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135 lines
4 KiB
Go
135 lines
4 KiB
Go
// Copyright The OpenTelemetry Authors
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// SPDX-License-Identifier: Apache-2.0
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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 an attribute set into a specific
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// string representation that supports caching, to avoid repeated
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// serialization. An example could be an exporter encoding the attribute
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// set into a wire representation.
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Encoder interface {
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// Encode returns the serialized encoding of the attribute set using
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// its Iterator. This result may be cached 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 attribute
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// encoder. Attribute encoders allocate these using `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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// defaultAttrEncoder uses a sync.Pool of buffers to reduce the number of
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// allocations used in encoding attributes. This implementation encodes a
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// comma-separated list of key=value, with '/'-escaping of '=', ',', and
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// '\'.
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defaultAttrEncoder struct {
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// pool is a pool of attribute set builders. The buffers in this pool
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// grow to a size that most attribute encodings will not allocate new
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// 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 attribute encoding where
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// keys or values contain either '=' or ','. Since there is no parser needed
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// for this encoding and its only requirement is to be unique, this choice is
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// arbitrary. Users will see these in some exporters (e.g., stdout), so the
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// backslash ('\') is used as a conventional choice.
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const escapeChar = '\\'
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var (
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_ Encoder = &defaultAttrEncoder{}
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// encoderIDCounter is for generating IDs for other attribute 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 *defaultAttrEncoder
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)
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// NewEncoderID returns a unique attribute encoder ID. It should be called
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// once per each type of attribute encoder. Preferably in init() or in var
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// 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 an attribute encoder that encodes attributes in such
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// a way that each escaped attribute's key is followed by an equal sign and
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// then by an escaped attribute's value. All key-value pairs are separated by
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// a comma.
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//
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// Escaping is done by prepending a backslash before either a backslash, equal
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// sign or a comma.
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func DefaultEncoder() Encoder {
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defaultEncoderOnce.Do(func() {
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defaultEncoderInstance = &defaultAttrEncoder{
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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 AttributeEncoder interface.
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func (d *defaultAttrEncoder) 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.IndexedAttribute()
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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 AttributeEncoder interface.
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func (*defaultAttrEncoder) 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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