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https://issues.apache.org/jira/browse/THRIFT-1394?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13167961#comment-13167961
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Diwaker Gupta commented on THRIFT-1394:
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Jake, considering that the current C++ <-> Java wire translation is
inconsistent and likely to be inconsistent across other languages as well AND
considering that this hasn't been a huge issue in the community so far, my
sense is that most Thrift users just haven't run into this.
Given our limited resources, we are unable to provide patches for other client
libraries. But I don't see why that should prevent this patch from going in --
it passes all tests and doesn't break any existing clients and/or functionality.
What would it take to get this patch into the next release?
> Treatment of optional fields is not consistent between C++ and Java
> -------------------------------------------------------------------
>
> Key: THRIFT-1394
> URL: https://issues.apache.org/jira/browse/THRIFT-1394
> Project: Thrift
> Issue Type: Bug
> Components: C++ - Compiler, Java - Compiler
> Affects Versions: 0.7
> Environment: Mac OSX, Thrift trunk
> Reporter: Diwaker Gupta
> Assignee: Jake Farrell
> Labels: C++, Java
> Attachments: THRIFT-1394.patch
>
>
> *Motivation*
> We are trying to implement message signing in the application layer for an
> internal project. The transport is over Thrift -- the server side is using
> Java and the client side is using C++. We noticed that the message signing
> would fail because the client and server would serialize the same Thrift
> object in different ways.
> *Problem*
> The semantics of "optional" fields differ between thrift code generated for
> Java and CPP. In CPP, all optional fields are guarded by the {{isset}} helper
> struct. On Java, however, the generated code takes advantage of nullable
> types: for containers, structs, exceptions, enums, and, notably, strings, the
> generator elides explicit use of an "isset" bit vector and instead emits
> checks of the form "field null". This leads to varying behavior between the
> two languages: an optional string field with a default value will have
> {{isset[fieldid]}} false on C, but the equivalent test in Java will be true.
> To be concrete, consider the following example:
> {code}
> struct Foo {
> 1: optional string bar = "hello";
> 2: optional i32 baz;
> }
> {code}
> In C++, the checks for 'bar' and 'i' are similar:
> {code}
> if (this->__isset.bar) {
> xfer += oprot->writeFieldBegin("bar",
> ::apache::thrift::protocol::T_STRING, 1);
> xfer += oprot->writeString(this->bar);
> xfer += oprot->writeFieldEnd();
> }
> if (this->__isset.baz) {
> xfer += oprot->writeFieldBegin("baz", ::apache::thrift::protocol::T_I32,
> 2);
> xfer += oprot->writeI32(this->baz);
> xfer += oprot->writeFieldEnd();
> }
> {code}
> However, in Java, the checks are different:
> {code}
> /** Returns true if field bar is set (has been assigned a value) and false
> otherwise */
> public boolean isSetBar() {
> return this.bar != null;
> }
> /** Returns true if field baz is set (has been assigned a value) and false
> otherwise */
> public boolean isSetBaz() {
> return __isset_bit_vector.get(__BAZ_ISSET_ID);
> }
> {code}
> As a result, when the Java object is serialized, the value for 'bar' _is_
> included. But when the C++ object is serialized, the value for 'bar' is NOT
> included.
> For a system like Thrift, I would eschew a few bytes saved over correctness
> and reliability. As a user of Thrift, I *do* expect that the wire data
> generated for identical Thrift objects will be identical, regardless of the
> language used.
> *Proposal*
> We already use a BitSet to track primitive types in Java. The compiler should
> extend the bit vector to also guard nullable types, to be consistent with
> C++. This is pretty easy and low impact -- I'm happy to provide a patch.
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