package pbrt_yojson

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Runtime library for ocaml-protoc to support JSON encoding/decoding


Dune Dependency






  • fix segfault in pbrt in bytecode


  • fix bug where code for services would be generated even if --services is not passed on the CLI


Major version that breaks code for every user. Sorry!


  • Generated code now always fits into 2 files: code for foo.proto is produced in and foo.mli. This follows a fairly large internal refactor that enables a plugin architecture internally (which facilitated codegen for services). All encoder/decoder functions also have a new name now, so that they don't collide inside the same file.

  • CLI flags now use --this-style rather than -this-style

  • Bump minimal OCaml version to 4.08


  • encode probotufs backward, which means we can write directly into a single buffer (which is not possible in a forward mode because sub-messages require an unknown amount of prefix space to write their size as a varint)

  • add C stubs for pbrt

  • use Bytes functions to read/write fixed size integers

  • inlining annotations

  • more benchmarks, helping optimization overall

  • reduce allocations drastically, by having the generated code create fewer closures


  • add pbrt_services runtime library

  • generate code for service statements. This is a big feature for users who want to implement RPC systems using protobuf. The generated code is agnostic to whatever RPC implementation will use it, it only packs together RPC method names and path with the relevant encoders/decoders. Services require both JSON and binary encoders/decoders to be present.


  • migrate pbrt_yojson into the main ocaml-protoc repo

  • JSON runtime support for empty messages

  • Add support for bytes in JSON encoding

  • Add support for encoding and decoding maps in JSON

Other features and fixes

  • add --make flag to generate make functions that take fewer optional arguments. This helps preventing the user from forgetting important arguments when they're encoding to protobuf. Arguments actually marked as optional in the .proto file are still optional.

  • Support maps/lists in options

  • add Pbrt.Decoder.of_substring

  • Allow options to be named like (validate.rules).message.required

  • support code generation for empty messages

  • Empty proto file is a valid proto as well


  • expect-style tests for parser

  • Tests for option parsing

  • Test demonstrating parse error printing


  • expose compiler library as ocaml-protoc.compiler-lib

  • option to differentiate unsigned arg from signed arguments, taggings uint32/64 with `unsigned

internal changes:

  • fix(test): change integration test, protoc produces broken C++ code

  • automatic generation of gh-pages

  • add basic CI

  • use ocamlformat


  • allow optional in proto3 files

  • improve compatibility with OCaml 5


  • handle stream as a name (#179)

  • support hexadecimal notation for integers

  • improve generated pretty printers

  • move to dune 2.0

  • rename runtime library to pbrt, with a separate opam package

  • print bytes opaquely


  • perf: nested buffer to reduce allocations for nested messages

  • perf: improvements in runtime library, varint encoding/decoding, add benchmarks

  • Update docs/tests to reflect that sfixed is supported

  • add clear/reset to the encoder

  • Add ability to parse stream modifier


  • parsing of services


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