Firkin

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A Plug-based library for building S3-compatible object storage APIs in Elixir.

Firkin handles the S3 HTTP protocol — signature verification, XML response formatting, operation routing, multipart upload orchestration — and delegates actual storage operations to a user-provided backend module implementing the Firkin.Backend behaviour.

Installation

Add firkin to your list of dependencies in mix.exs:

def deps do
  [
    {:firkin, "~> 0.2.2"}
  ]
end

Documentation is published on HexDocs.

Usage

Define a backend module implementing Firkin.Backend:

defmodule MyApp.S3Backend do
  @behaviour Firkin.Backend

  @impl true
  def lookup_credential(access_key_id) do
    # Return {:ok, %Firkin.Credential{}} or {:error, :not_found}
  end

  @impl true
  def list_buckets(_context) do
    {:ok, [%Firkin.Bucket{name: "my-bucket", creation_date: ~U[2024-01-01 00:00:00Z]}]}
  end

  # ... implement remaining callbacks
end

Mount the plug in your router:

forward "/s3", Firkin.Plug, backend: MyApp.S3Backend, region: "us-east-1"

Telemetry

Firkin emits a [:firkin, :request, :start | :stop | :exception] span for every request. Attach handlers using module/function captures — not anonymous functions — ideally from your Application.start/2:

:telemetry.attach_many(
  "my-firkin-handler",
  [
    [:firkin, :request, :start],
    [:firkin, :request, :stop],
    [:firkin, :request, :exception]
  ],
  &MyApp.FirkinTelemetry.handle_event/4,
  %{}
)

Stop metadata includes the S3 :operation (e.g. :put_object), the :bucket, :key, HTTP :status, the authenticated :access_key_id and (for error responses) the :error_code. See Firkin.Telemetry for the full event contract.

GitHub Mirror

Eventually, Forgejo will support fully federated operation, but for now there's a mirror of this repository on GitHub - feel free to open issues and PRs there.

Licence

Apache-2.0