The Google Cloud Print (aka GCP) CUPS Connector shares CUPS printers with users of Google Cloud Print.

Copyright 2015 Google Inc. All rights reserved.

Use of this source code is governed by a BSD-style license that can be found in the LICENSE file or at https://developers.google.com/open-source/licenses/bsd

Get the most recent version of the Go compiler: https://golang.org/doc/install

Go 1.4 or newer is required. We recommend using the latest release. To check run:

$ go version
go version go1.5.1 linux/arm

Make sure you see at least go.1.4 or higher returned. Old versions of Go can't compile cups-connector and will throw errors in the next step.

The CUPS Connector also uses some C libraries. Get the necessary build tools and libraries for your platform:

Make sure you are running CUPS 1.7 or later. If using the distribution-bundled CUPS package, upgrade to Debian >= 8.0 jessie or Ubuntu >= 14.04 trusty.

A special note to Raspbian users: Although 8.0 jessie isn't mentioned at raspbian.org, it is possible to upgrade: https://raspberrypi.stackexchange.com/questions/27858/upgrade-to-raspbian-jessie

Ready? Install build tools and libraries:

$ sudo apt-get install build-essential libcups2-dev libsnmp-dev libavahi-client-dev

Install XCode: https://itunes.apple.com/us/app/xcode/id497799835

Install the command line developer tools:

$ xcode-select --install

Accept the license agreement:

$ xcodebuild -license

Any Linux distribution or *BSD flavor should support the CUPS Connector. If you have trouble (or success!) with another platform, please open an issue so that we can integrate the feedback here.

$ go get github.com/google/cups-connector/...

Once installation completes, four binaries will be placed in $GOPATH/bin.

To create a config file called cups-connector.config.json, run connector-init. The default config file looks something like this:

{
  "xmpp_jid": "e73b3deadc7bbbeefc1d2d22@cloudprint.googleusercontent.com",
  "robot_refresh_token": "1/D39yourG_KMbeefjnsis1peMIp5DeadMyOkwOQMZhSo",
  "user_refresh_token": "1/fBXneverhZHieath_2an2UxDVsourGE8pwatermelon",
  "share_scope": "somedude@gmail.com",
  "proxy_name": "joes-crab-shack",
  "gcp_max_concurrent_downloads": 5,
  "cups_max_connections": 5,
  "cups_connect_timeout": "5s",
  "cups_job_queue_size": 3,
  "cups_printer_poll_interval": "1m",
  "cups_printer_attributes": [
    "printer-name",
    "printer-info",
    "printer-location",
    "printer-make-and-model",
    "printer-state",
    "printer-state-reasons",
    "printer-uuid",
    "marker-names",
    "marker-types",
    "marker-levels"
  ],
  "cups_job_full_username": false,
  "cups_ignore_raw_printers": true,
  "copy_printer_info_to_display_name": true,
  "monitor_socket_filename": "/var/run/cups-connector/monitor.sock",
  "gcp_base_url": "https://www.google.com/cloudprint/",
  "xmpp_server": "talk.google.com",
  "xmpp_port": 443,
  "gcp_xmpp_ping_timeout": "5s",
  "gcp_xmpp_ping_interval_default": "2m",
  "gcp_oauth_client_id": "539833558011-35iq8btpgas80nrs3o7mv99hm95d4dv6.apps.googleusercontent.com",
  "gcp_oauth_client_secret": "V9BfPOvdiYuw12hDx5Y5nR0a",
  "gcp_oauth_auth_url": "https://accounts.google.com/o/oauth2/auth",
  "gcp_oauth_token_url": "https://accounts.google.com/o/oauth2/token",
  "snmp_enable": false,
  "snmp_community": "public",
  "snmp_max_connections": 100,
  "local_enable": false,
  "cloud_enable": true
}

Your platform is probably configured to talk to the CUPS server on localhost, and that's probably what you want. If not, this next part is for you.

When deciding which CUPS server to connect to, the connector asks the CUPS client library, specifically the cupsServer() and cupsEncryption() functions, which return values found in:

• CUPS_SERVER and CUPS_ENCRYPTION environment variables
• ~/.cups/client.conf
• /etc/cups/client.conf

The simplest way to start the connector on boot is to edit /etc/rc.local. Add the following lines before exit 0. The example user is "pi", which you should change to your own username:

# CUPS Connector:
#   su ... pi: run as user "pi"
#   --login:   environment similar to "pi" instead of "root"
#   --command: run this thing
#   &:         run the command "in the background"
su --login --command "go/bin/connector" pi &

In order for the connector to function properly, it needs to make the following connections:

• accounts.google.com - HTTPS port 443 (OAuth authorize and token refresh)
• www.google.com - HTTPS port 443 (/cloudprint API endpoints)
• talk.google.com - XMPP port 443 (print job notification channel)

Ensure your firewall allows connections to each of these hosts.