net: make writeAfterFIN() return false

If `false` is not returned a readable stream piped into the socket
might continue reading indefinitely until the process goes out of
memory.

PR-URL: #27996
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/net.js

@@ -410,6 +410,8 @@ function writeAfterFIN(chunk, encoding, cb) {
   if (typeof cb === 'function') {
     defaultTriggerAsyncIdScope(this[async_id_symbol], process.nextTick, cb, er);
   }
+
+  return false;
 }
 
 Socket.prototype.setTimeout = setStreamTimeout;

test/parallel/test-net-write-after-end-nt.js

@@ -4,7 +4,7 @@ const common = require('../common');
 const assert = require('assert');
 const net = require('net');
 
-const { mustCall } = common;
+const { expectsError, mustCall } = common;
 
 // This test ensures those errors caused by calling `net.Socket.write()`
 // after sockets ending will be emitted in the next tick.
@@ -18,7 +18,13 @@ const server = net.createServer(mustCall((socket) => {
       server.close();
     }));
     client.on('end', mustCall(() => {
-      client.write('hello', mustCall());
+      const ret = client.write('hello', expectsError({
+        code: 'EPIPE',
+        message: 'This socket has been ended by the other party',
+        type: Error
+      }));
+
+      assert.strictEqual(ret, false);
       assert(!hasError, 'The error should be emitted in the next tick.');
     }));
     client.end();