A C library and example program for fetching OCI container images (manifests, blobs) from OCI-compliant registries. Supports token authentication, manifest parsing, blob downloading, and extracting tar.gz layers.

About the Project

Features

Prerequisites

Building

Usage

API

Contributing

License

This project provides a simple C OCI client library exposing a clean API to:

• Fetch authentication tokens from OCI registries
• Get manifests by image tag and select platform-specific manifests
• Download layer blobs by digest
• Extract downloaded .tar.gz layers to directories

The library hides dependencies on libcurl, cJSON, and libarchive so that applications only need to link against this library without dealing with external dependencies directly.

The included example program demonstrates how to fetch and extract all layers of an OCI image using the library.

• Full OCI registry API support for image pulls
• Token authentication support
• Multi-architecture manifest parsing
• Blob fetching and tar.gz extraction
• Simple, dependency-encapsulating API
• Shared or static library build via Meson
• Graceful error handling and resource cleanup

• C compiler supporting C11 (e.g., GCC 7+, Clang)
• Meson build system
• Ninja build tool

Dependencies installed on system:

• libcurl (development files)
• libcjson (development files)
• libarchive (development files)

On Debian/Ubuntu, install dependencies with:

sudo apt install build-essential meson ninja-build libcurl4-openssl-dev libcjson-dev libarchive-dev

Configure and build the project using Meson:

meson setup builddir -Dlibrary_type=shared   # or static
meson compile -C builddir

This builds the oci_client library (shared or static) and the example executable oci_client_demo.

Run the example program to fetch and extract an image:

./builddir/oci_client_demo -r https://harbor.nbfc.io -R nubificus/torchscript-v2-vaccel-gpu -t x86_64 -a amd64 -o linux -d output

The program downloads all layers, saves them as layer-*.tar.gz, and extracts them under the output directory.

Main functions:

• void oci_client_init(void)
• void oci_client_cleanup(void)
• char *fetch_token(const char *registry, const char *repo)
• char *fetch_manifest(const char *registry, const char *repo, const char *tag, const char *arch, const char *os, char *token)
• struct Memory *fetch_blob(const char *registry, const char *repo, const char *digest, const char *token, int *out_code)
• int extract_tar_gz(const char *filename, const char *dest_dir)
• int oci_manifest_parse_layers(const char *manifest_json, struct OciLayer **layers_out)
• void oci_layers_free(struct OciLayer *layers, int n)

See oci_client.h for full declarations.

Contributions welcome! Please fork the repo, make changes, and submit pull requests. Report bugs or suggest features via issues.

This project is licensed under the Apache-2.0 License. See LICENSE for details.