base: don't overwrite errno in unique_fd::~unique_fd.

unique_fd's destructor potentially mangling errno makes it difficult to
use correctly in code that sets errno (or, in reality, it makes it so
that errno values get randomly stomped upon if close actually sets
errno, because no one accounts for this case).

Preserve errno ourselves to avoid this.

Test: treehugger
Change-Id: Ib06e6f65866d86fff4032b2311021eaf9226a1af

1 files changed, 5 insertions, 1 deletions

diff --git a/base/include/android-base/unique_fd.h b/base/include/android-base/unique_fd.h
index 2c890b42d..83213e9c4 100644
--- a/base/include/android-base/unique_fd.h
+++ b/base/include/android-base/unique_fd.h
@@ -17,10 +17,10 @@
 #pragma once
 
 #include <dirent.h>
+#include <errno.h>
 #include <fcntl.h>
 
 #if !defined(_WIN32)
-#include <dirent.h>
 #include <sys/socket.h>
 #endif
 
@@ -114,6 +114,8 @@ class unique_fd_impl final {
 
  private:
   void reset(int new_value, void* previous_tag) {
+    int previous_errno = errno;
+
     if (fd_ != -1) {
       close(fd_, this);
     }
@@ -122,6 +124,8 @@ class unique_fd_impl final {
     if (new_value != -1) {
       tag(new_value, previous_tag, this);
     }
+
+    errno = previous_errno;
   }
 
   int fd_ = -1;