cmd/pprof/internal: use and accept packed encoding for repeated fields

Packed encoding is the default on the proto3 format. Profiles generated
in the profile.proto format by third parties cannot be decoded by the
Go pprof tool, since its proto decoder does not recognize packed
encoding for repeated fields.

In particular this issue prevents go tool pprof from reading profiles
generated by the version of pprof in github.com/google/pprof

Profiles generated by go tool pprof after this change will use packed
repeating fields, so older versions of pprof will not be able to read
them. pprof will continue to be able to read profiles generated before
this change.

Change-Id: Ife0b353a535ae1e495515b9bcec588dd967e171b
Reviewed-on: https://go-review.googlesource.com/21240
Reviewed-by: David Symonds <dsymonds@golang.org>
Run-TryBot: David Symonds <dsymonds@golang.org>

src/cmd/pprof/internal/profile/proto.go

@@ -64,6 +64,20 @@ func encodeUint64(b *buffer, tag int, x uint64) {
 }
 
 func encodeUint64s(b *buffer, tag int, x []uint64) {
+	if len(x) > 2 {
+		// Use packed encoding
+		n1 := len(b.data)
+		for _, u := range x {
+			encodeVarint(b, u)
+		}
+		n2 := len(b.data)
+		encodeLength(b, tag, n2-n1)
+		n3 := len(b.data)
+		copy(b.tmp[:], b.data[n2:n3])
+		copy(b.data[n1+(n3-n2):], b.data[n1:n2])
+		copy(b.data[n1:], b.tmp[:n3-n2])
+		return
+	}
 	for _, u := range x {
 		encodeUint64(b, tag, u)
 	}
@@ -88,6 +102,26 @@ func encodeInt64Opt(b *buffer, tag int, x int64) {
 	encodeInt64(b, tag, x)
 }
 
+func encodeInt64s(b *buffer, tag int, x []int64) {
+	if len(x) > 2 {
+		// Use packed encoding
+		n1 := len(b.data)
+		for _, u := range x {
+			encodeVarint(b, uint64(u))
+		}
+		n2 := len(b.data)
+		encodeLength(b, tag, n2-n1)
+		n3 := len(b.data)
+		copy(b.tmp[:], b.data[n2:n3])
+		copy(b.data[n1+(n3-n2):], b.data[n1:n2])
+		copy(b.data[n1:], b.tmp[:n3-n2])
+		return
+	}
+	for _, u := range x {
+		encodeInt64(b, tag, u)
+	}
+}
+
 func encodeString(b *buffer, tag int, x string) {
 	encodeLength(b, tag, len(x))
 	b.data = append(b.data, x...)
@@ -243,6 +277,20 @@ func decodeInt64(b *buffer, x *int64) error {
 }
 
 func decodeInt64s(b *buffer, x *[]int64) error {
+	if b.typ == 2 {
+		// Packed encoding
+		data := b.data
+		for len(data) > 0 {
+			var u uint64
+			var err error
+
+			if u, data, err = decodeVarint(data); err != nil {
+				return err
+			}
+			*x = append(*x, int64(u))
+		}
+		return nil
+	}
 	var i int64
 	if err := decodeInt64(b, &i); err != nil {
 		return err
@@ -260,6 +308,20 @@ func decodeUint64(b *buffer, x *uint64) error {
 }
 
 func decodeUint64s(b *buffer, x *[]uint64) error {
+	if b.typ == 2 {
+		data := b.data
+		// Packed encoding
+		for len(data) > 0 {
+			var u uint64
+			var err error
+
+			if u, data, err = decodeVarint(data); err != nil {
+				return err
+			}
+			*x = append(*x, u)
+		}
+		return nil
+	}
 	var u uint64
 	if err := decodeUint64(b, &u); err != nil {
 		return err

src/cmd/pprof/internal/profile/proto_test.go

@@ -0,0 +1,67 @@
+package profile
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestPackedEncoding(t *testing.T) {
+
+	type testcase struct {
+		uint64s []uint64
+		int64s  []int64
+		encoded []byte
+	}
+	for i, tc := range []testcase{
+		{
+			[]uint64{0, 1, 10, 100, 1000, 10000},
+			[]int64{1000, 0, 1000},
+			[]byte{10, 8, 0, 1, 10, 100, 232, 7, 144, 78, 18, 5, 232, 7, 0, 232, 7},
+		},
+		{
+			[]uint64{10000},
+			nil,
+			[]byte{8, 144, 78},
+		},
+		{
+			nil,
+			[]int64{-10000},
+			[]byte{16, 240, 177, 255, 255, 255, 255, 255, 255, 255, 1},
+		},
+	} {
+		source := &packedInts{tc.uint64s, tc.int64s}
+		if got, want := marshal(source), tc.encoded; !reflect.DeepEqual(got, want) {
+			t.Errorf("failed encode %d, got %v, want %v", i, got, want)
+		}
+
+		dest := new(packedInts)
+		if err := unmarshal(tc.encoded, dest); err != nil {
+			t.Errorf("failed decode %d: %v", i, err)
+			continue
+		}
+		if got, want := dest.uint64s, tc.uint64s; !reflect.DeepEqual(got, want) {
+			t.Errorf("failed decode uint64s %d, got %v, want %v", i, got, want)
+		}
+		if got, want := dest.int64s, tc.int64s; !reflect.DeepEqual(got, want) {
+			t.Errorf("failed decode int64s %d, got %v, want %v", i, got, want)
+		}
+	}
+}
+
+type packedInts struct {
+	uint64s []uint64
+	int64s  []int64
+}
+
+func (u *packedInts) decoder() []decoder {
+	return []decoder{
+		nil,
+		func(b *buffer, m message) error { return decodeUint64s(b, &m.(*packedInts).uint64s) },
+		func(b *buffer, m message) error { return decodeInt64s(b, &m.(*packedInts).int64s) },
+	}
+}
+
+func (u *packedInts) encode(b *buffer) {
+	encodeUint64s(b, 1, u.uint64s)
+	encodeInt64s(b, 2, u.int64s)
+}