Context helpers

When an event is dispatched through the event bus, the Envelope fields are injected into the context via WithEnvelope. Event handlers can read these values using the helper functions below.

WithEnvelope

func WithEnvelope(ctx context.Context, env *Envelope) context.Context

Injects all envelope fields into the context. Called automatically by the event bus before invoking handlers. You should not normally need to call this directly.

Reader functions

func StreamIDFromContext(ctx context.Context) string
func AggregateIDFromContext(ctx context.Context) string
func EventIDFromContext(ctx context.Context) uuid.UUID
func VersionFromContext(ctx context.Context) uint64
func GlobalVersionFromContext(ctx context.Context) uint64
func OccurredAtFromContext(ctx context.Context) time.Time
func MetadataFromContext(ctx context.Context) map[string]any

All functions return the zero value for their type if the key is not present in the context.

Example

func (p *Projector) OnTaskCreated(ctx context.Context, e *events.TaskCreated) error {
    eventID  := eventsourcing.EventIDFromContext(ctx)          // uuid.UUID
    streamID := eventsourcing.StreamIDFromContext(ctx)         // string
    version  := eventsourcing.VersionFromContext(ctx)          // uint64
    occurred := eventsourcing.OccurredAtFromContext(ctx)       // time.Time
    meta     := eventsourcing.MetadataFromContext(ctx)         // map[string]any

    log.Printf("[%s] event %s v%d at %s", streamID, eventID, version, occurred)
    _ = meta
    return nil
}

Causation

func WithCausation(ctx context.Context, causation string) context.Context
func CausationFromContext(ctx context.Context) string

Propagate a causation ID (e.g., the originating command or event ID) through the context for correlation in event chains.

ctx = eventsourcing.WithCausation(ctx, commandID.String())
_, err := handler(ctx, cmd)

// In event handler:
cause := eventsourcing.CausationFromContext(ctx)