Gitility.ODB.RangeBackend behaviour (Gitility v0.2.0)

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The behaviour for byte-range access to a published pack store.

One backend module serves both access policies — eager hydration (Gitility.ODB.PackFetch) and lazy range reads (Gitility.ODB.PackRange) — because they differ in policy, not transport. The backend speaks whatever moves bytes: Req against S3-style signed URLs, database blob chunks, a local directory of published artifacts. Credentials stay inside the provider process unless a native transport is explicitly chosen.

The provider model matches Gitility.ODB.Backend: read-only state from init/1, stateless callbacks dispatched concurrently.

Ranges arrive coalesced (adjacent wanted ranges merged up to a configured request maximum). Every returned binary must be exactly range.length bytes — a short read is a backend error, never padded or truncated silently. All fetched pack data is checksum-verified downstream before use, so a corrupt or stale byte range fails loudly.

Summary

Types

state()

Opaque backend state, produced by init/1, passed read-only.

Callbacks

init(term)

Builds the backend state from the configuration term given to the adapter (Gitility.ODB.PackFetch.start_link/1 or Gitility.ODB.PackRange.start_link/1).

manifest(state)

Fetches the current pack inventory. Called at open and on refresh; a new manifest generation must never rewrite an existing pack's bytes.

read_ranges(list, state)

Reads the requested byte ranges. Every requested range must appear in the result map with exactly length bytes.

terminate(term, state)

Cleanup on provider shutdown. Optional.

Types

state()

@type state() :: term()

Opaque backend state, produced by init/1, passed read-only.

Callbacks

init(term)

@callback init(term()) :: {:ok, state()} | {:error, term()}

Builds the backend state from the configuration term given to the adapter (Gitility.ODB.PackFetch.start_link/1 or Gitility.ODB.PackRange.start_link/1).

This callback runs in the process calling start_link/1, before the provider tree exists. Processes it starts are linked to that caller unless the backend supervises them itself. Start long-lived resources under your own supervisor and pass their registered name or pid in the init argument.

manifest(state)

@callback manifest(state()) :: {:ok, Gitility.PackManifest.t()} | {:error, term()}

Fetches the current pack inventory. Called at open and on refresh; a new manifest generation must never rewrite an existing pack's bytes.

read_ranges(list, state)

@callback read_ranges([Gitility.ByteRange.t()], state()) ::
  {:ok, %{required(Gitility.ByteRange.t()) => binary()}} | {:error, term()}

Reads the requested byte ranges. Every requested range must appear in the result map with exactly length bytes.

terminate(term, state)

(optional) 
@callback terminate(term(), state()) :: term()

Cleanup on provider shutdown. Optional.