Make {Un}Marshal{Bytes/Unsafe} return remaining buffer.

Change marshal.Marshallable method signatures to return the remaining buffer.
This makes it easier to implement these method manually. Without this, we would
have to manually do buffer shifting which is error prone.

tools/go_marshal/test:benchmark test does not show change in performance.
Additionally fixed some marshalling bugs in fsimpl/fuse.

Updated multiple callpoints to get rid of redundant slice indexing work and
simplified code using this new signature.

Updates #6450

PiperOrigin-RevId: 407857019

1 files changed, 22 insertions, 19 deletions

diff --git a/pkg/lisafs/sample_message.go b/pkg/lisafs/sample_message.go
index 3868dfa08..745736b6d 100644
--- a/pkg/lisafs/sample_message.go
+++ b/pkg/lisafs/sample_message.go
@@ -53,18 +53,24 @@ func (m *MsgDynamic) SizeBytes() int {
 }
 
 // MarshalBytes implements marshal.Marshallable.MarshalBytes.
-func (m *MsgDynamic) MarshalBytes(dst []byte) {
-	m.N.MarshalUnsafe(dst)
-	dst = dst[m.N.SizeBytes():]
-	MarshalUnsafeMsg1Slice(m.Arr, dst)
+func (m *MsgDynamic) MarshalBytes(dst []byte) []byte {
+	dst = m.N.MarshalUnsafe(dst)
+	n, err := MarshalUnsafeMsg1Slice(m.Arr, dst)
+	if err != nil {
+		panic(err)
+	}
+	return dst[n:]
 }
 
 // UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.
-func (m *MsgDynamic) UnmarshalBytes(src []byte) {
-	m.N.UnmarshalUnsafe(src)
-	src = src[m.N.SizeBytes():]
+func (m *MsgDynamic) UnmarshalBytes(src []byte) []byte {
+	src = m.N.UnmarshalUnsafe(src)
 	m.Arr = make([]MsgSimple, m.N)
-	UnmarshalUnsafeMsg1Slice(m.Arr, src)
+	n, err := UnmarshalUnsafeMsg1Slice(m.Arr, src)
+	if err != nil {
+		panic(err)
+	}
+	return src[n:]
 }
 
 // Randomize randomizes the contents of m.
@@ -90,21 +96,18 @@ func (v *P9Version) SizeBytes() int {
 }
 
 // MarshalBytes implements marshal.Marshallable.MarshalBytes.
-func (v *P9Version) MarshalBytes(dst []byte) {
-	v.MSize.MarshalUnsafe(dst)
-	dst = dst[v.MSize.SizeBytes():]
+func (v *P9Version) MarshalBytes(dst []byte) []byte {
+	dst = v.MSize.MarshalUnsafe(dst)
 	versionLen := primitive.Uint16(len(v.Version))
-	versionLen.MarshalUnsafe(dst)
-	dst = dst[versionLen.SizeBytes():]
-	copy(dst, v.Version)
+	dst = versionLen.MarshalUnsafe(dst)
+	return dst[copy(dst, v.Version):]
 }
 
 // UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.
-func (v *P9Version) UnmarshalBytes(src []byte) {
-	v.MSize.UnmarshalUnsafe(src)
-	src = src[v.MSize.SizeBytes():]
+func (v *P9Version) UnmarshalBytes(src []byte) []byte {
+	src = v.MSize.UnmarshalUnsafe(src)
 	var versionLen primitive.Uint16
-	versionLen.UnmarshalUnsafe(src)
-	src = src[versionLen.SizeBytes():]
+	src = versionLen.UnmarshalUnsafe(src)
 	v.Version = string(src[:versionLen])
+	return src[versionLen:]
 }