Fix regression introduced in c08e708037d33271825ce6a6a1ac640e96b70c36

When writing nothing to a file, not actually writing anything is not an
error.

Also, from a change introduced in the same commit, there is no point in
checking for EOF when writing.

Task-number: QTBUG-5847
Reviewed-by: Olivier Goffart
(cherry picked from commit 72ee915bb0465549b7ca8e62d2af146cc44fdeac)

2 files changed, 14 insertions, 4 deletions

diff --git a/src/corelib/io/qfsfileengine.cpp b/src/corelib/io/qfsfileengine.cpp
index 9ab831f..3cf9b7e 100644
--- a/src/corelib/io/qfsfileengine.cpp
+++ b/src/corelib/io/qfsfileengine.cpp
@@ -762,12 +762,10 @@ qint64 QFSFileEnginePrivate::writeFdFh(const char *data, qint64 len)
         // Buffered stdlib mode.
 
         size_t result;
-        bool eof;
         do {
             result = fwrite(data + writtenBytes, 1, size_t(len - writtenBytes), fh);
             writtenBytes += result;
-            eof = feof(fh);
-        } while (!eof && (result == 0 ? errno == EINTR : writtenBytes < len));
+        } while (result == 0 ? errno == EINTR : writtenBytes < len);
 
     } else if (fd != -1) {
         // Unbuffered stdio mode.
@@ -783,7 +781,7 @@ qint64 QFSFileEnginePrivate::writeFdFh(const char *data, qint64 len)
                 || (result > 0 && (writtenBytes += result) < len));
     }
 
-    if (writtenBytes == 0) {
+    if (len &&  writtenBytes == 0) {
         writtenBytes = -1;
         q->setError(errno == ENOSPC ? QFile::ResourceError : QFile::WriteError, qt_error_string(errno));
     }
diff --git a/tests/auto/qfile/tst_qfile.cpp b/tests/auto/qfile/tst_qfile.cpp
index 880498e..c4e6d50 100644
--- a/tests/auto/qfile/tst_qfile.cpp
+++ b/tests/auto/qfile/tst_qfile.cpp
@@ -210,6 +210,7 @@ private slots:
     void task167217();
 
     void openDirectory();
+    void writeNothing();
 
 public:
 // disabled this test for the moment... it hangs
@@ -2840,5 +2841,16 @@ void tst_QFile::openStandardStreams()
     }
 }
 
+void tst_QFile::writeNothing()
+{
+    for (int i = 0; i < 3; ++i) {
+        QFile file("file.txt");
+        QVERIFY( openFile(file, QIODevice::WriteOnly | QIODevice::Unbuffered, FileType(i)) );
+        QVERIFY( 0 == file.write((char *)0, 0) );
+        QCOMPARE( file.error(), QFile::NoError );
+        closeFile(file);
+    }
+}
+
 QTEST_MAIN(tst_QFile)
 #include "tst_qfile.moc"