storepb: construct labels.Labels directly during unmarshal

Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>

go.mod

@@ -124,6 +124,8 @@ require (
 	golang.org/x/exp v0.0.0-20240613232115-7f521ea00fb8
 )
 
+require github.com/VictoriaMetrics/easyproto v0.1.4 // indirect
+
 require (
 	cloud.google.com/go/auth v0.5.1 // indirect
 	cloud.google.com/go/auth/oauth2adapt v0.2.2 // indirect

go.sum

@@ -564,6 +564,8 @@ github.com/OneOfOne/xxhash v1.2.6 h1:U68crOE3y3MPttCMQGywZOLrTeF5HHJ3/vDBCJn9/bA
 github.com/OneOfOne/xxhash v1.2.6/go.mod h1:eZbhyaAYD41SGSSsnmcpxVoRiQ/MPUTjUdIIOT9Um7Q=
 github.com/QcloudApi/qcloud_sign_golang v0.0.0-20141224014652-e4130a326409/go.mod h1:1pk82RBxDY/JZnPQrtqHlUFfCctgdorsd9M06fMynOM=
 github.com/StackExchange/wmi v0.0.0-20190523213315-cbe66965904d/go.mod h1:3eOhrUMpNV+6aFIbp5/iudMxNCF27Vw2OZgy4xEx0Fg=
+github.com/VictoriaMetrics/easyproto v0.1.4 h1:r8cNvo8o6sR4QShBXQd1bKw/VVLSQma/V2KhTBPf+Sc=
+github.com/VictoriaMetrics/easyproto v0.1.4/go.mod h1:QlGlzaJnDfFd8Lk6Ci/fuLxfTo3/GThPs2KH23mv710=
 github.com/ajstarks/deck v0.0.0-20200831202436-30c9fc6549a9/go.mod h1:JynElWSGnm/4RlzPXRlREEwqTHAN3T56Bv2ITsFT3gY=
 github.com/ajstarks/deck/generate v0.0.0-20210309230005-c3f852c02e19/go.mod h1:T13YZdzov6OU0A1+RfKZiZN9ca6VeKdBdyDV+BY97Tk=
 github.com/ajstarks/svgo v0.0.0-20180226025133-644b8db467af/go.mod h1:K08gAheRH3/J6wwsYMMT4xOr94bZjxIelGM0+d/wbFw=

