iostream: fix incorrect rfcomm error case when writing

This is the exact same case as the previous commit, just for the writing
side.

Once again, it's the subsurface rfcomm iostream code that can return
DC_STATUS_SUCCESS with a byte count of zero when something goes wrong
with the write.

And once again, our libdivecomputer iostream code didn't try to be
robust and protect itself from that case.

The fix is equivalent, although slightly simpler, since the write side
doesn't have the whole timeout issue.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 17 deletions

diff --git a/core/qtserialbluetooth.cpp b/core/qtserialbluetooth.cpp
index f6bbcafdf..1c0270ff9 100644
--- a/core/qtserialbluetooth.cpp
+++ b/core/qtserialbluetooth.cpp
@@ -172,32 +172,27 @@ static dc_status_t qt_serial_write(void *io, const void* data, size_t size, size
 {
 	qt_serial_t *device = (qt_serial_t*) io;
 
-	if (device == NULL || device->socket == NULL)
+	if (device == NULL || device->socket == NULL || !actual)
 		return DC_STATUS_INVALIDARGS;
 
-	size_t nbytes = 0;
-	int rc;
+	*actual = 0;
+	for (;;) {
+		int rc;
+
+		if (device->socket->state() != QBluetoothSocket::ConnectedState)
+			return DC_STATUS_IO;
 
-	while(nbytes < size && device->socket->state() == QBluetoothSocket::ConnectedState)
-	{
-		rc = device->socket->write((char *) data + nbytes, size - nbytes);
+		rc = device->socket->write((char *) data, size);
 
 		if (rc < 0) {
 			if (errno == EINTR || errno == EAGAIN)
-			    continue; // Retry.
-
-			return DC_STATUS_IO; // Something really bad happened :-(
-		} else if (rc == 0) {
-			break;
+				continue;
+			return DC_STATUS_IO;
 		}
 
-		nbytes += rc;
+		*actual = rc;
+		return rc ? DC_STATUS_SUCCESS : DC_STATUS_IO;
 	}
-
-	if (actual)
-		*actual = nbytes;
-
-	return DC_STATUS_SUCCESS;
 }
 
 static dc_status_t qt_serial_poll(void *io, int timeout)