NAME

       hddemux - demultiplexes incoming TCP connections between HTTP and DNS

SYNOPSIS

       hddemux

DESCRIPTION

       hddemux  takes a set of listening stream-based file descriptors (see sd_listen_fds(3)) and
       accepts new connections on them.

       When a new connection comes  in,  it  decides  from  the  first  few  octets  whether  the
       connection  is  HTTP/1.x or DNS.  If it thinks it’s HTTP/1.x, it splices the connection to
       the HTTP_TARGET.  If it thinks it’s DNS, it splices the connection to the DNS_TARGET.

ENVIRONMENT VARIABLES

       HTTP_TARGET and DNS_TARGET should be either a  DNS  name  or  an  IP  address,  optionally
       followed  by  a  colon and a port number.  If either variable is unset, it will default to
       “localhost”.

       If the port number is not specified, HTTP_TARGET defaults to TCP port 80,  and  DNS_TARGET
       defaults to TCP port 53.

       If  HDDEMUX_DEBUG  is  set  to  a  non-empty  string,  then  it will send a lot of verbose
       debugging info to stderr.

       IDLE_TIMEOUT is used to set the number of milliseconds that hddemux will permit a  session
       to  be  in an open state with no traffic passing before it tries to close both sides.  The
       default is 600000 (10 minutes).  Set this variable to 0 to never try to do  this  kind  of
       cleanup.

SIGNALS

       When  hddemux  receives  SIGUSR1, it dumps an overview of the current state of the demuxer
       (configuration, outstanding established streams, etc) to stderr.

EXAMPLES

       For systemd, you need a .socket unit file:

              #/lib/systemd/hddemux.socket
              [Unit]
              Description=HTTP/1.x and DNS demuxer socket
              Documentation=man:hddemux(1)

              [Socket]
              ListenStream=/run/hddemux/socket

              [Install]
              WantedBy=sockets.target

       and a .service unit file:

              #/lib/systemd/hddemux.service
              [Unit]
              Description=HTTP/1.x and DNS demuxer service
              Documentation=man:hddemux(1)
              Requires=hddemux.socket

              [Service]
              Type=notify
              ExecStart=/usr/bin/hddemux
              WorkingDirectory=/run/hddemux/workdir
              User=hddemux
              Group=hddemux

              [Install]
              Also=hddemux.socket

       Configuration can be done by overriding the .service file (e.g. with  Service.Environment=
       entries).   See  the  “edit”  documentation  in  systemctl(1)  and  the “Overriding vendor
       settings” section of systemd.unit(5).

CONSTRAINTS

       hddemux is designed to demultiplex HTTP/1.x from stream-based DNS.  Trying to  demultiplex
       other   protocols   (including   HTTP/2   or   later)   is   not   advised.    Please  see
       draft-dkg-dprive-demux-dns-http for more information and analysis.

WARNING

       Note that this effectively acts as a stream redirector once the client’s first flight  has
       been  processed.  It does this with no attempt to defend against stream redirection loops,
       so be careful not to redirect it to itself or it will eat all of your memory  in  infinite
       recursion.

SEE ALSO

       sd_listen_fds(3),                      systemctl(1),                      systemd.unit(5),
       https://datatracker.ietf.org/doc/draft-dkg-dprive-demux-dns-http/

AUTHORS

       Daniel Kahn Gillmor <dkg@fifthhorseman.net>.

                                             2017 May                                  HDDEMUX(1)