Clarify readLine() behavior on sequential devices

QIODevice::readLine() can also return partial lines, which was not
properly documented. Add an autotest for QLocalSocket to illustrate
and test this behavior.

Change-Id: Ia2c1c438cc68d2672d34881e11fdf7837232f3b4
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
(cherry picked from commit 03272e601ce0b03c36717dac0a60c2fdd8987bee)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index f3354cad65..b776f6fddb 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -1320,12 +1320,17 @@ QByteArray QIODevice::readAll()
     newline will not be inserted into the buffer. On windows newline
     characters are replaced with '\\n'.
 
+    Note that on sequential devices, data may not be immediately available,
+    which may result in a partial line being returned. By calling the
+    canReadLine() function before reading, you can check whether a complete
+    line (including the newline character) can be read.
+
     This function calls readLineData(), which is implemented using
     repeated calls to getChar(). You can provide a more efficient
     implementation by reimplementing readLineData() in your own
     subclass.
 
-    \sa getChar(), read(), write()
+    \sa getChar(), read(), canReadLine(), write()
 */
 qint64 QIODevice::readLine(char *data, qint64 maxSize)
 {