fix: use Long_val for sendfile() parameters to fix file copying in …

…docker (ocaml#10333)

* fix: sendfile() in docker

Signed-off-by: Haoxiang Fei <feihaoxiang2014@gmail.com>

* use ssize_t for return value

Co-authored-by: Etienne Millon <etienne.millon@gmail.com>
Signed-off-by: Haoxiang Fei <tonyfettes@tonyfettes.com>

* update test

Signed-off-by: Etienne Millon <me@emillon.org>

* Add changelog

Signed-off-by: Etienne Millon <me@emillon.org>

---------

Signed-off-by: Haoxiang Fei <feihaoxiang2014@gmail.com>
Signed-off-by: Haoxiang Fei <tonyfettes@tonyfettes.com>
Signed-off-by: Etienne Millon <me@emillon.org>
Co-authored-by: Etienne Millon <etienne.millon@gmail.com>
Co-authored-by: Etienne Millon <me@emillon.org>

10333.md

@@ -0,0 +1,2 @@
+- fix overflow in sendfile stubs (copy of large files could fail or end with
+  truncated files) (#10333, @tonyfettes)

otherlibs/stdune/src/copyfile_stubs.c

@@ -73,8 +73,8 @@ CAMLprim value stdune_copyfile(value v_from, value v_to) {
   caml_failwith("copyfile: only on macos");
 }
 
-static int dune_sendfile(int in, int out, int length) {
-  int ret;
+static int dune_sendfile(int in, int out, size_t length) {
+  ssize_t ret;
   while (length > 0) {
     ret = sendfile(out, in, NULL, length);
     if (ret < 0) {
@@ -90,7 +90,7 @@ CAMLprim value stdune_sendfile(value v_in, value v_out, value v_size) {
   caml_release_runtime_system();
   /* TODO Use copy_file_range once we have a good mechanism to test for its
    * existence */
-  int ret = dune_sendfile(FD_val(v_in), FD_val(v_out), Int_val(v_size));
+  int ret = dune_sendfile(FD_val(v_in), FD_val(v_out), Long_val(v_size));
   caml_acquire_runtime_system();
   if (ret < 0) {
     uerror("sendfile", Nothing);

test/blackbox-tests/test-cases/sendfile-large-file.t

@@ -17,6 +17,6 @@ We create a large file and check that it is copied completely.
   4294967299
 
   $ dune_cmd stat size _build/default/file.dat
-  3
+  4294967299
 
 (3 indicates that the file size is taken modulo 2**32)