fs: fix async iterator partial writes

fix an issue where chunks might be partially written when
using writeFile with an async iterator.

PR-URL: https://github.com/nodejs/node/pull/38615
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 10 insertions, 4 deletions

diff --git a/lib/internal/fs/promises.js b/lib/internal/fs/promises.js
index 7a575e69491..0253a29c7d5 100644
--- a/lib/internal/fs/promises.js
+++ b/lib/internal/fs/promises.js
@@ -296,10 +296,16 @@ async function writeFileHandle(filehandle, data, signal, encoding) {
   if (isCustomIterable(data)) {
     for await (const buf of data) {
       checkAborted(signal);
-      await write(
-        filehandle, buf, undefined,
-        isArrayBufferView(buf) ? buf.byteLength : encoding);
-      checkAborted(signal);
+      const toWrite =
+        isArrayBufferView(buf) ? buf : Buffer.from(buf, encoding || 'utf8');
+      let remaining = toWrite.byteLength;
+      while (remaining > 0) {
+        const writeSize = MathMin(kWriteFileMaxChunkSize, remaining);
+        const { bytesWritten } = await write(
+          filehandle, toWrite, toWrite.byteLength - remaining, writeSize);
+        remaining -= bytesWritten;
+        checkAborted(signal);
+      }
     }
     return;
   }