perl - 继续获取部分下载的文件

Question

是否有一个 Perl 工具，其行为类似于 wget --continue 并且能够继续获取部分下载的文件？

Answer 1

AnyEvent::HTTP的文档包含使用 HTTP 1.1 的能力来恢复下载的代码。不过我从未使用过它，所以我无法评论它的适用性。

显然这个例子希望你已经知道如何使用 AnyEvent ，当然，我不知道。您需要修改代码以使其预期的事件循环已经到位:

#!/usr/bin/perl

use strict;
use warnings;

use AnyEvent::HTTP;

my $url  = "http://localhost/foo.txt";
my $file = "foo.txt";

sub download {
    my ($url, $file, $cb) = @_;

    open my $fh, "+>>:raw", $file
        or die "could not open $file: $!";

    my %hdr;
    my $ofs = 0;

    if (stat $fh and $ofs = -s _) {
        $hdr{"if-unmodified-since"} = AnyEvent::HTTP::format_date((stat _)[9]);
        $hdr{"range"} = "bytes=$ofs-";
    }

    http_get $url, (
        headers   => \%hdr,
        on_header => sub {
            my ($hdr) = @_;

            if ($hdr->{Status} == 200 && $ofs) {
                # resume failed
                truncate $fh, $ofs = 0;
            }

            sysseek $fh, $ofs, 0;

            return 1;
        },
        on_body   => sub {
            my ($data, $hdr) = @_;

            if ($hdr->{Status} =~ /^2/) {
                length $data == syswrite $fh, $data
                    or return; # abort on write errors
            }

            return 1;
        },
        sub {
            my (undef, $hdr) = @_;

            my $status = $hdr->{Status};

            if (my $time = AnyEvent::HTTP::parse_date $hdr->{"last-modified"}) {
                utime $fh, $time, $time;
            }

            if ($status == 200 || $status == 206 || $status == 416) {
                # download ok || resume ok || file already fully downloaded
                $cb->(1, $hdr);

            } elsif ($status == 412) {
                # file has changed while resuming, delete and retry
                unlink $file;
                $cb->(0, $hdr);

            } elsif ($status == 500 or $status == 503 or $status =~ /^59/) {
                # retry later
                $cb->(0, $hdr);

            } else {
                $cb->(undef, $hdr);
            }
        }
    );
}

my $quit = AnyEvent->condvar; #create a handle to exit the loop

download $url, $file, sub {
    if ($_[0]) {
        print "OK!\n";
    } elsif (defined $_[0]) {
        print "please retry later\n";
    } else {
        print "ERROR\n";
    }
    $quit->send; #quit the loop
};

$quit->recv; #start the loop

让它工作的关键是$quit条件变量:

my $quit = AnyEvent->condvar; #handle to exit the loop
.
.
.
$quit->recv;

这会设置一个事件循环。在没有事件循环的情况下，程序会在调用 http_get 有机会执行除创建文件之外的任何操作之前退出。要退出事件循环，我们在 download 函数的回调中调用 $quit->send。