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    ngx_http_proxy_module 与缓存

    nginx admin 4121浏览 0评论

    概述

    proxy模块是通过ups机制实现了反向代理功能的。该模块非常复杂。
    在这里不会说ups机制，除非引入的非常深入。其余的均会带过，了解ups机制请看上篇。

    proxy模块通过proxy_cache[_xxx]指令控制proxy缓存。

    • 指令：

    proxy_cache 是否开启缓存，可以为变量，如果是变量则需要配置proxy_cache_path。
    proxy_cache_path 配置缓存的路径，和缓存的策略。
    proxy_cache_convert_head 是否把head请求转成get请求缓存。
    proxy_cache_bypass 有缓存但是不从缓存获取。bypass。

    代码

    • proxy_cache对应的处理函数ngx_http_proxy_cache。
      其作用是是否开启缓存，可以配置变量和常量，如果是变量则该变量的值如果等于proxy_cache_path指令的keys_zone的name，则会走缓存。
      如果是常量，则所有的请求都会走缓存。
    static char *
ngx_http_proxy_cache(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_proxy_loc_conf_t *plcf = conf;

    ngx_str_t                         *value;
    ngx_http_complex_value_t           cv;
    ngx_http_compile_complex_value_t   ccv;

    value = cf->args->elts;

    if (plcf->upstream.cache != NGX_CONF_UNSET) {
        return "is duplicate";
    }

    if (ngx_strcmp(value[1].data, "off") == 0) {
        plcf->upstream.cache = 0;
        return NGX_CONF_OK;
    }

    if (plcf->upstream.store > 0) {
        return "is incompatible with \"proxy_store\"";
    }

    plcf->upstream.cache = 1;

    ngx_memzero(&ccv, sizeof(ngx_http_compile_complex_value_t));

    ccv.cf = cf;
    ccv.value = &value[1];
    ccv.complex_value = &cv;

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

    if (cv.lengths != NULL) {
        // zone  有变量
        plcf->upstream.cache_value = ngx_palloc(cf->pool,
                                             sizeof(ngx_http_complex_value_t));
        if (plcf->upstream.cache_value == NULL) {
            return NGX_CONF_ERROR;
        }

        *plcf->upstream.cache_value = cv;

        return NGX_CONF_OK;
    }

    // zone 有变量
    plcf->upstream.cache_zone = ngx_shared_memory_add(cf, &value[1], 0,
                                                      &ngx_http_proxy_module);
    if (plcf->upstream.cache_zone == NULL) {
        return NGX_CONF_ERROR;
    }

    return NGX_CONF_OK;
}
    • proxy_cache_path 的解析，
    struct ngx_http_file_cache_s {
    ngx_http_file_cache_sh_t        *sh;
    ngx_slab_pool_t                 *shpool;

    ngx_path_t                      *path;

    off_t                            max_size;
    size_t                           bsize;

    time_t                           inactive;

    time_t                           fail_time;

    ngx_uint_t                       files;
    ngx_uint_t                       loader_files;
    ngx_msec_t                       last;
    ngx_msec_t                       loader_sleep;
    ngx_msec_t                       loader_threshold;

    ngx_uint_t                       manager_files;
    ngx_msec_t                       manager_sleep;
    ngx_msec_t                       manager_threshold;

    ngx_shm_zone_t                  *shm_zone;

    ngx_uint_t                       use_temp_path;
                                     /* unsigned use_temp_path:1 */
};


char *
ngx_http_file_cache_set_slot(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    char  *confp = conf;

    off_t                   max_size;
    u_char                 *last, *p;
    time_t                  inactive;
    ssize_t                 size;
    ngx_str_t               s, name, *value;
    ngx_int_t               loader_files, manager_files;
    ngx_msec_t              loader_sleep, manager_sleep, loader_threshold,
                            manager_threshold;
    ngx_uint_t              i, n, use_temp_path;
    ngx_array_t            *caches;
    ngx_http_file_cache_t  *cache, **ce;

    cache = ngx_pcalloc(cf->pool, sizeof(ngx_http_file_cache_t));
    if (cache == NULL) {
        return NGX_CONF_ERROR;
    }

    cache->path = ngx_pcalloc(cf->pool, sizeof(ngx_path_t));
    if (cache->path == NULL) {
        return NGX_CONF_ERROR;
    }

    use_temp_path = 1;

