github.com/containerd/containerd@v22.0.0-20200918172823-438c87b8e050+incompatible/events/events.go (about)

     1  /*
     2     Copyright The containerd Authors.
     3  
     4     Licensed under the Apache License, Version 2.0 (the "License");
     5     you may not use this file except in compliance with the License.
     6     You may obtain a copy of the License at
     7  
     8         http://www.apache.org/licenses/LICENSE-2.0
     9  
    10     Unless required by applicable law or agreed to in writing, software
    11     distributed under the License is distributed on an "AS IS" BASIS,
    12     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13     See the License for the specific language governing permissions and
    14     limitations under the License.
    15  */
    16  
    17  package events
    18  
    19  import (
    20  	"context"
    21  	"time"
    22  
    23  	"github.com/containerd/typeurl"
    24  	"github.com/gogo/protobuf/types"
    25  )
    26  
    27  // Envelope provides the packaging for an event.
    28  type Envelope struct {
    29  	Timestamp time.Time
    30  	Namespace string
    31  	Topic     string
    32  	Event     *types.Any
    33  }
    34  
    35  // Field returns the value for the given fieldpath as a string, if defined.
    36  // If the value is not defined, the second value will be false.
    37  func (e *Envelope) Field(fieldpath []string) (string, bool) {
    38  	if len(fieldpath) == 0 {
    39  		return "", false
    40  	}
    41  
    42  	switch fieldpath[0] {
    43  	// unhandled: timestamp
    44  	case "namespace":
    45  		return e.Namespace, len(e.Namespace) > 0
    46  	case "topic":
    47  		return e.Topic, len(e.Topic) > 0
    48  	case "event":
    49  		decoded, err := typeurl.UnmarshalAny(e.Event)
    50  		if err != nil {
    51  			return "", false
    52  		}
    53  
    54  		adaptor, ok := decoded.(interface {
    55  			Field([]string) (string, bool)
    56  		})
    57  		if !ok {
    58  			return "", false
    59  		}
    60  		return adaptor.Field(fieldpath[1:])
    61  	}
    62  	return "", false
    63  }
    64  
    65  // Event is a generic interface for any type of event
    66  type Event interface{}
    67  
    68  // Publisher posts the event.
    69  type Publisher interface {
    70  	Publish(ctx context.Context, topic string, event Event) error
    71  }
    72  
    73  // Forwarder forwards an event to the underlying event bus
    74  type Forwarder interface {
    75  	Forward(ctx context.Context, envelope *Envelope) error
    76  }
    77  
    78  // Subscriber allows callers to subscribe to events
    79  type Subscriber interface {
    80  	Subscribe(ctx context.Context, filters ...string) (ch <-chan *Envelope, errs <-chan error)
    81  }