don't do atomic overrides with failed files

We deploy atomic renames for some files, but these renames also happen
if something about the file failed which isn't really the point of the
exercise…

Closes: 828908

2 files changed, 36 insertions, 1 deletions

diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index 94d1432cf..388849144 100644
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -2623,7 +2623,7 @@ bool FileFd::Close()
    }
 
    if ((Flags & Replace) == Replace) {
-      if (rename(TemporaryFileName.c_str(), FileName.c_str()) != 0)
+      if (Failed() == false && rename(TemporaryFileName.c_str(), FileName.c_str()) != 0)
 	 Res &= _error->Errno("rename",_("Problem renaming the file %s to %s"), TemporaryFileName.c_str(), FileName.c_str());
 
       FileName = TemporaryFileName; // for the unlink() below.
diff --git a/test/libapt/fileutl_test.cc b/test/libapt/fileutl_test.cc
index 8cd5132ce..0a299b51a 100644
--- a/test/libapt/fileutl_test.cc
+++ b/test/libapt/fileutl_test.cc
@@ -327,6 +327,7 @@ TEST(FileUtlTest, flAbsPath)
 
 static void TestDevNullFileFd(unsigned int const filemode)
 {
+   SCOPED_TRACE(filemode);
    FileFd f("/dev/null", filemode);
    EXPECT_FALSE(f.Failed());
    EXPECT_TRUE(f.IsOpen());
@@ -354,3 +355,37 @@ TEST(FileUtlTest, WorkingWithDevNull)
    TestDevNullFileFd(FileFd::WriteTemp);
    TestDevNullFileFd(FileFd::WriteAtomic);
 }
+constexpr char const * const TESTSTRING = "This is a test";
+static void TestFailingAtomicKeepsFile(char const * const label, std::string const &filename)
+{
+   SCOPED_TRACE(label);
+   EXPECT_TRUE(FileExists(filename));
+   FileFd fd;
+   EXPECT_TRUE(fd.Open(filename, FileFd::ReadOnly));
+   char buffer[50];
+   EXPECT_NE(nullptr, fd.ReadLine(buffer, sizeof(buffer)));
+   EXPECT_STREQ(TESTSTRING, buffer);
+}
+TEST(FileUtlTest, FailingAtomic)
+{
+   FileFd fd;
+   std::string filename;
+   createTemporaryFile("failingatomic", fd, &filename, TESTSTRING);
+   TestFailingAtomicKeepsFile("init", filename);
+
+   FileFd f;
+   EXPECT_TRUE(f.Open(filename, FileFd::ReadWrite | FileFd::Atomic));
+   f.EraseOnFailure();
+   EXPECT_FALSE(f.Failed());
+   EXPECT_TRUE(f.IsOpen());
+   TestFailingAtomicKeepsFile("before-fail", filename);
+   EXPECT_TRUE(f.Write("Bad file write", 10));
+   f.OpFail();
+   EXPECT_TRUE(f.Failed());
+   TestFailingAtomicKeepsFile("after-fail", filename);
+   EXPECT_TRUE(f.Close());
+   TestFailingAtomicKeepsFile("closed", filename);
+
+   if (filename.empty() == false)
+      unlink(filename.c_str());
+}