Because CBOR strings are encoded in UTF-8, it's possible that the string
that won't fit a QString in UTF-16 would still fit QByteArray in UTF-8
(e.g., anything US-ASCII and most Latin text).
The previous solution was an improvement because we used to read into a
QByteArray then convert the QByteArray to QString, thus using 3x the
amount of memory (1x in QByteArray, 2x in QString). The previous commit
skipped the middle allocation and made the regular readString() function
do the decoding either directly on source memory or by reading in small
chunks (16 kB).
Future improvement for Qt 6.1: add readStringChunk(char16_t *, qsizetype)
so we can do the validation / skipping at O(1) memory.
Pick-to: 5.15 6.0
Change-Id: I7b9b97ae9b32412abdc6fffd1645458c655cc566
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
58bea7f3a2