    inactive = 600;

    loader_files = 100;
    loader_sleep = 50;
    loader_threshold = 200;

    manager_files = 100;
    manager_sleep = 50;
    manager_threshold = 200;

    name.len = 0;
    size = 0;
    max_size = NGX_MAX_OFF_T_VALUE;

    value = cf->args->elts;

    cache->path->name = value[1];

    if (cache->path->name.data[cache->path->name.len - 1] == '/') {
        cache->path->name.len--;
    }

    if (ngx_conf_full_name(cf->cycle, &cache->path->name, 0) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    for (i = 2; i < cf->args->nelts; i++) {

        if (ngx_strncmp(value[i].data, "levels=", 7) == 0) {

            p = value[i].data + 7;
            last = value[i].data + value[i].len;

            for (n = 0; n < NGX_MAX_PATH_LEVEL && p < last; n++) {

                if (*p > '0' && *p < '3') {
                    // level[3] 最多3级子目录，每一级子目录长度为1，2。
                    // proxy_cache_path /data/nginx/cache levels=1:2 
                    // 最后保存的目录是：/data/nginx/cache/c/29/
                    cache->path->level[n] = *p++ - '0';
                    cache->path->len += cache->path->level[n] + 1;

                    if (p == last) {
                        break;
                    }

                    if (*p++ == ':' && n < NGX_MAX_PATH_LEVEL - 1 && p < last) {
                        continue;
                    }

                    goto invalid_levels;
                }

                goto invalid_levels;
            }

            // level 小于3级，每级加上分隔符长度为3
            if (cache->path->len < 10 + NGX_MAX_PATH_LEVEL) {
                continue;
            }

        invalid_levels:

            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid \"levels\" \"%V\"", &value[i]);
            return NGX_CONF_ERROR;
        }

        if (ngx_strncmp(value[i].data, "use_temp_path=", 14) == 0) {

            if (ngx_strcmp(&value[i].data[14], "on") == 0) {
                use_temp_path = 1;

            } else if (ngx_strcmp(&value[i].data[14], "off") == 0) {
                use_temp_path = 0;

            } else {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid use_temp_path value \"%V\", "
                                   "it must be \"on\" or \"off\"",
                                   &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "keys_zone=", 10) == 0) {

            name.data = value[i].data + 10;

            p = (u_char *) ngx_strchr(name.data, ':');

            if (p) {
                name.len = p - name.data;

                p++;

                s.len = value[i].data + value[i].len - p;
                s.data = p;

                size = ngx_parse_size(&s);
                if (size > 8191) {
                    continue;
                }
            }

            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "invalid keys zone size \"%V\"", &value[i]);
            return NGX_CONF_ERROR;
        }

        if (ngx_strncmp(value[i].data, "inactive=", 9) == 0) {

            s.len = value[i].len - 9;
            s.data = value[i].data + 9;

            inactive = ngx_parse_time(&s, 1);
            if (inactive == (time_t) NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid inactive value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "max_size=", 9) == 0) {

            s.len = value[i].len - 9;
            s.data = value[i].data + 9;

            max_size = ngx_parse_offset(&s);
            if (max_size < 0) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                                   "invalid max_size value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "loader_files=", 13) == 0) {

            loader_files = ngx_atoi(value[i].data + 13, value[i].len - 13);
            if (loader_files == NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid loader_files value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "loader_sleep=", 13) == 0) {

            s.len = value[i].len - 13;
            s.data = value[i].data + 13;

            loader_sleep = ngx_parse_time(&s, 0);
            if (loader_sleep == (ngx_msec_t) NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid loader_sleep value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "loader_threshold=", 17) == 0) {

            s.len = value[i].len - 17;
            s.data = value[i].data + 17;

            loader_threshold = ngx_parse_time(&s, 0);
            if (loader_threshold == (ngx_msec_t) NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid loader_threshold value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "manager_files=", 14) == 0) {

            manager_files = ngx_atoi(value[i].data + 14, value[i].len - 14);
            if (manager_files == NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid manager_files value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "manager_sleep=", 14) == 0) {

            s.len = value[i].len - 14;
            s.data = value[i].data + 14;

            manager_sleep = ngx_parse_time(&s, 0);
            if (manager_sleep == (ngx_msec_t) NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid manager_sleep value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        if (ngx_strncmp(value[i].data, "manager_threshold=", 18) == 0) {

