perl - 窥探不同 plack 中间件之间的 http header

Question

如果我理解正确，PSGI 应用程序的工作方式如下:

收到来自浏览器的请求

该请求是通过一些中间件按顺序“冒泡”的，因为它们在 builder 中定义

请求来到我的应用程序

我的应用产生了一些响应

此响应再次通过一些中间件冒泡

最后响应发送到浏览器

当请求到达我的 $app 时，我可以轻松地调试打印所有 header (例如 cookie)。 .

问题是:
如何调试打印headers的实际状态当请求通过许多中间件到达我的应用程序时，而响应又通过中间件发出。

所以，有一个(简化) app.psgi ，如下:

use strict;
use warnings;
use Plack::Builder;

my $app = sub { ... };

builder {
         # <- debug-print the first request headers
         #                and the last respond headers here
    enable "Debug";
         # <- debug-print the actual state of request/respond headers here
    enable "mid2";
         # <- and here
    enable "mid3";
         # <- and here

    $app; # <- and finally here - this is of course EASY
}

这可能不像这样的事情那么容易，

print STDERR Dumper $dont_know_what->request->headers(); #HTTP::Headers ???
print STDERR Dumper $dont_know_what->respond->headers();

所以添加赏金:) ;)

Answer 1

一种基本方法是创建一个中间件，在执行包装的应用程序之前转储 header ，然后立即转储。然后，您在伪代码中指出的每个要查看 header 的位置启用此中间件。

以下代码通过在每次启用它时构建一个内嵌中间件来完成此操作。

use Plack::Builder;
use Plack::Request;
use Plack::Response;

sub headers_around {
  my $position = shift;

  # build and return the headers_around middleware as a closure
  return sub {
    my $app = shift;
    # gets called each request
    return sub {
      my $env = shift;

      my $req = Plack::Request->new($env);
      # display headers before next middleware
      print STDERR "req headers before $position:\n" . $req->headers->as_string . "\n=====\n";

      # execute the next app on the stack
      my $res = $app->($env);

      my $response = Plack::Response->new(@$res);

      # display headers after previous middleware
      print STDERR "res headers after $position:\n" . $response->headers->as_string . "\n=====\n";
      return $res;
    };
  };
};

builder {

  enable headers_around('Debug');
  enable 'Debug';

  enable headers_around('Lint');
  enable 'Lint';

  enable headers_around('StackTrace');
  enable 'StackTrace', force => 1;

  enable headers_around('App');
  mount '/' => builder { sub {
    return [ 200, [ 'Content-Type' => 'text/plain' ], [ 'Hello World' ] ];
  }}
};

# now build the application enabling regular middleware with our inline middleware
builder {

  enable headers_around('Debug');
  enable 'Debug';

  enable headers_around('Lint');
  enable 'Lint';

  enable headers_around('StackTrace');
  enable 'StackTrace', force => 1;

  enable headers_around('App');
  mount '/' => builder { sub {
        return [ 200, [ 'Content-Type' => 'text/plain' ], [ 'Hello World' ] ];
  }}
};

当我使用 plackup 运行它时，我得到以下输出:

$ plackup --app between_middleware.psgi
HTTP::Server::PSGI: Accepting connections at http://0:5000/
req headers before Debug:
Connection: Keep-Alive
Accept: */*
Host: 0:5000
User-Agent: Wget/1.12 (linux-gnu)

=====
req headers before Lint:
Connection: Keep-Alive
Accept: */*
Host: 0:5000
User-Agent: Wget/1.12 (linux-gnu)

=====
req headers before StackTrace:
Connection: Keep-Alive
Accept: */*
Host: 0:5000
User-Agent: Wget/1.12 (linux-gnu)

=====
req headers before App:
Connection: Keep-Alive
Accept: */*
Host: 0:5000
User-Agent: Wget/1.12 (linux-gnu)

=====
res headers after App:
Content-Type: text/plain

=====
res headers after StackTrace:
Content-Type: text/plain

=====
res headers after Lint:
Content-Type: text/plain

=====
res headers after Debug:
Content-Type: text/plain

=====
127.0.0.1 - - [02/Apr/2014:19:37:30 -0700] "GET / HTTP/1.0" 200 11 "-" "Wget/1.12 (linux-gnu)"

显然你可以把它变成一个像 Ashley 那样的真正的中间件，你可能需要调整它以使用你现有的任何工具发送日志消息。