builtin: add carray_to_varray, closes #15493 (#15499)

vlib/builtin/array.v

@@ -126,6 +126,15 @@ fn new_array_from_c_array_no_alloc(len int, cap int, elm_size int, c_array voidp
 	return arr
 }
 
+// carray_to_varray copies a C byte array into a V `u8` array.
+// See also: `cstring_to_vstring`
+[unsafe]
+pub fn carray_to_varray(c_array voidptr, c_array_len int) []u8 {
+	mut v_array := []u8{len: c_array_len}
+	unsafe { vmemcpy(v_array.data, c_array, c_array_len * int(sizeof(u8))) }
+	return v_array
+}
+
 // Private function. Increases the `cap` of an array to the
 // required value by copying the data to a new memory location
 // (creating a clone) unless `a.cap` is already large enough.

vlib/v/tests/c_array_test.c

@@ -0,0 +1,8 @@
+void* gen_c_array(int size) {
+    unsigned char *c_array = malloc(size);
+    for(int i = 0; i < size; i++) {
+        c_array[i] = i & 0xFF;
+    }
+    return c_array;
+}
+

vlib/v/tests/c_array_test.v

@@ -0,0 +1,14 @@
+#insert "@VEXEROOT/vlib/v/tests/c_array_test.c"
+
+fn C.gen_c_array(size int) voidptr
+
+fn test_carray_to_varray() {
+	size := 10
+	mut c_array := C.gen_c_array(size)
+	v_array := unsafe { carray_to_varray(c_array, size) }
+	unsafe { C.free(c_array) }
+	assert v_array.len == size
+	for i, elem in v_array {
+		assert elem == i
+	}
+}