Nginx The configuration file of is a micro programming language , A lot of real world Nginx The configuration file is actually a small program . Of course , Is it right? “ Turing is complete ” For the time being , At least according to my observation , It's designed by Perl and Bourne Shell These two languages have a great influence . At this point , comparison Apache and Lighttpd Others, such as Web Server configuration notation , I can't help saying it's Nginx It's a big feature of . Since it's a programming language , In general, it is necessary to “ Variable ” This kind of thing （ Of course ,Haskell Except for such strange functional languages ）.

be familiar with Perl、Bourne Shell、C/C++ And so on imperative programming language's friend certainly knew , Variables are simply stored “ value ” The container of . And so called “ value ”, In many programming languages , It can be either  3.14  Something like that , It can also be  hello world  Such a string , It can even be like arrays 、 Hash table is a complex data structure . However , stay Nginx Configuration in progress , Variables can hold only one type of value , Because there is only one type of value , That's the string .

Like our  nginx.conf  The file has the following line configuration ：

    set $a "hello world";

We used standards  ngx_rewrite  Modular  set  Configuration instruction pair variables  $a  The assignment operation is carried out . Specially , We put the string  hello world  Given it .

We see ,Nginx The variable name is preceded by a  $  Symbol , This is the requirement of notation . be-all Nginx Variable in Nginx All references in the configuration file must be accompanied with  $  Prefix . This representation is similar to Perl、PHP These languages are similar .

although  $  Such variable prefixes make orthodox  Java  and  C#  Programmers are not comfortable , But the benefits of this representation are obvious , That is, you can directly embed variables into string constants to construct new strings ：

    set $a hello;
    set $b "$a, $a";

Here we go through what we have Nginx Variable  $a  Value , To construct variables  $b  Value , So after these two instructions are executed in sequence ,$a  The value of is hello, and  $b  The value of is  hello, hello. This technology Perl The world is called “ Variable interpolation ”（variable interpolation）, It makes specialized string splicing operators less necessary . We might as well use this term here .

Let's look at a more complete configuration example ：

    server {
        listen 8080;
 
        location /test {
            set $foo hello;
            echo "foo: $foo";
        }
    }

This example omits  nginx.conf  The outermost part of the configuration file  http  Configuration block and  events  Configuration block . Use  curl  This HTTP The client requests this on the command line  /test  Interface , We can get 

    $ curl 'http://localhost:8080/test'
    foo: hello

Here we use a third party  ngx_echo  Modular  echo  Configuration instructions will  $foo  The value of the variable is output as the response body of the current request .

We see ,echo  The parameters of the configuration command also support “ Variable interpolation ”. however , It should be noted that , Not all configuration instructions support “ Variable interpolation ”. in fact , Whether the instruction parameter allows “ Variable interpolation ”, Depending on the implementation module of the instruction .

If we want to pass  echo  Instruction direct output contains “ Dollar symbol ”（$） String , So is there any way to put the special  $  Characters are escaped ？ The answer is No （ At least up to date Nginx Stable version  1.0.10）. But fortunately , We can get around this limitation , For example, by not supporting “ Variable interpolation ” The module configuration instruction of is specially constructed with the value of  $  Of Nginx Variable , And then in  echo  Use this variable . Here's an example ：

    geo $dollar {
        default "$";
    }
 
    server {
        listen 8080;
 
        location /test {
            echo "This is a dollar sign: $dollar";
        }
    }

The test results are as follows ：

    $ curl 'http://localhost:8080/test'
    This is a dollar sign: $

Standard modules are used here  ngx_geo  Configuration instructions provided  geo  To be a variable  $dollar  Give the string  "$", So we need to use the dollar sign below , Just quote our  $dollar  Variables are OK . Actually  ngx_geo  The most common use of modules is based on the client's IP The address pair specifies Nginx Variable assignment , This is just borrowing it to “ Unconditionally ” To our  $dollar  Variables give “ Dollar symbol ” This value .

