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IPPUSBXD Coverity analysis status

Version 1.34

About

IPPUSBXD is a userland driver for IPP-over-USB class USB devices. It has been designed for Linux but uses a cross platform usb library allowing eventual porting to Windows and other non-POSIX platforms.

The IPP-over-USB standard was ratified by the USB forum in 2012. As of 2014 Mac OS X implemented this standard and with the addition of ippusbxd Linux shall as well.

IPPUSBXD depends on POSIX threads, POSIX networking, and libusb as developed by the community at libusb.info

IPPUSBXD has the following advantages;

  1. At runtime links only with libc, pthreads, libusb, and libavahi*. On a typical system these libraries will already be in RAM. This gives ippusbxd a minimal ram footprint.
  2. Requires no read access to any files.
  3. Ships with a strict AppArmor profile.
  4. Runs warning & leak free in valgrind
  5. Compiles warning free in clang
  6. Analyzed warning free in Coverity
  7. Can be installed anywhere
  8. Near zero CPU usage while idle
  9. Low CPU usage while working

Before you begin: ippusbxd or ipp-usb?

ippusbxd was the first approach to implement IPP-over-USB for Linux and similar, POSIX-style operating systems. Its architecture is simple: ippusbxd simply relays a TCP connection to USB. This does not work very well.

Bumping into problems when trying to scan via IPP-over-USB with ippusbxd, the author of the "airscan" SANE backend, Alexander Pevzner, created the alternative approach ipp-usb and writes:

Unfortunately, the naive implementation, which simply relays a TCP connection to USB, does not work. It happens because closing the TCP connection on the client side has a useful side effect of discarding all data sent to this connection from the server side, but it does not happen with USB connections. In the case of USB, all data not received by the client will remain in the USB buffers, and the next time the client connects to the device, it will receive unexpected data, left from the previous abnormally completed request.

Actually, it is an obvious flaw in the IPP-over-USB standard, but we have to live with it.

So the implementation, once the HTTP request is sent, must read the entire HTTP response, which means that the implementation must understand the HTTP protocol, and effectively implement a HTTP reverse proxy, backed by the IPP-over-USB connection to the device.

And this is what the ipp-usb program actually does.

ipp-usb is written in Go, as Go provides an HTTP library with the needed functionality, which is missing in C. But as Go links executables statically, they have a large memory footprint. Therefore the ChromeOS developers do not accept Go programs and continued with ippusbxd for some time and later they came with another from-scratch approach, ippusb_bridge, written in Rust.

Due to this there is no known operating system using ippusbxd any more. Therefore development of this project is currently suspended. Nevertheless, anyone coming up with a solution of ippusbxd's problems, making it working as well as ipp-usb is highly welcome and we are open for appropriate Pull Requests.

Generally, I highly recommend to use ipp-usb instead of ippusbxd. It works absolutely reliably, wheras ippusbxd often has problems, especially with the web admin interfaces of the devices.

Building

To build ippusbxd you must have the development headers of libusb 1.0, libavahi-common, and libavahi-client installed along with cmake.

Under Ubuntu and Debian:

sudo apt-get install libusb-1.0-0-dev libavahi-common-dev libavahi-client-dev libcups2-dev libxml2-dev cmake

Under Fedora:

sudo yum install libusbx-devel.* cmake

Install also the *-devel packages of libxml2, cups, libavahi-common and libavahi-client

Once the dependencies are installed simply run:

make

That will run a makefile which will in turn run cmake. This makefile also supports several GNU-style make commands such as clean, and redep.

Installation on a system with systemd, UDEV, and cups-filters

Most systems nowadays use systemd for starting up all system services (instead of System V "init", as PID 1), UDEV to automatically set up hardware added to the system while it is running, and cups-filters to provide non-Mac-OS filters, backends, and cups-browsed. Therefore we explain only a method using systemd and UDEV here.

In these systems it is recommended to start ippusbxd via systemd when an appropriate printer is connected and discovered by UDEV. cups-filters from version 1.13.2 on and CUPS from version 2.2.2 has everything needed for driverless printer setup. "driverless" means that no printer driver, with the driver being any software or data specific to (a) certain printer model(s) is needed. driverless printing makes use of IPP to allow the client to query the printer's capabilities and IPP-over-USB was developed to allow these queries also if the printer is not on the network but connected via USB. Therefore we can assume that all IPP-over-USB printers support driverless printing.

