On Tuesday, 9 June 2015 01:27:24 UTC+1, Feng Xiao wrote:
On Mon, Jun 8, 2015 at 7:43 AM, Colin Deasy cde...@demonware.net
javascript: wrote:
Hey,
When reading
https://developers.google.com/protocol-buffers/docs/proto#simple I see a
stark warning indicating that Required is Forever advocating the use of
optional with additional application level validation routines. This is
because if at some point a required field is no longer written, the readers
will break.
However IMO, there are common cases where 'required' is a good thing -
given that it's enforced only during encoding/decoding.
For example there may be some field that is 'required' (right now) to
both the reader and writer. Even if that changes at some point in the
future to become optional, the reader would likely have to be updated
regardless of the protocol decoding routine as it may make assumptions
(reasonable considering it was required in the first place) on the presence
of the field (e.g. the field being a key to a certain bit of data). In this
case the approach would be to update the .proto of all readers to make that
field optional, followed by updating all writers to remove the field.
In simpler scenarios, yes, it's possible to migrate a required field to
optional even though it's an incompatible change, but in a more complicated
system, where you have many different binaries using the same proto file
running on thousands of machines, it's hard to tell whether all readers of
a proto has been updated or not. You have to be very careful with such
changes, and if you miss one, bad things can happen.
My point is that regardless of the size of the cluster, you will need to
update every reader - it doesn't matter whether the 'required' constraint
is within the protobuf deserialization logic or within the application
logic itself.
Similar to missing an update to a certain application instance's proto
file, you could miss an update the to application's binary itself. This is
precisely why I don't understand the logic behind deprecating the
'required' constraint.
Given this, I feel that the current language of the linked document gives
the impression that the 'required' attribute is a Bad Thing and should be
avoided. I hope you can clarify if I'm missing some crucial bit of
information regarding it's usage.
Thanks
Colin
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