On 6/18/2017 1:05 AM, Jaap Akkerhuis wrote:
> the problem with do-gooder software is that
>
> when it tries and fails, you may or may not know it, but it is a real
> mess. and usually the do-gooder receiver is blamed.
>
> when it succeeds, no one says thanks, and the incorrect sender goes on
> to find some other implementation to break.
and thus completely ignoring the "be conservative what you send" part
No part of the Postel Principle says to ignore explicit errors.
The issue is how to treat something unexpected, and the implications
thereof.
If everything unexpected must be loudly rejected (as this doc claims), then:
a) specs will become unnecessarily detailed
b) implementations will be come unnecessarily detailed
c) receivers will be vulnerable to increased DOS attacks
The Postel Principle just tries to get the sender to avoid doing
something unexpected (because it could result in unexpected receiver
behavior), and to get the receiver to avoid over-reacting. It is, in a
sense, the dampener that enables practical protocol specification and
implementation.
IMO, it's somewhat an extension of Shannon's recognition that
communication is about symbol agreement, not semantics or intent.
Joe