Unclearness in the specification

[Mattias Hansson]

I am currently trying to implement a protobuf parser but it's a bit unclear to me how I should interpret some parts of the specification.

Lets start with RPC option. Options for normal fields and enum fields are pretty clear.

Here's the specification for normal fields:

field = [ "repeated" ] type fieldName "=" fieldNumber [ "[" fieldOptions "]" ] ";" fieldOptions = fieldOption { "," fieldOption } fieldOption = optionName "=" constant

Here's the specification for enum fields:

enum = "enum" enumName enumBody enumBody = "{" { option | enumField | emptyStatement | reserved } "}" enumField = ident "=" [ "-" ] intLit [ "[" enumValueOption { "," enumValueOption } "]" ]";" enumValueOption = optionName "=" constant

Both fields boils down to optionName which is specified as:

optionName = ( ident | "(" ["."] fullIdent ")" ) 

Here's the specification for RPC:

service = "service" serviceName "{" { option | rpc | emptyStatement } "}" rpc = "rpc" rpcName "(" [ "stream" ] messageType ")" "returns" "(" [ "stream" ] messageType ")" (( "{" {option | emptyStatement } "}" ) | ";")

RPC refers to plain option. Does this mean that the following is valid and intended syntax?

rpc Foo (Req) returns (Res);

rpc Foo (Req) returns (Res) {option opt1 = "opt1"; option opt2 = true; };

rpc Foo (Req) returns (Res) {option opt1 = "opt1"; ;;; option opt2 = true; ;;;};

I added number 3, because it seems like repetition is allowed together with emptyStatement. As a side note, I could not find any examples with RPC options as inspiration or to clear things up.

Further, I also find the specification for optionName a bit unclear.

Here's the specification for option and optionName:

option = "option" optionName "=" constant ";" optionName = ( ident | "(" ["."] fullIdent ")" )

optionName does not seem to allow for repetition and fullIdent is only allowed within parenthesis(custom option). However multiple examples on https://protobuf.dev/programming-guides/proto3/#option-targets use custom-like options on the format:

option (bar).baz = "value";

For me it's pretty clear that the following optionNames are allowed:

foo

(foo)

(foo.bar)

(.foo)

(.foo.bar)

I don't really get which part of the specification that states that "baz", in the example above, is allowed outside of the parenthesis.

Thanks in advance,

/Mattias

[Em Rauch]

This part of the official grammar unfortunately unclear; you may find Buf's reverse engineering of the protobuf grammar to be more clear on this point for your usecase: https://protobuf.com/docs/language-spec