go.uber.org/yarpc@v1.72.1/internal/digester/digester.go (about)

     1  // Copyright (c) 2022 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 digester
    22  
    23  import "sync"
    24  
    25  var _digesterPool = sync.Pool{New: func() interface{} {
    26  	return &Digester{make([]byte, 0, 128)}
    27  }}
    28  
    29  // Digester creates a null-delimited byte slice from a series of strings. It's
    30  // an efficient way to create map keys.
    31  //
    32  // This helps because (1) appending to a string allocates and (2) converting a
    33  // byte slice to a string allocates, but (3) the Go compiler optimizes away
    34  // byte-to-string conversions in map lookups. Using this type to build up a key
    35  // and doing map lookups with myMap[string(d.digest())] is fast and
    36  // zero-allocation.
    37  type Digester struct {
    38  	bs []byte
    39  }
    40  
    41  // New creates a new Digester.
    42  // For optimal performance, be sure to call "Free" on each digester.
    43  func New() *Digester {
    44  	d := _digesterPool.Get().(*Digester)
    45  	d.bs = d.bs[:0]
    46  	return d
    47  }
    48  
    49  // Add adds a string to the digester slice.
    50  func (d *Digester) Add(s string) {
    51  	if len(d.bs) > 0 {
    52  		// separate labels with a null byte
    53  		d.bs = append(d.bs, '\x00')
    54  	}
    55  	d.bs = append(d.bs, s...)
    56  }
    57  
    58  // Digest returns a map key for the digester.
    59  func (d *Digester) Digest() []byte {
    60  	return d.bs
    61  }
    62  
    63  // Free is called to indicate that the digester can be returned to the pool to
    64  // be used in another context.
    65  func (d *Digester) Free() {
    66  	_digesterPool.Put(d)
    67  }