BufferedFileFdPrivate: Make InternalFlush() save against errors

Previously, if flush errored inside the loop, data could have
already been written to the wrapped descriptor without having
been removed from the buffer.

Also try to work around EINTR here. A better solution might be
to have the individual privates detect an interrupt and return
0 in such a case, instead of relying on errno being untouched
in between the syscall and the return from InternalWrite.

diff --git a/apt-pkg/contrib/fileutl.cc b/apt-pkg/contrib/fileutl.cc
index 0c5d76290ed5d9c26803cb3d7f9b0a5889f61ddd..7f3ed673a13144e7563a7c8e136d57371c98415a 100644 (file)
--- a/apt-pkg/contrib/fileutl.cc
+++ b/apt-pkg/contrib/fileutl.cc
@@ -1218,16 +1218,16 @@ public:
    }
    virtual bool InternalFlush() override
    {
-      size_t written = 0;
-      char *data = writebuffer.get();
-      auto size = writebuffer.size();
-
-      while (written < size) {
-        auto written_this_time = wrapped->InternalWrite(data + written, size - written);
-        if (written_this_time < 0)
+      while (writebuffer.empty() == false) {
+        auto written = wrapped->InternalWrite(writebuffer.get(),
+                                              writebuffer.size());
+        // Ignore interrupted syscalls
+        if (written < 0 && errno == EINTR)
+           continue;
+        if (written < 0)
            return false;
 
-        written += written_this_time;
+        writebuffer.bufferstart += written;
       }
 
       writebuffer.reset();