reflect: allow Value.Bytes on addressable byte arrays

Modify Value.Bytes to be callable addressable byte arrays.
While related, the behavior of Value.SetBytes was not modified.

Fixes #47066

Change-Id: Ic3ba4432353b8da5f33b3188e20034a33b2f6ee8
Reviewed-on: https://go-review.googlesource.com/c/go/+/357331
Trust: Joseph Tsai <joetsai@digital-static.net>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 20 insertions, 6 deletions

diff --git a/src/reflect/value.go b/src/reflect/value.go
index dcc359dae4..89f0253570 100644
--- a/src/reflect/value.go
+++ b/src/reflect/value.go
@@ -286,14 +286,28 @@ func (v Value) Bool() bool {
 }
 
 // Bytes returns v's underlying value.
-// It panics if v's underlying value is not a slice of bytes.
+// It panics if v's underlying value is not a slice of bytes or
+// an addressable array of bytes.
 func (v Value) Bytes() []byte {
-	v.mustBe(Slice)
-	if v.typ.Elem().Kind() != Uint8 {
-		panic("reflect.Value.Bytes of non-byte slice")
+	switch v.kind() {
+	case Slice:
+		if v.typ.Elem().Kind() != Uint8 {
+			panic("reflect.Value.Bytes of non-byte slice")
+		}
+		// Slice is always bigger than a word; assume flagIndir.
+		return *(*[]byte)(v.ptr)
+	case Array:
+		if v.typ.Elem().Kind() != Uint8 {
+			panic("reflect.Value.Bytes of non-byte array")
+		}
+		if !v.CanAddr() {
+			panic("reflect.Value.Bytes of unaddressable byte array")
+		}
+		p := (*byte)(v.ptr)
+		n := int((*arrayType)(unsafe.Pointer(v.typ)).len)
+		return unsafe.Slice(p, n)
 	}
-	// Slice is always bigger than a word; assume flagIndir.
-	return *(*[]byte)(v.ptr)
+	panic(&ValueError{"reflect.Value.Bytes", v.kind()})
 }
 
 // runes returns v's underlying value.