Calling hasFoo on a protocol buffer when foo has a default value.

[cushon]

Original issue created by gmoura@google.com on 2013-02-27 at 08:10 PM

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The problem is described in detail in this thread:
https://groups.google.com/a/google.com/forum/?fromgroups=#!search/protocol$20buffer$20set$20optional$20values/nehen/QnlmlEEEC_g/z9CUEb76aBQJ

But here's a summary. Consider the following proto:

message Query {
  optional bool use_new_backend = 1 [default = true];
}

The new backend is to be used by default, so clients might not set it. Now consider the following server side code:

if (query.hasUseNewBackend() && query.getUseNewBackend()) {
  useNewBackend();
} else {
  useOldBackend();
}

This would be incorrectly using the old backend. When a default is set in the protocol buffer, you shouldn't need to call "hasFoo()" and more-over, doing it may introduce bugs.

[cushon]

Original comment posted by eaftan@google.com on 2013-03-05 at 04:44 AM

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So the problem is that if the proto has an explicit default value and you call hasValue() on it, it will return false. That's a surprising behavior.

I'm not sure whether we would be able to know whether the proto has an explicit default value, from the generated Java code. If so I think would make a good warning.

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Status: Accepted
Labels: -Priority-Medium, Priority-Low