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https://issues.apache.org/jira/browse/THRIFT-3650?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15156106#comment-15156106
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Hudson commented on THRIFT-3650:
--------------------------------
SUCCESS: Integrated in Thrift-precommit #188 (See
[https://builds.apache.org/job/Thrift-precommit/188/])
THRIFT-3650 incorrect union serialization Client: Compiler (general) (jensg:
[https://github.com/apache/thrift/commit/b72bb94a8212edc83864edc435896fdcda6e796c])
* compiler/cpp/src/parse/t_struct.h
> incorrect union serialization
> ------------------------------
>
> Key: THRIFT-3650
> URL: https://issues.apache.org/jira/browse/THRIFT-3650
> Project: Thrift
> Issue Type: Bug
> Components: C++ - Compiler, Compiler (General)
> Affects Versions: 0.9.3
> Reporter: Jens Geyer
> Assignee: Jens Geyer
> Fix For: 0.10.0
>
> Attachments: 0001-THRIFT-3650-incorrect-union-serialization.patch
>
>
> With C++ the following {{union}} generates incorrect serialization code:
> {code}
> union type_ex {
> 1 : string foo
> 2 : i32 bar
> 3 : double baz
> }
> {code}
> This results in all three fields being *unconditionally* written, which not
> only wastes space on the wire, but also sets all {{__isset}} bits during
> deserialization. This makes it a bit hard to the other side to find out which
> {{union}} field is the right one.
> {code}
> uint32_t type_ex::write(::apache::thrift::protocol::TProtocol* oprot) const {
> uint32_t xfer = 0;
> apache::thrift::protocol::TOutputRecursionTracker tracker(*oprot);
> xfer += oprot->writeStructBegin("type_ex");
> xfer += oprot->writeFieldBegin("STRING",
> ::apache::thrift::protocol::T_STRING, 1);
> xfer += oprot->writeString(this->STRING);
> xfer += oprot->writeFieldEnd();
> xfer += oprot->writeFieldBegin("INT64", ::apache::thrift::protocol::T_I64,
> 2);
> xfer += oprot->writeI64(this->INT64);
> xfer += oprot->writeFieldEnd();
> xfer += oprot->writeFieldBegin("DOUBLE",
> ::apache::thrift::protocol::T_DOUBLE, 3);
> xfer += oprot->writeDouble(this->DOUBLE);
> xfer += oprot->writeFieldEnd();
> xfer += oprot->writeFieldStop();
> xfer += oprot->writeStructEnd();
> return xfer;
> }
> {code}
> *Note* that the code above is just right (due to "default" requiredness) if
> we talk about structs. But these rules do not really apply to union members
> where *by definition* only one value is used. Hence, union members implicitly
> have {{optional}} requiredness
> *Workaround*
> Add explicit {{optionals}}:
> {code}
> union type_ex {
> 1 : optional string foo
> 2 : optional i32 bar
> 3 : optional double baz
> }
> {code}
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