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, 8 insertions, 6 deletions

diff --git a/pkg/marshal/marshal.go b/pkg/marshal/marshal.go
index 7da450ce8..9e34eae80 100644
--- a/pkg/marshal/marshal.go
+++ b/pkg/marshal/marshal.go
@@ -59,13 +59,15 @@ type Marshallable interface {
 	// likely make use of the type of these fields).
 	SizeBytes() int
 
-	// MarshalBytes serializes a copy of a type to dst.
+	// MarshalBytes serializes a copy of a type to dst and returns the remaining
+	// buffer.
 	// Precondition: dst must be at least SizeBytes() in length.
-	MarshalBytes(dst []byte)
+	MarshalBytes(dst []byte) []byte
 
-	// UnmarshalBytes deserializes a type from src.
+	// UnmarshalBytes deserializes a type from src and returns the remaining
+	// buffer.
 	// Precondition: src must be at least SizeBytes() in length.
-	UnmarshalBytes(src []byte)
+	UnmarshalBytes(src []byte) []byte
 
 	// Packed returns true if the marshalled size of the type is the same as the
 	// size it occupies in memory. This happens when the type has no fields
@@ -86,7 +88,7 @@ type Marshallable interface {
 	// return false, MarshalUnsafe should fall back to the safer but slower
 	// MarshalBytes.
 	// Precondition: dst must be at least SizeBytes() in length.
-	MarshalUnsafe(dst []byte)
+	MarshalUnsafe(dst []byte) []byte
 
 	// UnmarshalUnsafe deserializes a type by directly copying to the underlying
 	// memory allocated for the object by the runtime.
@@ -96,7 +98,7 @@ type Marshallable interface {
 	// UnmarshalUnsafe should fall back to the safer but slower unmarshal
 	// mechanism implemented in UnmarshalBytes.
 	// Precondition: src must be at least SizeBytes() in length.
-	UnmarshalUnsafe(src []byte)
+	UnmarshalUnsafe(src []byte) []byte
 
 	// CopyIn deserializes a Marshallable type from a task's memory. This may
 	// only be called from a task goroutine. This is more efficient than calling