一个Perl套接字在Linux下如何解析主机名？ [英] How does a Perl socket resolve hostnames under Linux?

问题描述

我有一个（从我能说的）完美的Linux设置（Ubuntu 8.04），其中所有工具（nslookup，curl，wget，firefox等）都能够解析地址。然而，以下代码失败：

  $ s = new IO :: Socket :: INET（
 PeerAddr => ;'stackoverflow.com'，
 PeerPort => 80，
 Proto =>'tcp'，
）; 
 
 dieError：$！\\\
除非$ s; 
  

我验证了以下内容：

• Perl可以使用gethostbyname解析地址（即代码如下）：

  
  
  

  my $ ret = gethostbyname（'stackoverflow.com'）;
打印inet_ntoa（$ ret）;




• 原始源代码在Windows下工作



• 这是它应该如何工作（即它应该解析主机名），因为LWP试图使用这个行为（实际上我试图调试为什么LWP不工作我）


• 运行脚本不会发出DNS请求（因此甚至不会尝试解析名称）。验证与Wireshark

解决方案

从一个快速的看，下面的代码从IO :: Socket： ：INET

  sub _get_addr {
 my（$ sock，$ addr_str，$ multi）= @_; 
我的@addr; 
 if（$ multi&& $ addr_str！〜/^\d+(?:\.\d+){3}$/）{
（undef，undef，undef，undef ，@addr）= gethostbyname（$ addr_str）; 
} else {
 my $ h = inet_aton（$ addr_str）; 
 push（@addr，$ h）if defined $ h; 
} 
 @addr; 
} 
  

建议（如果你看这个代码的调用者）添加 MultiHomed => 1，到你的代码。

没有这个解决方法，上面的代码似乎试图调用 inet_aton hostname.com）使用inet_aton（）从Socket.pm。这对Win32和Unix都有用，所以我猜这是破坏你的地方。

请参阅 Socket.xs ：

  void 
 inet_aton（host）
 char * host 
 CODE：
 {
 struct in_addr ip_address; 
 struct hostent * phe; 
 
 if（phe = gethostbyname（host））{
复制（phe-> h_addr，& ip_address，phe-> h_length，char）; 
} else {
 ip_address.s_addr = inet_addr（host）; 
} 
 
 ST（0）= sv_newmortal（）; 
 if（ip_address.s_addr！= INADDR_NONE）{
 sv_setpvn（ST（0），（char *）& ip_address，sizeof ip_address）; 
} 
} 
  

看起来Perl的gethostbyname（） C gethostbyname（）为您。

I have a (from what I can tell) perfectly working Linux setup (Ubuntu 8.04) where all tools (nslookup, curl, wget, firefox, etc) are able to resolve addresses. Yet, the following code fails:

$s = new IO::Socket::INET(
    PeerAddr => 'stackoverflow.com',
    PeerPort => 80,
    Proto => 'tcp',
);

die "Error: $!\n" unless $s;

I verified the following things:

• Perl is able to resolve addresses with gethostbyname (ie the code below works):

  my $ret = gethostbyname('stackoverflow.com'); print inet_ntoa($ret);

• The original source code works under Windows

• This is how it supposed to work (ie. it should resolve hostnames), since LWP tries to use this behavior (in fact I stumbled uppon the problem by trying to debug why LWP wasn't working for me)
• Running the script doesn't emit DNS requests (so it doesn't even try to resolve the name). Verified with Wireshark

解决方案

From a quick look, the following code from IO::Socket::INET

sub _get_addr {
    my($sock,$addr_str, $multi) = @_;
    my @addr;
    if ($multi && $addr_str !~ /^\d+(?:\.\d+){3}$/) {
        (undef, undef, undef, undef, @addr) = gethostbyname($addr_str);
    } else {
        my $h = inet_aton($addr_str);
        push(@addr, $h) if defined $h;
    }
    @addr;
}

suggests (if you look at the caller of this code) the work-around of adding MultiHomed => 1, to your code.

Without that work-around, the above code appears to try to call inet_aton("hostname.com") using the inet_aton() from Socket.pm. That works for me in both Win32 and Unix, so I guess that is where the breakage lies for you.

See Socket.xs for the source code of inet_aton:

void
inet_aton(host)
    char *  host
    CODE:
    {
        struct in_addr ip_address;
        struct hostent * phe;

        if (phe = gethostbyname(host)) {
            Copy( phe->h_addr, &ip_address, phe->h_length, char );
        } else {
            ip_address.s_addr = inet_addr(host);
        }

        ST(0) = sv_newmortal();
        if(ip_address.s_addr != INADDR_NONE) {
            sv_setpvn( ST(0), (char *)&ip_address, sizeof ip_address );
        }
    }

It appears that the Perl gethostbyname() works better than the C gethostbyname() for you.

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