Read the plugin request until end of input, not the first short read

[jeong-sik]

Problem

read_all in src/plugin/protoc_gen_ocaml.ml stops at the first input call that returns fewer than 1024 bytes, and treats that as the end of the request. Stdlib.input does not promise full reads:

A return value between 0 and [len] exclusive means that not all requested [len] characters were read, either because no more characters were available at that time, or because the implementation found it convenient to do a partial read; input must be called again to read the remaining characters, if desired.

On macOS a pipe hands the first read 512 bytes. The CodeGeneratorRequest is then cut at 512 bytes, and the plugin fails:

Fatal error: exception Ocaml_protoc_plugin.Result.Error (`Premature_end_of_input)
--ocaml_out: protoc-gen-ocaml: Plugin failed with status code 2.

Reproduction

Environment: macOS 26.6.1 (arm64), protoc 34.0 from Homebrew (33.5 fails the same way), OCaml 5.5.1.

• On main (7cea929), dune runtest fails. There are 10 plugin failures, all Premature_end_of_input. The 6.2.0 release fails the same way.
• I captured one request protoc sent (16,903 bytes) and fed it to the 6.2.0 plugin. From a file it works. Through a pipe it fails every way I tried: cat request | protoc-gen-ocaml, and a pipe that sends the first 1000 or 2048 bytes and then the rest.
• A copy of read_all run on that pipe reads 512 of the 16,903 bytes before it stops (OCaml 5.4.0, 5.5.0 and 5.5.1 alike).

Fix

Read until input returns 0. The loop uses only input and Buffer, so it keeps the ocaml >= 4.08.0 bound (In_channel.input_all needs 4.14).

Testing

With this change, on the same machine:

• dune runtest passes.
• The rebuilt plugin decodes the captured request piped in whole, and split at 1000 bytes.
• protoc 34.0 generates code through the rebuilt plugin. Its output differs from the 6.2.0 output only by package_service_name, which is already on main.

🤖 Generated with Claude Code

[andersfugmann]

Thanks for reporting. The PR looks good. I'll merge once checks have completed.

[andersfugmann]

LGTM

[Copilot]

Copilot review overview

🟢 Approval recommended

No unresolved review issues were identified, and all assessments support approval.

Review effort: Lite
Findings: None

What changed in this PR

Fixes plugin request truncation by reading stdin until EOF, handling partial pipe reads correctly.

Changes:

• Repeatedly reads input until EOF.
• Reuses buffers while preserving OCaml compatibility.

File	Description
src/​plugin/​protoc_gen_ocaml.ml	Reads complete protobuf requests from stdin.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.