######################################################################
# HTTP connection to backend node
#
# Copyright 2004, Danga Interactive, Inc.
# Copyright 2005-2007, Six Apart, Ltd.
#

package Perlbal::BackendHTTP;
use strict;
use warnings;
no  warnings qw(deprecated);

use base "Perlbal::Socket";
use fields ('client',  # Perlbal::ClientProxy connection, or undef
            'service', # Perlbal::Service
            'pool',    # Perlbal::Pool; whatever pool we spawned from
            'ip',      # IP scalar
            'port',    # port scalar
            'ipport',  # "$ip:$port"
            'reportto', # object; must implement reporter interface

            'has_attention', # has been accepted by a webserver and
                             # we know for sure we're not just talking
                             # to the TCP stack

            'waiting_options', # if true, we're waiting for an OPTIONS *
                               # response to determine when we have attention

            'disconnect_at', # time this connection will be disconnected,
                             # if it's kept-alive and backend told us.
                             # otherwise undef for unknown.

            # The following only apply when the backend server sends
            # a content-length header
            'content_length',  # length of document being transferred
            'content_length_remain',    # bytes remaining to be read

            'use_count',  # number of requests this backend's been used for
            'generation', # int; counts what generation we were spawned in
            'buffered_upload_mode', # bool; if on, we're doing a buffered upload transmit
            );
use Socket qw(PF_INET IPPROTO_TCP SOCK_STREAM SOL_SOCKET SO_ERROR
              AF_UNIX PF_UNSPEC
              );
use IO::Handle;

use Perlbal::ClientProxy;

# if this is made too big, (say, 128k), then perl does malloc instead
# of using its slab cache.
use constant BACKEND_READ_SIZE => 61449;  # 60k, to fit in a 64k slab

# keys set here when an endpoint is found to not support persistent
# connections and/or the OPTIONS method
our %NoVerify; # { "ip:port" => next-verify-time }
our %NodeStats; # { "ip:port" => { ... } }; keep statistics about nodes

# constructor for a backend connection takes a service (pool) that it's
# for, and uses that service to get its backend IP/port, as well as the
# client that will be using this backend connection.  final parameter is
# an options hashref that contains some options:
#       reportto => object obeying reportto interface
sub new {
    my ($class, $svc, $ip, $port, $opts) = @_;
    $opts ||= {};

    my $sock;
    socket $sock, PF_INET, SOCK_STREAM, IPPROTO_TCP;

    unless ($sock && defined fileno($sock)) {
        Perlbal::log('crit', "Error creating socket: $!");
        return undef;
    }

    IO::Handle::blocking($sock, 0);
    connect $sock, Socket::sockaddr_in($port, Socket::inet_aton($ip));

    my $self = fields::new($class);
    $self->SUPER::new($sock);

    Perlbal::objctor($self);

    $self->{ip}      = $ip;       # backend IP
    $self->{port}    = $port;     # backend port
    $self->{ipport}  = "$ip:$port";  # often used as key
    $self->{service} = $svc;      # the service we're serving for
    $self->{pool}    = $opts->{pool}; # what pool we came from.
    $self->{reportto} = $opts->{reportto} || $svc; # reportto if specified
    $self->state("connecting");

    # mark another connection to this ip:port
    $NodeStats{$self->{ipport}}->{attempts}++;
    $NodeStats{$self->{ipport}}->{lastattempt} = $self->{create_time};

    # setup callback in case we get stuck in connecting land
    Perlbal::Socket::register_callback(15, sub {
        if ($self->state eq 'connecting' || $self->state eq 'verifying_backend') {
            # shouldn't still be connecting/verifying ~15 seconds after create
            $self->close('callback_timeout');
        }
        return 0;
    });

    # for header reading:
    $self->init;

    bless $self, ref $class || $class;
    $self->watch_write(1);
    return $self;
}

sub init {
    my $self = shift;
    $self->{req_headers} = undef;
    $self->{res_headers} = undef;  # defined w/ headers object once all headers in
    $self->{headers_string} = "";  # blank to start
    $self->{generation}    = $self->{service}->{generation};
    $self->{read_size} = 0;        # total bytes read from client

