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
(cherry picked from commit fc5db01bb7d1546944200d197866b0b5c378f100)

2 files changed, 36 insertions, 1 deletions

diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index 68298d785..09dce4123 100644
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -2619,7 +2619,7 @@ 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 607c4a195..ff13e9e92 100644
--- a/test/libapt/fileutl_test.cc
+++ b/test/libapt/fileutl_test.cc
@@ -317,6 +317,7 @@ 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());
@@ -344,3 +345,37 @@ 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());
+}