ngx.shared.DICT.get

原文： ngx.shared.DICT.get

syntax: value, flags = ngx.shared.DICT:get(key)

context: init_by_lua*, set_by_lua*, rewrite_by_lua*, access_by_lua*, content_by_lua*,

         header_filter_by_lua*, body_filter_by_lua*, log_by_lua*, ngx.timer.*,

         balancer_by_lua*, ssl_certificate_by_lua*, ssl_session_fetch_by_lua*,

         ssl_session_store_by_lua*

requires: resty.core.shdict or resty.core

检索 ngx.shared.DICT 共享内存中 key 对应的值。如果 key 不存在或者超时，则返回 nil。

如果发生错误，返回 nil 和错误描述字符串。

在插入字典后，返回的值具有原始数据类型，如 Lua boolean，number，或者 string。

该方法的第一个参数是字典自身，如下：

local cats = ngx.shared.cats

local value, flags = cats.get(cats, "Mary")

或者用如下方法调用：

local cats = ngx.shared.cats

local value, flags = cats:get("Marry")

如果用户标志 flag 为 0（默认），则不返回任何标志值。

get 源码实现如下

local value_type = ffi_new("int[1]")

local user_flags = ffi_new("int[1]")

local num_value = ffi_new("double[1]")

local is_stale = ffi_new("int[1]")

local str_value_buf = ffi_new("unsigned char *[1]")

local errmsg = base.get_errmsg_ptr()

local function shdict_get(zone, key)

    zone = check_zone(zone)

    if key == nil then

        return nil, "nil key"

    end

    if type(key) ~= "string" then

        key = tostring(key)

    end

    local key_len = #key

    if key_len == 0 then

        return nil, "empty key"

    end

    if key_len > 65535 then

        return nil, "key too long"

    end

    local size = get_string_buf_size() -- 4096

    local buf = get_string_buf(size)

    str_value_buf[0] = buf      -- str_value_buf = ffi_new("unsigned char *[1]")

    local value_len = get_size_ptr()

    value_len[0] = size

    local rc = C.ngx_http_lua_ffi_shdict_get(zone, key, key_len, value_type,

                                             str_value_buf, value_len,

                                             num_value, user_flags, 0,

                                             is_stale, errmsg)

    if rc ~= 0 then

        if errmsg[0] then

            return nil, ffi_str(errmsg[0])

        end

        error("failed to get the key")

    end

    local typ = value_type[0]

    if typ == 0 then -- LUA_TNIL

        return nil

    end

    local flags = tonumber(user_flags[0])

    local val

    if typ == 4 then -- LUA_TSTRING

        if str_value_buf[0] ~= buf then

            -- ngx.say("len: ", tonumber(value_len[0]))

            buf = str_value_buf[0]

            val = ffi_str(buf, value_len[0])

            C.free(buf)

        else

            val = ffi_str(buf, value_len[0])

        end

    elseif typ == 3 then -- LUA_TNUMBER

        val = tonumber(num_value[0])

    elseif typ == 1 then -- LUA_TBOOLEAN

        val = (tonumber(buf[0]) ~= 0)

    else

        error("unknown value type: " .. typ)

    end

    if flags ~= 0 then

        return val, flags

    end

    return val

end

get_string_buf_size 和 get_string_buf

这两个函数位于 resty.core.base.lua 文件中:

local ffi = require = 'ffi'

local ffi_new = ffi.new

local str_buf_size = 4096

local str_buf

local size_ptr

local FREE_LIST_REF = 0

local c_buf_type = ffi.typeof("char[?]")

local errmsg 

function _M.get_errmsg_ptr()

    if not errmsg then

        errmsg = ffi_new("char *[1]")

    end

    return errmsg

end

function _M.get_string_buf_size()

    return str_buf_size

end

function _M.get_string_buf(size, must_alloc)

    -- ngx.log(ngx.ERR, "str buf size: ", str_buf_size)

    if size > str_buf_size or must_alloc then

        return ffi_new(c_buf_type, size)

    end

    if not str_buf then

        str_buf = ffi_new(c_buf_type, str_buf_size)

    end

    return str_buf

end

function _M.get_size_ptr()

    if not size_ptr then

        size_ptr = ffi_new("size_t[1]")

    end

    return size_ptr

end

ngx_http_lua_ffi_shdict_get

int

ngx_http_lua_ffi_shdict_get(ngx_shm_zone_t *zone, u_char *key,

    size_t key_len, int *value_type, u_char **str_value_buf,

    size_t *str_value_len, double *num_value, int *user_flags,

    int get_stale, int *is_stale, char **err)