    $self->{client}   = undef;     # Perlbal::ClientProxy object, initially empty
                                   #    until we ask our service for one

    $self->{has_attention} = 0;
    $self->{use_count}     = 0;
    $self->{buffered_upload_mode} = 0;
}


sub new_process {
    my ($class, $svc, $prog) = @_;

    my ($psock, $csock);
    socketpair($csock, $psock, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
        or  die "socketpair: $!";

    $csock->autoflush(1);
    $psock->autoflush(1);

    my $pid = fork;
    unless (defined $pid) {
        warn "fork failed: $!\n";
        return undef;
    }

    # child process
    unless ($pid) {
        close(STDIN);
        close(STDOUT);
        #close(STDERR);
        open(STDIN, '<&', $psock);
        open(STDOUT, '>&', $psock);
        #open(STDERR, ">/dev/null");
        exec $prog;
    }

    close($psock);
    my $sock = $csock;

    my $self = fields::new($class);
    $self->SUPER::new($sock);
    Perlbal::objctor($self);

    $self->{ipport}   = $prog; # often used as key
    $self->{service}  = $svc; # the service we're serving for
    $self->{reportto} = $svc; # reportto interface (same as service)
    $self->state("connecting");

    $self->init;
    bless $self, ref $class || $class;
    $self->watch_write(1);
    return $self;
}

sub close {
    my Perlbal::BackendHTTP $self = shift;

    # OSX Gives EPIPE on bad connects, and doesn't fail the connect
    # so lets treat EPIPE as a event_err so the logic there does
    # the right thing
    if (defined $_[0] && $_[0] eq 'EPIPE') {
        $self->event_err;
        return;
    }

    # don't close twice
    return if $self->{closed};

    # this closes the socket and sets our closed flag
    $self->SUPER::close(@_);

    # tell our client that we're gone
    if (my $client = $self->{client}) {
        $client->backend(undef);
        $self->{client} = undef;
    }

    # tell our owner that we're gone
    if (my $reportto = $self->{reportto}) {
        $reportto->note_backend_close($self);
        $self->{reportto} = undef;
    }
}

# return our defined generation counter with no parameter,
# or set our generation if given a parameter
sub generation {
    my Perlbal::BackendHTTP $self = $_[0];
    return $self->{generation} unless $_[1];
    return $self->{generation} = $_[1];
}

# return what ip and port combination we're using
sub ipport {
    my Perlbal::BackendHTTP $self = $_[0];
    return $self->{ipport};
}

# called to tell backend that the client has gone on to do something else now.
sub forget_client {
    my Perlbal::BackendHTTP $self = $_[0];
    $self->{client} = undef;
}

# called by service when it's got a client for us, or by ourselves
# when we asked for a client.
# returns true if client assignment was accepted.
sub assign_client {
    my Perlbal::BackendHTTP $self = shift;
    my Perlbal::ClientProxy $client = shift;
    return 0 if $self->{client};

    my $svc = $self->{service};

    # set our client, and the client's backend to us
    $svc->mark_node_used($self->{ipport});
    $self->{client} = $client;
    $self->state("sending_req");
    $self->{client}->backend($self);

    my Perlbal::HTTPHeaders $hds = $client->{req_headers}->clone;
    $self->{req_headers} = $hds;

    my $client_ip = $client->peer_ip_string;

    # I think I've seen this be undef in practice.  Double-check
    unless ($client_ip) {
        warn "Undef client_ip ($client) in assign_client.  Closing.";
        $client->close;
        return 0;
    }

    # Use HTTP/1.0 to backend (FIXME: use 1.1 and support chunking)
    $hds->set_version("1.0");

    my $persist = $svc->{persist_backend};

    $hds->header("Connection", $persist ? "keep-alive" : "close");

    if ($svc->{enable_reproxy}) {
        $hds->header("X-Proxy-Capabilities", "reproxy-file");
    }

