Use a sync.Pool for Unmarshal

Attributes cause the most memory pressure. Start with caching those

Before
"""
12904 B/op         48 allocs/op
"""

After
"""
7483 B/op         34 allocs/op
"""

unmarshal.go

@@ -9,13 +9,22 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
+	"sync"
 )
 
 var (
 	errSDPInvalidSyntax       = errors.New("sdp: invalid syntax")
 	errSDPInvalidNumericValue = errors.New("sdp: invalid numeric value")
 	errSDPInvalidValue        = errors.New("sdp: invalid value")
 	errSDPInvalidPortValue    = errors.New("sdp: invalid port value")
+	errSDPCacheInvalid        = errors.New("sdp: invalid cache")
+
+	//nolint: gochecknoglobals
+	unmarshalCachePool = sync.Pool{
+		New: func() interface{} {
+			return &unmarshalCache{}
+		},
+	}
 )
 
 // UnmarshalString is the primary function that deserializes the session description
@@ -100,16 +109,27 @@ var (
 // |   s16  |    |    14 |    |     |    |  15 |   |    | 12 |   |   |     |   |   |    |   |    |
 // +--------+----+-------+----+-----+----+-----+---+----+----+---+---+-----+---+---+----+---+----+
 func (s *SessionDescription) UnmarshalString(value string) error {
+	var ok bool
 	l := new(lexer)
+	if l.cache, ok = unmarshalCachePool.Get().(*unmarshalCache); !ok {
+		return errSDPCacheInvalid
+	}
+	defer unmarshalCachePool.Put(l.cache)
+
+	l.cache.reset()
 	l.desc = s
 	l.value = value
+
 	for state := s1; state != nil; {
 		var err error
 		state, err = state(l)
 		if err != nil {
 			return err
 		}
 	}
+
+	s.Attributes = l.cache.cloneSessionAttributes()
+	populateMediaAttributes(l.cache, l.desc)
 	return nil
 }
 
@@ -730,18 +750,19 @@ func unmarshalSessionAttribute(l *lexer) (stateFn, error) {
 	}
 
 	i := strings.IndexRune(value, ':')
-	var a Attribute
+	a := l.cache.getSessionAttribute()
 	if i > 0 {
-		a = NewAttribute(value[:i], value[i+1:])
+		a.Key = value[:i]
+		a.Value = value[i+1:]
 	} else {
-		a = NewPropertyAttribute(value)
+		a.Key = value
 	}
 
-	l.desc.Attributes = append(l.desc.Attributes, a)
 	return s11, nil
 }
 
 func unmarshalMediaDescription(l *lexer) (stateFn, error) {
+	populateMediaAttributes(l.cache, l.desc)
 	var newMediaDesc MediaDescription
 
 	// <media>
@@ -869,15 +890,14 @@ func unmarshalMediaAttribute(l *lexer) (stateFn, error) {
 	}
 
 	i := strings.IndexRune(value, ':')
-	var a Attribute
+	a := l.cache.getMediaAttribute()
 	if i > 0 {
-		a = NewAttribute(value[:i], value[i+1:])
+		a.Key = value[:i]
+		a.Value = value[i+1:]
 	} else {
-		a = NewPropertyAttribute(value)
+		a.Key = value
 	}
 
-	latestMediaDesc := l.desc.MediaDescriptions[len(l.desc.MediaDescriptions)-1]
-	latestMediaDesc.Attributes = append(latestMediaDesc.Attributes, a)
 	return s14, nil
 }
 
@@ -927,3 +947,10 @@ func parsePort(value string) (int, error) {
 
 	return port, nil
 }
+
+func populateMediaAttributes(c *unmarshalCache, s *SessionDescription) {
+	if len(s.MediaDescriptions) != 0 {
+		lastMediaDesc := s.MediaDescriptions[len(s.MediaDescriptions)-1]
+		lastMediaDesc.Attributes = c.cloneMediaAttributes()
+	}
+}

unmarshal_cache.go

@@ -0,0 +1,44 @@
+// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
+// SPDX-License-Identifier: MIT
+
+package sdp
+
+type unmarshalCache struct {
+	sessionAttributes []Attribute
+	mediaAttributes   []Attribute
+}
+
+func (c *unmarshalCache) reset() {
+	c.sessionAttributes = c.sessionAttributes[:0]
+	c.mediaAttributes = c.mediaAttributes[:0]
+}
+
+func (c *unmarshalCache) getSessionAttribute() *Attribute {
+	c.sessionAttributes = append(c.sessionAttributes, Attribute{})
+	return &c.sessionAttributes[len(c.sessionAttributes)-1]
+}
+
+func (c *unmarshalCache) cloneSessionAttributes() []Attribute {
+	if len(c.sessionAttributes) == 0 {
+		return nil
+	}
+	s := make([]Attribute, len(c.sessionAttributes))
+	copy(s, c.sessionAttributes)
+	c.sessionAttributes = c.sessionAttributes[:0]
+	return s
+}
+
+func (c *unmarshalCache) getMediaAttribute() *Attribute {
+	c.mediaAttributes = append(c.mediaAttributes, Attribute{})
+	return &c.mediaAttributes[len(c.mediaAttributes)-1]
+}
+
+func (c *unmarshalCache) cloneMediaAttributes() []Attribute {
+	if len(c.mediaAttributes) == 0 {
+		return nil
+	}
+	s := make([]Attribute, len(c.mediaAttributes))
+	copy(s, c.mediaAttributes)
+	c.mediaAttributes = c.mediaAttributes[:0]
+	return s
+}

util.go

@@ -311,7 +311,8 @@ func (s *SessionDescription) GetPayloadTypeForCodec(wanted Codec) (uint8, error)
 type stateFn func(*lexer) (stateFn, error)
 
 type lexer struct {
-	desc *SessionDescription
+	desc  *SessionDescription
+	cache *unmarshalCache
 	baseLexer
 }