peake100/rogerRabbit-go

package amqpmiddleware

import "context"

// MetadataKey is used to store and fetch values on a context.Context
// amqpmiddleware.EventMetadata.
type MetadataKey string

// MethodInfo holds extracted information from the context passed into a method
// handler.
type MethodInfo struct {
    // OpAttempt: Some operations retry over disconnections. This is the attempt number,
    // starting at 0. Will be -1 if this is not an operation that is re-tried.
    OpAttempt int
}

// GetMethodInfo extracts context info from a middleware context.
func GetMethodInfo(ctx context.Context) (info MethodInfo) {
    if opAttempt, ok := ctx.Value(MetadataKey("opAttempt")).(int); ok {
        info.OpAttempt = opAttempt
    } else {
        info.OpAttempt = -1
    }

    return info
}

// EventMetadata is metadata passed into an event handler. Events cannot be cancelled,
// and therefore do not have contexts, so middleware-centric metadata should be added to
// and fetched from this argument.
type EventMetadata map[MetadataKey]interface{}

// EventInfo is information provided from the base library  that can be extracted from
// EventMetadata.
type EventInfo struct {
    // EventNum is the event number starting at 0. For Relays, this value will reset
    // each leg. -1 if unknown.
    EventNum int64
    // RelayLeg is the leg of the relay we are on. Each time a connection is
    // re-established, we hit a new relay "leg".
    //
    // -1 if this event feed does not pull directly from an underlying connection, and
    // therefore does not have a "LEG"
    RelayLeg int
}

// GetKey gets key from metadata. Returns nil if key could not be found
func (metadata EventMetadata) GetKey(key MetadataKey) interface{} {
    value, _ := metadata[key]
    return value
}

// GetEventInfo extracts EventInfo from EventMetadata.
func GetEventInfo(metadata EventMetadata) (info EventInfo) {
    if eventNum, ok := metadata.GetKey("EventNum").(int64); ok {
        info.EventNum = eventNum
    } else {
        info.EventNum = -1
    }

    if relayLeg, ok := metadata.GetKey("LegNum").(int); ok {
        info.RelayLeg = relayLeg
    } else {
        info.RelayLeg = -1
    }

    return info
}