feat: add font MIME types and fix dfont/ico detection collision

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/mime.js

@@ -1,4 +1,6 @@
 import { fileTypeFromFile } from 'file-type';
+import fs from 'node:fs/promises';
+import { probeDfont } from './converters/dfont.js';
 
 const OUTPUT_MIME_TYPES = {
   jpg: 'image/jpeg',
@@ -17,6 +19,9 @@ const OUTPUT_MIME_TYPES = {
   md: 'text/markdown',
   csv: 'text/csv',
   xlsx: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
+  ttf: 'font/ttf',
+  otf: 'font/otf',
+  woff: 'font/woff',
 };
 
 export async function detectInputMime(filePath) {
@@ -46,6 +51,13 @@ function normalizeFormat(format) {
 }
 
 export async function resolveInputFormat(filePath, declaredFormat) {
+  if (declaredFormat === 'dfont') {
+    const buffer = await fs.readFile(filePath);
+    return probeDfont(buffer)
+      ? { mime: 'application/x-dfont', valid: true }
+      : { mime: null, valid: false };
+  }
+
   const detected = await detectInputMime(filePath);
 
   if (!detected) {

test/mime.test.js

@@ -104,3 +104,35 @@ describe('resolveInputFormat — heic/heif alias', () => {
     expect(result.valid).toBe(true);
   });
 });
+
+describe('outputMimeType — fonts', () => {
+  it('returns the correct MIME type for each font target format', () => {
+    expect(outputMimeType('ttf')).toBe('font/ttf');
+    expect(outputMimeType('otf')).toBe('font/otf');
+    expect(outputMimeType('woff')).toBe('font/woff');
+  });
+});
+
+describe('resolveInputFormat — dfont', () => {
+  it('confirms file-type alone misidentifies the dfont fixture as ico (documents the bug this fix works around)', async () => {
+    const fixturePath = path.join(import.meta.dirname, 'fixtures', 'sample.dfont');
+    const detected = await detectInputMime(fixturePath);
+    expect(detected.ext).toBe('ico');
+  });
+
+  it('accepts a real dfont file despite that misidentification', async () => {
+    const fixturePath = path.join(import.meta.dirname, 'fixtures', 'sample.dfont');
+    const result = await resolveInputFormat(fixturePath, 'dfont');
+    expect(result).toEqual({ mime: 'application/x-dfont', valid: true });
+  });
+
+  it('rejects content starting with the colliding magic bytes that is not a real dfont', async () => {
+    const fixturePath = path.join(import.meta.dirname, 'fixtures', 'sample-fake.dfont');
+    await fs.writeFile(fixturePath, Buffer.from([0x00, 0x00, 0x01, 0x00, 0x01, 0x00, 0x10, 0x10]));
+
+    const result = await resolveInputFormat(fixturePath, 'dfont');
+    expect(result).toEqual({ mime: null, valid: false });
+
+    await fs.unlink(fixturePath);
+  });
+});