Optimize tonic metadata serialization

CHANGELOG.md

@@ -3,6 +3,13 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+## [0.24.3] - 2025-10-19
+
+### Fixed
+- Reused stack-allocated format buffers when emitting gRPC metadata for HTTP
+  status codes and retry hints, and added regression coverage to ensure metadata
+  strings remain ASCII encoded.
+
 ## [0.24.2] - 2025-10-18
 
 ### Added

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "masterror"
-version = "0.24.2"
+version = "0.24.3"
 rust-version = "1.90"
 edition = "2024"
 license = "MIT OR Apache-2.0"

README.md

@@ -74,9 +74,9 @@ The build script keeps the full feature snippet below in sync with
 
 ~~~toml
 [dependencies]
-masterror = { version = "0.24.2", default-features = false }
+masterror = { version = "0.24.3", default-features = false }
 # or with features:
-# masterror = { version = "0.24.2", features = [
+# masterror = { version = "0.24.3", features = [
 #   "std", "axum", "actix", "openapi",
 #   "serde_json", "tracing", "metrics", "backtrace",
 #   "sqlx", "sqlx-migrate", "reqwest", "redis",

src/convert/tonic.rs

@@ -21,6 +21,7 @@
 use core::convert::Infallible;
 use std::borrow::Cow;
 
+use itoa::Buffer as IntegerBuffer;
 use tonic::{
     Code, Status,
     metadata::{MetadataMap, MetadataValue}
@@ -68,11 +69,9 @@ fn status_from_error(error: &Error) -> Status {
     let mut meta = MetadataMap::new();
 
     insert_ascii(&mut meta, "app-code", error.code.as_str());
-    insert_ascii(
-        &mut meta,
-        "app-http-status",
-        mapping.http_status().to_string()
-    );
+    let mut http_status_buffer = IntegerBuffer::new();
+    let http_status = http_status_buffer.format(mapping.http_status());
+    insert_ascii(&mut meta, "app-http-status", http_status);
     insert_ascii(&mut meta, "app-problem-type", mapping.problem_type());
 
     if let Some(advice) = error.retry {
@@ -104,7 +103,9 @@ fn sanitize_detail(
 }
 
 fn insert_retry(meta: &mut MetadataMap, retry: RetryAdvice) {
-    insert_ascii(meta, "retry-after", retry.after_seconds.to_string());
+    let mut retry_after_buffer = IntegerBuffer::new();
+    let retry_after = retry_after_buffer.format(retry.after_seconds);
+    insert_ascii(meta, "retry-after", retry_after);
 }
 
 fn attach_metadata(meta: &mut MetadataMap, metadata: &Metadata) {
@@ -215,4 +216,22 @@ mod tests {
             Some("2")
         );
     }
+
+    #[test]
+    fn timeout_status_carries_ascii_metadata() {
+        let status = Status::from(AppError::timeout("deadline exceeded").with_retry_after_secs(7));
+        let metadata = status.metadata();
+        assert_eq!(
+            metadata
+                .get("app-http-status")
+                .and_then(|value| value.to_str().ok()),
+            Some("504")
+        );
+        assert_eq!(
+            metadata
+                .get("retry-after")
+                .and_then(|value| value.to_str().ok()),
+            Some("7")
+        );
+    }
 }