Flatc not generating JOSN

[swapniil]

First of all thanks for this very impressive serialization library with quite good documentation. I'm using it for now for a year. The issue I'm creating might be a trivial but I think it is needed to be fixed at least for my usage :) . Or this might be a non issue causing due to some incorrect IDL I have written :(.

I have written simple .fbs schema file contains line as below:
table test_type { inventory:[ubyte]; }

I need to generate C++ headers for this and jsonschema as well for string representation of this data.
when I'm executing command below:

flatc --jsonschema -o /tmp/fbs/ test.fbs --jsonschema

flatc has 'Segmentation fault'

The stack trace for this is as below:
` (gdb) r --jsonschema -o /tmp/fbs/ samples/test.fbs
Starting program: /usr/local/bin/flatc --jsonschema -o /tmp/fbs/ samples/test.fbs

Program received signal SIGSEGV, Segmentation fault.
0x00000000005410f0 in std::string flatbuffers::jsons::GenFullNameflatbuffers::StructDef(flatbuffers::StructDef const*) ()
(gdb) bt
#0 0x00000000005410f0 in std::string flatbuffers::jsons::GenFullNameflatbuffers::StructDef(flatbuffers::StructDef const*) ()
#1 0x00000000005428da in flatbuffers::jsons::JsonSchemaGenerator::generate() ()
#2 0x00000000005409e2 in flatbuffers::GenerateJsonSchema(flatbuffers::Parser const&, std::string const&, std::string const&) ()
#3 0x00000000005459b9 in flatbuffers::FlatCompiler::Compile(int, char const**) ()
#4 0x000000000041e46b in main ()
(gdb)
`

I have created a debug build of flatc to trace it down. It seems that there need to be a null check on below line.

Line Number:src/idl_gen_json_schema.cpp:202

Patch diff for this fix is :

diff --git a/src/idl_gen_json_schema.cpp b/src/idl_gen_json_schema.cpp
index b152fb2..2efa66c 100644
--- a/src/idl_gen_json_schema.cpp
+++ b/src/idl_gen_json_schema.cpp
@@ -199,8 +199,9 @@ class JsonSchemaGenerator : public BaseGenerator {
code_ += " },"; // close definitions

 // mark root type

• code_ += " "$ref" : "#/definitions/" +

•         GenFullName(parser_.root_struct_def_) + "\"";
  

• if (parser_.root_struct_def_)

•    code_ += "  \"$ref\" : \"#/definitions/" +
  

•             GenFullName(parser_.root_struct_def_) + "\"";
  

  code_ += "}"; // close schema root
  const std::string file_path = GeneratedFileName(path_, file_name_);

Let me know if its a valid issue or there is incorrect IDL declaration.

Thanks,
Swapnil

[vglavnyy]

Probably, this issue already fixed by #5622.

[swapniil]

Yes It seems so but it fails to generate JOSN.
I'm debugging it with latest code. Crash is fixed but JSON is still pending on this. What is going wrong on this 3 lines IDL .

[vglavnyy]

I have got flatc.exe: error: Unable to generate JsonSchema for test without SegFault (MSVC2019).
Code (#5622) works well.

    if (parser_.root_struct_def_ == nullptr) { return false; }

[vglavnyy]

It is impossible to generate json-schema if a root table is unknown.
Can you try this schema?

table test_type { inventory:[ubyte]; }

root_type test_type;

[swapniil]

It is impossible to generate json-schema if a root table is unknown.
Can you try this schema?

table test_type { inventory:[ubyte]; }

root_type test_type;

Yes that seems to be the cause. Thanks for immediate response. closing this issue with incorrect schema definition issue.