[Flatbuffers codec] Content-subtype only set for go lang

[mustiikhalil]

Hello,

I am working on updating the flatbuffers Grpc support to v1.35.0 for all the languages that are implemented. However I am facing a small issue, whenever I try to make different languages communicate the go server would usually crash. Since I was told all the other languages actually ignore the appended suffix into the application/grpc+{custom} where custom is usually removed. I've dig into the code and found out that processHeaderField func has a comment about how it might be better if it was switched to (subtype).

A suggested solution might be; checking for a content-subtype within f hpack.HeaderField and if present use that as a codec type/subtype, this can be set by the user as a custom metadata. and if its not it can default back to the content-type

It would be really nice to allow the go lang server to communicate with other Flatbuffers implemented clients.

Things I've tried:

• Communicating with the go server from the following implementations; JS, python, swift.
• Setting them separately in the languages but that just always gets ignored.

[menghanl]

whenever I try to make different languages communicate the go server would usually crash

Can you provide more details of how you ran the client/server, and the error you saw on each side?

[mustiikhalil]

Sorry, it seems that it's an issue with the core lib, not setting the custom suffix

[menghanl]

The root cause might be core not setting custom suffix, but a panic in the go server should never happen.

Do you have more information of where the panic happened? Can you paste the full stacktrace? Thanks.

[mustiikhalil]

:scheme http
:method POST
:authority localhost:3000
:path /models.Greeter/SayHello
from ts
te trailers
content-type application/grpc
user-agent grpc-node/1.24.5 grpc-c/8.0.0 (osx; chttp2; ganges)
grpc-accept-encoding identity,deflate,gzip
accept-encoding identity,gzip
----
panic: interface conversion: *models.HelloRequest is not protoiface.MessageV1: missing method ProtoMessage

goroutine 12 [running]:
google.golang.org/grpc/encoding/proto.codec.Unmarshal(...)
        /Users/silly/go/pkg/mod/google.golang.org/[email protected]/encoding/proto/proto.go:43
google.golang.org/grpc.(*Server).processUnaryRPC.func2(0x146e3e0, 0xc0002040a0, 0x30, 0x14aa2c0)
        /Users/silly/go/pkg/mod/google.golang.org/[email protected]/server.go:1194 +0xd9
github.com/google/flatbuffers/grpc/examples/go/greeter/models._Greeter_SayHello_Handler(0x146f760, 0x1839340, 0x156f760, 0xc00020e000, 0xc0002022a0, 0x0, 0x156f760, 0xc00020e000, 0xc00020c000, 0x20)
        /Users/silly/development/flatbuffers/grpc/examples/go/greeter/models/Greeter_grpc.go:105 +0x53
google.golang.org/grpc.(*Server).processUnaryRPC(0xc0000f6fc0, 0x1573ce0, 0xc0001ca000, 0xc0001cc000, 0xc0001a0930, 0x17f6240, 0x0, 0x0, 0x0)
        /Users/silly/go/pkg/mod/google.golang.org/[email protected]/server.go:1217 +0x522
google.golang.org/grpc.(*Server).handleStream(0xc0000f6fc0, 0x1573ce0, 0xc0001ca000, 0xc0001cc000, 0x0)
        /Users/silly/go/pkg/mod/google.golang.org/[email protected]/server.go:1540 +0xd05
google.golang.org/grpc.(*Server).serveStreams.func1.2(0xc000026f14, 0xc0000f6fc0, 0x1573ce0, 0xc0001ca000, 0xc0001cc000)
        /Users/silly/go/pkg/mod/google.golang.org/[email protected]/server.go:878 +0xa5
created by google.golang.org/grpc.(*Server).serveStreams.func1
        /Users/silly/go/pkg/mod/google.golang.org/[email protected]/server.go:876 +0x1fd
exit status 2

This should be the full trace I am getting out of the console.

[mustiikhalil]

Thanks!