stay “ Variable interpolation ” In the context of , There is another special case , That is, when the referenced variable name is followed by the constituent character of the variable name （ For example, followed by letters 、 Numbers and underscores ）, We need to use special notation to disambiguate , for example ：

    server {
        listen 8080;
 
        location /test {
            set $first "hello ";
            echo "${first}world";
        }
    }

here , We are  echo  Variables are referenced in parameter values of configuration instructions  $first  When , Followed closely by  world  The word , So if you write directly  "$firstworld"  be Nginx “ Variable interpolation ” The computing engine recognizes it as a reference to a variable  $firstworld. To solve this problem ,Nginx The string notation of supports the use of curly braces in  $  Then enclose the variable name , Like here  ${first}. The output of the above example is ：

    $ curl 'http://localhost:8080/test
    hello world

set  Instructions （ And as mentioned earlier  geo  Instructions ） It not only has the function of assignment , It also creates Nginx Side effects of variables , That is, when the variable as the assignment object does not exist yet , It automatically creates the variable . For example, in the above example , If  $a  This variable has not been created yet , be  set  Instructions are created automatically  $a  This user variable . If we don't create it, we just use its value , May be an error . for example 

    ? server {
    ?     listen 8080;
    ?
    ?     location /bad {
    ?         echo $foo;
    ?     }
    ? }

here Nginx The server will refuse to load the configuration :

    [emerg] unknown "foo" variable

Yes , We can't even start the service ！

Interestingly ,Nginx The creation and assignment of variables take place at very different times .Nginx Variable creation can only happen in Nginx When the configuration is loaded , Or say Nginx When it starts ; Assignment only happens when the request is actually processed . This means that using variables directly without creating them causes the startup to fail , It also means that we can't create new ones dynamically while the request is being processed Nginx Variable .

Nginx Once the variable is created , The visible range of its variable name is the entire Nginx To configure , Even across different virtual hosts  server Configuration block . Let's take an example ：

    server {
        listen 8080;
 
        location /foo {
            echo "foo = [$foo]";
        }
 
        location /bar {
            set $foo 32;
            echo "foo = [$foo]";
        }
    }

Here we are  location /bar  of use  set  Instructions create variables  $foo, So this variable is visible throughout the configuration file , So we can  location /foo  You can refer to this variable directly without worrying about it Nginx Will report a mistake .

Here's how to use  curl  The result of the tool accessing these two interfaces ：

    $ curl 'http://localhost:8080/foo'
    foo = []
 
    $ curl 'http://localhost:8080/bar'
    foo = [32]
 
    $ curl 'http://localhost:8080/foo'
    foo = []

From this example we can see that ,set  Because the command is  location /bar  Used in , So the assignment will only be done when accessing  /bar  To execute . The request  /foo  Interface , We always get empty  $foo  value , Because the user variable is output without assignment , You get an empty string .

Another important feature we can see from this example is ,Nginx The visible range of variable names is the entire configuration , But each request has a separate copy of all variables , In other words, there are independent copies of the container in which each variable is used to store values , Don't interfere with each other . For example, we asked /bar  After the interface ,$foo  Variables are given values  32, But it doesn't affect the follow-up to  /foo  Interface request corresponding to  $foo  value （ It's still empty ！）, Because each request has its own independent  $foo  Copies of variables .

about Nginx beginners , One of the most common mistakes , Will be Nginx Variables are understood as something that is globally shared between requests , Or say “ Global variables ”. As a matter of fact ,Nginx The lifetime of a variable cannot cross the request boundary .

（ To be continued ）

from:http://blog.sina.com.cn/s/blog_6d579ff40100wi7p.html

Nginx Random talk about variables （ One ） More articles about

  1. Nginx Random talk about variables （ 8、 ... and ）

    And  $arg_XXX  similar , We are  ( Two )  Built in variables mentioned in  $cookie_XXX  Variables will also be called  XXX  Of cookie Returns a special value when it does not exist “ Did not find ”:     location /test  ...

  2. Nginx Random talk about variables （ 7、 ... and ）

    stay  ( One )  We mentioned in ,Nginx The value of a variable has only one type , That's the string , But it's also possible that variables don't have meaningful values at all . Variables without values have two special values : One is “ illegal ”(invalid), The other is “ Did not find ”( ...

  3. Nginx Random talk about variables （ 5、 ... and ）

    In the front  ( Two )  We have learned that the lifetime of the variable value container is bound to the request , But I deliberately avoided “ request ” Formal definition of . You should always acquiesce in “ request ” They are initiated by the client HTTP request . Actually in Nginx There are... In the world ...

