Category: programming

Here’s a quick overview on how to start writing a custom publishing plugin. This is being done on Ubuntu 14.04, so no promises it will function on any other version.

1. Install valac-0.22, libgphoto2-dev, gnome-doc-utils,libgstreamer-plugins-base1.0-dev, libgee-0.8-dev libsqlite3-dev libraw-dev librest-dev libwebkitgtk-3.0-dev libgexiv2-dev libgudev-1.0-dev libgtk-3-dev libjson-glib-dev
2. Download the shotwell 0.20.2 sources and not the current version from github. The current version in get uses some new gtk features which are not available in ubuntu 14.04.
3. Copy the shotwell/samples/simple-plugin from the shotwell git repo to a new directory
4. Build/install shotwell 0.20

   $ ./configure --install-headers
   $ sudo make -j6 install

    

5. In your new plugin, run ‘make; make install’ to ensure the basic build works.
6. Rename simple-plugin.vala to your publishing plugin name (ie, OnedrivePublishing.vala)
7. Modify the Makefile and set the PROGRAM to your plugin name (ie, OnedrivePublishing)
8. Running make should compile your new empty plugin.

Now that that’s done we can start creating out publishing plugin.

The plugin sample implements the Spit.Pluggable interface, in order to create a publishing plugin, we’ll need to use that to return our publishing module and create a new class to implement the Spit.Pluggable and Spit.Publishing.Service interface as well. Rename that class and include all the necessary interfaces. We’ll use the ShotwellPublishingCoreServices as a template for how to bootstrap out publishing service.

The basic do-nothing module which compiles w/ one warning (the return null) now contains the following:

extern const string _VERSION;
private class OnedriveModule : Object, Spit.Module {
    private Spit.Pluggable[] pluggables = new Spit.Pluggable[0];

    public OnedriveModule() {
        pluggables += new OnedriveService();
    }
    
    public unowned string get_module_name() {
        return _("OneDrive Publishing Services");
    }
    
    public unowned string get_version() {
        return _VERSION;
    }
    
    public unowned string get_id() {
        return "org.yorba.shotwell.publishing.onedrive";
    }
    
    public unowned Spit.Pluggable[]? get_pluggables() {
        return pluggables;
    }
}
// This is our new publishing class
private class OnedriveService : Object, Spit.Pluggable, Spit.Publishing.Service {
        

    public OnedriveService() {
    }

    public unowned string get_id() {
        return "org.yorba.shotwell.publishing.onedrive";
    }
    
    public Spit.Publishing.Publisher.MediaType get_supported_media() {
        return (Spit.Publishing.Publisher.MediaType.PHOTO |
            Spit.Publishing.Publisher.MediaType.VIDEO);
    }
    public Spit.Publishing.Publisher create_publisher(Spit.Publishing.PluginHost host) {
        //TODO
        return null;
    }

    public void get_info(ref Spit.PluggableInfo info) {
        info.authors = "Mike Smorul";
        info.version = _VERSION;
        info.is_license_wordwrapped = false;
        
    }    
    public unowned string get_pluggable_name() {
        return "OneDrive";
    }

    public int get_pluggable_interface(int min_host_interface, int max_host_interface) {
        return Spit.negotiate_interfaces(min_host_interface, max_host_interface,
            Spit.Publishing.CURRENT_INTERFACE);
    }
    
    public void activation(bool enabled) {
    }
}
// This entry point is required for all SPIT modules.
public Spit.Module? spit_entry_point(Spit.EntryPointParams *params) {
    params->module_spit_interface = Spit.negotiate_interfaces(params->host_min_spit_interface,
        params->host_max_spit_interface, Spit.CURRENT_INTERFACE);

    return (params->module_spit_interface != Spit.UNSUPPORTED_INTERFACE)
        ? new OnedriveModule() : null;
}

private void dummy_main() {
}

You can now compile this by:

$ make clean; make ; make install

This will install your new module into your local modules directory. To make sure it works, open up shotwell, go to Edit -> Preferences -> Plugins and you should see your new plugin listed under the Publishing section with a generic graphic next to it. If you enable the module you’ll notice the following error that will be fixed when we start implementing functionality

 GSettingsEngine.vala:457: GSettingsConfigurationEngine: error: schema 'org.yorba.shotwell.plugins.enable-state' does not define key 'publishing-onedrive'

Useful Links

• Writing Shotwell plugins
• Publishing Extension Point
• Gallery3 Plugin

The PBS/Torque scheduler that ships w/ Ubuntu 12.04 uses an interesting method to verify that user requests from a submission node cannot impersonate anyone else. In a nutshell, any Torque command (qsub, qstat, etc) calls a suid program (pbs_iff) which connects to the pbs server from a privileged port and notifies the server the client port and what user will be sending commands from that port. pbs_iff receives this information by looking at the source port on the file handle passed to if during its clone. The whole handshake looks like this:

1. Unprivileged client opens a socket to the pbs server
2. Client calls clone and passes the file handle number to a suid pbs_iff as an argument
3. pbs_iff reads the source port off of the file handle
4. pbs_iff opens a socket from a priviliged port to the pbs server and sends invoking user and source port .
5. The pbs server now trusts that commands from the initial socket belong to the user passed by pbs_iff
6. pbs_iff terminates and the original client sends whatever commands it desires.

This works nice in C where the default is to pass all file handles to the child process on a fork. However, many languages frown on this file handle leaking for a number of reasons and have decided this default is a bad idea. Java is one of these, so it nicely sets FD_CLOEXEC on all file handles it opens. This means when you use the ProcessBuilder or call Runtime.exec, you can’t see any file handles you previously had open thereby breaking Torque’s security mechanism.