%d",c->fd);if (ngx_close_file(c->fd) == NGX_FILE_ERROR) {    // 关闭文件描写叙述符ngx_log_error(NGX_LOG_ALERT, c->log, ngx_errno,ngx_close_file_n " \"%s\" failed", c->name);}
}

typedef struct {ngx_fd_t              fd;   // 文件描写叙述符u_char               *name; // 文件名称ngx_log_t            *log;  // 日志对象
} ngx_pool_cleanup_file_t;

• ngx_buf_t.ngx_file_t.df
• ngx_buf_t.ngx_file_t.name
• ngx_buf_t.ngx_file_t.log

#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>static char *ngx_http_mytest(ngx_conf_t *cf, ngx_command_t *cmd, void *conf);static ngx_int_t ngx_http_mytest_handler(ngx_http_request_t *r);static ngx_command_t ngx_http_mytest_commands[] =
{{ngx_string("mytest"),NGX_HTTP_MAIN_CONF | NGX_HTTP_SRV_CONF | NGX_HTTP_LOC_CONF | NGX_HTTP_LMT_CONF | NGX_CONF_NOARGS,ngx_http_mytest,NGX_HTTP_LOC_CONF_OFFSET,0,NULL},ngx_null_command
};static ngx_http_module_t  ngx_http_mytest_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_mytest_module =
{NGX_MODULE_V1,&ngx_http_mytest_module_ctx,           /* module context */ngx_http_mytest_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 char *ngx_http_mytest(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{ngx_http_core_loc_conf_t  *clcf;// 首先找到mytest配置项所属的配置块，clcf貌似是location块内的数据// 结构，事实上不然。它能够是main、srv或者loc级别配置项，也就是说在每一个// http{}和server{}内也都有一个ngx_http_core_loc_conf_t结构体clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);// http框架在处理用户请求进行到NGX_HTTP_CONTENT_PHASE阶段时。假设// 请求的主机域名、URI与mytest配置项所在的配置块相匹配，就将调用我们// 实现的ngx_http_mytest_handler方法处理这个请求clcf->handler = ngx_http_mytest_handler;return NGX_CONF_OK;
}static ngx_int_t ngx_http_mytest_handler(ngx_http_request_t *r)
{// 必须是GET或者HEAD方法，否则返回405 Not Allowedif (!(r->method & (NGX_HTTP_GET | NGX_HTTP_HEAD)))return NGX_HTTP_NOT_ALLOWED;// 丢弃请求中的包体ngx_int_t rc = ngx_http_discard_request_body(r);if (rc != NGX_OK)return rc;ngx_buf_t *b;b = ngx_palloc(r->pool, sizeof(ngx_buf_t));u_char* filename = (u_char*)"/tmp/test.txt";   // 要打开的文件名称b->in_file = 1;     // 设置为1表示缓冲区中发送的是文件// 分配代表文件的结构体空间。file成员表示缓冲区引用的文件b->file = ngx_pcalloc(r->pool, sizeof(ngx_file_t));b->file->fd = ngx_open_file(filename, NGX_FILE_RDONLY | NGX_FILE_NONBLOCK, NGX_FILE_OPEN, 0);b->file->log = r->connection->log;  // 日志对象b->file->name.data = filename;      // name成员表示文件名称称b->file->name.len = sizeof(filename) - 1;if (b->file->fd <= 0)return NGX_HTTP_NOT_FOUND;r->allow_ranges = 1;    //支持断点续传// 获取文件长度，ngx_file_info方法封装了stat系统调用// info成员就表示stat结构体if (ngx_file_info(filename, &b->file->info) == NGX_FILE_ERROR)return NGX_HTTP_INTERNAL_SERVER_ERROR;// 设置缓冲区指向的文件块b->file_pos = 0;                        // 文件起始位置b->file_last = b->file->info.st_size;   // 文件结束为止// 用于告诉HTTP框架。请求结束时调用cln->handler成员函数ngx_pool_cleanup_t* cln = ngx_pool_cleanup_add(r->pool, sizeof(ngx_pool_cleanup_file_t));if (cln == NULL)return NGX_ERROR;cln->handler = ngx_pool_cleanup_file;       // ngx_pool_cleanup_file专用于关闭文件句柄ngx_pool_cleanup_file_t  *clnf = cln->data; // cln->data为上述回调函数的參数clnf->fd = b->file->fd;clnf->name = b->file->name.data;clnf->log = r->pool->log;// 设置返回的Content-Type// 注意，ngx_str_t有一个非常方便的初始化宏// ngx_string，它能够把ngx_str_t的data和len成员都设置好ngx_str_t type = ngx_string("text/plain");//设置返回状态码r->headers_out.status = NGX_HTTP_OK;r->headers_out.content_length_n = b->file->info.st_size;    // 正文长度r->headers_out.content_type = type;// 发送http头部rc = ngx_http_send_header(r);if (rc == NGX_ERROR || rc > NGX_OK || r->header_only)return rc;// 构造发送时的ngx_chain_t结构体ngx_chain_t out;out.buf = b;out.next = NULL;//最后一步发送包体，http框架会调用ngx_http_finalize_request方法return ngx_http_output_filter(r, &out);
}

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