ngx.ctx ------- **环境:** *init_worker_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.*\* 本 Lua 表可以用来存储基于请求的 Lua 环境数据，其生存周期与当前请求相同 (类似 Nginx 变量)。 参考下面例子， ```nginx location /test { rewrite_by_lua ' ngx.ctx.foo = 76 '; access_by_lua ' ngx.ctx.foo = ngx.ctx.foo + 3 '; content_by_lua ' ngx.say(ngx.ctx.foo) '; } ``` 访问 `GET /test` 输出 ```bash 79 ``` 也就是说，`ngx.ctx.foo` 条目跨越一个请求的 rewrite (重写)，access (访问)，和 content (内容) 各处理阶段保持一致。 每个请求，包括子请求，都有一份自己的 `ngx.ctx` 表。例如： ```nginx location /sub { content_by_lua ' ngx.say("sub pre: ", ngx.ctx.blah) ngx.ctx.blah = 32 ngx.say("sub post: ", ngx.ctx.blah) '; } location /main { content_by_lua ' ngx.ctx.blah = 73 ngx.say("main pre: ", ngx.ctx.blah) local res = ngx.location.capture("/sub") ngx.print(res.body) ngx.say("main post: ", ngx.ctx.blah) '; } ``` 访问 `GET /main` 输出 ```bash main pre: 73 sub pre: nil sub post: 32 main post: 73 ``` 这里，在子请求中修改 `ngx.ctx.blah` 条目并不影响父请求中的同名条目，因为它们各自维护不同版本的 `ngx.ctx.blah`。 内部重定向将摧毁原始请求中的 `ngx.ctx` 数据 (如果有)，新请求将会有一个空白的 `ngx.ctx` 表。例如， ```nginx location /new { content_by_lua ' ngx.say(ngx.ctx.foo) '; } location /orig { content_by_lua ' ngx.ctx.foo = "hello" ngx.exec("/new") '; } ``` 访问 `GET /orig` 将输出 ```bash nil ``` 而不是原始的 `"hello"` 值。 任意数据值，包括 Lua 闭包与嵌套表，都可以被插入这个“魔法”表，也允许注册自定义元方法。 也可以将 `ngx.ctx` 覆盖为一个新 Lua 表，例如， ```lua ngx.ctx = { foo = 32, bar = 54 } ``` 当用在 [init_worker_by_lua*](#init_worker_by_lua) 环境中，这个表与当前 Lua 句柄生命周期相同。 `ngx.ctx` 表查询需要相对昂贵的元方法调用，这比通过用户自己的函数参数直接传递基于请求的数据要慢得多。所以不要为了节约用户函数参数而滥用此 API，因为它可能对性能有明显影响。而且由于元方法“魔法”，不要在用户函数作用域外试图 "local" `ngx.ctx` 表。 > English Source **context:** *init_worker_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.*\* This table can be used to store per-request Lua context data and has a life time identical to the current request (as with the Nginx variables). Consider the following example, ```nginx location /test { rewrite_by_lua ' ngx.ctx.foo = 76 '; access_by_lua ' ngx.ctx.foo = ngx.ctx.foo + 3 '; content_by_lua ' ngx.say(ngx.ctx.foo) '; } ``` Then `GET /test` will yield the output ```bash 79 ``` That is, the `ngx.ctx.foo` entry persists across the rewrite, access, and content phases of a request. Every request, including subrequests, has its own copy of the table. For example: ```nginx location /sub { content_by_lua ' ngx.say("sub pre: ", ngx.ctx.blah) ngx.ctx.blah = 32 ngx.say("sub post: ", ngx.ctx.blah) '; } location /main { content_by_lua ' ngx.ctx.blah = 73 ngx.say("main pre: ", ngx.ctx.blah) local res = ngx.location.capture("/sub") ngx.print(res.body) ngx.say("main post: ", ngx.ctx.blah) '; } ``` Then `GET /main` will give the output ```bash main pre: 73 sub pre: nil sub post: 32 main post: 73 ``` Here, modification of the `ngx.ctx.blah` entry in the subrequest does not affect the one in the parent request. This is because they have two separate versions of `ngx.ctx.blah`. Internal redirection will destroy the original request `ngx.ctx` data (if any) and the new request will have an empty `ngx.ctx` table. For instance, ```nginx location /new { content_by_lua ' ngx.say(ngx.ctx.foo) '; } location /orig { content_by_lua ' ngx.ctx.foo = "hello" ngx.exec("/new") '; } ``` Then `GET /orig` will give ```bash nil ``` rather than the original `"hello"` value. Arbitrary data values, including Lua closures and nested tables, can be inserted into this "magic" table. It also allows the registration of custom meta methods. Overriding `ngx.ctx` with a new Lua table is also supported, for example, ```lua ngx.ctx = { foo = 32, bar = 54 } ``` When being used in the context of [init_worker_by_lua*](#init_worker_by_lua), this table just has the same lifetime of the current Lua handler. The `ngx.ctx` lookup requires relatively expensive metamethod calls and it is much slower than explicitly passing per-request data along by your own function arguments. So do not abuse this API for saving your own function arguments because it usually has quite some performance impact. And because of the metamethod magic, never "local" the `ngx.ctx` table outside your function scope. [返回目录](#nginx-api-for-lua)