encoding: add front matter module (denoland#2335)

Co-authored-by: Yoshiya Hinosawa <[email protected]>

encoding/front_matter.ts

@@ -0,0 +1,63 @@
+// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+// Copyright (c) Jason Campbell. MIT license.
+// https://github.com/jxson/front-matter/blob/36f139ef797bd9e5196a9ede03ef481d7fbca18e/index.js
+
+import { parse } from "./yaml.ts";
+
+const pattern = "^(" +
+ "\\ufeff?" + // Maybe byte order mark
+ "(= yaml =|---)" +
+ "$([\\s\\S]*?)" +
+ "^(?:\\2|\\.\\.\\.)\\s*" +
+ "$" +
+ (Deno.build.os === "windows" ? "\\r?" : "") +
+ "(?:\\n)?)";
+const regex = new RegExp(pattern, "m");
+
+export type Extract<T> = {
+ frontMatter: string;
+ body: string;
+ attrs: T;
+};
+
+/**
+ * Extracts front matter from a string.
+ * @param str String to extract from.
+ *
+ * ```ts
+ * import { extract } from "https://deno.land/std@$STD_VERSION/encoding/front_matter.ts";
+ * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
+ *
+ * const { attrs, body, frontMatter } = extract<{ title: string }>("---\ntitle: Three dashes marks the spot\n---\n");
+ * assertEquals(attrs.title, "Three dashes marks the spot");
+ * assertEquals(body, "");
+ * assertEquals(frontMatter, "---\ntitle: Three dashes marks the spot\n---\n");
+ * ```
+ */
+export function extract<T = unknown>(str: string): Extract<T> {
+ const lines = str.split(/(\r?\n)/);
+ if (/= yaml =|---/.test(lines[0])) {
+ const match = regex.exec(str);
+ if (!match) throw new TypeError("Unexpected end of input");
+ const frontMatter = match.at(-1)?.replace(/^\s+|\s+$/g, "") || "";
+ const attrs = parse(frontMatter) as T;
+ const body = str.replace(match[0], "");
+ return { frontMatter, body, attrs };
+ }
+ throw new TypeError("Failed to extract front matter");
+}
+
+/**
+ * Tests if a string has valid front matter.
+ * @param str String to test.
+ *
+ * ```ts
+ * import { test } from "https://deno.land/std@$STD_VERSION/encoding/front_matter.ts";
+ * import { assert } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
+ *
+ * assert(test("---\ntitle: Three dashes marks the spot\n---\n"));
+ * ```
+ */
+export function test(str: string): boolean {
+ return regex.test(str);
+}

encoding/front_matter_test.ts

@@ -0,0 +1,77 @@
+// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+
+import { extract, test } from "./front_matter.ts";
+import { assert, assertEquals, assertThrows } from "../testing/asserts.ts";
+
+Deno.test("test valid input true", () => {
+ [
+ "---\nname: deno\n---\n",
+ "= yaml =\nname: deno\n= yaml =\n",
+ "= yaml =\nname: deno\n= yaml =\ndeno is awesome\n",
+ ].forEach((str) => {
+ assert(test(str));
+ });
+});
+
+Deno.test("test invalid input false", () => {
+ [
+ "",
+ "---",
+ "= yaml =",
+ "---\n",
+ "= yaml =\n",
+ "---\nasdasdasd",
+ ].forEach((str) => {
+ assert(!test(str));
+ });
+});
+
+Deno.test("extract type error on invalid input", () => {
+ [
+ "",
+ "---",
+ "= yaml =",
+ "---\n",
+ "= yaml =\n",
+ "---\nasdasdasd",
+ ].forEach((str) => {
+ assertThrows(() => extract(str), TypeError);
+ });
+});
+
+Deno.test("parse yaml delinetead by `---`", () => {
+ const content = extract<
+ { title: string; tags: string[]; "expaned-description": string }
+ >(`---
+title: Three dashes marks the spot
+tags:
+ - yaml
+ - front-matter
+ - dashes
+expaned-description: with some --- crazy stuff in it
+---
+don't break
+---
+Also this shouldn't be a problem
+`);
+ assert(content !== undefined);
+ assertEquals(
+ content.frontMatter,
+ `title: Three dashes marks the spot
+tags:
+ - yaml
+ - front-matter
+ - dashes
+expaned-description: with some --- crazy stuff in it`,
+ );
+ assertEquals(
+ content.body,
+ "don't break\n---\nAlso this shouldn't be a problem\n",
+ );
+ assertEquals(content.attrs.title, "Three dashes marks the spot");
+ assertEquals(content.attrs.tags, ["yaml", "front-matter", "dashes"]);
+ assertEquals(
+ content.attrs["expaned-description"],
+ "with some --- crazy stuff in it",
+ );
+});