Add stringify method to mirror parse

src/index.ts

@@ -89,17 +89,19 @@ export interface ParseOptions {
   decode?: (str: string) => string | undefined;
 }
 
+/**
+ * Cookies object.
+ */
+export type Cookies = Record<string, string | undefined>;
+
 /**
  * Parse a cookie header.
  *
  * Parse the given cookie header string into an object
  * The object has the various cookies as keys(names) => values
  */
-export function parse(
-  str: string,
-  options?: ParseOptions,
-): Record<string, string | undefined> {
-  const obj: Record<string, string | undefined> = new NullObject();
+export function parse(str: string, options?: ParseOptions): Cookies {
+  const obj: Cookies = new NullObject();
   const len = str.length;
   // RFC 6265 sec 4.1.1, RFC 2616 2.2 defines a cookie name consists of one char minimum, plus '='.
   if (len < 2) return obj;
@@ -155,6 +157,46 @@ function endIndex(str: string, index: number, min: number) {
   return min;
 }
 
+export interface StringifyOptions {
+  /**
+   * Specifies a function that will be used to encode a [cookie-value](https://datatracker.ietf.org/doc/html/rfc6265#section-4.1.1).
+   * Since value of a cookie has a limited character set (and must be a simple string), this function can be used to encode
+   * a value into a string suited for a cookie's value, and should mirror `decode` when parsing.
+   *
+   * @default encodeURIComponent
+   */
+  encode?: (str: string) => string;
+}
+
+/**
+ * Stringify a set of cookies into a `Cookie` header string.
+ */
+export function stringify(
+  cookies: Cookies,
+  options?: StringifyOptions,
+): string {
+  const enc = options?.encode || encodeURIComponent;
+  const cookieStrings: string[] = [];
+
+  for (const [name, val] of Object.entries(cookies)) {
+    if (val === undefined) continue;
+
+    if (!cookieNameRegExp.test(name)) {
+      throw new TypeError(`cookie name is invalid: ${name}`);
+    }
+
+    const value = enc(val);
+
+    if (!cookieValueRegExp.test(value)) {
+      throw new TypeError(`cookie val is invalid: ${val}`);
+    }
+
+    cookieStrings.push(`${name}=${value}`);
+  }
+
+  return cookieStrings.join("; ");
+}
+
 /**
  * Serialize options.
  */

src/stringify.spec.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+import { stringify } from "./index.js";
+
+describe("stringify", () => {
+  it("should stringify object", () => {
+    expect(stringify({ key: "value" })).toEqual("key=value");
+  });
+
+  it("should stringify objects with multiple entries", () => {
+    expect(stringify({ a: "1", b: "2" })).toEqual("a=1; b=2");
+  });
+
+  it("should ignore undefined values", () => {
+    expect(stringify({ a: "1", b: undefined })).toEqual("a=1");
+  });
+
+  it("should error on invalid keys", () => {
+    expect(() => stringify({ "test=": "" })).toThrow(/cookie name is invalid/);
+  });
+
+  it("should error on invalid values", () => {
+    expect(() => stringify({ test: ";" }, { encode: (x) => x })).toThrow(
+      /cookie val is invalid/,
+    );
+  });
+});