fix: download legacy build for unknown os (thanks @wingedfox)

* GH-43 download legacy build for unknown os

* style: fix eslint warnings

Author: wingedfox

src/util/MongoBinaryDownloadUrl.js

@@ -82,7 +82,8 @@ export default class MongoBinaryDownloadUrl {
     } else if (/mint/i.test(os.dist)) {
       return this.getMintVersionString(os);
     }
-    throw new Error(`Cannot determine version string for ${JSON.stringify(os)}`);
+    console.warn(`Unknown linux distro ${os.dist}, falling back to legacy MongoDB build`);
+    return this.getLegacyVersionString(os);
   }
 
   getDebianVersionString(os: OS): string {
@@ -135,6 +136,11 @@ export default class MongoBinaryDownloadUrl {
     return 'ubuntu1404';
   }
 
+  // eslint-disable-next-line no-unused-vars
+  getLegacyVersionString(os: OS): string {
+    return '';
+  }
+
   getSuseVersionString(os: any): string {
     const [release]: [string | null] = os.release.match(/(^11|^12)/) || [null];
 

src/util/__tests__/MongoBinaryDownloadUrl-test.js

@@ -44,6 +44,20 @@ describe('MongoBinaryDownloadUrl', () => {
         'https://downloads.mongodb.org/win32/mongodb-win32-x86_64-3.4.4.zip'
       );
     });
+
+    it('fallback', async () => {
+      const du = new MongoBinaryDownloadUrl({
+        platform: 'linux',
+        arch: 'x64',
+        version: '3.4.4',
+        os: {
+          dist: 'Gentoo Linux',
+        },
+      });
+      expect(await du.getDownloadUrl()).toBe(
+        'https://downloads.mongodb.org/linux/mongodb-linux-x86_64-3.4.4.tgz'
+      );
+    });
   });
 
   describe('getUbuntuVersionString()', () => {
@@ -154,4 +168,16 @@ describe('MongoBinaryDownloadUrl', () => {
       expect(downloadUrl.getMintVersionString({ dist: 'Linux Mint' })).toBe('ubuntu1404');
     });
   });
+
+  describe('getLegacyVersionString', () => {
+    const downloadUrl = new MongoBinaryDownloadUrl({
+      platform: 'linux',
+      arch: 'x64',
+      version: '3.4.4',
+    });
+
+    it('should return an archive name for Gentoo Linux', () => {
+      expect(downloadUrl.getLegacyVersionString({ dist: 'Gentoo Linux' })).toBe('');
+    });
+  });
 });