/
labelencoder.go
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/
labelencoder.go
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// Copyright The OpenTelemetry 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 metric
import (
"bytes"
"sync"
"go.opentelemetry.io/otel/api/core"
)
// escapeChar is used to ensure uniqueness of the label encoding where
// keys or values contain either '=' or ','. Since there is no parser
// needed for this encoding and its only requirement is to be unique,
// this choice is arbitrary. Users will see these in some exporters
// (e.g., stdout), so the backslash ('\') is used a conventional choice.
const escapeChar = '\\'
type defaultLabelEncoder struct {
// pool is a pool of labelset builders. The buffers in this
// pool grow to a size that most label encodings will not
// allocate new memory.
pool sync.Pool // *bytes.Buffer
}
var _ LabelEncoder = &defaultLabelEncoder{}
// NewDefaultLabelEncoder returns a label encoder that encodes labels
// in such a way that each escaped label's key is followed by an equal
// sign and then by an escaped label's value. All key-value pairs are
// separated by a comma.
//
// Escaping is done by prepending a backslash before either a
// backslash, equal sign or a comma.
func NewDefaultLabelEncoder() LabelEncoder {
return &defaultLabelEncoder{
pool: sync.Pool{
New: func() interface{} {
return &bytes.Buffer{}
},
},
}
}
// Encode is a part of an implementation of the LabelEncoder
// interface.
func (d *defaultLabelEncoder) Encode(iter LabelIterator) string {
buf := d.pool.Get().(*bytes.Buffer)
defer d.pool.Put(buf)
buf.Reset()
for iter.Next() {
i, kv := iter.IndexedLabel()
if i > 0 {
_, _ = buf.WriteRune(',')
}
copyAndEscape(buf, string(kv.Key))
_, _ = buf.WriteRune('=')
if kv.Value.Type() == core.STRING {
copyAndEscape(buf, kv.Value.AsString())
} else {
_, _ = buf.WriteString(kv.Value.Emit())
}
}
return buf.String()
}
// ID is a part of an implementation of the LabelEncoder interface.
func (*defaultLabelEncoder) ID() int64 {
return defaultLabelEncoderID
}
func copyAndEscape(buf *bytes.Buffer, val string) {
for _, ch := range val {
switch ch {
case '=', ',', escapeChar:
buf.WriteRune(escapeChar)
}
buf.WriteRune(ch)
}
}