  4. Nginx Random talk about variables （ Four ）

    In setting up the “ Access handler ” Under the circumstances ,Nginx A variable can also choose to use its value container as a cache , In this way, when the variable is read many times , Just call “ Access handler ” Calculate once . Let's take a look at an example :     map $args  ...

  5. Nginx Random talk about variables （ 3、 ... and ）

    There are also some built-in variables that support rewriting , One example is  $args. This variable returns the current requested URL Parameter string ( I.e. request URL The part after the question mark in , If any ), In the assignment, you can directly modify the parameter string . Let's take a look at one ...

  6. Nginx Random talk about variables （ Two ）

    About Nginx Another common misconception about variables is that the lifetime of a variable container , Is with the  location  Configuration block bound . It's not . Let's look at one that involves “ Jump inside ” Example :     server {        listen ...

  7. Nginx Random talk about variables

    from :http://blog.sina.com.cn/openrestyNginx The configuration file of is a micro programming language , A lot of real world Nginx The configuration file is actually a small program . Of course , Is it right? ...

  8. Nginx Random talk about variables （ 6、 ... and ）

    Nginx Built in variables are used in “ Sub request ” In the context of , Its behavior will also become a little subtle . In the front  ( 3、 ... and )  We already know , Many built-in variables are not simple “ A container for storing values ”, They usually register “ Access handler ” To be different , ...

  9. Nginx Variable implementation mechanism

    Nginx There are two ways to define variables , One is to use... In the configuration file set Instructions ( from rewrite Modules provide support ), The other is to define variables within a module . Variable related structures : struct ngx_http_variable_s { ...

Random recommendation

  1. 【 Answer key 】【 Bit operation 】【Leetcode】Single Number II

    Given an array of integers, every element appears three times except for one. Find that single one. ...

  2. Solr4.8.0 Source code analysis (22) And SolrCloud Of Recovery Strategy ( 3、 ... and )

    Solr4.8.0 Source code analysis (22) And SolrCloud Of Recovery Strategy ( 3、 ... and ) This article is about SolrCloud Of Recovery The third article in the strategy series , The first two articles mainly introduce Recovery The overall process of , as well as P ...

  3. DSOframer Microsoft official API How to look up

    Don't understand DSOframer Friend, , You can refer to the article first DSOframer Brief introduction and resource arrangement of . We are using DSOframer when , I often don't know where to look it up API file , The articles on the Internet are very scattered , It's hard to find self ...

  4. VAXVOIP SDK Licensekey

    Insert the following key to the SDK with SetLicenseKey call: VAXVOIP.COM-191P238P55P253P97P229P51P76 ...

  5. MySQL Concurrent replication series 2 ： Multithreaded replication 2016

    Concurrent replication (Parallel Replication)  Series two : Enhanced Multi-threaded Slaves author : Wok Technology MySQL Database Engineer   Ma Pengfei First, sort out the tradition MySQL/M ...

  6. Android art ——Bitmap Efficient loading and caching （1）

    adopt Bitmap We can design a ImageLoader, The function that the implementation should have is : Synchronous loading of pictures : Asynchronous loading of pictures : Image compression : Memory cache : Disk caching : Internet access : 1. load First of all, load :BitmapFact ...

  7. [ Codeforces Round #554 (Div. 2) C]

    C. Neko does Maths time limit per test 1 second memory limit per test 256 megabytes input standard i ...

  8. Android programming resource file string The use of placeholders in

    Here's a detailed introduction to the use of placeholders , Put it into practice , It can simplify the layout file , Reduce string resources . 1. Use in resource files . Open... In the resource file strings.xml file , Editing . As shown in the figure below : chart   1.0 2. ...

  9. caffe Network structure visualization online tool

    http://ethereon.github.io/netscope/#/editor shift+enter

  10. Please make sure ASP.NET State Service (ASP.NET State Service ) Started Problem solving

    When iis The deployed web site encountered the following error : Unable to issue session state request to session state server . Please make sure ASP.NET State Service (ASP.NET State Service ) Started , And the client port is the same as the server port . Such as ...