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https://issues.apache.org/jira/browse/MESOS-7828?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16100152#comment-16100152
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Qian Zhang commented on MESOS-7828:
-----------------------------------
My proposal is, when we fail to get an enum for a string, check if it is an
optional enum field, if yes, call FieldDescriptor::default_value_enum() to get
the default value, and use that default value.
> Current approach to parse protobuf enum from JSON does not support upgrades
> ---------------------------------------------------------------------------
>
> Key: MESOS-7828
> URL: https://issues.apache.org/jira/browse/MESOS-7828
> Project: Mesos
> Issue Type: Bug
> Reporter: Qian Zhang
> Assignee: Qian Zhang
>
> To use protobuf enum in a backwards compatible way, [the suggestion on the
> protobuf mailing
> list|https://groups.google.com/forum/#!msg/protobuf/NhUjBfDyGmY/pf294zMi2bIJ]
> is to use optional enum fields and include an UNKNOWN value as the first
> entry in the enum list (and/or explicitly specifying it as the default). This
> can handle the case of parsing protobuf message from a serialized string, but
> it can not handle the case of parsing protobuf message from JSON.
> E.g., when I access master endpoint with an inexistent enum {{xxx}}, I will
> get an error:
> {code}
> $ curl -X POST -H "Content-Type: application/json" -d '{"type": "xxx"}'
> 127.0.0.1:5050/api/v1
> Failed to convert JSON into Call protobuf: Failed to find enum for 'xxx'%
> {code}
> In the {{Call}} protobuf message, the enum {{Type}} already has a default
> value {{UNKNOWN}} (see
> [here|https://github.com/apache/mesos/blob/1.3.0/include/mesos/v1/master/master.proto#L45]
> for details) and the field {{Call.type}} is optional, but the above curl
> command will still fail. The root cause is, in the code
> [here|https://github.com/apache/mesos/blob/1.3.0/3rdparty/stout/include/stout/protobuf.hpp#L449:L454]
> when we try to get the enum value for the string "xxx", it will fail since
> there is no any enum value corresponding to "xxx".
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