Extract pure native request header helpers

src/modules/services/nativeRequestHeaders.unit.spec.ts

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+import { describe, expect, it } from "vitest";
+import { createNativeRequestHeaders, shouldRevalidateNativeRequest } from "./nativeRequestHeaders";
+
+describe("native cache revalidation decision", () => {
+    it.each(["GET", "HEAD", "get", "head"])("revalidates explicit no-cache/no-store for %s", (method) => {
+        expect(shouldRevalidateNativeRequest(method, "no-cache")).toBe(true);
+        expect(shouldRevalidateNativeRequest(method, "no-store")).toBe(true);
+    });
+
+    it.each([undefined, "default", "reload", "force-cache", "only-if-cached"] as const)(
+        "does not strengthen cache mode %s",
+        (mode) => {
+            expect(shouldRevalidateNativeRequest("GET", mode)).toBe(false);
+            expect(shouldRevalidateNativeRequest("HEAD", mode)).toBe(false);
+        }
+    );
+
+    it.each(["POST", "PUT", "PATCH", "DELETE", "OPTIONS"])("does not revalidate %s", (method) => {
+        expect(shouldRevalidateNativeRequest(method, "no-cache")).toBe(false);
+        expect(shouldRevalidateNativeRequest(method, "no-store")).toBe(false);
+    });
+});
+
+describe("native request header creation", () => {
+    it("copies input headers and removes the existing native-controlled header forms", () => {
+        const input = Object.freeze({
+            host: "first.test",
+            Host: "second.test",
+            "content-length": "1",
+            "Content-Length": "2",
+            Authorization: "Bearer fixture",
+            "Cache-Control": "max-age=60",
+        });
+        const result = createNativeRequestHeaders(input, "GET", "default");
+        expect(result).toEqual({ Authorization: "Bearer fixture", "Cache-Control": "max-age=60" });
+        expect(result).not.toBe(input);
+        expect(input.host).toBe("first.test");
+        expect(input["Content-Length"]).toBe("2");
+    });
+
+    it.each(["GET", "HEAD"])("creates no-store revalidation headers for %s", (method) => {
+        expect(createNativeRequestHeaders({}, method, "no-store")).toEqual({
+            "cache-control": "no-cache, no-store",
+            pragma: "no-cache",
+        });
+    });
+
+    it("preserves an existing no-store directive when enforcing no-cache", () => {
+        expect(
+            createNativeRequestHeaders(
+                { "Cache-Control": "no-store, max-age=3600", Pragma: "legacy" },
+                "GET",
+                "no-cache"
+            )
+        ).toEqual({ "Cache-Control": "no-store, no-cache", Pragma: "legacy, no-cache" });
+    });
+
+    it("combines differently cased header fields and retains non-conflicting directives", () => {
+        const input = Object.freeze({
+            "Cache-Control": 'Max-Age=99, no-transform, custom="a,b", No-Cache',
+            "cache-control": "max-stale=5, min-fresh=6, only-if-cached, NO-STORE, private",
+            Pragma: 'legacy="a,b", No-Cache',
+            pragma: "extension, no-cache",
+        });
+        expect(createNativeRequestHeaders(input, "get", "no-store")).toEqual({
+            "Cache-Control": 'no-transform, custom="a,b", private, no-cache, no-store',
+            Pragma: 'legacy="a,b", extension, no-cache',
+        });
+        expect(input["cache-control"]).toContain("max-stale=5");
+    });
+
+    it("does not split directive commas inside escaped quoted strings", () => {
+        const custom = String.raw`custom="a\"b,c"`;
+        expect(createNativeRequestHeaders({ "cache-control": `${custom}, max-age=1` }, "HEAD", "no-cache")).toEqual({
+            "cache-control": `${custom}, no-cache`,
+            pragma: "no-cache",
+        });
+    });
+
+    it("retains cache headers on a non-revalidated method", () => {
+        const headers = { "cache-control": "max-age=99", Pragma: "legacy" };
+        expect(createNativeRequestHeaders(headers, "POST", "no-store")).toEqual(headers);
+    });
+});