github.com/m3db/m3@v1.5.0/src/query/source/source.go (about)

     1  // Copyright (c) 2021 Uber Technologies, Inc.
     2  //
     3  // Permission is hereby granted, free of charge, to any person obtaining a copy
     4  // of this software and associated documentation files (the "Software"), to deal
     5  // in the Software without restriction, including without limitation the rights
     6  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
     7  // copies of the Software, and to permit persons to whom the Software is
     8  // furnished to do so, subject to the following conditions:
     9  //
    10  // The above copyright notice and this permission notice shall be included in
    11  // all copies or substantial portions of the Software.
    12  //
    13  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    14  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    15  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    16  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    17  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    18  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
    19  // THE SOFTWARE.
    20  
    21  // Package source identifies the source of query requests.
    22  package source
    23  
    24  import (
    25  	"context"
    26  )
    27  
    28  type key int
    29  
    30  const (
    31  	typedKey key = iota
    32  	rawKey
    33  )
    34  
    35  // Deserializer deserializes the raw source bytes into a type for easier use.
    36  // The raw source can be nil and the Deserializer can return a typed empty value for the application.
    37  type Deserializer func([]byte) (interface{}, error)
    38  
    39  // NewContext returns a new context with the source bytes as a value if the source is non-nil.
    40  // If a non-nil deserializer is provided an additional typed value is added for easier use.
    41  func NewContext(ctx context.Context, source []byte, deserialize Deserializer) (context.Context, error) {
    42  	if source == nil {
    43  		return ctx, nil
    44  	}
    45  	ctx = context.WithValue(ctx, rawKey, source)
    46  	if deserialize != nil {
    47  		typed, err := deserialize(source)
    48  		if err != nil {
    49  			return nil, err
    50  		}
    51  		ctx = context.WithValue(ctx, typedKey, typed)
    52  	}
    53  	return ctx, nil
    54  }
    55  
    56  // FromContext extracts the typed source, or false if it doesn't exist.
    57  func FromContext(ctx context.Context) (interface{}, bool) {
    58  	typed := ctx.Value(typedKey)
    59  	if typed == nil {
    60  		return nil, false
    61  	}
    62  	return typed, true
    63  }
    64  
    65  // RawFromContext extracts the raw bytes of the source, or false if it doesn't exist.
    66  // This is used by middleware to propagate the source across API boundaries. Application code should use FromContext.
    67  func RawFromContext(ctx context.Context) ([]byte, bool) {
    68  	b, ok := ctx.Value(rawKey).([]byte)
    69  	return b, ok
    70  }