stereoscope

           

A library for working with container image contents, layer file trees, and squashed file trees.

Getting Started

See examples/basic.go

docker image save centos:8 -o centos.tar
go run examples/basic.go ./centos.tar

Note: To run tests you will need skopeo installed.

Overview

This library provides the means to:

• parse and read images from multiple sources, supporting:
  • docker V2 schema images from the docker daemon, podman, or archive
  • OCI images from disk, directory, or registry
  • images in the local containers-storage store (e.g. images built with buildah or rootless podman) — see containers-storage source
  • singularity formatted image files
• build a file tree representing each layer blob
• create a squashed file tree representation for each layer
• search one or more file trees for selected paths
• catalog file metadata in all layers
• query the underlying image tar for content (file content within a layer)

containers-storage source

Images that are built with buildah (or rootless podman) usually live in the local containers-storage store rather than in the docker daemon. The containers-storage source resolves these images directly from the current user's default store, before falling back to a remote registry pull.

Storage location follows the current process/user via the default containers-storage configuration: rootless users use their rootless store (typically ~/.local/share/containers/storage) and root uses the rootful store (typically /var/lib/containers/storage). Stereoscope does not probe both locations; it uses the default store for the current user.

Usage (assuming the consuming binary, e.g. syft, was itself built with the containers_image_openpgp build tag described below — a stock syft release build does not include this source):

# explicit source selection
syft containers-storage:localhost/myimage:latest

# implicit resolution: a plain reference is checked against the local containers-storage
# store before falling back to the OCI registry
syft localhost/myimage:latest

Note

The containers-storage source depends on the image and storage libraries (the go.podman.io/image and go.podman.io/storage module paths that github.com/containers/image and github.com/containers/storage have moved to) and is only compiled into binaries built with the containers_image_openpgp build tag:

go build -tags containers_image_openpgp ./...

Without that tag, a stub provider keeps the source registered but reports that support was not compiled in, so default builds (and downstream consumers) are unaffected. On Linux you may additionally need to exclude the cgo graph drivers you do not have headers for, e.g. -tags "containers_image_openpgp exclude_graphdriver_btrfs exclude_graphdriver_devicemapper".