[FEAT] added ability for client to set a status on a header

nats-base-client/headers.ts

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2021 The NATS Authors
+ * Copyright 2020-2022 The NATS Authors
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
@@ -77,8 +77,11 @@ export function canonicalMIMEHeaderKey(k: string): string {
   return String.fromCharCode(...buf);
 }
 
-export function headers(): MsgHdrs {
-  return new MsgHdrsImpl();
+export function headers(code = 0, description = ""): MsgHdrs {
+  if ((code === 0 && description !== "") || (code > 0 && description === "")) {
+    throw new Error("setting status requires both code and description");
+  }
+  return new MsgHdrsImpl(code, description);
 }
 
 const HEADER = "NATS/1.0";
@@ -93,14 +96,14 @@ export enum Match {
 }
 
 export class MsgHdrsImpl implements MsgHdrs {
-  code: number;
+  _code: number;
   headers: Map<string, string[]>;
-  description: string;
+  _description: string;
 
-  constructor() {
-    this.code = 0;
+  constructor(code = 0, description = "") {
+    this._code = code;
+    this._description = description;
     this.headers = new Map();
-    this.description = "";
   }
 
   [Symbol.iterator]() {
@@ -114,7 +117,7 @@ export class MsgHdrsImpl implements MsgHdrs {
   equals(mh: MsgHdrsImpl): boolean {
     if (
       mh && this.headers.size === mh.headers.size &&
-      this.code === mh.code
+      this._code === mh._code
     ) {
       for (const [k, v] of this.headers) {
         const a = mh.values(k);
@@ -141,10 +144,10 @@ export class MsgHdrsImpl implements MsgHdrs {
     const h = lines[0];
     if (h !== HEADER) {
       let str = h.replace(HEADER, "");
-      mh.code = parseInt(str, 10);
-      const scode = mh.code.toString();
+      mh._code = parseInt(str, 10);
+      const scode = mh._code.toString();
       str = str.replace(scode, "");
-      mh.description = str.trim();
+      mh._description = str.trim();
     }
     if (lines.length >= 1) {
       lines.slice(1).map((s) => {
@@ -162,10 +165,13 @@ export class MsgHdrsImpl implements MsgHdrs {
   }
 
   toString(): string {
-    if (this.headers.size === 0) {
+    if (this.headers.size === 0 && this._code === 0) {
       return "";
     }
     let s = HEADER;
+    if (this._code > 0 && this._description !== "") {
+      s += ` ${this._code} ${this._description}`;
+    }
     for (const [k, v] of this.headers) {
       for (let i = 0; i < v.length; i++) {
         s = `${s}\r\n${k}: ${v[i]}`;
@@ -278,11 +284,11 @@ export class MsgHdrsImpl implements MsgHdrs {
   }
 
   get hasError() {
-    return this.code >= 300;
+    return this._code >= 300;
   }
 
   get status(): string {
-    return `${this.code} ${this.description}`.trim();
+    return `${this._code} ${this._description}`.trim();
   }
 
   toRecord(): Record<string, string[]> {
@@ -293,6 +299,14 @@ export class MsgHdrsImpl implements MsgHdrs {
     return data;
   }
 
+  get code(): number {
+    return this._code;
+  }
+
+  get description(): string {
+    return this._description;
+  }
+
   static fromRecord(r: Record<string, string[]>): MsgHdrs {
     const h = new MsgHdrsImpl();
     for (const k in r) {

nats-base-client/jsutil.ts

@@ -1,5 +1,5 @@
 /*
- * Copyright 2021 The NATS Authors
+ * Copyright 2021-2022 The NATS Authors
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
@@ -116,9 +116,7 @@ export function newJsErrorMsg(
   description: string,
   subject: string,
 ): Msg {
-  const h = headers() as MsgHdrsImpl;
-  h.code = code;
-  h.description = description;
+  const h = headers(code, description) as MsgHdrsImpl;
 
   const arg = { hdr: 1, sid: 0, size: 0 } as MsgArg;
   const msg = new MsgImpl(arg, Empty, {} as Publisher);

nats-base-client/msg.ts

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020 The NATS Authors
+ * Copyright 2020-2022 The NATS Authors
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
@@ -20,15 +20,11 @@ import { TD } from "./encoders.ts";
 import { ErrorCode, NatsError } from "./error.ts";
 
 export function isRequestError(msg: Msg): NatsError | null {
-  // to consider an error from the server we expect no payload
-  if (msg && msg.data.length === 0 && msg.headers) {
-    const headers = msg.headers as MsgHdrsImpl;
-    if (headers.hasError) {
-      // only 503s are expected from core NATS (404/408/409s are JetStream)
-      if (headers.code === 503) {
-        return NatsError.errorForCode(ErrorCode.NoResponders);
-      }
-    }
+  // NATS core only considers errors 503s on messages that have no payload
+  // everything else simply forwarded as part of the message and is considered
+  // application level information
+  if (msg && msg.data.length === 0 && msg.headers?.code === 503) {
+    return NatsError.errorForCode(ErrorCode.NoResponders);
   }
   return null;
 }

tests/headers_test.ts

@@ -1,5 +1,5 @@
 /*
- * Copyright 2020-2021 The NATS Authors
+ * Copyright 2020-2022 The NATS Authors
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
@@ -28,6 +28,7 @@ import { NatsServer } from "./helpers/launcher.ts";
 import {
   assert,
   assertEquals,
+  assertRejects,
   assertThrows,
 } from "https://deno.land/std@0.152.0/testing/asserts.ts";
 import {
@@ -37,6 +38,7 @@ import {
 } from "../nats-base-client/internal_mod.ts";
 import { Publisher } from "../nats-base-client/protocol.ts";
 import { TestDispatcher } from "./parser_test.ts";
+import { cleanup, setup } from "./jstest_util.ts";
 
 Deno.test("headers - illegal key", () => {
   const h = headers();
@@ -321,3 +323,38 @@ Deno.test("headers - error headers may have other entries", () => {
   assertEquals(m.headers.get(JsHeaders.LastConsumerSeqHdr), "1");
   assertEquals(m.headers.get(JsHeaders.LastStreamSeqHdr), "1");
 });
+
+Deno.test("headers - code/description", () => {
+  assertThrows(
+    () => {
+      headers(500);
+    },
+    Error,
+    "setting status requires both code and description",
+  );
+
+  assertThrows(
+    () => {
+      headers(0, "some message");
+    },
+    Error,
+    "setting status requires both code and description",
+  );
+});
+
+Deno.test("headers - codec", async () => {
+  const { ns, nc } = await setup({}, {});
+
+  nc.subscribe("foo", {
+    callback: (err, msg) => {
+      const h = headers(500, "custom status from client");
+      msg.respond(Empty, { headers: h });
+    },
+  });
+
+  const r = await nc.request("foo", Empty);
+  assertEquals(r.headers?.code, 500);
+  assertEquals(r.headers?.description, "custom status from client");
+
+  await cleanup(ns, nc);
+});