>From 9043cf8adea070fa2c714e7295389d908101d912 Mon Sep 17 00:00:00 2001
From: apache2 <apache2+poke-devel@ageinghacker.net>
Date: Sun, 10 Apr 2022 12:15:40 +0200
Subject: [PATCH] with_cur_ios function

---
 doc/poke.texi     | 35 +++++++++++++++++++++++++++++++++++
 libpoke/pkl-rt.pk | 21 +++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/doc/poke.texi b/doc/poke.texi
index 2c8201e0..8a315307 100644
--- a/doc/poke.texi
+++ b/doc/poke.texi
@@ -12644,6 +12644,7 @@ memory of some process.
 * get_ios::			Getting the current IO space.
 * set_ios::			Setting the current IO space.
 * openset::                     Opening and setting combined.
+* with_cur_ios::                Exception-safe IO wrapper.
 * iosize::			Getting the size of an IO space.
 * iohandler::                   Getting the handler string of an IO space.
 * ioflags::                     Getting the flags of an IO space.
@@ -12859,6 +12860,40 @@ fun openset = (string @var{handler}, uint<64> @var{flags} = 0) int<32>
 Where the meaning of @var{handler}, @var{flags} and the returned value
 are exactly like in @code{open}.
 
+@node with_cur_ios
+@subsubsection @code{with_cur_ios}
+@cindex @code{with_cur_ios}
+
+@example
+fun with_cur_ios = (string @var{handle}, With_Ios_Fn do = lambda void:{}, uint<64> flags = 0) void
+@end example
+
+The @code{with_cur_ios} utility function opens a IO space, like @code{openset},
+but takes care of calling @code{close} and restoring the original current IO space
+after the lambda returns or raises an exception.
+
+It can be used to deal with files without risk of leaking file descriptors.
+
+@example
+with_cur_ios("*buf*", lambda void:
+  @{
+    var arr = uint<32>[1] @ 0#B;
+    arr[0] = 0x1234;
+    printf("%v", byte[4] @ 0#b);
+  @});
+[0x00UB,0x00UB,0x12UB,0x34UB]
+
+with_cur_ios
+  :handle "*buf*"
+  :flags IOS_F_CREATE
+  :do lambda void:
+  @{
+    var arr = uint<32>[1] @ 0#B;
+    arr[0] = 0x1234;
+    printf("%v", byte[4] @ 0#b);
+  @}
+@end example
+
 @node iosize
 @subsubsection @code{iosize}
 @cindex @code{iosize}
diff --git a/libpoke/pkl-rt.pk b/libpoke/pkl-rt.pk
index c6b3209c..03d39970 100644
--- a/libpoke/pkl-rt.pk
+++ b/libpoke/pkl-rt.pk
@@ -563,6 +563,27 @@ immutable fun _pkl_run_ios_set_hook = (int<32> ios) void:
     f (ios);
 }
 
+immutable type With_Ios_Fn = () void;
+
+immutable fun with_cur_ios = (string handle, With_Ios_Fn do = lambda void:{}, uint<32> flags = 0) void:
+{
+  var old_ios = get_ios ?! E_no_ios ? get_ios : -1;
+  var new_ios = open(handle, flags);
+  set_ios(new_ios);
+  try
+  {
+    do();
+    close(new_ios);
+    if (-1 != old_ios) set_ios(old_ios);
+  }
+  catch (Exception exc)
+  {
+    close(new_ios);
+    if (-1 != old_ios) set_ios(old_ios);
+    raise exc;
+  }
+}
+
 /**** Set the default load path ****/
 
 immutable var load_path = "";
-- 
2.30.2