Fix regression introduced in 1e6b424b692b20dcfec920f8d3563e520ec1ff05

When processing the result of QIODevice::readLine, forgot to take into
account that a '\0' is appended to the array. The terminating character
is not accounted for in the number of bytes returned.

By pre-allocating a byte for the terminating null character, we make
sure we'll actually read 16k bytes on each and every iteration.

Task-number: QTBUG-6019
Reviewed-by: Thiago Macieira
(cherry picked from commit b7692016f282251002b3e85dfcb5567bd91a12c0)

1 files changed, 5 insertions, 1 deletions

diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index 0248224..3b569b7 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -1164,6 +1164,10 @@ QByteArray QIODevice::readLine(qint64 maxSize)
         // If resize fails or maxSize == 0, read incrementally
         if (maxSize == 0)
             maxSize = INT_MAX;
+
+        // The first iteration needs to leave an extra byte for the terminating null
+        result.resize(1);
+
         qint64 readResult;
         do {
             result.resize(int(qMin(maxSize, result.size() + QIODEVICE_BUFFERSIZE)));
@@ -1171,7 +1175,7 @@ QByteArray QIODevice::readLine(qint64 maxSize)
             if (readResult > 0 || readBytes == 0)
                 readBytes += readResult;
         } while (readResult == QIODEVICE_BUFFERSIZE
-                && result[int(readBytes)] != '\n');
+                && result[int(readBytes - 1)] != '\n');
     } else
         readBytes = readLine(result.data(), result.size());