Nginx的header_filter模块

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1.相关指令

header_filter模块主要有以下几个指令

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Syntax:	add_header name value [always];
Default:	—

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Context:	http, server, location, if in location
Syntax:	add_trailer name value [always];
Default:	—
Context:	http, server, location, if in location
This directive appeared in version 1.13.2.
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Syntax:	expires [modified] time;
expires epoch | max | off;
Default:	
expires off;
Context:	http, server, location, if in location

配置示例

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expires    24h;
expires    modified +24h;
expires    @24h;
expires    0;
expires    -1;
expires    epoch;
expires    $expires;
add_header Cache-Control private;

2. 源码解析

2.1 配置解析函数

  1. 首先来看下add_header指令解析函数
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    static char *
    ngx_http_headers_add(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
    {
        ngx_http_headers_conf_t *hcf = conf;

        ngx_str_t                          *value;
        ngx_uint_t                          i;
        ngx_array_t                       **headers;
        ngx_http_header_val_t              *hv;
        ngx_http_set_header_t              *set;
        ngx_http_compile_complex_value_t    ccv;

        value = cf->args->elts;

        // 取到数组指针
        headers = (ngx_array_t **) ((char *) hcf + cmd->offset);

        if (*headers == NULL) {
            *headers = ngx_array_create(cf->pool, 1,
                                        sizeof(ngx_http_header_val_t));
            if (*headers == NULL) {
                return NGX_CONF_ERROR;
            }
        }

        //从数组中push一个元素
        hv = ngx_array_push(*headers);
        if (hv == NULL) {
            return NGX_CONF_ERROR;
        }

        // 取配置header的key
        hv->key = value[1];
        hv->handler = NULL;
        hv->offset = 0;
        hv->always = 0;

        if (headers == &hcf->headers) {
            hv->handler = ngx_http_add_header;

            set = ngx_http_set_headers;
            for (i = 0; set[i].name.len; i++) {
                if (ngx_strcasecmp(value[1].data, set[i].name.data) != 0) {
                    continue;
                }

                hv->offset = set[i].offset;
                hv->handler = set[i].handler;

                break;
            }
        }

        if (value[2].len == 0) {
            ngx_memzero(&hv->value, sizeof(ngx_http_complex_value_t));

        } else {
            ngx_memzero(&ccv, sizeof(ngx_http_compile_complex_value_t));

            ccv.cf = cf;
            ccv.value = &value[2];
            ccv.complex_value = &hv->value;

            if (ngx_http_compile_complex_value(&ccv) != NGX_OK) {
                return NGX_CONF_ERROR;
            }
        }

        if (cf->args->nelts == 3) {
            return NGX_CONF_OK;
        }

        if (ngx_strcmp(value[3].data, "always") != 0) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid parameter \"%V\"", &value[3]);
            return NGX_CONF_ERROR;
        }

        hv->always = 1;

        return NGX_CONF_OK;
    }

  1. 接下来看下expires指令解析函数
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    static char *
    ngx_http_headers_expires(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
    {
        ngx_http_headers_conf_t *hcf = conf;

        char                              *err;
        ngx_str_t                         *value;
        ngx_int_t                          rc;
        ngx_uint_t                         n;
        ngx_http_complex_value_t           cv;
        ngx_http_compile_complex_value_t   ccv;

        // 判断是否已经设置过该指令
        if (hcf->expires != NGX_HTTP_EXPIRES_UNSET) {
            return "is duplicate";
        }

        value = cf->args->elts;

        //判断指令后的参数
        if (cf->args->nelts == 2) {

            hcf->expires = NGX_HTTP_EXPIRES_ACCESS;

            n = 1;

        } else { /* cf->args->nelts == 3 */

            if (ngx_strcmp(value[1].data, "modified") != 0) {
                return "invalid value";
            }

            hcf->expires = NGX_HTTP_EXPIRES_MODIFIED;

            n = 2;
        }

        // 准备变量
        ngx_memzero(&ccv, sizeof(ngx_http_compile_complex_value_t));

        ccv.cf = cf;
        ccv.value = &value[n];
        ccv.complex_value = &cv;

        //编译变量
        if (ngx_http_compile_complex_value(&ccv) != NGX_OK) {
            return NGX_CONF_ERROR;
        }

        if (cv.lengths != NULL) {

            hcf->expires_value = ngx_palloc(cf->pool,
                                            sizeof(ngx_http_complex_value_t));
            if (hcf->expires_value == NULL) {
                return NGX_CONF_ERROR;
            }

            *hcf->expires_value = cv;

            return NGX_CONF_OK;
        }

        rc = ngx_http_parse_expires(&value[n], &hcf->expires, &hcf->expires_time,
                                    &err);
        if (rc != NGX_OK) {
            return err;
        }

        return NGX_CONF_OK;
    }

2.2 filter函数

2.2.1 headers_filter函数

首先看下ngx_http_headers_filter函数实现

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static ngx_int_t
ngx_http_headers_filter(ngx_http_request_t *r)
{
    ngx_str_t                 value;
    ngx_uint_t                i, safe_status;
    ngx_http_header_val_t    *h;
    ngx_http_headers_conf_t  *conf;

