[AVRO-1636] C++ JsonDecoder expects json object to be ordered

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 1.7.7
• Component/s: c++
• Assignee: Unassigned
• Reporter: Mann Du
• Created: 29/Jan/15 04:07
• Updated: 19/Nov/18 04:22
• Resolved: 19/Nov/18 04:22

Description

I am using Shafquat Rahman's original post for this problem reported in Avro user mailing list in last May for the description - ( Thiru provided a fix for the exact problem for Java in Oct. 2011 with Avro-895.)

I have been experimenting with avro in C++ (version 1.7.5) and ran into an issue with the json decoder which expects ordered json objects. The problem I am seeing appears similar to this post I found for an older avro java library:

http://search-hadoop.com/m/7WG37aVaBd/v=plain

I have a simple record:

{
"name" : "SimpleRecord",
"type" : "record",
"fields" :[

{ "name" : "A", "type" : "int"}

,

{ "name" : "B", "type" : "int"}

]
}

I generate the C++ header using avrogencpp. The generated code has codec_traits specialization for SimpleRecord that fixes the order for the JsonEncoder and JsonDecoder.

...snip...
namespace avro {
template<> struct codec_traits<SimpleRecord> {
static void encode(Encoder& e, const SimpleRecord& v)

{ avro::encode(e, v.A); avro::encode(e, v.B); }

static void decode(Decoder& d, SimpleRecord& v)

{ avro::decode(d, v.A); avro::decode(d, v.B); }

};
...snip...

The JsonDecoder successfully decodes json objects of the form

{"A" : 1, "B" : 2}

into SimpleRecord. But if I try to decode

{"B" : 2, "A" : 1}

it throws 'avro::Exception' with "Incorrect field" from impl/parsing/JsonCodec.cc:182 in the following method:

JsonDecoderHandler(JsonParser& p) : in_(p) { }
size_t handle(const Symbol& s) {
switch (s.kind()) {
case Symbol::sRecordStart:
expectToken(in_, JsonParser::tkObjectStart);
break;
case Symbol::sRecordEnd:
expectToken(in_, JsonParser::tkObjectEnd);
break;
case Symbol::sField:
expectToken(in_, JsonParser::tkString);
if (s.extra<string>() != in_.stringValue())

{ throw Exception("Incorrect field"); }

break;
default:
break;
}
return 0;
}

The stack shows that avro::decode(d, v.A) is the call the eventually causes the exception.

According to the json spec the fields in a json object are unordered. ...