A remark to driverless printing: There are several very similar standards: AirPrint, a proprietary standard from Apple and IPP Everywhere, an open standard of the Printer Working Group (PWG, http://www.pwg.org/), and also Mopria and Wi-Fi Direct. They all use the same methods of DNS-SD broadcasting of network printers, IPP-over-USB via the USB interface class 7, subclass 1, protocol 4, and IPP 2.0 with all its attributes for querying of capabilities, sending jobs with options as IPP attributes, and monitoring the status of the printer. The only difference is that IPP Everywhere uses PWG Raster as its raster data format, AirPrint uses Apple Raster, and Mopria and Wi-Fi Direct use PWG Raster or PCLm. All standards also support PDF as page description language. Even the PWG and Apple Raster formats are very similar. Therefore CUPS and CUPS filters simply support all methods.

Note that these instructions and the sample files are tested on Ubuntu. On other distributions there are perhaps some changes needed, for example of the directories where to place the file and of paths in the files.

There are two methods to install ippusbxd, one exposing the printer on localhost. and one exposing the printer on the dummy0 interface.

Exposing the printer on localhost is the way how the IPP-over-USB standard is intended and therefore this is how it is intended to proceed on production systems and especially on Linux distributions.

This requires Avahi 0.8.0 or newer, as older versions of Avahi do not support advertising services on localhost. The new Avahi versions allow advertising services on the loopback network interface "lo" only to the local machine, what is what we need here. Older Avahi versions can be used after applying a simple patch though.

Exposing the printer on the dummy0 interface does not require Avahi 0.8.0 or any changes on older Avahi versions, but it is more awkward to set up the system and to access the printer and its web administration interface.

1. Expose the printer on localhost

First, install ippusbxd:

sudo cp exe/ippusbxd /usr/sbin

Make sure that this file is owned by root and world-readable and -executable.

Now install the files to manage the automatic start of ippusbxd:

sudo cp systemd-udev/55-ippusbxd.rules /lib/udev/rules.d/
sudo cp systemd-udev/ippusbxd@.service /lib/systemd/system/

Make sure that they are owned by root and world-readable.

Why do we not start ippusbxd directly out of the UDEV rules file?

If we would do so, UDEV would kill ippusbxd after a timeout of 5 minutes. Out of UDEV rules you can only start programs which do not need to keep running permanently, like daemons. Therefore we use systemd here.

Make sure that you have Avahi 0.8.0 or newer installed or apply the following patch to the source code of older Avahi versions (tested with version 0.6.32 and 0.7):

--- avahi-core/iface-linux.c~
+++ avahi-core/iface-linux.c
@@ -104,8 +104,8 @@
         hw->flags_ok =
             (ifinfomsg->ifi_flags & IFF_UP) &&
             (!m->server->config.use_iff_running || (ifinfomsg->ifi_flags & IFF_RUNNING)) &&
-            !(ifinfomsg->ifi_flags & IFF_LOOPBACK) &&
-            (ifinfomsg->ifi_flags & IFF_MULTICAST) &&
+            ((ifinfomsg->ifi_flags & IFF_LOOPBACK) ||
+             (ifinfomsg->ifi_flags & IFF_MULTICAST)) &&
             (m->server->config.allow_point_to_point || !(ifinfomsg->ifi_flags & IFF_POINTOPOINT));
 
         /* Handle interface attributes */
--- avahi-core/iface-pfroute.c~
+++ avahi-core/iface-pfroute.c
@@ -80,8 +80,8 @@
   hw->flags_ok =
     (ifm->ifm_flags & IFF_UP) &&
     (!m->server->config.use_iff_running || (ifm->ifm_flags & IFF_RUNNING)) &&
-    !(ifm->ifm_flags & IFF_LOOPBACK) &&
-    (ifm->ifm_flags & IFF_MULTICAST) &&
+    ((ifm->ifm_flags & IFF_LOOPBACK) ||
+     (ifm->ifm_flags & IFF_MULTICAST)) &&
     (m->server->config.allow_point_to_point || !(ifm->ifm_flags & IFF_POINTOPOINT));
 
   avahi_free(hw->name);
@@ -427,8 +427,8 @@
         hw->flags_ok =
             (flags & IFF_UP) &&
             (!m->server->config.use_iff_running || (flags & IFF_RUNNING)) &&
-            !(flags & IFF_LOOPBACK) &&
-            (flags & IFF_MULTICAST) &&
+            ((flags & IFF_LOOPBACK) ||
+             (flags & IFF_MULTICAST)) &&
             (m->server->config.allow_point_to_point || !(flags & IFF_POINTOPOINT));
         hw->name = avahi_strdup(lifreq->lifr_name);
         hw->mtu = mtu;
--- avahi-core/resolve-service.c~
+++ avahi-core/resolve-service.c
@@ -24,6 +24,7 @@
 #include <string.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <net/if.h>
 
