QBBSystemLocale: Do not set fixed buffer size when reading pps objects

Set dynamically the buffer size when reading pps objects since a pps file
size is not always fix.

Cherry-picked: qtbase/edf29a9aa93660ac8e4927db7fef2b5d925e9b59

Change-Id: Id55df6a474b6b79d96e3459e807f0bbfeacbf0cb
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>

1 files changed, 20 insertions, 4 deletions

diff --git a/src/corelib/tools/qlocale_blackberry.cpp b/src/corelib/tools/qlocale_blackberry.cpp
index 44bf133..56bffbc 100644
--- a/src/corelib/tools/qlocale_blackberry.cpp
+++ b/src/corelib/tools/qlocale_blackberry.cpp
@@ -60,7 +60,7 @@ static const char ppsRegionLocalePath[] = "/pps/services/locale/settings";
 static const char ppsLanguageLocalePath[] = "/pps/services/confstr/_CS_LOCALE";
 static const char ppsHourFormatPath[] = "/pps/system/settings";
 
-static const size_t ppsBufferSize = 256;
+static const int MAX_PPS_SIZE = 16000;
 
 QBBSystemLocaleData::QBBSystemLocaleData()
     : languageNotifier(0)
@@ -186,9 +186,25 @@ QByteArray QBBSystemLocaleData::readPpsValue(const char *ppsObject, int ppsFd)
     if (!ppsObject || ppsFd == -1)
         return result;
 
-    char buffer[ppsBufferSize];
 
-    int bytes = qt_safe_read(ppsFd, buffer, ppsBufferSize - 1);
+    // PPS objects are of unknown size, but must be read all at once.
+    // Relying on the file size may not be a good idea since the size may change before reading.
+    // Let's try with an initial size (512), and if the buffer is too small try with bigger one,
+    // until we succeed or until other non buffer-size-related error occurs.
+    // Using QVarLengthArray means the first try (of size == 512) uses a buffer on the stack - no allocation necessary.
+     // Hopefully that covers most use cases.
+    int bytes;
+    QVarLengthArray<char, 512> buffer;
+    for (;;) {
+        errno = 0;
+        bytes = qt_safe_read(ppsFd, buffer.data(), buffer.capacity() - 1);
+        const bool bufferIsTooSmall = (bytes == -1 && errno == EMSGSIZE && buffer.capacity() < MAX_PPS_SIZE);
+        if (!bufferIsTooSmall)
+            break;
+
+        buffer.resize(qMin(buffer.capacity()*2, MAX_PPS_SIZE));
+    }
+
     // This method is called in the ctor(), so do not use qWarning to log warnings
     // if qt_safe_read fails to read the pps file
     // since the user code may install a message handler that invokes QLocale API again
@@ -202,7 +218,7 @@ QByteArray QBBSystemLocaleData::readPpsValue(const char *ppsObject, int ppsFd)
 
     pps_decoder_t ppsDecoder;
     pps_decoder_initialize(&ppsDecoder, 0);
-    if (pps_decoder_parse_pps_str(&ppsDecoder, buffer) == PPS_DECODER_OK) {
+    if (pps_decoder_parse_pps_str(&ppsDecoder, buffer.data()) == PPS_DECODER_OK) {
         pps_decoder_push(&ppsDecoder, 0);
         const char *ppsBuff;
         if (pps_decoder_get_string(&ppsDecoder, ppsObject, &ppsBuff) == PPS_DECODER_OK) {