    # decide whether we trust the upstream or not, to give us useful
    # forwarding info headers
    if ($svc->trusted_ip($client_ip)) {
        # yes, we trust our upstream, so just append our client's IP
        # to the existing list of forwarded IPs
        my @ips = split /,\s*/, ($hds->header("X-Forwarded-For") || '');
        $hds->header("X-Forwarded-For", join ", ", @ips, $client_ip);
    } else {
        # no, don't trust upstream (untrusted client), so remove all their
        # forwarding headers and tag their IP as the x-forwarded-for
        $hds->header("X-Forwarded-For", $client_ip);
        $hds->header("X-Host", undef);
        $hds->header("X-Forwarded-Host", undef);
    }

    $self->tcp_cork(1);
    $client->state('backend_req_sent');

    $self->{content_length} = undef;
    $self->{content_length_remain} = undef;

    # run hooks
    return 1 if $svc->run_hook('backend_client_assigned', $self);

    # now cleanup the headers before we send to the backend
    $svc->munge_headers($hds) if $svc;

    $self->write($hds->to_string_ref);
    $self->write(sub {
        $self->tcp_cork(0);
        if (my $client = $self->{client}) {
            # start waiting on a reply
            $self->watch_read(1);
            $self->state("wait_res");
            $client->state('wait_res');
            $client->backend_ready($self);
        }
    });

    return 1;
}

# called by ClientProxy after we tell it our backend is ready and
# it has an upload ready on disk
sub invoke_buffered_upload_mode {
    my Perlbal::BackendHTTP $self = shift;

    # so, we're receiving a buffered upload, we need to go ahead and
    # start the buffered upload retransmission to backend process. we
    # have to turn watching for writes on, since that's what is doing
    # the triggering, NOT the normal client proxy watch for read
    $self->{buffered_upload_mode} = 1;
    $self->watch_write(1);
}

# Backend
sub event_write {
    my Perlbal::BackendHTTP $self = shift;
    print "Backend $self is writeable!\n" if Perlbal::DEBUG >= 2;

    my $now = time();
    delete $NoVerify{$self->{ipport}} if
        defined $NoVerify{$self->{ipport}} &&
        $NoVerify{$self->{ipport}} < $now;

    if (! $self->{client} && $self->{state} eq "connecting") {
        # not interested in writes again until something else is
        $self->watch_write(0);
        $NodeStats{$self->{ipport}}->{connects}++;
        $NodeStats{$self->{ipport}}->{lastconnect} = $now;

        # OSX returns writeable even if the connect fails
        # so explicitly check for the error
        # TODO: make a smaller test case and show to the world
        if (my $error = unpack('i', getsockopt($self->{sock}, SOL_SOCKET, SO_ERROR))) {
            $self->event_err;
            return;
        }

        if (defined $self->{service} && $self->{service}->{verify_backend} &&
            !$self->{has_attention} && !defined $NoVerify{$self->{ipport}}) {

            # the backend should be able to answer this incredibly quickly.
            $self->write("OPTIONS * HTTP/1.0\r\nConnection: keep-alive\r\n\r\n");
            $self->watch_read(1);
            $self->{waiting_options} = 1;
            $self->{content_length_remain} = undef;
            $self->state("verifying_backend");
        } else {
            # register our boredom (readiness for a client/request)
            $self->state("bored");
            $self->{reportto}->register_boredom($self);
        }
        return;
    }

    # if we have a client, and we're currently doing a buffered upload
    # sendfile, then tell the client to continue sending us data
    if ($self->{client} && $self->{buffered_upload_mode}) {
        $self->{client}->continue_buffered_upload($self);
        return;
    }

    my $done = $self->write(undef);
    $self->watch_write(0) if $done;
}

sub verify_failure {
    my Perlbal::BackendHTTP $self = shift;
    $NoVerify{$self->{ipport}} = time() + 60;
    $self->{reportto}->note_bad_backend_connect($self);
    $self->close('no_keep_alive');
    return;
}

sub event_read_waiting_options { # : void
    my Perlbal::BackendHTTP $self = shift;
    if ($self->{content_length_remain}) {
        # the HTTP/1.1 spec says OPTIONS responses can have content-lengths,
        # but the meaning of the response is reserved for a future spec.
        # this just gobbles it up for.
        my $bref = $self->read(BACKEND_READ_SIZE);
        return $self->verify_failure unless defined $bref;
        $self->{content_length_remain} -= length($$bref);
    } elsif (my $hd = $self->read_response_headers) {
        # see if we have keep alive support
        return $self->verify_failure unless $hd->res_keep_alive_options;
        $self->{content_length_remain} = $hd->header("Content-Length");
    }

