fix: Use fs.watchFile instead of fs.watch to detect changes to lo…

…aded database file (#368)

* Use `watchFile` instead of `watch` to better handle database replacements

* Try 3 times when db changes to find new file before failing

src/fs.ts

@@ -4,6 +4,5 @@ import util from 'util';
 export default {
   existsSync: fs.existsSync,
   readFile: util.promisify(fs.readFile),
-  readFileSync: fs.readFileSync,
-  watch: fs.watch,
+  watchFile: fs.watchFile,
 };

src/index.test.ts

@@ -15,11 +15,10 @@ describe('index', () => {
   beforeEach(() => {
     sandbox = sinon.createSandbox();
     // @ts-ignore
-    sandbox.stub(fs, 'watch').callsFake((paramA, paramB, cb) => {
+    sandbox.stub(fs, 'watchFile').callsFake((paramA, paramB, cb) => {
       watchHandler = cb;
     });
     sandbox.spy(fs, 'readFile');
-    sandbox.spy(fs, 'readFileSync');
   });
   afterEach(() => {
     sandbox.restore();
@@ -51,17 +50,17 @@ describe('index', () => {
       const options = { cache: { max: 1000 }, watchForUpdates: true };
       const lookup = await maxmind.open(dbPath, options);
       assert(lookup.get('2001:230::'));
-      assert((fs.watch as SinonSpy).calledOnce);
+      assert((fs.watchFile as SinonSpy).calledOnce);
       assert((fs.readFile as SinonSpy).calledOnce);
     });
 
     it('should work with auto updates', async () => {
       const options = { watchForUpdates: true };
       const lookup = await maxmind.open(dbPath, options);
       assert(lookup.get('2001:230::'));
-      assert((fs.watch as SinonSpy).calledOnce);
+      assert((fs.watchFile as SinonSpy).calledOnce);
       assert((fs.readFile as SinonSpy).calledOnce);
-      watchHandler();
+      await watchHandler();
       assert((fs.readFile as SinonSpy).calledTwice);
     });
 

src/index.ts

@@ -46,10 +46,21 @@ export const open = async <T>(
       persistent: opts.watchForUpdatesNonPersistent !== true,
     };
 
-    fs.watch(filepath, watcherOptions, async () => {
+    fs.watchFile(filepath, watcherOptions, async () => {
       // When database file is being replaced,
       // it could be removed for a fraction of a second.
-      if (!fs.existsSync(filepath)) {
+      const waitExists = async () => {
+        for (let i = 0; i < 3; i++) {
+          if (fs.existsSync(filepath)) {
+            return true;
+          }
+
+          await new Promise(a => setTimeout(a, 500));
+        }
+
+        return false;
+      }
+      if (!(await waitExists())) {
         return;
       }
       const updateDatabase = await fs.readFile(filepath);
@@ -83,4 +94,4 @@ export default {
   validate: ip.validate,
 };
 
-export { Reader };
+export { Reader };