bollard-llb constructs synchronous BuildKit Low-Level Builder (LLB) definitions. It emits bollard-buildkit-proto::pb::Definition values and can write them as binary protobuf for buildctl.

The current BuildKit compatibility baseline is recorded in the repository's provenance lock.

• Scratch and image sources with platform, resolve-mode, checksum and layer-limit options.
• Local sources with include, exclude, follow-path, session and shared-key options.
• Exec arguments, shell splitting, environment variables and working directories.
• Sandbox, host and none networking; sandbox and insecure security modes.
• Bind, scratch and cache mounts.
• File and environment secrets.
• SSH agent sockets with named IDs, targets, permissions and optional providers.
• Copy, mkdir, mkfile, remove and symlink file actions.
• Merge operations, worker filters, metadata, deterministic serialization and text/JSON dumps.

Session-less local sources receive a fresh local.unique on each marshal. For reproducible definitions, pin it with MarshalOpts::with_local_unique_id or Local::with_unique_id. The JSON dump is a Rust diagnostic format, not the buildctl debug dump-llb JSON schema.

SSH forwarding is Unix-only for the first release. Empty SSH IDs select the BuildKit default provider. Direct solves must register a provider with Bollard's solve driver; an unavailable required provider is rejected, while an optional provider is allowed to remain unavailable.

This crate only constructs graphs. Bollard's direct-definition solve API currently supports the DockerContainer and BuildkitDaemon drivers with the local exporter. A caller must explicitly grant network.host and security.insecure entitlements to a direct solve and, for a Docker-container daemon, configure the matching daemon allowance.

Direct solves own their session ID. Do not add a local.session attribute to a definition submitted through that API. Local sources without that attribute use the active solve session.

The graph builder is synchronous and does not use a network transport. With default features disabled, it resolves bollard-buildkit-proto without its RPC feature and does not pull tokio, tonic, TLS or an HTTP client stack.

The following features remain outside the initial release and are tracked for later compatible expansion: Git and HTTP sources, OCI-layout and image-blob sources, Diff and CDI operations, tmpfs and richer mount controls, richer exec metadata, multi-action file operations, richer exporters, gateway/frontend APIs and progress streaming.