            s.len = value[i].len - 18;
            s.data = value[i].data + 18;

            manager_threshold = ngx_parse_time(&s, 0);
            if (manager_threshold == (ngx_msec_t) NGX_ERROR) {
                ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid manager_threshold value \"%V\"", &value[i]);
                return NGX_CONF_ERROR;
            }

            continue;
        }

        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "invalid parameter \"%V\"", &value[i]);
        return NGX_CONF_ERROR;
    }

    if (name.len == 0 || size == 0) {
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "\"%V\" must have \"keys_zone\" parameter",
                           &cmd->name);
        return NGX_CONF_ERROR;
    }

    cache->path->manager = ngx_http_file_cache_manager;
    cache->path->loader = ngx_http_file_cache_loader;
    cache->path->data = cache;
    cache->path->conf_file = cf->conf_file->file.name.data;
    cache->path->line = cf->conf_file->line;
    cache->loader_files = loader_files;
    cache->loader_sleep = loader_sleep;
    cache->loader_threshold = loader_threshold;
    cache->manager_files = manager_files;
    cache->manager_sleep = manager_sleep;
    cache->manager_threshold = manager_threshold;
    // 添加到cycle这个结构体的path数组中，由nginx框架统一管理
    if (ngx_add_path(cf, &cache->path) != NGX_OK) {
        return NGX_CONF_ERROR;
    }

    cache->shm_zone = ngx_shared_memory_add(cf, &name, size, cmd->post);
    if (cache->shm_zone == NULL) {
        return NGX_CONF_ERROR;
    }

    if (cache->shm_zone->data) {
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "duplicate zone \"%V\"", &name);
        return NGX_CONF_ERROR;
    }


    cache->shm_zone->init = ngx_http_file_cache_init;
    cache->shm_zone->data = cache;

    cache->use_temp_path = use_temp_path;

    cache->inactive = inactive;
    cache->max_size = max_size;

    caches = (ngx_array_t *) (confp + cmd->offset);

    ce = ngx_array_push(caches);
    if (ce == NULL) {
        return NGX_CONF_ERROR;
    }

    *ce = cache;

    return NGX_CONF_OK;
}
    • proxy_pass 指令解析ngx_http_proxy_pass函数。
    static char *
ngx_http_proxy_pass(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_proxy_loc_conf_t *plcf = conf;

    size_t                      add;
    u_short                     port;
    ngx_str_t                  *value, *url;
    ngx_url_t                   u;
    ngx_uint_t                  n;
    ngx_http_core_loc_conf_t   *clcf;
    ngx_http_script_compile_t   sc;

    if (plcf->upstream.upstream || plcf->proxy_lengths) {
        return "is duplicate";
    }

    clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module);

    clcf->handler = ngx_http_proxy_handler;

    if (clcf->name.data[clcf->name.len - 1] == '/') {
        clcf->auto_redirect = 1;
    }

    value = cf->args->elts;

    url = &value[1];

    n = ngx_http_script_variables_count(url);

    if (n) {

        ngx_memzero(&sc, sizeof(ngx_http_script_compile_t));

        sc.cf = cf;
        sc.source = url;
        sc.lengths = &plcf->proxy_lengths;
        sc.values = &plcf->proxy_values;
        sc.variables = n;
        sc.complete_lengths = 1;
        sc.complete_values = 1;

        if (ngx_http_script_compile(&sc) != NGX_OK) {
            return NGX_CONF_ERROR;
        }

#if (NGX_HTTP_SSL)
        plcf->ssl = 1;
#endif

        return NGX_CONF_OK;
    }

    if (ngx_strncasecmp(url->data, (u_char *) "http://", 7) == 0) {
        add = 7;
        port = 80;

    } else if (ngx_strncasecmp(url->data, (u_char *) "https://", 8) == 0) {

#if (NGX_HTTP_SSL)
        plcf->ssl = 1;

        add = 8;
        port = 443;
#else
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                           "https protocol requires SSL support");
        return NGX_CONF_ERROR;
#endif