 #include <avahi-common/domain.h>
 #include <avahi-common/timeval.h>
@@ -129,7 +130,7 @@
                 r->service_name,
                 r->service_type,
                 r->domain_name,
-                r->srv_record->data.srv.name,
+                (r->interface == if_nametoindex("lo")) ? "localhost" : r->srv_record->data.srv.name,
                 r->address_record ? &a : NULL,
                 r->srv_record->data.srv.port,
                 r->txt_record ? r->txt_record->data.txt.string_list : NULL,

Build and install Avahi.

Avahi 0.8.0 and newer have this patch already included.

This makes Avahi not only advertising services on the usual network interfaces but also on the "lo" (loopback) interface (localhost). The services on the loopback interface (on localhost) are only advertised on the local machine, so no additional info gets exposed to the network, especially no local-only service gets shared by this.

This works well as long as your machine is connected to some kind of network (does not necessarily need to be a connection to the Internet, a virtual network interface to virtual machines running locally is enough). It is possible that the advertising of the printer stops if the loopback interface is the only network interface running due to lack of a multicast-capable interface.

Now we can restart systemd and UDEV to activate all this:

sudo systemctl daemon-reload
sudo systemctl restart udev

If we connect and turn on an IPP-over-USB printer, ippusbxd gets started and makes the printer available under the IPP URI

ipp://localhost:60000/ipp/print

the scanner (if the device has one built-in) under

http://localhost:60000/eSCL

and its web administration interface under

http://localhost:60000/

(if you have problems with the Chrome browser, use Firefox).

It is also DNS-SD-broadcasted via Avahi on the lo interface.

To set up a print queue you could simply run

lpadmin -p printer -E -v ipp://localhost:60000/ipp/print -meverywhere

The "-meverywhere" makes CUPS auto-generate the PPD file for the printer, based on an IPP query of the printer's capabilities, independent whether the printer is an IPP Everywhere printer or an AirPrint printer. This method does not support PCLm-only printers, but the methods described below do.

To create a print queue with the web interface of CUPS (http://localhost:631/), look for your printer under the discovered network printers (CUPS does not see that it is USB in reality) and select the entry which contains "driverless". On the page to select the models/PPDs/drivers, also select the entry containing "driverless". Then complete the setup as ususal.

The best solution is to let cups-browsed auto-create a print queue when the printer gets connected and remove it when the printer gets turned off or disconnected (do not worry about option settings, cups-browsed saves them).

To do so, edit /etc/cups/cups-browsed.conf making sure that there is a line

CreateIPPPrinterQueues driverless

or

CreateIPPPrinterQueues all

and no other line beginning with

CreateIPPPrinterQueues

After editing the file restart cups-browsed with

sudo systemctl stop cups-browsed
sudo systemctl start cups-browsed

Now you have a print queue whenever the printer is available and no print queue cluttering your print dialogs when the printer is not available.

If your printer is a multi-function device with a built-in scanner it supports the eSCL (AirScan) scanning standard in most cases. This standard is supported by the "escl" backend in SANE 1.0.29 or newer or by the "airscan" backend:

https://github.com/alexpevzner/sane-airscan

To actually scan you simply start the scanning software of your choice and select the scanner device entry for your printer. If your device is connected both via network and IPP-over-USB, the latter is marked with "USB".

2. Expose the printer on the dummy0 interface

This is an alternative method if you have Avahi 0.7.x or older installed and do not want to patch it. With Avahi 0.8.0 or newer you can use the localhost-based method described above.

First, install ippusbxd:

sudo cp exe/ippusbxd /usr/sbin

Make sure that this file is owned by root and world-readable and -executable.

Now install the files to manage the automatic start of ippusbxd:

sudo cp systemd-udev/55-ippusbxd.rules /lib/udev/rules.d/
sudo cp systemd-udev/ippusbxd@.service.dummy0 /lib/systemd/system/ippusbxd@.service

Make sure that they are owned by root and world-readable.

