Detailed Description

Stateful decoder class, modelled after QTextDecoder.

Overview

KCodecs decoders are designed to be able to process encoded data in chunks of arbitrary size and to work with output buffers of also arbitrary size. They maintain any state necessary to go on where the previous call left off.

The class consists of only two methods of interest: see decode, which decodes an input block and finalize, which flushes any remaining data to the output stream.

Typically, you will create a decoder instance, call decode as often as necessary, then call finalize (most often a single call suffices, but it might be that during that call the output buffer is filled, so you should be prepared to call finalize as often as necessary, i.e. until it returns true).

Return Values

Both methods return true to indicate that they've finished their job. For decode, a return value of true means that the current input block has been finished (false most often means that the output buffer is full, but that isn't required behavior. The decode call is free to return at arbitrary times during processing).

For finalize, a return value of true means that all data implicitly or explicitly stored in the decoder instance has been flushed to the output buffer. A false return value should be interpreted as "check if the output buffer is full and call me again", just as with decode.

Usage Pattern

Since the decoder maintains state, you can only use it once. After a sequence of input blocks has been processed, you finalize the output and then delete the decoder instance. If you want to process another input block sequence, you create a new instance.

Typical usage (in contains the (base64-encoded) input data), taking into account all the conventions detailed above:

KCodecs::Codec *codec = KCodecs::Codec::codecForName("base64");
if (!codec) {
    qFatal() << "No codec found for base64!";
}
KCodecs::Decoder *dec = codec->makeDecoder();
Q_ASSERT(dec); // should not happen
QByteArray out(256); // small buffer is enough ;-)
QByteArray::Iterator iit = in.begin();
QByteArray::Iterator oit = out.begin();
// decode the chunk
while (!dec->decode(iit, in.end(), oit, out.end()))
  if (oit == out.end()) { // output buffer full, process contents
    do_something_with(out);
    oit = out.begin();
  }
// repeat while loop for each input block
// ...
// finish (flush remaining data from decoder):
while (!dec->finish(oit, out.end()))
  if (oit == out.end()) { // output buffer full, process contents
    do_something_with(out);
    oit = out.begin();
  }
// now process last chunk:
out.resize(oit - out.begin());
do_something_with(out);
// _delete_ the decoder, but not the codec:
delete dec;