151 lines
4.4 KiB
Go
151 lines
4.4 KiB
Go
// Copyright The OpenTelemetry Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package attribute // import "go.opentelemetry.io/otel/attribute"
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import (
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"bytes"
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"sync"
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"sync/atomic"
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)
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type (
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// Encoder is a mechanism for serializing a label set into a
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// specific string representation that supports caching, to
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// avoid repeated serialization. An example could be an
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// exporter encoding the label set into a wire representation.
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Encoder interface {
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// Encode returns the serialized encoding of the label
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// set using its Iterator. This result may be cached
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// by a attribute.Set.
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Encode(iterator Iterator) string
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// ID returns a value that is unique for each class of
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// label encoder. Label encoders allocate these using
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// `NewEncoderID`.
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ID() EncoderID
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}
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// EncoderID is used to identify distinct Encoder
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// implementations, for caching encoded results.
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EncoderID struct {
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value uint64
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}
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// defaultLabelEncoder uses a sync.Pool of buffers to reduce
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// the number of allocations used in encoding labels. This
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// implementation encodes a comma-separated list of key=value,
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// with '/'-escaping of '=', ',', and '\'.
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defaultLabelEncoder struct {
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// pool is a pool of labelset builders. The buffers in this
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// pool grow to a size that most label encodings will not
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// allocate new memory.
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pool sync.Pool // *bytes.Buffer
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}
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)
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// escapeChar is used to ensure uniqueness of the label encoding where
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// keys or values contain either '=' or ','. Since there is no parser
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// needed for this encoding and its only requirement is to be unique,
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// this choice is arbitrary. Users will see these in some exporters
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// (e.g., stdout), so the backslash ('\') is used as a conventional choice.
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const escapeChar = '\\'
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var (
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_ Encoder = &defaultLabelEncoder{}
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// encoderIDCounter is for generating IDs for other label
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// encoders.
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encoderIDCounter uint64
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defaultEncoderOnce sync.Once
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defaultEncoderID = NewEncoderID()
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defaultEncoderInstance *defaultLabelEncoder
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)
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// NewEncoderID returns a unique label encoder ID. It should be
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// called once per each type of label encoder. Preferably in init() or
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// in var definition.
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func NewEncoderID() EncoderID {
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return EncoderID{value: atomic.AddUint64(&encoderIDCounter, 1)}
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}
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// DefaultEncoder returns a label encoder that encodes labels
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// in such a way that each escaped label's key is followed by an equal
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// sign and then by an escaped label's value. All key-value pairs are
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// separated by a comma.
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//
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// Escaping is done by prepending a backslash before either a
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// backslash, equal sign or a comma.
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func DefaultEncoder() Encoder {
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defaultEncoderOnce.Do(func() {
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defaultEncoderInstance = &defaultLabelEncoder{
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pool: sync.Pool{
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New: func() interface{} {
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return &bytes.Buffer{}
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},
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},
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}
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})
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return defaultEncoderInstance
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}
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// Encode is a part of an implementation of the LabelEncoder
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// interface.
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func (d *defaultLabelEncoder) Encode(iter Iterator) string {
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buf := d.pool.Get().(*bytes.Buffer)
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defer d.pool.Put(buf)
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buf.Reset()
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for iter.Next() {
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i, keyValue := iter.IndexedLabel()
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if i > 0 {
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_, _ = buf.WriteRune(',')
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}
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copyAndEscape(buf, string(keyValue.Key))
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_, _ = buf.WriteRune('=')
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if keyValue.Value.Type() == STRING {
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copyAndEscape(buf, keyValue.Value.AsString())
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} else {
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_, _ = buf.WriteString(keyValue.Value.Emit())
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}
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}
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return buf.String()
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}
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// ID is a part of an implementation of the LabelEncoder interface.
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func (*defaultLabelEncoder) ID() EncoderID {
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return defaultEncoderID
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}
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// copyAndEscape escapes `=`, `,` and its own escape character (`\`),
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// making the default encoding unique.
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func copyAndEscape(buf *bytes.Buffer, val string) {
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for _, ch := range val {
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switch ch {
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case '=', ',', escapeChar:
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buf.WriteRune(escapeChar)
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}
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buf.WriteRune(ch)
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}
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}
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// Valid returns true if this encoder ID was allocated by
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// `NewEncoderID`. Invalid encoder IDs will not be cached.
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func (id EncoderID) Valid() bool {
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return id.value != 0
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}
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