Utility functions to allow using string/[]byte interchangeably without copies

tools/utils/unsafeutil.go

@@ -0,0 +1,45 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"unsafe"
+)
+
+// stringHeader is the runtime representation of a string.
+// It should be identical to reflect.StringHeader
+type stringHeader struct {
+	data      unsafe.Pointer
+	stringLen int
+}
+
+// sliceHeader is the runtime representation of a slice.
+// It should be identical to reflect.sliceHeader
+type sliceHeader struct {
+	data     unsafe.Pointer
+	sliceLen int
+	sliceCap int
+}
+
+// Unsafely converts s into a byte slice.
+// If you modify b, then s will also be modified. This violates the
+// property that strings are immutable.
+func UnsafeStringToBytes(s string) (b []byte) {
+	stringHeader := (*stringHeader)(unsafe.Pointer(&s))
+	sliceHeader := (*sliceHeader)(unsafe.Pointer(&b))
+	sliceHeader.data = stringHeader.data
+	sliceHeader.sliceLen = len(s)
+	sliceHeader.sliceCap = len(s)
+	return b
+}
+
+// Unsafely converts b into a string.
+// If you modify b, then s will also be modified. This violates the
+// property that strings are immutable.
+func UnsafeBytesToString(b []byte) (s string) {
+	sliceHeader := (*sliceHeader)(unsafe.Pointer(&b))
+	stringHeader := (*stringHeader)(unsafe.Pointer(&s))
+	stringHeader.data = sliceHeader.data
+	stringHeader.stringLen = len(b)
+	return s
+}