context.go

Documentation: go.opentelemetry.io/otel/internal/baggage

     1  // Copyright The OpenTelemetry Authors
     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 baggage // import "go.opentelemetry.io/otel/internal/baggage"
    16  
    17  import "context"
    18  
    19  type baggageContextKeyType int
    20  
    21  const baggageKey baggageContextKeyType = iota
    22  
    23  // SetHookFunc is a callback called when storing baggage in the context.
    24  type SetHookFunc func(context.Context, List) context.Context
    25  
    26  // GetHookFunc is a callback called when getting baggage from the context.
    27  type GetHookFunc func(context.Context, List) List
    28  
    29  type baggageState struct {
    30  	list List
    31  
    32  	setHook SetHookFunc
    33  	getHook GetHookFunc
    34  }
    35  
    36  // ContextWithSetHook returns a copy of parent with hook configured to be
    37  // invoked every time ContextWithBaggage is called.
    38  //
    39  // Passing nil SetHookFunc creates a context with no set hook to call.
    40  func ContextWithSetHook(parent context.Context, hook SetHookFunc) context.Context {
    41  	var s baggageState
    42  	if v, ok := parent.Value(baggageKey).(baggageState); ok {
    43  		s = v
    44  	}
    45  
    46  	s.setHook = hook
    47  	return context.WithValue(parent, baggageKey, s)
    48  }
    49  
    50  // ContextWithGetHook returns a copy of parent with hook configured to be
    51  // invoked every time FromContext is called.
    52  //
    53  // Passing nil GetHookFunc creates a context with no get hook to call.
    54  func ContextWithGetHook(parent context.Context, hook GetHookFunc) context.Context {
    55  	var s baggageState
    56  	if v, ok := parent.Value(baggageKey).(baggageState); ok {
    57  		s = v
    58  	}
    59  
    60  	s.getHook = hook
    61  	return context.WithValue(parent, baggageKey, s)
    62  }
    63  
    64  // ContextWithList returns a copy of parent with baggage. Passing nil list
    65  // returns a context without any baggage.
    66  func ContextWithList(parent context.Context, list List) context.Context {
    67  	var s baggageState
    68  	if v, ok := parent.Value(baggageKey).(baggageState); ok {
    69  		s = v
    70  	}
    71  
    72  	s.list = list
    73  	ctx := context.WithValue(parent, baggageKey, s)
    74  	if s.setHook != nil {
    75  		ctx = s.setHook(ctx, list)
    76  	}
    77  
    78  	return ctx
    79  }
    80  
    81  // ListFromContext returns the baggage contained in ctx.
    82  func ListFromContext(ctx context.Context) List {
    83  	switch v := ctx.Value(baggageKey).(type) {
    84  	case baggageState:
    85  		if v.getHook != nil {
    86  			return v.getHook(ctx, v.list)
    87  		}
    88  		return v.list
    89  	default:
    90  		return nil
    91  	}
    92  }
    93
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