    } else {
        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "invalid URL prefix");
        return NGX_CONF_ERROR;
    }

    ngx_memzero(&u, sizeof(ngx_url_t));

    u.url.len = url->len - add;
    u.url.data = url->data + add;
    u.default_port = port;
    u.uri_part = 1;
    u.no_resolve = 1;

    plcf->upstream.upstream = ngx_http_upstream_add(cf, &u, 0);
    if (plcf->upstream.upstream == NULL) {
        return NGX_CONF_ERROR;
    }

    plcf->vars.schema.len = add;
    plcf->vars.schema.data = url->data;
    plcf->vars.key_start = plcf->vars.schema;

    ngx_http_proxy_set_vars(&u, &plcf->vars);

    plcf->location = clcf->name;

    if (clcf->named
#if (NGX_PCRE)
        || clcf->regex
#endif
        || clcf->noname)
    {
        if (plcf->vars.uri.len) {
            ngx_conf_log_error(NGX_LOG_EMERG, cf, 0,
                               "\"proxy_pass\" cannot have URI part in "
                               "location given by regular expression, "
                               "or inside named location, "
                               "or inside \"if\" statement, "
                               "or inside \"limit_except\" block");
            return NGX_CONF_ERROR;
        }

        plcf->location.len = 0;
    }

    plcf->url = *url;

    return NGX_CONF_OK;
}

    执行请求的时候会调用ngx_http_proxy_handler函数。

    struct ngx_http_upstream_s {
    ngx_http_upstream_handler_pt     read_event_handler;
    ngx_http_upstream_handler_pt     write_event_handler;

    ngx_peer_connection_t            peer;

    ngx_event_pipe_t                *pipe;

    ngx_chain_t                     *request_bufs;

    ngx_output_chain_ctx_t           output;
    ngx_chain_writer_ctx_t           writer;

    ngx_http_upstream_conf_t        *conf;
    ngx_http_upstream_srv_conf_t    *upstream;
#if (NGX_HTTP_CACHE)
    ngx_array_t                     *caches;
#endif

    ngx_http_upstream_headers_in_t   headers_in;

    ngx_http_upstream_resolved_t    *resolved;

    ngx_buf_t                        from_client;

    ngx_buf_t                        buffer;
    off_t                            length;

    ngx_chain_t                     *out_bufs;
    ngx_chain_t                     *busy_bufs;
    ngx_chain_t                     *free_bufs;

    ngx_int_t                      (*input_filter_init)(void *data);
    ngx_int_t                      (*input_filter)(void *data, ssize_t bytes);
    void                            *input_filter_ctx;

#if (NGX_HTTP_CACHE)
    // proxy 模块配置为ngx_http_proxy_create_key
    ngx_int_t                      (*create_key)(ngx_http_request_t *r);
#endif
    ngx_int_t                      (*create_request)(ngx_http_request_t *r);
    ngx_int_t                      (*reinit_request)(ngx_http_request_t *r);
    ngx_int_t                      (*process_header)(ngx_http_request_t *r);
    void                           (*abort_request)(ngx_http_request_t *r);
    void                           (*finalize_request)(ngx_http_request_t *r,
                                         ngx_int_t rc);
    ngx_int_t                      (*rewrite_redirect)(ngx_http_request_t *r,
                                         ngx_table_elt_t *h, size_t prefix);
    ngx_int_t                      (*rewrite_cookie)(ngx_http_request_t *r,
                                         ngx_table_elt_t *h);

    ngx_msec_t                       timeout;

    ngx_http_upstream_state_t       *state;

    ngx_str_t                        method;
    ngx_str_t                        schema;
    ngx_str_t                        uri;

#if (NGX_HTTP_SSL || NGX_COMPAT)
    ngx_str_t                        ssl_name;
#endif

    ngx_http_cleanup_pt             *cleanup;

    unsigned                         store:1;
    unsigned                         cacheable:1;
    unsigned                         accel:1;
    unsigned                         ssl:1;
#if (NGX_HTTP_CACHE)
    unsigned                         cache_status:3;
#endif

    unsigned                         buffering:1;
    unsigned                         keepalive:1;
    unsigned                         upgrade:1;

    unsigned                         request_sent:1;
    unsigned                         request_body_sent:1;
    unsigned                         header_sent:1;
};


struct ngx_peer_connection_s {
    ngx_connection_t                *connection;

    struct sockaddr                 *sockaddr;
    socklen_t                        socklen;
    ngx_str_t                       *name;

    ngx_uint_t                       tries;
    ngx_msec_t                       start_time;

    ngx_event_get_peer_pt            get;
    ngx_event_free_peer_pt           free;
    ngx_event_notify_peer_pt         notify;
    void                            *data;

