stream: do not deadlock duplexpair

If nothing is buffered then _read will not be called and the
callback will not be invoked, effectivly deadlocking.

Fixes: #29758

PR-URL: #29836
Refs: #29649
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Minwoo Jung <[email protected]>

Author: ronag

doc/api/stream.md

@@ -2059,7 +2059,9 @@ when `_read()` is called again after it has stopped should it resume pushing
 additional data onto the queue.
 
 Once the `readable._read()` method has been called, it will not be called again
-until the [`readable.push()`][stream-push] method is called.
+until more data is pushed through the [`readable.push()`][stream-push] method.
+Empty data such as empty buffers and strings will not cause `readable._read()`
+to be called.
 
 The `size` argument is advisory. For implementations where a "read" is a
 single operation that returns data can use the `size` argument to determine how

lib/internal/streams/duplexpair.js

@@ -20,8 +20,12 @@ class DuplexSocket extends Duplex {
   }
 
   _write(chunk, encoding, callback) {
-    this[kOtherSide][kCallback] = callback;
-    this[kOtherSide].push(chunk);
+    if (chunk.length === 0) {
+      process.nextTick(callback);
+    } else {
+      this[kOtherSide].push(chunk);
+      this[kOtherSide][kCallback] = callback;
+    }
   }
 
   _final(callback) {

test/common/duplexpair.js

@@ -24,8 +24,12 @@ class DuplexSocket extends Duplex {
   _write(chunk, encoding, callback) {
     assert.notStrictEqual(this[kOtherSide], null);
     assert.strictEqual(this[kOtherSide][kCallback], null);
-    this[kOtherSide][kCallback] = callback;
-    this[kOtherSide].push(chunk);
+    if (chunk.length === 0) {
+      process.nextTick(callback);
+    } else {
+      this[kOtherSide].push(chunk);
+      this[kOtherSide][kCallback] = callback;
+    }
   }
 
   _final(callback) {