| Subject: | Incorrect example of Net::HTTP::NB usage |
In SYNOPSIS section we can see an example of how you can send request and read response with Net::HTTP::NB. But this example has potential problems. Let's see this test server:
use strict;
use IO::Socket;
my $serv = IO::Socket::INET->new(Listen => 10, LocalPort => 8080)
or die $@;
my $body = 'This is the body';
my $header = join(
"\r\n",
"HTTP/1.1 200 OK",
"Server: nginx/1.0.4",
"Date: Thu, 06 Oct 2011 16:14:01 GMT",
"Content-Type: text/html",
"Content-Length: ".length($body),
"Connection: keep-alive",
"Vary: Accept-Encoding",
"X-Powered-By: PHP/5.3.6",
"\r\n"
);
while (warn("waiting for next request...\n") and my $client = $serv->accept()) {
my $req;
while ($req !~ /\r\n\r\n$/) {
$client->sysread($req, 1024, length $req) or die $!;
}
$client->syswrite($header.$body);
<$client>; # keep-alive ;)
}
__END__
And this client (a little reworked example from SYNOPSIS):
use strict;
use Net::HTTP::NB;
my $s = Net::HTTP::NB->new(Host => "localhost:8080") || die $@;
$s->write_request(GET => "/", 'User-Agent' => "Mozilla/5.0");
use IO::Select;
my $sel = IO::Select->new($s);
READ_HEADER: {
die "Header timeout" unless $sel->can_read(10);
my($code, $mess, %h) = $s->read_response_headers;
redo READ_HEADER unless $code;
}
while (1) {
die "Body timeout" unless $sel->can_read(10);
my $buf;
my $n = $s->read_entity_body($buf, 1024);
last unless $n;
print $buf;
}
__END__
And output of this client will be "Body timeout" error, instead of expected "This is the body" body content.
The problem is that Net::HTTP::Methods internally uses a buffer when reading data from the server. Here read_response_headers() call readed both headers and data, returned headers for us and stored body in the buffer. So, body now in the buffer instead of a socket and socket will not be available for read anymore (until server will close connection, but our uses keep-alive, so will not do it). This is why our can_read(10) call timed out after 10 seconds.
And this is how this example may looks like to work properly:
use strict;
use Net::HTTP::NB;
use Errno qw/EAGAIN EWOULDBLOCK/;
my $s = Net::HTTP::NB->new(Host => "localhost:8080", KeepAlive => 1) || die $@;
$s->write_request(GET => "/", 'User-Agent' => "Mozilla/5.0");
use IO::Select;
my $sel = IO::Select->new($s);
READ_HEADER: {
die "Header timeout" unless $sel->can_read(10);
my($code, $mess, %h) = $s->read_response_headers;
redo READ_HEADER unless $code;
}
# Net::HTTP::NB uses internal buffer, so we should check it before
# socket check by calling read_entity_body()
# make socket non-blocking, so read_entity_body() will not block
$s->blocking(0);
while (1) {
my $buf;
my $n;
# try to read until error or all data received
while (1) {
my $tmp_buf;
$n = $s->read_entity_body($tmp_buf, 1024);
if ($n == -1 || (!defined($n) && ($! == EWOULDBLOCK || $! == EAGAIN))) {
last; # no data available this time
}
elsif ($n) {
$buf .= $tmp_buf; # data received
}
elsif (defined $n) {
last; # $n == 0, all readed
}
else {
die "Read error occured: ", $!; # $n == undef
}
}
print $buf if length $buf;
last if defined $n && $n == 0; # all readed
die "Body timeout" unless $sel->can_read(10); # wait for new data
}
__END__
The bad news is that most modules which uses Net::HTTP::NB doing it wrong, as showed in the example from the documentation.