pkg/store/labelpb/stringlabels.go

@@ -0,0 +1,165 @@
+package labelpb
+
+import (
+	fmt "fmt"
+	"unsafe"
+
+	"github.com/VictoriaMetrics/easyproto"
+	"github.com/prometheus/prometheus/model/labels"
+)
+
+type StringLabelsBuilder struct {
+	buf []byte
+}
+
+func EncodeStringSize(stringLen int) int {
+	return sizeVarint(uint64(stringLen)) + stringLen
+}
+
+func labelSize(m *Label) (n int) {
+	// strings are encoded as length followed by contents.
+	l := len(m.Name)
+	n += l + sizeVarint(uint64(l))
+	l = len(m.Value)
+	n += l + sizeVarint(uint64(l))
+	return n
+}
+
+func encodeSize(data []byte, offset, v int) int {
+	if v < 1<<7 {
+		offset--
+		data[offset] = uint8(v)
+		return offset
+	}
+	return encodeVarint(data, offset, uint64(v))
+}
+
+func sizeVarint(x uint64) (n int) {
+	// Most common case first
+	if x < 1<<7 {
+		return 1
+	}
+	if x >= 1<<56 {
+		return 9
+	}
+	if x >= 1<<28 {
+		x >>= 28
+		n = 4
+	}
+	if x >= 1<<14 {
+		x >>= 14
+		n += 2
+	}
+	if x >= 1<<7 {
+		n++
+	}
+	return n + 1
+}
+
+func encodeVarint(data []byte, offset int, v uint64) int {
+	offset -= sizeVarint(v)
+	base := offset
+	for v >= 1<<7 {
+		data[offset] = uint8(v&0x7f | 0x80)
+		v >>= 7
+		offset++
+	}
+	data[offset] = uint8(v)
+	return base
+}
+
+func NewStringsLabelsBuilder(size int) *StringLabelsBuilder {
+	return &StringLabelsBuilder{
+		buf: make([]byte, size),
+	}
+}
+
+func (b *StringLabelsBuilder) Labels() labels.Labels {
+	return *(*labels.Labels)(unsafe.Pointer(&struct {
+		data string
+	}{
+		data: unsafe.String(unsafe.SliceData(b.buf), len(b.buf)),
+	}))
+}
+
+// GetLabelsBufferSize returns how many bytes you will need
+// for labels.Labels allocation. fieldNumLabels must be
+// repeated Labels foo = fieldNumLabels; (in proto file).
+func GetLabelsBufferSize(src []byte, fieldNumLabels uint32) (int, error) {
+	var (
+		fc   easyproto.FieldContext
+		size int
+		err  error
+	)
+
+	for len(src) > 0 {
+		src, err = fc.NextField(src)
+		if err != nil {
+			return 0, fmt.Errorf("cannot read next field in given byte slice: %w", err)
+		}
+
+		switch fc.FieldNum {
+		case fieldNumLabels:
+			data, ok := fc.MessageData()
+			if !ok {
+				return 0, fmt.Errorf("cannot read message data")
+			}
+			sz, err := getLabelEncodingProtobufSize(data)
+			if err != nil {
+				return 0, fmt.Errorf("getting label encoding size: %w", err)
+			}
+			size += sz
+		}
+	}
+	return size, nil
+}
+
+func getLabelEncodingProtobufSize(src []byte) (int, error) {
+	var (
+		fc  easyproto.FieldContext
+		err error
+		n   int
+	)
+	for len(src) > 0 {
+		src, err = fc.NextField(src)
+		if err != nil {
+			return 0, fmt.Errorf("cannot read next field in labels")
+		}
+		if fc.FieldNum > 2 {
+			return 0, fmt.Errorf("unexpected field number in labels")
+		}
+		val, ok := fc.String()
+		if !ok {
+			return 0, fmt.Errorf("cannot read string value in labels")
+		}
+
+		n += EncodeStringSize(len(val))
+	}
+	return n, nil
+}
+
+func (b *StringLabelsBuilder) Add(name, value string) {
+	i := len(b.buf)
+	i -= len(value)
+	copy(b.buf[i:], value)
+	i = encodeSize(b.buf, i, len(value))
+
+	i -= len(name)
+	copy(b.buf[i:], name)
+	encodeSize(b.buf, i, len(name))
+}
+
+func init() {
+	b := NewStringsLabelsBuilder(labelSize(&Label{
+		Name:  "name",
+		Value: "value",
+	}))
+
+	b.Add("name", "value")
+
+	lbls := b.Labels()
+
+	if lbls.String() != `{name="value"}` {
+		panic("only stringlabels build is supported in Thanos")
+	}
+}

pkg/store/labelpb/stringlabels_test.go

@@ -0,0 +1,20 @@
+package labelpb
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestStringLabelsBuilder(t *testing.T) {
+	b := NewStringsLabelsBuilder(labelSize(&Label{
+		Name:  "name",
+		Value: "value",
+	}))
+
+	b.Add("name", "value")
+
+	lbls := b.Labels()
+
+	require.Equal(t, `{name="value"}`, lbls.String())
+}

pkg/store/storepb/custom_test.go

@@ -20,6 +20,28 @@ import (
 	"github.com/thanos-io/thanos/pkg/store/labelpb"
 )
 
+func TestGetLabelsSize(t *testing.T) {
+	s := &Series{
+		Labels: labelpb.PromLabelsToLabelpbLabels(labels.FromStrings("a", "b")),
+		Chunks: []*AggrChunk{
+			{
+				MinTime: 1,
+				MaxTime: 2,
+				Raw:     &Chunk{Type: Chunk_XOR, Data: []byte{1, 2, 3}},
+			},
+		},
+	}
+
+	in, err := s.MarshalVT()
+	testutil.Ok(t, err)
+
+	sz, err := labelpb.GetLabelsBufferSize(in, 1)
+	testutil.Ok(t, err)
+
+	// 2 sizes, 2 values (a, b).
+	testutil.Equals(t, 4, sz)
+}
+
 type sample struct {
 	t int64
 	v float64