fs: defer the writestream 'open' event by a nextTick

Fixes: nodejs#51993

lib/internal/fs/streams.js

@@ -75,13 +75,19 @@ function _construct(callback) {
       } else {
         stream.fd = fd;
         callback();
-        stream.emit('open', stream.fd);
-        stream.emit('ready');
+        // Ready must be deferred to the next tick, because callback will schedule
+        // some microtick work that we need to complete first.
+        process.nextTick(emitReady, stream);
       }
     });
   }
 }
 
+function emitReady(stream) {
+  stream.emit('open', stream.fd);
+  stream.emit('ready');
+}
+
 // This generates an fs operations structure for a FileHandle
 const FileHandleOperations = (handle) => {
   return {

test/parallel/test-fs-writestream-open-write.js

@@ -0,0 +1,27 @@
+'use strict'
+
+const common = require('../common');
+const { strictEqual } = require('assert');
+const { tmpdir } = require('os');
+const { join } = require('path');
+const fs = require('fs');
+
+// Regression test for https://github.com/nodejs/node/issues/51993
+
+const file = join(tmpdir(), `test-fs-writestream-open-write-${process.pid}.txt`);
+
+const w = fs.createWriteStream(file);
+
+w.on('open', common.mustCall(() => {
+  w.write('hello');
+
+  process.nextTick(() => {
+    w.write('world');
+    w.end();
+  });
+}));
+
+w.on('close', common.mustCall(() => {
+  strictEqual(fs.readFileSync(file, 'utf8'), 'helloworld');
+  fs.unlinkSync(file);
+}));