{

    ngx_str_t                    name;

    uint32_t                     hash;

    ngx_int_t                    rc;

    ngx_http_lua_shdict_ctx_t   *ctx;

    ngx_http_lua_shdict_node_t  *sd;

    ngx_str_t                    value;

    if (zone == NULL) {

        return NGX_ERROR;

    }

    *err = NULL;

    ctx = zone->data;

    name = ctx->name;

    hash = ngx_crc32_short(key, key_len);

#if (NGX_DEBUG)

    ngx_log_debug3(NGX_LOG_DEBUG_HTTP, ctx->log, 0,

                   "fetching key \"%*s\" in shared dict \"%V\"", key_len,

                   key, &name);

end

    ngx_shmtx_lock(&ctx->shpool->mutex);

#if 1

    if (!get_stale) {

        /* 删除共享内存中过期的 1~2 个项 */

        ngx_http_lua_shdict_expire(ctx, 1);

    }

end

    rc = ngx_http_lua_shdict_lookup(zone, hash, key, key_len, &sd);

    dd("shdict lookup returns %d", (int) rc);

    if (rc == NGX_DECLINED || (rc == NGX_DONE && !get_stale)) {

        ngx_shmtx_unlock(&ctx->shpool->mutex);

        *value_type = LUA_TNIL;

        return NGX_OK;

    }

    /* rc == NGX_OK || (rc == NGX_DONE && get_stale) */

    *value_type = sd->value_type;

    dd("data: ", sd->data);

    dd("key len: %d", (int) sd->key_len);

    value.data = sd->data + sd->key_len;

    value.len = (size_t) sd->value_len;

    if (*str_value_len < (size_t) value.len) {

        if (*value_type == SHDICT_TBOOLEAN) {

            ngx_shmtx_unlock(&ctx->shpool->mutex);

            return NGX_ERROR;

        }

        if (*value_type == SHDICT_TSTRING) {

            *str_value_buf = malloc(value.len);

            if (*str_value_buf == NULL) {

                ngx_shmtx_unlock(&ctx->shpool->mutex);

                return NGX_ERROR;

            }

        }

    }

    switch (*value_type) {

    case SHDICT_TSTRING:

        *str_value_len = value.len;

        ngx_memcpy(*str_value_buf, value.data, value.len);

        break;

    case SHDCIT_TNUMBER:

        if (value.len != sizeof(double)) {

            ngx_shmtx_unlock(&ctx->shpool->mutex);

            ngx_log_error(NGX_LOG_ERR, ngx_cycle->log, 0,

                          "bad lua number value size found for key %*s "

                          "in shared_dict %V: %z", key_len, key,

                          &name, value.len);

            return NGX_ERROR;

        }

        *str_value_len = value.len;

        ngx_memcpy(num_value, value.data, sizeof(double));

        break;

    case SHDICT_TBOOLEAN:

        if (value.len != sizeof(u_char)) {

            ngx_shmtx_unlock(&ctx->shpool->mutex);

            ngx_log_error(NGX_LOG_ERR, ngx_cycle->log, 0,

                          "bad lua boolean value size found for key %*s "

                          "in shared_dict %V: %z", key_len, key, &name,

                          value.len);

            return NGX_ERROR;

        }

        ngx_memcpy(*str_value_buf, value.data, value.len);

        break;

    case SHDICT_TLIST:

        ngx_shmtx_unlock(&ctx->shpool->mutex);

        *err = "value is a list";

        return NGX_ERROR;

    default:

        ngx_shmtx_unlock(&ctx->shpool->mutex);

        ngx_log_error(NGX_LOG_ERR, ngx_cycle->log, 0,

                      "bad value type found for key %*s in "

                      "shared_dict %V: %d", key_len, key, &name,

                      *value_type);

        return NGX_ERROR;

    }

    *user_flags = sd->user_flags;

    dd("user flags: %d", *user_flags);

    ngx_shmtx_unlock(&ctx->shpool->mutex);

    if (get_stale) {

        /* always return value, flags, stale */

        /* 为 true 表示已经过期了 */

        *is_stale = (rc == NGX_DONE);

        return NGX_OK;

    }

    return NGX_OK;

}

巴特西

ngx.shared.DICT.get 详解

ngx.shared.DICT.get

get 源码实现如下

get_string_buf_size 和 get_string_buf

ngx_http_lua_ffi_shdict_get

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