abstractfs

intermediate representation for directory trees / filesystems with fine control over metadata

Quick start

go install github.com/malt3/abstractfs@latest
abstractfs json --source-type tar --source /path/to/archive.tar | yq -P
abstractfs json --source-type dir --source /path/to/directory | yq -P
abstractfs convert --source-type dir --source /path/to/directory --sink-type tar --sink /path/to/archive.tar

Architecture

flowchart LR
    transform["transformations (strip metadata, ...)"]
    source
    sink
    json
    ir --> transform --> ir
    subgraph ir[intermediate representation]
        direction TB
        root["/"]
        etc
        usr
        passwd
        resolv["resolv.conf"]
        root --- etc
        etc --- passwd
        etc --- resolv
        root --- usr
    end
    source -->|nodes| ir -->|nodes| sink
    ir --> json

Design goals

• Simple
• Arbitrary input and output formats
  • directory of a mounted filesystem (dir)
  • archive formats (tar, cpio, zip)
  • package formats (rpm, deb)
  • container image formats (oci image, oci layer)
  • filesystems (squashfs, fat, ext4)
  • go fs.FS (embed.FS)
  • in-memory sources and sinks
  • user-extensible, programmable via an interface
• Efficient in-memory representation
• Clean interfaces for sources and sinks
• Human readable metadata representation
• File contents stored in abstract CAS and can come from anywhere (even other computers)
  • represent hash using Subresource Integrity Format
  • File tree operates on nodes containing only file metadata and SRI. Contents handled out-of-band.
• Composable (support overlaying / nesting / merging operations)
• Support reproducible / repeatable operations / transformations as event stream
  • add / remove a file
  • replace contents or metadata
  • serializable event format
• Uses canonical representation by default
• Explicitly support the absence / presence of metadata
• Should allow for metadata normalization operations
  • Strip attributes, normalize timestamps...
  • Overlay metadata from a different source
• Designed for file system forensics / diffing / reproducible builds

Supported sources and sinks

	Source	Sink	xattr	CAS Source
dir	✅	🔜	✅	✅
go fs.FS	✅	❌	🔜	✅
tar	✅	✅	✅	✅
cpio	🔜	🔜	🤷	🤷
zip	🔜	🔜	🤷	🤷
rpm	🔜	🔜	🤷	🤷
deb	🔜	🔜	🤷	🤷
oci	🔜	🔜	🤷	🤷
squashfs	🔜	🔜	🤷	🤷
fat	🔜	🔜	🤷	🤷

Content addressable storage (CAS) backends

• in-memory
• dir
• S3 / object storage

🚧 JSON Format

The current format is not stabilized and still work in progress.

Core

The core is implemented in a separate module and has no dependencies.