    # if we've got the option response and read any response data
    # if present:
    if ($self->{res_headers} && ! $self->{content_length_remain}) {
        # other setup to mark being done with options checking
        $self->{waiting_options} = 0;
        $self->{has_attention} = 1;
        $NodeStats{$self->{ipport}}->{verifies}++;
        $self->next_request(1); # initial
    }
    return;
}

sub handle_response { # : void
    my Perlbal::BackendHTTP $self = shift;
    my Perlbal::HTTPHeaders $hd = $self->{res_headers};
    my Perlbal::ClientProxy $client = $self->{client};

    print "BackendHTTP: handle_response\n" if Perlbal::DEBUG >= 2;

    my $res_code = $hd->response_code;

    # keep a rolling window of the last 500 response codes
    my $ref = ($NodeStats{$self->{ipport}}->{responsecodes} ||= []);
    push @$ref, $res_code;
    if (scalar(@$ref) > 500) {
        shift @$ref;
    }

    # call service response received function
    return if $self->{reportto}->backend_response_received($self);

    # standard handling
    $self->state("xfer_res");
    $client->state("xfer_res");
    $self->{has_attention} = 1;

    # RFC 2616, Sec 4.4: Messages MUST NOT include both a
    # Content-Length header field and a non-identity
    # transfer-coding. If the message does include a non-
    # identity transfer-coding, the Content-Length MUST be
    # ignored.
    my $te = $hd->header("Transfer-Encoding");
    if ($te && $te !~ /\bidentity\b/i) {
        $hd->header("Content-Length", undef);
    }

    my Perlbal::HTTPHeaders $rqhd = $self->{req_headers};

    # setup our content length so we know how much data to expect, in general
    # we want the content-length from the response, but if this was a head request
    # we know it's a 0 length message the client wants
    if ($rqhd->request_method eq 'HEAD') {
        $self->{content_length} = 0;
    } else {
        $self->{content_length} = $hd->content_length;
    }
    $self->{content_length_remain} = $self->{content_length} || 0;

    my $reproxy_cache_for = $hd->header('X-REPROXY-CACHE-FOR') || 0;

    # special cases:  reproxying and retrying after server errors:
    if ((my $rep = $hd->header('X-REPROXY-FILE')) && $self->may_reproxy) {
        # make the client begin the async IO while we move on
        $client->start_reproxy_file($rep, $hd);
        $self->next_request;
        return;
    } elsif ((my $urls = $hd->header('X-REPROXY-URL')) && $self->may_reproxy) {
        $self->{service}->add_to_reproxy_url_cache($rqhd, $hd)
            if $reproxy_cache_for;
        $client->start_reproxy_uri($self->{res_headers}, $urls);
        $self->next_request;
        return;
    } elsif ((my $svcname = $hd->header('X-REPROXY-SERVICE')) && $self->may_reproxy) {
        $self->{client} = undef;
        $client->start_reproxy_service($self->{res_headers}, $svcname);
        $self->next_request;
        return;
    } elsif ($res_code == 500 &&
             $rqhd->request_method =~ /^GET|HEAD$/ &&
             $client->should_retry_after_500($self)) {
        # eh, 500 errors are rare.  just close and don't spend effort reading
        # rest of body's error message to no client.
        $self->close;

        # and tell the client to try again with a new backend
        $client->retry_after_500($self->{service});
        return;
    }

    # regular path:
    my $res_source = $client->{primary_res_hdrs} || $hd;
    my $thd = $client->{res_headers} = $res_source->clone;

