stream: ensure text() stream consumer flushes correctly

Signed-off-by: James M Snell <[email protected]>

PR-URL: #39737
Reviewed-By: Robert Nagy <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>

Author: jasnell

lib/stream/consumers.js

@@ -63,6 +63,9 @@ async function text(stream) {
     else
       str += dec.decode(chunk, { stream: true });
   }
+  // Flush the streaming TextDecoder so that any pending
+  // incomplete multibyte characters are handled.
+  str += dec.decode(undefined, { stream: false });
   return str;
 }
 

test/parallel/test-stream-consumers.js

@@ -232,3 +232,17 @@ const kArrayBuffer =
   stream.write({});
   stream.end({});
 }
+
+{
+  const stream = new TransformStream();
+  text(stream.readable).then(common.mustCall((str) => {
+    // Incomplete utf8 character is flushed as a replacement char
+    assert.strictEqual(str.charCodeAt(0), 0xfffd);
+  }));
+  const writer = stream.writable.getWriter();
+  Promise.all([
+    writer.write(new Uint8Array([0xe2])),
+    writer.write(new Uint8Array([0x82])),
+    writer.close(),
+  ]).then(common.mustCall());
+}