Nginx的mirror模块详解

1.相关指令

Syntax:	mirror uri | off;
Default:	
mirror off;
Context:	http, server, location

Syntax:	mirror_request_body on | off;
Default:	
mirror_request_body on;
Context:	http, server, location

2.配置解析函数

首先看下指令mirror的配置解析函数ngx_http_mirror的实现

static char *
ngx_http_mirror(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_mirror_loc_conf_t *mlcf = conf;

    ngx_str_t  *value, *s;

    value = cf->args->elts;
    //判断参数是否为off
    if (ngx_strcmp(value[1].data, "off") == 0) {
        if (mlcf->mirror != NGX_CONF_UNSET_PTR) {
            return "is duplicate";
        }

        mlcf->mirror = NULL;
        return NGX_CONF_OK;
    }

    if (mlcf->mirror == NULL) {
        return "is duplicate";
    }
    // 构造数组mlcf->mirror
    if (mlcf->mirror == NGX_CONF_UNSET_PTR) {
        mlcf->mirror = ngx_array_create(cf->pool, 4, sizeof(ngx_str_t));
        if (mlcf->mirror == NULL) {
            return NGX_CONF_ERROR;
        }
    }
    // push一个数组元素，用于保存mirror配置
    s = ngx_array_push(mlcf->mirror);
    if (s == NULL) {
        return NGX_CONF_ERROR;
    }
    // 保存参数，也就是url
    *s = value[1];

    return NGX_CONF_OK;
}

接下来看看handler函数ngx_http_mirror_handler的实现

static ngx_int_t
ngx_http_mirror_handler(ngx_http_request_t *r)
{
    ngx_int_t                    rc;
    ngx_http_mirror_ctx_t       *ctx;
    ngx_http_mirror_loc_conf_t  *mlcf;
    // 子请求，直接返回
    if (r != r->main) {
        return NGX_DECLINED;
    }
    // 获取location级别的配置
    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_mirror_module);
    // 没有配置mirror，直接返回
    if (mlcf->mirror == NULL) {
        return NGX_DECLINED;
    }

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0, "mirror handler");
    // 处理请求body
    if (mlcf->request_body) {
        ctx = ngx_http_get_module_ctx(r, ngx_http_mirror_module);

        if (ctx) {
            return ctx->status;
        }
        // 申请ctx内存
        ctx = ngx_pcalloc(r->pool, sizeof(ngx_http_mirror_ctx_t));
        if (ctx == NULL) {
            return NGX_ERROR;
        }

        ctx->status = NGX_DONE;
        // 设置ctx
        ngx_http_set_ctx(r, ctx, ngx_http_mirror_module);
        // 读request_body
        rc = ngx_http_read_client_request_body(r, ngx_http_mirror_body_handler);
        if (rc >= NGX_HTTP_SPECIAL_RESPONSE) {
            return rc;
        }
        // 结束请求
        ngx_http_finalize_request(r, NGX_DONE);
        return NGX_DONE;
    }
    // 调用handler
    return ngx_http_mirror_handler_internal(r);
}

接下来看看ngx_http_mirror_body_handler处理逻辑

static void
ngx_http_mirror_body_handler(ngx_http_request_t *r)
{
    ngx_http_mirror_ctx_t  *ctx;
    // get ctx
    ctx = ngx_http_get_module_ctx(r, ngx_http_mirror_module);
    //调用internal
    ctx->status = ngx_http_mirror_handler_internal(r);

    r->preserve_body = 1;
    // 重新执行各个阶段
    r->write_event_handler = ngx_http_core_run_phases;
    ngx_http_core_run_phases(r);
}

接下来看下ngx_http_mirror_init的处理逻辑

static ngx_int_t
ngx_http_mirror_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);
    // precontent阶段，push出一个元素，用于保存handler
    h = ngx_array_push(&cmcf->phases[NGX_HTTP_PRECONTENT_PHASE].handlers);
    if (h == NULL) {
        return NGX_ERROR;
    }
    // handler赋值
    *h = ngx_http_mirror_handler;

    return NGX_OK;
}

接下来看看ngx_http_mirror_handler_internal实现，主要是遍历所有mirror指令，创建子请求

static ngx_int_t
ngx_http_mirror_handler_internal(ngx_http_request_t *r)
{
    ngx_str_t                   *name;
    ngx_uint_t                   i;
    ngx_http_request_t          *sr;
    ngx_http_mirror_loc_conf_t  *mlcf;

    mlcf = ngx_http_get_module_loc_conf(r, ngx_http_mirror_module);

    name = mlcf->mirror->elts;
    // 遍历location下的mirror指令
    for (i = 0; i < mlcf->mirror->nelts; i++) {
        //创建子请求
        if (ngx_http_subrequest(r, &name[i], &r->args, &sr, NULL,
                                NGX_HTTP_SUBREQUEST_BACKGROUND)
            != NGX_OK)
        {
            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        sr->header_only = 1;
        sr->method = r->method;
        sr->method_name = r->method_name;
    }

    return NGX_DECLINED;
}

以上就是mirror模块主要功能