fs: fix memory leak in WriteString

src/node_file.cc

@@ -1356,7 +1356,6 @@ static void WriteString(const FunctionCallbackInfo<Value>& args) {
 
   const auto enc = ParseEncoding(env->isolate(), args[3], UTF8);
 
-  std::unique_ptr<char[]> delete_on_return;
   Local<Value> value = args[1];
   char* buf = nullptr;
   size_t len;
@@ -1384,24 +1383,42 @@ static void WriteString(const FunctionCallbackInfo<Value>& args) {
     }
   }
 
-  if (buf == nullptr) {
+  if (is_async) {  // write(fd, string, pos, enc, req)
+    CHECK_NE(req_wrap, nullptr);
     len = StringBytes::StorageSize(env->isolate(), value, enc);
-    buf = new char[len];
-    // SYNC_CALL returns on error.  Make sure to always free the memory.
-    if (!is_async) delete_on_return.reset(buf);
+    FSReqBase::FSReqBuffer& stack_buffer =
+        req_wrap->Init("write", len, enc);
     // StorageSize may return too large a char, so correct the actual length
     // by the write size
-    len = StringBytes::Write(env->isolate(), buf, len, args[1], enc);
-  }
-
-  uv_buf_t uvbuf = uv_buf_init(buf, len);
-
-  if (is_async) {  // write(fd, string, pos, enc, req)
-    AsyncCall(env, req_wrap, args, "write", UTF8, AfterInteger,
-              uv_fs_write, fd, &uvbuf, 1, pos);
+    len = StringBytes::Write(env->isolate(), *stack_buffer, len, args[1], enc);
+    stack_buffer.SetLengthAndZeroTerminate(len);
+    uv_buf_t uvbuf = uv_buf_init(*stack_buffer, len);
+    int err = uv_fs_write(env->event_loop(), req_wrap->req(),
+                          fd, &uvbuf, 1, pos, AfterInteger);
+    req_wrap->Dispatched();
+    if (err < 0) {
+      uv_fs_t* uv_req = req_wrap->req();
+      uv_req->result = err;
+      uv_req->path = nullptr;
+      AfterInteger(uv_req);  // after may delete req_wrap if there is an error
+    } else {
+      req_wrap->SetReturnValue(args);
+    }
   } else {  // write(fd, string, pos, enc, undefined, ctx)
     CHECK_EQ(argc, 6);
     fs_req_wrap req_wrap;
+    FSReqBase::FSReqBuffer stack_buffer;
+    if (buf == nullptr) {
+      len = StringBytes::StorageSize(env->isolate(), value, enc);
+      stack_buffer.AllocateSufficientStorage(len + 1);
+      // StorageSize may return too large a char, so correct the actual length
+      // by the write size
+      len = StringBytes::Write(env->isolate(), *stack_buffer,
+                               len, args[1], enc);
+      stack_buffer.SetLengthAndZeroTerminate(len);
+      buf = *stack_buffer;
+    }
+    uv_buf_t uvbuf = uv_buf_init(buf, len);
     int bytesWritten = SyncCall(env, args[5], &req_wrap, "write",
                                 uv_fs_write, fd, &uvbuf, 1, pos);
     args.GetReturnValue().Set(bytesWritten);

src/node_file.h

@@ -22,6 +22,8 @@ namespace fs {
 
 class FSReqBase : public ReqWrap<uv_fs_t> {
  public:
+  typedef MaybeStackBuffer<char, 64> FSReqBuffer;
+
   FSReqBase(Environment* env, Local<Object> req, AsyncWrap::ProviderType type)
       : ReqWrap(env, req, type) {
     Wrap(object(), this);
@@ -32,9 +34,9 @@ class FSReqBase : public ReqWrap<uv_fs_t> {
   }
 
   void Init(const char* syscall,
-            const char* data = nullptr,
-            size_t len = 0,
-            enum encoding encoding = UTF8) {
+            const char* data,
+            size_t len,
+            enum encoding encoding) {
     syscall_ = syscall;
     encoding_ = encoding;
 
@@ -47,6 +49,16 @@ class FSReqBase : public ReqWrap<uv_fs_t> {
     }
   }
 
+  FSReqBuffer& Init(const char* syscall, size_t len,
+                    enum encoding encoding) {
+    syscall_ = syscall;
+    encoding_ = encoding;
+
+    buffer_.AllocateSufficientStorage(len + 1);
+    has_data_ = false;  // so that the data does not show up in error messages
+    return buffer_;
+  }
+
   virtual void FillStatsArray(const uv_stat_t* stat) = 0;
   virtual void Reject(Local<Value> reject) = 0;
   virtual void Resolve(Local<Value> value) = 0;
@@ -66,7 +78,7 @@ class FSReqBase : public ReqWrap<uv_fs_t> {
 
   // Typically, the content of buffer_ is something like a file name, so
   // something around 64 bytes should be enough.
-  MaybeStackBuffer<char, 64> buffer_;
+  FSReqBuffer buffer_;
 
   DISALLOW_COPY_AND_ASSIGN(FSReqBase);
 };