text: // Copyright 2017, OpenCensus Authors
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  //
  
  // Package tagencoding contains the tag encoding
  // used interally by the stats collector.
  package tagencoding // import "go.opencensus.io/internal/tagencoding"
  
  // Values represent the encoded buffer for the values.
  type Values struct {
  	Buffer     []byte
  	WriteIndex int
  	ReadIndex  int
  }
  
  func (vb *Values) growIfRequired(expected int) {
  	if len(vb.Buffer)-vb.WriteIndex < expected {
  		tmp := make([]byte, 2*(len(vb.Buffer)+1)+expected)
  		copy(tmp, vb.Buffer)
  		vb.Buffer = tmp
  	}
  }
  
  // WriteValue is the helper method to encode Values from map[Key][]byte.
  func (vb *Values) WriteValue(v []byte) {
  	length := len(v) & 0xff
  	vb.growIfRequired(1 + length)
  
  	// writing length of v
  	vb.Buffer[vb.WriteIndex] = byte(length)
  	vb.WriteIndex++
  
  	if length == 0 {
  		// No value was encoded for this key
  		return
  	}
  
  	// writing v
  	copy(vb.Buffer[vb.WriteIndex:], v[:length])
  	vb.WriteIndex += length
  }
  
  // ReadValue is the helper method to decode Values to a map[Key][]byte.
  func (vb *Values) ReadValue() []byte {
  	// read length of v
  	length := int(vb.Buffer[vb.ReadIndex])
  	vb.ReadIndex++
  	if length == 0 {
  		// No value was encoded for this key
  		return nil
  	}
  
  	// read value of v
  	v := make([]byte, length)
  	endIdx := vb.ReadIndex + length
  	copy(v, vb.Buffer[vb.ReadIndex:endIdx])
  	vb.ReadIndex = endIdx
  	return v
  }
  
  // Bytes returns a reference to already written bytes in the Buffer.
  func (vb *Values) Bytes() []byte {
  	return vb.Buffer[:vb.WriteIndex]
  }
  