    // 子请求不做处理，直接返回
    if (r != r->main) {
        return ngx_http_next_header_filter(r);
    }

    // 获取location级别配置
    conf = ngx_http_get_module_loc_conf(r, ngx_http_headers_filter_module);

    if (conf->expires == NGX_HTTP_EXPIRES_OFF
        && conf->headers == NULL
        && conf->trailers == NULL)
    {
        return ngx_http_next_header_filter(r);
    }

    switch (r->headers_out.status) {

    case NGX_HTTP_OK:
    case NGX_HTTP_CREATED:
    case NGX_HTTP_NO_CONTENT:
    case NGX_HTTP_PARTIAL_CONTENT:
    case NGX_HTTP_MOVED_PERMANENTLY:
    case NGX_HTTP_MOVED_TEMPORARILY:
    case NGX_HTTP_SEE_OTHER:
    case NGX_HTTP_NOT_MODIFIED:
    case NGX_HTTP_TEMPORARY_REDIRECT:
    case NGX_HTTP_PERMANENT_REDIRECT:
        safe_status = 1;
        break;

    default:
        safe_status = 0;
        break;
    }

    if (conf->expires != NGX_HTTP_EXPIRES_OFF && safe_status) {
        if (ngx_http_set_expires(r, conf) != NGX_OK) {
            return NGX_ERROR;
        }
    }

    if (conf->headers) {
        h = conf->headers->elts;
        for (i = 0; i < conf->headers->nelts; i++) {

            if (!safe_status && !h[i].always) {
                continue;
            }

            if (ngx_http_complex_value(r, &h[i].value, &value) != NGX_OK) {
                return NGX_ERROR;
            }

            if (h[i].handler(r, &h[i], &value) != NGX_OK) {
                return NGX_ERROR;
            }
        }
    }

    if (conf->trailers) {
        h = conf->trailers->elts;
        for (i = 0; i < conf->trailers->nelts; i++) {

            if (!safe_status && !h[i].always) {
                continue;
            }

            r->expect_trailers = 1;
            break;
        }
    }

    return ngx_http_next_header_filter(r);
}

2.2.2 ngx_http_trailers_filter函数

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static ngx_int_t
ngx_http_trailers_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
    ngx_str_t                 value;
    ngx_uint_t                i, safe_status;
    ngx_chain_t              *cl;
    ngx_table_elt_t          *t;
    ngx_http_header_val_t    *h;
    ngx_http_headers_conf_t  *conf;

    //获取location级别配置
    conf = ngx_http_get_module_loc_conf(r, ngx_http_headers_filter_module);

    // 如果满足如下条件，则跳过本filter
    if (in == NULL
        || conf->trailers == NULL
        || !r->expect_trailers
        || r->header_only)
    {
        return ngx_http_next_body_filter(r, in);
    }

    // 找到最后一个buf
    for (cl = in; cl; cl = cl->next) {
        if (cl->buf->last_buf) {
            break;
        }
    }

    // 如果cl为null，则跳过本filter
    if (cl == NULL) {
        return ngx_http_next_body_filter(r, in);
    }

    // 根据响应码做选择
    switch (r->headers_out.status) {

    case NGX_HTTP_OK:
    case NGX_HTTP_CREATED:
    case NGX_HTTP_NO_CONTENT:
    case NGX_HTTP_PARTIAL_CONTENT:
    case NGX_HTTP_MOVED_PERMANENTLY:
    case NGX_HTTP_MOVED_TEMPORARILY:
    case NGX_HTTP_SEE_OTHER:
    case NGX_HTTP_NOT_MODIFIED:
    case NGX_HTTP_TEMPORARY_REDIRECT:
    case NGX_HTTP_PERMANENT_REDIRECT:
        safe_status = 1;
        break;

    default:
        safe_status = 0;
        break;
    }

    // 遍历配置的所有trailer
    h = conf->trailers->elts;
    for (i = 0; i < conf->trailers->nelts; i++) {

        if (!safe_status && !h[i].always) {
            continue;
        }

        if (ngx_http_complex_value(r, &h[i].value, &value) != NGX_OK) {
            return NGX_ERROR;
        }

        if (value.len) {
            t = ngx_list_push(&r->headers_out.trailers);
            if (t == NULL) {
                return NGX_ERROR;
            }

            t->key = h[i].key;
            t->value = value;
            t->hash = 1;
        }
    }

    return ngx_http_next_body_filter(r, in);
}

weeweetanBackend Developer

初级程序猿，之前主要涉及数据备份相关领域，现在研究CDN方向。业余时间也喜欢锻炼下，目前参过一次半程马拉松，四次全程马拉松，半马最好成绩99分钟，全马最好成绩3小时47分钟。