From 8c3612fb638d356579c446de68421288164484dc Mon Sep 17 00:00:00 2001
From: Brent Traut <btraut@openai.com>
Date: Wed, 30 Sep 2026 02:04:12 +0000
Subject: [PATCH] Use `memrchr` to find newlines in reverse JSONL scans
 (#49444)

Replace the byte-by-byte reverse newline search with `memchr::memrchr` and add `memchr` as a dependency of `codex-rollout`.

GitOrigin-RevId: b07e42e15efb0d63d7b00ee9a2ee29c446f4cf59
---
 codex-rs/Cargo.lock                           | 1 +
 codex-rs/rollout/Cargo.toml                   | 1 +
 codex-rs/rollout/src/reverse_jsonl_scanner.rs | 2 +-
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/codex-rs/Cargo.lock b/codex-rs/Cargo.lock
index a26f2fd61e..10a8c44279 100644
--- a/codex-rs/Cargo.lock
+++ b/codex-rs/Cargo.lock
@@ -4432,6 +4432,7 @@ dependencies = [
  "codex-utils-absolute-path",
  "codex-utils-path",
  "codex-utils-process",
+ "memchr",
  "pretty_assertions",
  "regex",
  "serde",
diff --git a/codex-rs/rollout/Cargo.toml b/codex-rs/rollout/Cargo.toml
index 8981dd9662..fb2b5b39e4 100644
--- a/codex-rs/rollout/Cargo.toml
+++ b/codex-rs/rollout/Cargo.toml
@@ -25,6 +25,7 @@ codex-protocol = { workspace = true }
 codex-state = { workspace = true }
 codex-utils-absolute-path = { workspace = true }
 codex-utils-path = { workspace = true }
+memchr = { workspace = true }
 regex = { workspace = true }
 serde = { workspace = true, features = ["derive"] }
 serde_json = { workspace = true }
diff --git a/codex-rs/rollout/src/reverse_jsonl_scanner.rs b/codex-rs/rollout/src/reverse_jsonl_scanner.rs
index 9e0a836bee..ed0daed295 100644
--- a/codex-rs/rollout/src/reverse_jsonl_scanner.rs
+++ b/codex-rs/rollout/src/reverse_jsonl_scanner.rs
@@ -95,7 +95,7 @@ where
             }
 
             let chunk = &self.chunk[..self.chunk_position];
-            if let Some(newline_position) = chunk.iter().rposition(|byte| *byte == b'\n') {
+            if let Some(newline_position) = memchr::memrchr(b'\n', chunk) {
                 let fragment = &chunk[newline_position + 1..];
                 if !self.discarding_oversized_record {
                     if self.max_record_bytes.is_some_and(|max_record_bytes| {