compile with -safe-string

cli/jbuild

@@ -1,4 +1,5 @@
 (executables
  ((names (xencat))
   (libraries (cmdliner lwt vchan vchan-unix))
+  (flags (:standard -safe-string))
 ))

lib/jbuild

@@ -4,4 +4,5 @@
   (libraries (lwt cstruct io-page mirage-flow-lwt result xenstore.client sexplib))
   (c_names (vchan_stubs))
   (preprocess (pps (ppx_sexp_conv ppx_cstruct -no-check)))
+  (flags (:standard -safe-string))
 ))

lib_test/jbuild

@@ -1,6 +1,7 @@
 (executables
  ((names (test))
   (libraries (cmdliner lwt lwt.unix vchan oUnit io-page.unix))
+  (flags (:standard -safe-string))
 ))
 
 (alias

lwt/jbuild

@@ -4,4 +4,5 @@
   (libraries (lwt xen-evtchn-unix xen-evtchn xen-gnt-unix xen-gnt io-page.unix xenstore xenstore.client xenstore_transport xenstore_transport.lwt mirage-flow-lwt vchan))
   (wrapped false)
   (preprocess (pps (ppx_sexp_conv)))
+  (flags (:standard -safe-string))
 ))

lwt/vchan_lwt_unix.ml

@@ -58,9 +58,9 @@ module IO = struct
        | e -> Lwt.fail e)
 
   let read_exactly ic len =
-    let buf = String.create len in
+    let buf = Bytes.create len in
     read_exactly ic buf 0 len >>= function
-      | true -> return (Some buf)
+      | true -> return (Some (Bytes.to_string buf))
       | false -> return None
 
   let write = Lwt_io.write

xen/jbuild

@@ -4,4 +4,5 @@
   (libraries (lwt xen-evtchn xen-gnt xenstore xenstore.client mirage-xen mirage-flow-lwt vchan))
   (wrapped false)
   (preprocess (pps (ppx_sexp_conv)))
+  (flags (:standard -safe-string))
 ))