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Apache OpenDAL™ OCaml Binding

An OCaml binding for OpenDAL: access S3, GCS, Azure Blob, the local filesystem, and 50+ more services through one API, backed by the Rust core.

New to the model behind the API? Read Concepts first — service, operator, layer, and operation are the same four ideas in every language.

Experimental / Work in Progress

This binding is unreleased and experimental. APIs may change without notice. It is not published to opam. Build from source only.

Status​

Unreleased — work in progress. OCaml 4.10 or later (OCaml 5 not yet supported) due to an upstream constraint in ocaml-rs.

Capabilities​

  • Blocking API — all operations are synchronous; no async runtime required.
  • Full result-type error handling — every fallible function returns ('a, string) result; no exceptions for storage errors.
  • Streaming readers and writers — Operator.reader / Operator.writer for data that does not fit in memory.
  • Directory listing — batch (Operator.list) and streaming (Operator.lister + Operator.Lister.next) variants.
  • Capability introspection — check what a backend supports at runtime via Operator.info and the Operator.Capability module.
  • Services: every backend the Rust core supports is available; the binding is built against the full Rust crate.

Building from source​

The binding has no opam release yet. Install the toolchain, then build with dune:

# 1. Install opam (if not already installed)
bash -c "sh <(curl -fsSL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh)"

# 2. Create a 4.x switch (OCaml 5 is not supported)
opam switch create opendal-ocaml4.14 ocaml-base-compiler.4.14.0
eval $(opam env)

# 3. Install development tools (optional but recommended)
opam install -y utop odoc ounit2 ocaml-lsp-server ocamlformat ocamlformat-rpc

# 4. Build
cd bindings/ocaml
dune build

# 5. Run tests
dune test

You also need a working Rust toolchain (stable) for the build.rs step that compiles the Rust core into a native library.

  • Source: bindings/ocaml/
  • Services & configuration: /services
  • OCaml module reference: lib/operator.mli in the source tree

Next steps​

  1. Getting started — create an operator, read, write, and handle errors.