    # setup_keepalive will set Connection: and Keep-Alive: headers for us
    # as well as setup our HTTP version appropriately
    $client->setup_keepalive($thd);

    # if we had an alternate primary response header, make sure
    # we send the real content-length (from the reproxied URL)
    # and not the one the first server gave us
    if ($client->{primary_res_hdrs}) {
        $thd->header('Content-Length', $hd->header('Content-Length'));
        $thd->header('X-REPROXY-FILE', undef);
        $thd->header('X-REPROXY-URL', undef);
        $thd->header('X-REPROXY-EXPECTED-SIZE', undef);
        $thd->header('X-REPROXY-CACHE-FOR', undef);

        # also update the response code, in case of 206 partial content
        my $rescode = $hd->response_code;
        $thd->code($rescode) if $rescode == 206 || $rescode == 416;
        $thd->code(200) if $thd->response_code == 204;  # upgrade HTTP No Content (204) to 200 OK.
    }

    print "  writing response headers to client\n" if Perlbal::DEBUG >= 3;
    $client->write($thd->to_string_ref);

    print("  content_length=", (defined $self->{content_length} ? $self->{content_length} : "(undef)"),
          "  remain=",         (defined $self->{content_length_remain} ? $self->{content_length_remain} : "(undef)"), "\n")
        if Perlbal::DEBUG >= 3;

    if (defined $self->{content_length} && ! $self->{content_length_remain}) {
        print "  done.  detaching.\n" if Perlbal::DEBUG >= 3;
        # order important:  next_request detaches us from client, so
        # $client->close can't kill us
        $self->next_request;
        $client->write(sub {
            $client->backend_finished;
        });
    }
}

sub may_reproxy {
    my Perlbal::BackendHTTP $self = shift;
    my Perlbal::Service $svc = $self->{service};
    return 0 unless $svc;
    return $svc->{enable_reproxy};
}

# Backend
sub event_read {
    my Perlbal::BackendHTTP $self = shift;
    print "Backend $self is readable!\n" if Perlbal::DEBUG >= 2;

    return $self->event_read_waiting_options if $self->{waiting_options};

    my Perlbal::ClientProxy $client = $self->{client};

    # with persistent connections, sometimes we have a backend and
    # no client, and backend becomes readable, either to signal
    # to use the end of the stream, or because a bad request error,
    # which I can't totally understand.  in any case, we have
    # no client so all we can do is close this backend.
    return $self->close('read_with_no_client') unless $client;

    unless ($self->{res_headers}) {
        return unless $self->read_response_headers;
        return $self->handle_response;
    }

    # if our client's behind more than the max limit, stop buffering
    if ($client->too_far_behind_backend) {
        $self->watch_read(0);
        $client->{backend_stalled} = 1;
        return;
    }

    my $bref = $self->read(BACKEND_READ_SIZE);

    if (defined $bref) {
        $client->write($bref);

        # HTTP/1.0 keep-alive support to backend.  we just count bytes
        # until we hit the end, then we know we can send another
        # request on this connection
        if ($self->{content_length}) {
            $self->{content_length_remain} -= length($$bref);
            if (! $self->{content_length_remain}) {
                # order important:  next_request detaches us from client, so
                # $client->close can't kill us
                $self->next_request;
                $client->write(sub { $client->backend_finished; });
            }
        }
        return;
    } else {
        # backend closed
        print "Backend $self is done; closing...\n" if Perlbal::DEBUG >= 1;

        $client->backend(undef);    # disconnect ourselves from it
        $self->{client} = undef;    # .. and it from us
        $self->close('backend_disconnect'); # close ourselves

        $client->write(sub { $client->backend_finished; });
        return;
    }
}

# if $initial is on, then don't increment use count
sub next_request {
    my Perlbal::BackendHTTP $self = $_[0];
    my $initial = $_[1];