#if (NGX_SSL || NGX_COMPAT)
    ngx_event_set_peer_session_pt    set_session;
    ngx_event_save_peer_session_pt   save_session;
#endif

    ngx_addr_t                      *local;

    int                              type;
    int                              rcvbuf;

    // 赋值给原请求的log
    ngx_log_t                       *log;

    unsigned                         cached:1;
    unsigned                         transparent:1;

                                     /* ngx_connection_log_error_e */
    unsigned                         log_error:2;

    NGX_COMPAT_BEGIN(2)
    NGX_COMPAT_END
};

struct ngx_event_pipe_s {
    ngx_connection_t  *upstream;
    ngx_connection_t  *downstream;

    ngx_chain_t       *free_raw_bufs;
    ngx_chain_t       *in;
    ngx_chain_t      **last_in;

    ngx_chain_t       *writing;

    ngx_chain_t       *out;
    ngx_chain_t       *free;
    ngx_chain_t       *busy;

    /*
     * the input filter i.e. that moves HTTP/1.1 chunks
     * from the raw bufs to an incoming chain
     */

    ngx_event_pipe_input_filter_pt    input_filter;
    void                             *input_ctx;

    ngx_event_pipe_output_filter_pt   output_filter;
    void                             *output_ctx;

#if (NGX_THREADS || NGX_COMPAT)
    ngx_int_t                       (*thread_handler)(ngx_thread_task_t *task,
                                                      ngx_file_t *file);
    void                             *thread_ctx;
    ngx_thread_task_t                *thread_task;
#endif

    unsigned           read:1;
    unsigned           cacheable:1;
    unsigned           single_buf:1;
    unsigned           free_bufs:1;
    unsigned           upstream_done:1;
    unsigned           upstream_error:1;
    unsigned           upstream_eof:1;
    unsigned           upstream_blocked:1;
    unsigned           downstream_done:1;
    unsigned           downstream_error:1;
    unsigned           cyclic_temp_file:1;
    unsigned           aio:1;

    ngx_int_t          allocated;
    ngx_bufs_t         bufs;
    ngx_buf_tag_t      tag;

    ssize_t            busy_size;

    off_t              read_length;
    off_t              length;

    off_t              max_temp_file_size;
    ssize_t            temp_file_write_size;

    ngx_msec_t         read_timeout;
    ngx_msec_t         send_timeout;
    ssize_t            send_lowat;

    ngx_pool_t        *pool;
    ngx_log_t         *log;

    ngx_chain_t       *preread_bufs;
    size_t             preread_size;
    ngx_buf_t         *buf_to_file;

    size_t             limit_rate;
    time_t             start_sec;

    ngx_temp_file_t   *temp_file;

    /* STUB */ int     num;
};



typedef struct {
    ngx_list_t                       headers;

    ngx_uint_t                       status_n;
    ngx_str_t                        status_line;

    ngx_table_elt_t                 *status;
    ngx_table_elt_t                 *date;
    ngx_table_elt_t                 *server;
    ngx_table_elt_t                 *connection;

    ngx_table_elt_t                 *expires;
    ngx_table_elt_t                 *etag;
    ngx_table_elt_t                 *x_accel_expires;
    ngx_table_elt_t                 *x_accel_redirect;
    ngx_table_elt_t                 *x_accel_limit_rate;

    ngx_table_elt_t                 *content_type;
    ngx_table_elt_t                 *content_length;

    ngx_table_elt_t                 *last_modified;
    ngx_table_elt_t                 *location;
    ngx_table_elt_t                 *accept_ranges;
    ngx_table_elt_t                 *www_authenticate;
    ngx_table_elt_t                 *transfer_encoding;
    ngx_table_elt_t                 *vary;

#if (NGX_HTTP_GZIP)
    ngx_table_elt_t                 *content_encoding;
#endif

    ngx_array_t                      cache_control;
    ngx_array_t                      cookies;

    // body 长度
    off_t                            content_length_n;
    // 最后修改时间（http 缓存使用）
    time_t                           last_modified_time;

    unsigned                         connection_close:1;
    unsigned                         chunked:1;
} ngx_http_upstream_headers_in_t;

