Frequently Asked Questions

How do I work with .textproto files?

.textproto files are not currently supported by this package. You can, however, use the protoc compiler (e.g. via the protoc_jll package) to translate between text and binary formats using the --encode and --decode commands.

How do I work with oneof fields?

A oneof field represents a set of possible fields (members) of which only one can be set at a time. Individual members of a oneof field cannot be distinguished by their type alone, one needs to know the respective member field name as well. In this package, we use a OneOf{T} type to represent the chosen member, is only has two fields: a value::T and a name::Symbol. Dereferencing a OneOf instance will return the value.

Because Protocol Buffers stress that one needs to handle situations where message definitions evolve and when data transfer can fail, we need to have a default value for all fields, oneof fields included. Given multiple members, there is no clear default value to choose, so we represent the absence of a OneOf instance with nothing. This means that, by default, all oneof fields are presented as Union{Nothing,OneOf{...}} in Julia. These unions can sometimes be tricky to reason about for the Julia compiler so we recommend the following when working with OneOf types:

• Try to manually split the Union, i.e. instead of

if !isnothing(my_message.one_of_field)
elseif my_message.one_of_field === :option1
    do_someting(my_message.one_of_field[])
elseif my_message.one_of_field === :option2
    do_someting_else(my_message.one_of_field[])
# ...
end

do this:

one_of_field = my_message.one_of_field
if !isnothing(one_of_field)
elseif one_of_field === :option1
    do_someting(one_of_field[])
elseif one_of_field === :option2
    do_someting_else(one_of_field[])
# ...
end

• When you know that the oneof field is guaranteed to be received when decoding, you can tell the protojl not to use a Union by providing a force_requires keyword argument with Dict("my_proto_file.proto" => Set("MyMessage.one_of_field")).

• You can parametrize your structs on the type of oneofs by providing a parametrize_oneofs=true keyword argument to protojl.

How complete is this package?

The package should have fairly complete support for both proto2 and proto3 syntaxes with the following exceptions:

• Services and RPC are not yet supported
• Extensions are not yet supported
• Text Format is not yet supported (but see How do I work with .textproto files?)

Future development will focus on Services and RPC with an overall goal of getting a new, native Julia gRPC implementation.