github.com/hasnat/dolt/go@v0.0.0-20210628190320-9eb5d843fbb7/libraries/events/context.go (about)

     1  // Copyright 2019 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package events
    16  
    17  import (
    18  	"context"
    19  	"fmt"
    20  )
    21  
    22  type contextKeyT struct {
    23  }
    24  
    25  // contextEventKey key used for storing and retrieving an event from the context.
    26  var contextEventKey = contextKeyT{}
    27  
    28  // NewContextForEvent creates a new context with the event provided
    29  func NewContextForEvent(ctx context.Context, evt *Event) context.Context {
    30  	return context.WithValue(ctx, contextEventKey, evt)
    31  }
    32  
    33  // GetEventFromContext retrieves the event from the context if one exists.
    34  func GetEventFromContext(ctx context.Context) *Event {
    35  	val := ctx.Value(contextEventKey)
    36  
    37  	if val == nil {
    38  		return nil
    39  	}
    40  
    41  	evt, ok := val.(*Event)
    42  
    43  	if !ok {
    44  		panic(fmt.Errorf("value stored in context with key '%s' is not an event", contextEventKey))
    45  	}
    46  
    47  	return evt
    48  }