Document backward/forward compatibility rules for the UDP message protocol

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Bill Somerville 2019-07-18 20:30:48 +01:00
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@ -37,7 +37,8 @@
* offset qint32 only present if timespec=2
* timezone several-fields only present if timespec=3
*
* we will avoid using QDateTime fields with time zones for simplicity.
* we will avoid using QDateTime fields with time zones for
* simplicity.
*
* Type utf8 is a utf-8 byte string formatted as a QByteArray for
* serialization purposes (currently a quint32 size followed by size
@ -49,6 +50,7 @@
* strings and null strings. Empty strings have a length of zero
* whereas null strings have a length field of 0xffffffff.
*
*
* Schema Negotiation
* ------------------
*
@ -72,6 +74,36 @@
* Schema Version 3:- this schema uses the QDataStream::Qt_5_4 version.
*
*
* Backward Compatibility
* ----------------------
*
* It is important that applications developed at different times
* remain compatible with this protocol and with older or newer
* versions of WSJT-X. This is achieved by both third-party
* applications and WSJT-X honouring two basic rules.
*
* 1. New message types may be added to the protocol in the future,
* third-party applications and WSJT-X shall ignore silently any
* message types they do not recognize.
*
* 2. New fields may be added to existing message types, they will
* always be added to the end of the existing fields and the number
* and type of existing fields shall not change. If a field type
* must be changed; a new field will be added and the existing
* field will remain. The originator of such a message shall
* populate both the new and old field with reasonable
* values. Third-party applications and WSJT-X shall ignore
* silently any extra data received in datagrams after the fields
* they know about.
*
* Note that these rules are unrelated to the schema number above
* whose purpose is to distinguish between non-compatible encodings of
* field data types. New message types and extra fields in existing
* messages can and will be added without any change in schema number.
*
*
* Message Types
* -------------
*
* Message Direction Value Type
* ------------- --------- ---------------------- -----------