Converter: Provide "declarative" ByteStreamReaderConverter and ByteStreamWriterConverter

[ssproessig]

Todo

• provide a converter component that can be configured to read raw bytes received into meta-data KVPs
• make the parsing rules configurable
• for now support
  • q(u)int8|16|32|64
  • PascalString (with encoding)
  • C-Style String (with encoding)
  • FixedLength String (with encoding)

[ssproessig]

Idea

Provide a declarative complex configuration

<?xml version="1.0" encoding="UTF-8"?>
<configuration version="1" xmlns="urn:ipca-configuration-v1"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="urn:ipca-configuration-v1 ipca-configuration-v1.xsd">

    <configurations>
        <bsd:configuration id="cfgBsd" xmlns:bsd="urn:ipca-configuration-for-byte-stream-definitions-v1">
            <bsd:struct name="Sample">
                <bsd:uint8 name="index"/>
                <bsd:uint16-be name="shortField"/>
                <bsd:uint64-be name="longLongField"/>
                <bsd:string name="message" type="fixed" encoding="utf-8"/>
                <bsd:debug/>
            </bsd:struct>
        </bsd:configuration>
    </configurations>

    <components>
        <component id="bsrTest" type="ByteStreamReader">
            <configuration ref="cfgBsd"/>
        </component>
...

Design

• provide interface IByteHandler with methods
  • bool read(QByteArray const& readFrom, quint64 pos, Context&)
  • bool write(QByteArray& writeTo, Context&)
• use Context to share
  • QString namePrefix carries the prefix to add to local name, derived from the element hierarchy (@name in XML configuration)
  • QMap<QString, QVariant> metaData
• provide AbstractByteHandler that
  • handles parser errors (QString const& getLastError() const and void setError(QString const&)
• create a look-up table for XML tag to AbstractHandler (they are stateless! no factory needed) - compare to GlobalComponentRegistry for how to do it
• share this XML parser and the
• finally invoke
  • write(...) method from ByteStreamWriter, using the IPipelineFrame::getMetaData() as value provider for the context key
  • read(...) method from ByteStreamReader, updating the meta-data in the pipeline frame returned with Context.metaData just parsed

[ssproessig]

string usage

• string is a bit more complicated, as there are many different serialization forms for Strings
• we support
  • c reading from data until we encounter a 0x00 byte
    • fail parsing if we do not encounter a 0x00 byte until reaching
  • pascal where the first byte of the data is the length of the bytes to read as quint8
    • fail if this is greater than the max number of bytes available
  • fixed where fixed prefix means fixed number of bytes to write
    • here we need additional parameters: length, fill char, align left/right, overflow behavior - maybe don't add it yet
• after reading all bytes into the QByteArray, they must be encoded: https://doc.qt.io/qt-5/qtextcodec.html
• before writing a string, it must be encoded the other way around to QByteArray

[ssproessig]

debug usage

• the <debug/> realization of IByteHandler shall not alter any data
• it shall just LOG the current invocation parameters
  • current data buffer
  • position if reading
  • Context and its values

[ssproessig]

structuring

finally, think about to add <struct/> as sub-element into a <struct/> so that the parser structures the data better