feat(export): add markdown export utilities with url normalization tests

Made-with: Cursor

app/utils/markdown-export.test.ts

@@ -0,0 +1,57 @@
+import { describe, expect, test } from "bun:test";
+import {
+  buildMarkdownExportFileName,
+  normalizeMarkdownImageUrls,
+} from "./markdown-export";
+
+describe("normalizeMarkdownImageUrls", () => {
+  test("converts /public/assets image links to absolute URLs", () => {
+    const markdown = "![cover](/public/assets/posts/cover.png)";
+    const result = normalizeMarkdownImageUrls(markdown, "https://example.com");
+
+    expect(result).toBe("![cover](https://example.com/public/assets/posts/cover.png)");
+  });
+
+  test("keeps absolute http/https image links unchanged", () => {
+    const markdown = [
+      "![a](http://cdn.example.com/a.png)",
+      "![b](https://cdn.example.com/b.png)",
+    ].join("\n");
+
+    const result = normalizeMarkdownImageUrls(markdown, "https://example.com");
+
+    expect(result).toBe(markdown);
+  });
+
+  test("keeps protocol-relative and data URI image links unchanged", () => {
+    const markdown = [
+      "![protocol](//cdn.example.com/p.png)",
+      "![inline](data:image/png;base64,AAAB)",
+    ].join("\n");
+
+    const result = normalizeMarkdownImageUrls(markdown, "https://example.com");
+
+    expect(result).toBe(markdown);
+  });
+
+  test("does not change normal markdown links", () => {
+    const markdown = "[read more](/public/assets/posts/cover.png)";
+    const result = normalizeMarkdownImageUrls(markdown, "https://example.com");
+
+    expect(result).toBe(markdown);
+  });
+});
+
+describe("buildMarkdownExportFileName", () => {
+  test("prefers slug when slug is not empty", () => {
+    const result = buildMarkdownExportFileName({ slug: "hello-world", id: 42 });
+
+    expect(result).toBe("hello-world.md");
+  });
+
+  test("falls back to post-<id>.md when slug is empty", () => {
+    const result = buildMarkdownExportFileName({ slug: "", id: 42 });
+
+    expect(result).toBe("post-42.md");
+  });
+});

app/utils/markdown-export.ts

@@ -0,0 +1,48 @@
+type MarkdownExportFileNameInput = {
+  slug: string;
+  id: number;
+};
+
+const PUBLIC_ASSETS_PREFIX = "/public/assets/";
+
+function isAbsoluteOrSpecialUrl(url: string): boolean {
+  return /^(https?:)?\/\//i.test(url) || /^data:/i.test(url);
+}
+
+export function normalizeMarkdownImageUrls(markdown: string, origin: string): string {
+  const normalizedOrigin = origin.replace(/\/+$/, "");
+
+  return markdown.replace(/!\[([^\]]*)\]\(([^)\s]+)([^)]*)\)/g, (full, alt, rawUrl, rest) => {
+    if (isAbsoluteOrSpecialUrl(rawUrl)) {
+      return full;
+    }
+
+    if (!rawUrl.startsWith(PUBLIC_ASSETS_PREFIX)) {
+      return full;
+    }
+
+    return `![${alt}](${normalizedOrigin}${rawUrl}${rest})`;
+  });
+}
+
+export function buildMarkdownExportFileName(input: MarkdownExportFileNameInput): string {
+  const base = input.slug.trim() || `post-${input.id}`;
+  return `${base}.md`;
+}
+
+export function downloadMarkdownFile(filename: string, content: string): void {
+  if (typeof window === "undefined" || typeof document === "undefined") {
+    return;
+  }
+
+  const blob = new Blob([content], { type: "text/markdown;charset=utf-8" });
+  const url = URL.createObjectURL(blob);
+  const anchor = document.createElement("a");
+  anchor.href = url;
+  anchor.download = filename;
+  anchor.style.display = "none";
+  document.body.appendChild(anchor);
+  anchor.click();
+  anchor.remove();
+  URL.revokeObjectURL(url);
+}