【Nginx】开发一个HTTP过滤模块

static ngx_command_t  ngx_http_myfilter_commands[] =
{
    {
        ngx_string("myfilter"),
        NGX_HTTP_MAIN_CONF | NGX_HTTP_SRV_CONF | NGX_HTTP_LOC_CONF | NGX_HTTP_LMT_CONF | NGX_CONF_FLAG,
        ngx_conf_set_flag_slot,     // 自带的解析函数
        NGX_HTTP_LOC_CONF_OFFSET,
        offsetof(ngx_http_myfilter_conf_t, enable),
        NULL
    },
    ngx_null_command
};

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

 // 配置项结构体
typedef struct {
	ngx_flag_t enable;
} ngx_http_myfilter_conf_t;

// 上下文结构体
typedef struct {
	ngx_int_t add_prefix;
} ngx_http_myfilter_ctx_t;

ngx_module_t ngx_http_myfilter_module;	// 前向声明

static ngx_http_output_header_filter_pt ngx_http_next_header_filter;
static ngx_http_output_body_filter_pt ngx_http_next_body_filter;

// 需要添加的前缀内容
static ngx_str_t filter_prefix = ngx_string("~~~~~~~This is a prefix~~~~~~~\n");

static ngx_int_t ngx_http_myfilter_header_filter(ngx_http_request_t *r)
{
	ngx_http_myfilter_ctx_t  *ctx;
	ngx_http_myfilter_conf_t *conf;

	if (r->headers_out.status != NGX_HTTP_OK)
		return ngx_http_next_header_filter(r);	// 交由下一个过滤模块处理

	ctx = ngx_http_get_module_ctx(r, ngx_http_myfilter_module);
	if (ctx)
		return ngx_http_next_header_filter(r);	// 上下文已存在，不再处理

	conf = ngx_http_get_module_loc_conf(r, ngx_http_myfilter_module);	// 获取配置项结构体
	if (conf->enable == 0)
		return ngx_http_next_header_filter(r);	// 此过滤模块未打开

	ctx = ngx_pcalloc(r->pool, sizeof(ngx_http_myfilter_ctx_t));	// 创建上下文结构体
	if (ctx == NULL)
		return NGX_ERROR;

	ctx->add_prefix = 0;	// 0表示不需要添加前缀
	ngx_http_set_ctx(r, ctx, ngx_http_myfilter_module);

	// 只处理Content-Type为text/plain类型的HTTP请求
	if (r->headers_out.content_type.len >= sizeof("text/plain")-1 &&
		ngx_strncasecmp(r->headers_out.content_type.data, (u_char *)"text/plain", sizeof("text/plain")-1) == 0)
	{
			ctx->add_prefix = 1;	// 1表示需要加入前缀
			if (r->headers_out.content_length_n > 0)
				r->headers_out.content_length_n += filter_prefix.len;	// 响应包体长度增加
	}

	return ngx_http_next_header_filter(r);
}

static ngx_int_t ngx_http_myfilter_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
	ngx_http_myfilter_ctx_t  *ctx;

	ctx = ngx_http_get_module_ctx(r, ngx_http_myfilter_module);	// 获取上下文结构体
	if (ctx == NULL || ctx->add_prefix != 1)
		return ngx_http_next_body_filter(r, in);	// 不添加前缀

	ctx->add_prefix = 2;	// 2表示已添加前缀

	ngx_buf_t *b = ngx_create_temp_buf(r->pool, filter_prefix.len);
	b->start = b->pos = filter_prefix.data;
	b->last = b->pos + filter_prefix.len;

	// 链入待发送包体头部
	ngx_chain_t *cl = ngx_alloc_chain_link(r->pool);
	cl->buf = b;
	cl->next = in;

	return ngx_http_next_body_filter(r, cl);	// 跳到下一个过滤模块
}

// 初始化HTTP过滤模块
static ngx_int_t ngx_http_myfilter_init(ngx_conf_t *cf)
{
	ngx_http_next_header_filter = ngx_http_top_header_filter;	
	ngx_http_top_header_filter = ngx_http_myfilter_header_filter;

	ngx_http_next_body_filter = ngx_http_top_body_filter;
	ngx_http_top_body_filter = ngx_http_myfilter_body_filter;

	return NGX_OK;
}

// 创建存储配置项的结构体
static void* ngx_http_myfilter_create_conf(ngx_conf_t *cf)
{
	ngx_http_myfilter_conf_t *mycf;

	mycf = (ngx_http_myfilter_conf_t *)ngx_pcalloc(cf->pool, sizeof(ngx_http_myfilter_conf_t));
	if (mycf == NULL)
		return NULL;

	mycf->enable = NGX_CONF_UNSET;
	return mycf;
}

// 合并配置项
static char* ngx_http_myfilter_merge_conf(ngx_conf_t *cf, void *parent, void *child)
{
	ngx_http_myfilter_conf_t *prev = (ngx_http_myfilter_conf_t *)parent;
	ngx_http_myfilter_conf_t *conf = (ngx_http_myfilter_conf_t *)child;

	ngx_conf_merge_value(conf->enable, prev->enable, 0);	// 合并函数

	return NGX_CONF_OK;
}

static ngx_command_t ngx_http_myfilter_commands[] = {
    {
        ngx_string("myfilter"),
        NGX_HTTP_MAIN_CONF | NGX_HTTP_SRV_CONF | NGX_HTTP_LOC_CONF | NGX_HTTP_LMT_CONF | NGX_CONF_FLAG,
        ngx_conf_set_flag_slot,
        NGX_HTTP_LOC_CONF_OFFSET,
        offsetof(ngx_http_myfilter_conf_t, enable),
        NULL,
    },
    ngx_null_command
};
 

// HTTP框架初始化时调用的八个函数
static ngx_http_module_t ngx_http_myfilter_module_ctx = {
    NULL,
    ngx_http_myfilter_init,
    NULL,
    NULL,
    NULL,
    NULL,
    ngx_http_myfilter_create_conf,
    ngx_http_myfilter_merge_conf,
};
 
// 定义一个HTTP模块
ngx_module_t ngx_http_myfilter_module = {
    NGX_MODULE_V1,  // 0,0,0,0,0,0,1
    &ngx_http_myfilter_module_ctx,
    ngx_http_myfilter_commands,
    NGX_HTTP_MODULE,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NGX_MODULE_V1_PADDING,  // 0,0,0,0,0,0,0,0,保留字段
};