From 97c462264680b3c8618a11d2d0195ac0184cdf2f Mon Sep 17 00:00:00 2001
From: Steve Ayers <sayers@buf.build>
Date: Fri, 24 Jan 2025 14:14:12 -0500
Subject: [PATCH] Ensure any error metadata is appended to target grpc response

Signed-off-by: Steve Ayers <sayers@buf.build>
---
 .../src/protocol-grpc/trailer-status.spec.ts  | 30 +++++++++++++++++++
 .../src/protocol-grpc/trailer-status.ts       |  7 +++++
 2 files changed, 37 insertions(+)

diff --git a/packages/connect/src/protocol-grpc/trailer-status.spec.ts b/packages/connect/src/protocol-grpc/trailer-status.spec.ts
index 9ae0a348c..44a01c6c3 100644
--- a/packages/connect/src/protocol-grpc/trailer-status.spec.ts
+++ b/packages/connect/src/protocol-grpc/trailer-status.spec.ts
@@ -63,6 +63,36 @@ describe("setTrailerStatus()", function () {
       "CAgSDHNvaXLDqWUg8J+OiRo0Ci50eXBlLmdvb2dsZWFwaXMuY29tL2dvb2dsZS5wcm90b2J1Zi5JbnQzMlZhbHVlEgIIew",
     );
   });
+  it("should append any error metadata", function () {
+    const t = new Headers();
+    setTrailerStatus(
+      t,
+      new ConnectError("soirée 🎉", Code.ResourceExhausted, { foo: "bar" }),
+    );
+    let count = 0;
+    t.forEach(() => count++);
+    expect(count).toBe(3);
+    expect(t.get("grpc-status")).toBe("8"); // resource_exhausted
+    expect(t.get("grpc-message")).toBe("soir%C3%A9e%20%F0%9F%8E%89");
+    expect(t.get("foo")).toBe("bar");
+  });
+  it("should overwrite error metadata that uses reserved protocol headers", function () {
+    const t = new Headers();
+    setTrailerStatus(
+      t,
+      new ConnectError("soirée 🎉", Code.ResourceExhausted, {
+        foo: "bar",
+        "grpc-status": "foo-status",
+        "grpc-message": "foo-message",
+      }),
+    );
+    let count = 0;
+    t.forEach(() => count++);
+    expect(count).toBe(3);
+    expect(t.get("grpc-status")).toBe("8"); // resource_exhausted
+    expect(t.get("grpc-message")).toBe("soir%C3%A9e%20%F0%9F%8E%89");
+    expect(t.get("foo")).toBe("bar");
+  });
 });
 
 describe("findTrailerError()", function () {
diff --git a/packages/connect/src/protocol-grpc/trailer-status.ts b/packages/connect/src/protocol-grpc/trailer-status.ts
index 55a4cddd4..dfd1d8192 100644
--- a/packages/connect/src/protocol-grpc/trailer-status.ts
+++ b/packages/connect/src/protocol-grpc/trailer-status.ts
@@ -46,6 +46,13 @@ export function setTrailerStatus(
   error: ConnectError | undefined,
 ): Headers {
   if (error) {
+    // Copy any metadata specified in the error into the target Headers
+    // Note that if a protocol header happens to be specified in metadata, it
+    // its value will be overridden below by the official protocol headers.
+    error.metadata.forEach((value, key) => {
+      target.append(key, value);
+    });
+
     target.set(headerGrpcStatus, error.code.toString(10));
     target.set(headerGrpcMessage, encodeURIComponent(error.rawMessage));
     if (error.details.length > 0) {