vendor/go.opencensus.io/internal/tagencoding/tagencoding.go

   1 // Copyright 2017, OpenCensus 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
  16 // Package tagencoding contains the tag encoding
  17 // used interally by the stats collector.
  18 package tagencoding // import "go.opencensus.io/internal/tagencoding"
  19
  20 type Values struct {
  21         Buffer     []byte
  22         WriteIndex int
  23         ReadIndex  int
  24 }
  25
  26 func (vb *Values) growIfRequired(expected int) {
  27         if len(vb.Buffer)-vb.WriteIndex < expected {
  28                 tmp := make([]byte, 2*(len(vb.Buffer)+1)+expected)
  29                 copy(tmp, vb.Buffer)
  30                 vb.Buffer = tmp
  31         }
  32 }
  33
  34 func (vb *Values) WriteValue(v []byte) {
  35         length := len(v) & 0xff
  36         vb.growIfRequired(1 + length)
  37
  38         // writing length of v
  39         vb.Buffer[vb.WriteIndex] = byte(length)
  40         vb.WriteIndex++
  41
  42         if length == 0 {
  43                 // No value was encoded for this key
  44                 return
  45         }
  46
  47         // writing v
  48         copy(vb.Buffer[vb.WriteIndex:], v[:length])
  49         vb.WriteIndex += length
  50 }
  51
  52 // ReadValue is the helper method to read the values when decoding valuesBytes to a map[Key][]byte.
  53 func (vb *Values) ReadValue() []byte {
  54         // read length of v
  55         length := int(vb.Buffer[vb.ReadIndex])
  56         vb.ReadIndex++
  57         if length == 0 {
  58                 // No value was encoded for this key
  59                 return nil
  60         }
  61
  62         // read value of v
  63         v := make([]byte, length)
  64         endIdx := vb.ReadIndex + length
  65         copy(v, vb.Buffer[vb.ReadIndex:endIdx])
  66         vb.ReadIndex = endIdx
  67         return v
  68 }
  69
  70 func (vb *Values) Bytes() []byte {
  71         return vb.Buffer[:vb.WriteIndex]
  72 }