Get capabilities

GET

/v0/capabilities

Returns a summary of supported features and limits.

Authorizations

• bearer_auth

Responses

200

Capability document

A deployment’s self-description (API spec, “Capability discovery”).

A remote client fetches this from GET /v0/capabilities and caches it; an embedded engine exposes the same document as a constant. SDK gating logic is therefore identical for both backends: check supports or has_profile, and treat a not_supported error as authoritative when the two disagree.

object

features

Named features and whether this deployment supports them. An absent key means unsupported.

object

key

additional properties

boolean

limits

Advisory numeric limits clients may use to pre-validate requests.

object

key

additional properties

integer format: int64

profiles

required

Advertised profiles, each plane/version. All-or-nothing: every required op of an advertised profile is implemented.

Array<string>

protocol_version

required

The protocol generation, currently v0.

string

401

Unauthorized

HTTP error body used by LoonFS APIs.

object

code

required

Stable machine-readable reason from the ErrorCode registry.

Carried as a string so clients keep working when a newer server introduces a code they do not know; use ErrorCode::parse for typed access.

string

details

One of:

null

null

object

Structured context for the code, present when the failure carries machine-usable identity (API spec, “Standard error contract”). Boxed so the rare detailed error does not widen every error-carrying result.

object

active_acquired_at_ms

Unix milliseconds at which the current epoch’s acquirer took it, when the head recorded one. Writer ids are process labels, so two runs on one machine can share one; the stamp is what tells them apart.

integer | null format: int64

active_deletion_seq

One of:

null

null

integer

Deletion generation actually active for the inode.

integer format: int64

active_writer

Writer id recorded by the current epoch’s acquirer, when the head recorded one.

string | null

active_writer_epoch

One of:

null

null

integer

Epoch that currently owns the namespace.

integer format: int64

actual_revision

One of:

null

null

integer

Revision that is actually current; absent when the inode has none.

integer format: int64

after_seq

One of:

null

null

integer

Change-feed cursor the request asked to resume after.

integer format: int64

commit_id

One of:

null

null

string

Idempotency key of the commit the error concerns.

string

committed_seq

One of:

null

null

integer

Sequence at which that commit id already landed. Present when the failure was decided against a durable commit receipt, which is what holds the sequence; absent when nothing has committed under the id yet and two live requests are simply claiming it at once.

integer format: int64

expected_revision

One of:

null

null

integer

Revision the request expected to be current.

integer format: int64

fenced_epoch

One of:

null

null

integer

Epoch the failing writer session held when it was displaced.

integer format: int64

inode_id

One of:

null

null

integer

Inode the failed precondition or operation targeted.

integer format: int64

operation_index

Position, in the request’s operation list, of the operation that failed. A commit applies all of its operations or none of them, so this names the one that stopped the whole request.

integer | null format: int32

requested_deletion_seq

One of:

null

null

integer

Deletion generation an undelete asked to recover.

integer format: int64

retention_floor_seq

One of:

null

null

integer

Oldest sequence still promised for incremental replay.

integer format: int64

feature

For not_supported errors, the capability-document feature key the client should reconcile against.

string | null

message

required

Human-readable error message.

string

request_id

Correlation id the server assigned to the failed request; the same value is sent as the x-request-id response header.

string | null