    缓存

    static ngx_int_t
ngx_http_upstream_cache(ngx_http_request_t *r, ngx_http_upstream_t *u)
{
    ngx_int_t               rc;
    ngx_http_cache_t       *c;
    ngx_http_file_cache_t  *cache;

    c = r->cache;

    if (c == NULL) {
        // 是否是定义的缓存的方法
        if (!(r->method & u->conf->cache_methods)) {
            return NGX_DECLINED;
        }

        // 请求是否要缓存，如果返回NGX_OK 则cache返回要缓存的目录和参数
        rc = ngx_http_upstream_cache_get(r, u, &cache);

        if (rc != NGX_OK) {
            return rc;
        }

        if (r->method == NGX_HTTP_HEAD && u->conf->cache_convert_head) {
            u->method = ngx_http_core_get_method;
        }

        if (ngx_http_file_cache_new(r) != NGX_OK) {
            return NGX_ERROR;
        }

        if (u->create_key(r) != NGX_OK) {
            return NGX_ERROR;
        }

        /* TODO: add keys */

        ngx_http_file_cache_create_key(r);

        if (r->cache->header_start + 256 >= u->conf->buffer_size) {
            ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                          "%V_buffer_size %uz is not enough for cache key, "
                          "it should be increased to at least %uz",
                          &u->conf->module, u->conf->buffer_size,
                          ngx_align(r->cache->header_start + 256, 1024));

            r->cache = NULL;
            return NGX_DECLINED;
        }

        u->cacheable = 1;

        c = r->cache;

        c->body_start = u->conf->buffer_size;
        c->min_uses = u->conf->cache_min_uses;
        c->file_cache = cache;

        switch (ngx_http_test_predicates(r, u->conf->cache_bypass)) {

        case NGX_ERROR:
            return NGX_ERROR;

        case NGX_DECLINED:
            u->cache_status = NGX_HTTP_CACHE_BYPASS;
            return NGX_DECLINED;

        default: /* NGX_OK */
            break;
        }

        c->lock = u->conf->cache_lock;
        c->lock_timeout = u->conf->cache_lock_timeout;
        c->lock_age = u->conf->cache_lock_age;

        u->cache_status = NGX_HTTP_CACHE_MISS;
    }
    // 打开缓存文件
    rc = ngx_http_file_cache_open(r);

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http upstream cache: %i", rc);

    switch (rc) {

    case NGX_HTTP_CACHE_STALE:

        if (((u->conf->cache_use_stale & NGX_HTTP_UPSTREAM_FT_UPDATING)
             || c->stale_updating) && !r->background
            && u->conf->cache_background_update)
        {
            r->cache->background = 1;
            u->cache_status = rc;
            rc = NGX_OK;
        }

        break;

    case NGX_HTTP_CACHE_UPDATING:

        if (((u->conf->cache_use_stale & NGX_HTTP_UPSTREAM_FT_UPDATING)
             || c->stale_updating) && !r->background)
        {
            u->cache_status = rc;
            rc = NGX_OK;

        } else {
            rc = NGX_HTTP_CACHE_STALE;
        }

        break;

    case NGX_OK:
        u->cache_status = NGX_HTTP_CACHE_HIT;
    }

    switch (rc) {

    case NGX_OK:

        return NGX_OK;

    case NGX_HTTP_CACHE_STALE:

        c->valid_sec = 0;
        c->updating_sec = 0;
        c->error_sec = 0;

        u->buffer.start = NULL;
        u->cache_status = NGX_HTTP_CACHE_EXPIRED;

        break;

    case NGX_DECLINED:

        if ((size_t) (u->buffer.end - u->buffer.start) < u->conf->buffer_size) {
            u->buffer.start = NULL;

        } else {
            u->buffer.pos = u->buffer.start + c->header_start;
            u->buffer.last = u->buffer.pos;
        }

        break;

    case NGX_HTTP_CACHE_SCARCE:

        u->cacheable = 0;

        break;

    case NGX_AGAIN:

        return NGX_BUSY;

    case NGX_ERROR:

        return NGX_ERROR;

    default:

        /* cached NGX_HTTP_BAD_GATEWAY, NGX_HTTP_GATEWAY_TIME_OUT, etc. */

        u->cache_status = NGX_HTTP_CACHE_HIT;

        return rc;
    }

    if (ngx_http_upstream_cache_check_range(r, u) == NGX_DECLINED) {
        u->cacheable = 0;
    }

    r->cached = 0;

    return NGX_DECLINED;
}

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