Now create a "dummy0" network interface:

sudo modprobe dummy
sudo ifconfig dummy0 10.0.0.1 netmask 255.255.255.0 multicast
sudo ifconfig dummy0 up multicast

You could put these commands into /etc/rc.local to run them automatically at boot.

Why not simply use "localhost" with the always available loopback ("lo") interface?

We want that our IPP-over-USB printer appears to our system like a network printer, so that CUPS and cups-browsed auto-detect it with the usual methods so that we can easily set up a print queue, even fully automatically, and that we can use CUPS' IPP backend to send print jobs to our printer.

If we use "localhost", we can access the printer with the IPP CUPS backend and also access its web administration interface with a web browser, but the printer cannot get auto-discovered by cups-browsed or by CUPS backends like dnssd or driverless, making it awkward to create a print queue for the printer. This is because the loopback interface (which provides "localhost") is not multicast-capable and therefore cannot get DNS-SD-broadcasted by Avahi.

Now one could think why not simply use the standard network interface "eth0" or "wlan0"? The problem here is that the printer gets broadcasted and accessible in the whole local network, so we share our USB printer and do not want it. In addition, if our computer is not connected to a network, these interfaces are not available.

"dummy0" is always local-only but does multicast and therefore gets DNS-SD-broadcasted by Avahi, and that only on the local machine. So we have the full emulation of a driverless network printer only on our local machine, as we want a USB printer only be available on our local machine.

Now we can restart systemd and UDEV to activate all this:

sudo systemctl daemon-reload
sudo systemctl restart udev

If we connect and turn on an IPP-over-USB printer, ippusbxd gets started and makes the printer available under the IPP URI

ipp://10.0.0.1:60000/ipp/print

the scanner (if the device has one built-in) under

http://10.0.0.1:60000/eSCL

and its web administration interface under

http://10.0.0.1:60000/

(if you have problems with the Chrome browser, use Firefox).

It is also DNS-SD-broadcasted via Avahi on the dummy0 interface.

To set up a print queue you could simply run

lpadmin -p printer -E -v ipp://10.0.0.1:60000/ipp/print -meverywhere

The "-meverywhere" makes CUPS auto-generate the PPD file for the printer, based on an IPP query of the printer's capabilities, independent whether the printer is an IPP Everywhere printer or an AirPrint printer. This method does not support PCLm-only printers, but the methods described below do.

To create a print queue with the web interface of CUPS (http://localhost:631/), look for your printer under the discovered network printers (CUPS does not see that it is USB in reality) and select the entry which contains "driverless". On the page to select the models/PPDs/drivers, also select the entry containing "driverless". Then complete the setup as ususal.

The best solution is to let cups-browsed auto-create a print queue when the printer gets connected and remove it when the printer gets turned off or disconnected (do not worry about option settings, cups-browsed saves them).

To do so, edit /etc/cups/cups-browsed.conf making sure that there is a line

CreateIPPPrinterQueues driverless

or

CreateIPPPrinterQueues all

and no other line beginning with

CreateIPPPrinterQueues

After editing the file restart cups-browsed with

sudo systemctl stop cups-browsed
sudo systemctl start cups-browsed

Now you have a print queue whenever the printer is available and no print queue cluttering your print dialogs when the printer is not available.

If your printer is a multi-function device with a built-in scanner it supports the eSCL (AirScan) scanning standard in most cases. This standard is supported by the "escl" backend in SANE 1.0.29 or newer or by the "airscan" backend:

https://github.com/alexpevzner/sane-airscan

To actually scan you simply start the scanning software of your choice and select the scanner device entry for your printer. If your device is connected both via network and IPP-over-USB, the latter is marked with "USB".

Presentation on IPPUSBXD

On August 2014 at the Fall Printer Working Group meeting Daniel Dressler gave a presentation on ippusbxd and the IPP-over-USB protocol. Slides from this presentation can be found in the docs folder.

IPPUSBXD, the name

The original name for this project was ippusbd. Part way through development it came to my attention that ippusbd was the name of the ipp over usb implemented used by Mac OSX.

This prompted a rename and Ira of the OpenPrinting group and PWG suggested IPPUSBXD.

Either all-caps IPPUSBXD or all-lower-case ippusbxd are valid names.

License

Copyright 2014 Daniel Dressler, 2015-2016 Till Kamppeter

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.