Reference¶

Page	Covers
Subjects and patterns	The token rules, what `Match` does, and why validation refuses more than NATS does
The backend contract	`Backend`, `Session`, `Source`, `Capabilities`, `SubscriptionSpec`, and the one requirement placed on an implementer

Where the generated API listing lives¶

This tier is written by hand and states behaviour the type signatures do not. The generated listing of every exported symbol is on pkg.go.dev.

Errors¶

Sentinel	Returned by	When
`ErrInvalidPattern`	`ValidatePattern`, `New`	a subject pattern this module refuses
`ErrInvalidSubject`	`ValidateSubject`, `Publish`	a subject that cannot be published to
`ErrNotReady`	`Publish`, `Subscribe`	before the first `Start`, during a reactivation gap, or after `Stop`. `Publish` never returns `ErrStopped`, because a publisher's response to "no live activation" is the same whichever caused it
`ErrStopped`	`Subscribe`	once shutdown has begun: accepting a subscription that will never be supervised would be worse than refusing it
`ErrNoSource`	`PublishValue`	the bus was built without `Settings.Source`, which CloudEvents needs as half of an event's identity
`ErrNoSubscriptions`	`New`	`Settings.Subscriptions` is empty
`ErrQueueFull`	`Publish`	the subscription's overflow policy is `Fail`
`ErrNotSupported`	a backend, or `validateMode`	asked for a capability or delivery mode it does not have
`ErrContentType`	`Delivery.Decode`	the payload's `DataContentType` is not the bus's codec's
`ErrAlreadySettled`	`Delivery.Ack`, `Delivery.Nack`	a second settlement on one delivery; the first call wins
`ErrSettlementRefused`	a backend, via `Settle`	it could not perform a settlement: the source retired, the session closed, or the broker was unreachable

New also returns a plain error, not a sentinel, when called with a nil backend: "a bus needs a backend" is a caller mistake with nothing to match against programmatically, so it is not one of the sentinels above.

Constants¶

Symbol	Value	Meaning
`DefaultQueueBound`	`256`	How many messages a subscription may hold when `Bound` is zero. That there is a bound is this module's and not negotiable; the number is the caller's
`DefaultMaxProcessingTime`	five minutes	`MaxProcessingTime` when a subscription leaves it zero under `ExtendLease`