package DBD::Gofer::Transport::pipeone;

# $Id: pipeone.pm 10087 2007-10-16 12:42:37Z Tim $
#
# Copyright (c) 2007, Tim Bunce, Ireland
#
# You may distribute under the terms of either the GNU General Public
# License or the Artistic License, as specified in the Perl README file.

use strict;
use warnings;

use Carp;
use Fcntl;
use IO::Select;
use IPC::Open3 qw(open3);
use Symbol qw(gensym);

use base qw(DBD::Gofer::Transport::Base);

our $VERSION = "0.010088";

__PACKAGE__->mk_accessors(qw(
connection_info
go_perl
));


sub new {
my ($self, $args) = @_;
$args->{go_perl} ||= do {
($INC{"blib.pm"}) ? [ $^X, '-Mblib' ] : [ $^X ];
};
if (not ref $args->{go_perl}) {
# user can override the perl to be used, either with an array ref
# containing the command name and args to use, or with a string
# (ie via the DSN) in which case, to enable args to be passed,
# we split on two or more consecutive spaces (otherwise the path
# to perl couldn't contain a space itself).
$args->{go_perl} = [ split /\s{2,}/, $args->{go_perl} ];
}
return $self->SUPER::new($args);
}


# nonblock($fh) puts filehandle into nonblocking mode
sub nonblock {
my $fh = shift;
my $flags = fcntl($fh, F_GETFL, 0)
or croak "Can't get flags for filehandle $fh: $!";
fcntl($fh, F_SETFL, $flags | O_NONBLOCK)
or croak "Can't make filehandle $fh nonblocking: $!";
}


sub start_pipe_command {
my ($self, $cmd) = @_;
$cmd = [ $cmd ] unless ref $cmd eq 'ARRAY';

# if it's important that the subprocess uses the same
# (versions of) modules as us then the caller should
# set PERL5LIB itself.

# limit various forms of insanity, for now
local $ENV{DBI_TRACE}; # use DBI_GOFER_TRACE instead
local $ENV{DBI_AUTOPROXY};
local $ENV{DBI_PROFILE};

my ($wfh, $rfh, $efh) = (gensym, gensym, gensym);
my $pid = open3($wfh, $rfh, $efh, @$cmd)
or die "error starting @$cmd: $!\n";
if ($self->trace) {
$self->trace_msg(sprintf("Started pid $pid: @$cmd {fd: w%d r%d e%d, ppid=$$}\n", fileno $wfh, fileno $rfh, fileno $efh),0);
}
nonblock($rfh);
nonblock($efh);
my $ios = IO::Select->new($rfh, $efh);

return {
cmd=>$cmd,
pid=>$pid,
wfh=>$wfh, rfh=>$rfh, efh=>$efh,
ios=>$ios,
};
}


sub cmd_as_string {
my $self = shift;
# XXX meant to return a properly shell-escaped string suitable for system
# but its only for debugging so that can wait
my $connection_info = $self->connection_info;
return join " ", map { (m/^[-:\w]*$/) ? $_ : "'$_'" } @{$connection_info->{cmd}};
}


sub transmit_request_by_transport {
my ($self, $request) = @_;

my $frozen_request = $self->freeze_request($request);

my $cmd = [ @{$self->go_perl}, qw(-MDBI::Gofer::Transport::pipeone -e run_one_stdio)];
my $info = $self->start_pipe_command($cmd);

my $wfh = delete $info->{wfh};
# send frozen request
local $\;
print $wfh $frozen_request
or warn "error writing to @$cmd: $!\n";
# indicate that there's no more
close $wfh
or die "error closing pipe to @$cmd: $!\n";

$self->connection_info( $info );
return;
}


sub read_response_from_fh {
my ($self, $fh_actions) = @_;
my $trace = $self->trace;

my $info = $self->connection_info || die;
my ($ios) = @{$info}{qw(ios)};
my $errors = 0;
my $complete;

die "No handles to read response from" unless $ios->count;

while ($ios->count) {
my @readable = $ios->can_read();
for my $fh (@readable) {
local $_;
my $actions = $fh_actions->{$fh} || die "panic: no action for $fh";
my $rv = sysread($fh, $_='', 1024*31); # to fit in 32KB slab
unless ($rv) { # error (undef) or end of file (0)
my $action;
unless (defined $rv) { # was an error
$self->trace_msg("error on handle $fh: $!\n") if $trace >= 4;
$action = $actions->{error} || $actions->{eof};
++$errors;
# XXX an error may be a permenent condition of the handle
# if so we'll loop here - not good
}
else {
$action = $actions->{eof};
$self->trace_msg("eof on handle $fh\n") if $trace >= 4;
}
if ($action->($fh)) {
$self->trace_msg("removing $fh from handle set\n") if $trace >= 4;
$ios->remove($fh);
}
next;
}
# action returns true if the response is now complete
# (we finish all handles
$actions->{read}->($fh) && ++$complete;
}
last if $complete;
}
return $errors;
}


sub receive_response_by_transport {
my $self = shift;

my $info = $self->connection_info || die;
my ($pid, $rfh, $efh, $ios, $cmd) = @{$info}{qw(pid rfh efh ios cmd)};

my $frozen_response;
my $stderr_msg;

$self->read_response_from_fh( {
$efh => {
error => sub { warn "error reading response stderr: $!"; 1 },
eof => sub { warn "eof on stderr" if 0; 1 },
read => sub { $stderr_msg .= $_; 0 },
},
$rfh => {
error => sub { warn "error reading response: $!"; 1 },
eof => sub { warn "eof on stdout" if 0; 1 },
read => sub { $frozen_response .= $_; 0 },
},
});

waitpid $info->{pid}, 0
or warn "waitpid: $!"; # XXX do something more useful?

die ref($self)." command (@$cmd) failed: $stderr_msg"
if not $frozen_response; # no output on stdout at all

# XXX need to be able to detect and deal with corruption
my $response = $self->thaw_response($frozen_response);

if ($stderr_msg) {
# add stderr messages as warnings (for PrintWarn)
$response->add_err(0, $stderr_msg, undef, $self->trace)
# but ignore warning from old version of blib
unless $stderr_msg =~ /^Using .*blib/ && "@$cmd" =~ /-Mblib/;
}

return $response;
}


1;

__END__

=head1 NAME

DBD::Gofer::Transport::pipeone - DBD::Gofer client transport for testing

=head1 SYNOPSIS

$original_dsn = "...";
DBI->connect("dbi:Gofer:transport=pipeone;dsn=$original_dsn",...)

or, enable by setting the DBI_AUTOPROXY environment variable:

export DBI_AUTOPROXY="dbi:Gofer:transport=pipeone"

=head1 DESCRIPTION

Connect via DBD::Gofer and execute each request by starting executing a subprocess.

This is, as you might imagine, spectacularly inefficient!

It's only intended for testing. Specifically it demonstrates that the server
side is completely stateless.

It also provides a base class for the much more useful L<DBD::Gofer::Transport::stream>
transport.

=head1 AUTHOR

Tim Bunce, L<http://www.tim.bunce.name>

=head1 LICENCE AND COPYRIGHT

Copyright (c) 2007, Tim Bunce, Ireland. All rights reserved.

This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself. See L<perlartistic>.

=head1 SEE ALSO

L<DBD::Gofer::Transport::Base>

L<DBD::Gofer>

=cut