    # don't allow this if we're closed
    return if $self->{closed};

    # set alive_time so reproxy can intelligently reuse this backend
    my $now = time();
    $self->{alive_time} = $now;
    $NodeStats{$self->{ipport}}->{requests}++ unless $initial;
    $NodeStats{$self->{ipport}}->{lastresponse} = $now;

    my $hd = $self->{res_headers};  # response headers

    # verify that we have keep-alive support.  by passing $initial to res_keep_alive,
    # we signal that req_headers may be undef (if we just did an options request)
    return $self->close('next_request_no_persist')
        unless $hd->res_keep_alive($self->{req_headers}, $initial);

    # and now see if we should closed based on the pool we're from
    return $self->close('pool_requested_closure')
        if $self->{pool} && ! $self->{pool}->backend_should_live($self);

    # we've been used
    $self->{use_count}++ unless $initial;

    # service specific
    if (my Perlbal::Service $svc = $self->{service}) {
        # keep track of how many times we've been used, and don't
        # keep using this connection more times than the service
        # is configured for.
        if ($svc->{max_backend_uses} && ($self->{use_count} > $svc->{max_backend_uses})) {
            return $self->close('exceeded_max_uses');
        }
    }

    # if backend told us, keep track of when the backend
    # says it's going to boot us, so we don't use it within
    # a few seconds of that time
    if (($hd->header("Keep-Alive") || '') =~ /\btimeout=(\d+)/i) {
        $self->{disconnect_at} = $now + $1;
    } else {
        $self->{disconnect_at} = undef;
    }

    $self->{client} = undef;

    $self->state("bored");
    $self->watch_write(0);

    $self->{req_headers} = undef;
    $self->{res_headers} = undef;
    $self->{headers_string} = "";
    $self->{req_headers} = undef;

    $self->{read_size} = 0;
    $self->{content_length_remain} = undef;
    $self->{content_length} = undef;
    $self->{buffered_upload_mode} = 0;

    $self->{reportto}->register_boredom($self);
    return;
}

# Backend: bad connection to backend
sub event_err {
    my Perlbal::BackendHTTP $self = shift;

    # FIXME: we get this after backend is done reading and we disconnect,
    # hence the misc checks below for $self->{client}.

    print "BACKEND event_err\n" if
        Perlbal::DEBUG >= 2;

    if ($self->{client}) {
        # request already sent to backend, then an error occurred.
        # we don't want to duplicate POST requests, so for now
        # just fail
        # TODO: if just a GET request, retry?
        $self->{client}->close('backend_error');
        $self->close('error');
        return;
    }

    if ($self->{state} eq "connecting" ||
        $self->{state} eq "verifying_backend") {
        # then tell the service manager that this connection
        # failed, so it can spawn a new one and note the dead host
        $self->{reportto}->note_bad_backend_connect($self, 1);
    }

    # close ourselves first
    $self->close("error");
}

# Backend
sub event_hup {
    my Perlbal::BackendHTTP $self = shift;
    print "HANGUP for $self\n" if Perlbal::DEBUG;
    $self->close("after_hup");
}

sub as_string {
    my Perlbal::BackendHTTP $self = shift;

    my $ret = $self->SUPER::as_string;
    my $name = $self->{sock} ? getsockname($self->{sock}) : undef;
    my $lport = $name ? (Socket::sockaddr_in($name))[0] : undef;
    $ret .= ": localport=$lport" if $lport;
    if (my Perlbal::ClientProxy $cp = $self->{client}) {
        $ret .= "; client=$cp->{fd}";
    }
    $ret .= "; uses=$self->{use_count}; $self->{state}";
    if (defined $self->{service} && $self->{service}->{verify_backend}) {
        $ret .= "; has_attention=";
        $ret .= $self->{has_attention} ? 'yes' : 'no';
    }

    return $ret;
}

sub die_gracefully {
    # see if we need to die
    my Perlbal::BackendHTTP $self = shift;
    $self->close('graceful_death') if $self->state eq 'bored';
}

sub DESTROY {
    Perlbal::objdtor($_[0]);
    $_[0]->SUPER::DESTROY;
}

1;

# Local Variables:
# mode: perl
# c-basic-indent: 4
# indent-tabs-mode: nil
# End: