Loaders are a key component of what makes dissect.target work. They are responsible for mapping any kind of source data into something that dissect.target understands. Loaders can be incredibly complex or incredibly simple, depending on what you are trying to achieve.

Oftentimes, your data is not in a directly usable state or it’s split over multiple files that would make more sense to use as a single entity, but needs some molding to properly use it. A loader can be seen as a preprocessor of this source data, shaping it into something more useful. All the processing happens transparently or in-memory.

For example:

  • A loader for .vmx (VMware VM metadata) files parses the metadata and loads all of the discovered .vmdk (VMware virtual disk) files.

  • A loader for .vbox (Virtual Box metadata) and .vmcx (Hyper-V metadata) files does the same as the loader for .vmx, but for .vdi, .vhd and .vhdx files.

  • A loader for .vma (Proxmox VM backup) files can parse the backup and add each enclosed virtual disk stream as a separate disk, without having to extract the .vma file.

  • A loader for acquire tar files can map all files to virtual in-memory filesystems.

  • A loader for an EDR agent can use the live API to provide virtual filesystems and registry hives.

  • A loader for roaming profile managers can parse profile data and map files to a virtual in-memory filesystem and registry keys to a virtual in-memory registry hive.

  • A loader for iTunes backups can parse the metadata and map all the enclosed files into a virtual in-memory filesystem, providing transparent decryption for any file reads.

These are just some examples of the loaders currently available in dissect.target, but more are added as support grows or new use-cases are encountered.

This doesn’t mean that dissect.target only works with these types of files, however. As mentioned, a loader can be seen as a preprocessor; a way to work with more complex data or data that is scattered over multiple files. A target is usually a single file, but a loader for that single file can pull in as many files as it needs.

Using dissect.target on a single (supported) file, such as a .vmdk or .E01 works without needing a loader. In fact, the file support for .E01 actually cheats a little by pulling in more files (the other .E** part files) without needing a loader. This is not by accident, as a .E01 file is a completely self-contained disk container, so it’s possible to address it as such. In contrast, a .vma or .vmx file can produce multiple disk containers, so a loader is required to correctly open each disk container. It also allows for a separate tool that only consumes the Containers API to support opening .E01 files.

Writing your own#

There are a few methods of using your own loader in dissect.target:

  • Specify the path to your implementation(s) using the DISSECT_PLUGINS environment variable.

  • Specify the path to your implementation(s) using the --plugin-path argument with the various Dissect Tools.

  • Add a new implementation in the dissect.target source tree at dissect/target/loaders.

The last method requires you to have a source checkout and working development setup of dissect.target. This is the recommended method if you intend to contribute your loader back to the project.

See also

Read more about using your own modules in dissect.target at Loading your own modules.

Interested in developing for Dissect? Read more at Developing for Dissect.

Regardless of which method you use, you can use the boilerplate below. Do keep in mind that the final line is only required if you’re using either of the DISSECT_PLUGINS or --plugin-path options!

from pathlib import Path
from typing import TYPE_CHECKING

from dissect.target.loader import Loader, register

    from dissect.target import Target

class MyLoader(Loader):
    def detect(path: Path) -> bool:
        raise NotImplementedError()

    def map(self, target: Target) -> None:
        raise NotImplementedError()

# This line is necessary if your loader is outside the ``dissect.target`` source tree!
register(__name__, MyLoader.__name__, internal=False)

In the detect() method you can place detection logic that determines if your loader is compatible with the given path, simple return True if it is and False if it isn’t. Please note that path doesn’t necessarily have to be a path to an actual file on your local filesystem. It can also be a path on a filesystem of another target (a TargetPath, more information in Filesystems). It’s also possible to parse the path as a URI, the LocalLoader does this for example.

Keep this in mind when writing your own loader, and steer clear of any OS specific APIs such as those from the Python os or os.path module, unless explicitly intended.

If your loader is compatible with a given path, it will be instantiated with the path as an argument. If you want, you can provide additional initialization logic in the __init__ function by overriding it:

class MyLoader(Loader):
    def __init__(self, path: Path):
        # Your additional initialization logic here

The next important method to implement is the map() method. This is the meat and bones of your loader. Here you can do all the crazy logic you want for whatever it is you want to load into a Target. Common use-cases include opening Containers or mapping things into various (virtual) Filesystems. You can look at other loaders as an example or explore the documentation for other various Dissect components to discover all the possibilities.

One important detail to keep in mind is that in your map() method, the target is in an empty state. There are no disks, volumes or filesystems yet (you’re adding them, after all), and there’s no operating system information loaded yet. Another important detail is to understand that you generally don’t have to do things like volume or filesystem discovery yourself, unless you specifically require so in your loader. If you add a disk, things like volume and filesystem happen automatically as the Target object gets initialized. Read more about this process at Target initialization.

See also

You can refer to the API documentation of the Loader class for more documentation on the methods referenced here.

If you are placing your loader in the dissect.target source tree, you’ll need to register your loader. Do this by opening dissect/target/loader.py and add your loader to the bottom by using register():

register("myloader", "MyLoader")