win: restore file pos after positional read/write

File read or write from specified position will move file pointer on
Windows but not on POSIX. This makes Windows behave as other
supported platforms.

Ref: nodejs/node#9671

Author: bzoz

src/win/fs.c

@@ -556,9 +556,14 @@ void fs__read(uv_fs_t* req) {
   DWORD error;
   int result;
   unsigned int index;
+  LARGE_INTEGER original_position;
+  LARGE_INTEGER zero_offset;
+  int restore_position;
 
   VERIFY_FD(fd, req);
 
+  zero_offset.QuadPart = 0;
+  restore_position = 0;
   handle = uv__get_osfhandle(fd);
 
   if (handle == INVALID_HANDLE_VALUE) {
@@ -569,6 +574,10 @@ void fs__read(uv_fs_t* req) {
   if (offset != -1) {
     memset(&overlapped, 0, sizeof overlapped);
     overlapped_ptr = &overlapped;
+    if (SetFilePointerEx(handle, zero_offset, &original_position,
+                         FILE_CURRENT)) {
+      restore_position = 1;
+    }
   } else {
     overlapped_ptr = NULL;
   }
@@ -593,6 +602,9 @@ void fs__read(uv_fs_t* req) {
     ++index;
   } while (result && index < req->fs.info.nbufs);
 
+  if (restore_position)
+    SetFilePointerEx(handle, original_position, NULL, FILE_BEGIN);
+
   if (result || bytes > 0) {
     SET_REQ_RESULT(req, bytes);
   } else {
@@ -615,9 +627,14 @@ void fs__write(uv_fs_t* req) {
   DWORD bytes;
   int result;
   unsigned int index;
+  LARGE_INTEGER original_position;
+  LARGE_INTEGER zero_offset;
+  int restore_position;
 
   VERIFY_FD(fd, req);
 
+  zero_offset.QuadPart = 0;
+  restore_position = 0;
   handle = uv__get_osfhandle(fd);
   if (handle == INVALID_HANDLE_VALUE) {
     SET_REQ_WIN32_ERROR(req, ERROR_INVALID_HANDLE);
@@ -627,6 +644,10 @@ void fs__write(uv_fs_t* req) {
   if (offset != -1) {
     memset(&overlapped, 0, sizeof overlapped);
     overlapped_ptr = &overlapped;
+    if (SetFilePointerEx(handle, zero_offset, &original_position,
+                         FILE_CURRENT)) {
+      restore_position = 1;
+    }
   } else {
     overlapped_ptr = NULL;
   }
@@ -651,6 +672,9 @@ void fs__write(uv_fs_t* req) {
     ++index;
   } while (result && index < req->fs.info.nbufs);
 
+  if (restore_position)
+    SetFilePointerEx(handle, original_position, NULL, FILE_BEGIN);
+
   if (result || bytes > 0) {
     SET_REQ_RESULT(req, bytes);
   } else {

test/test-fs.c

@@ -2804,3 +2804,43 @@ TEST_IMPL(get_osfhandle_valid_handle) {
   MAKE_VALGRIND_HAPPY();
   return 0;
 }
+
+TEST_IMPL(fs_file_pos_after_op_with_offset) {
+  int r;
+
+  /* Setup. */
+  unlink("test_file");
+  loop = uv_default_loop();
+
+  r = uv_fs_open(loop,
+                 &open_req1,
+                 "test_file",
+                 O_RDWR | O_CREAT,
+                 S_IWUSR | S_IRUSR,
+                 NULL);
+  ASSERT(r >= 0);
+  uv_fs_req_cleanup(&open_req1);
+
+  iov = uv_buf_init(test_buf, sizeof(test_buf));
+  r = uv_fs_write(NULL, &write_req, open_req1.result, &iov, 1, 0, NULL);
+  ASSERT(r >= 0);
+  ASSERT(lseek(open_req1.result, 0, SEEK_CUR) == 0);
+  uv_fs_req_cleanup(&write_req);
+
+  iov = uv_buf_init(buf, sizeof(buf));
+  r = uv_fs_read(NULL, &read_req, open_req1.result, &iov, 1, 0, NULL);
+  ASSERT(r >= 0);
+  ASSERT(strcmp(buf, test_buf) == 0);
+  ASSERT(lseek(open_req1.result, 0, SEEK_CUR) == 0);
+  uv_fs_req_cleanup(&read_req);
+
+  r = uv_fs_close(NULL, &close_req, open_req1.result, NULL);
+  ASSERT(r == 0);
+  uv_fs_req_cleanup(&close_req);
+
+  /* Cleanup */
+  unlink("test_file");
+
+  MAKE_VALGRIND_HAPPY();
+  return 0;
+}

test/test-list.h

@@ -308,6 +308,7 @@ TEST_DECLARE   (fs_read_write_null_arguments)
 TEST_DECLARE   (get_osfhandle_valid_handle)
 TEST_DECLARE   (fs_write_alotof_bufs)
 TEST_DECLARE   (fs_write_alotof_bufs_with_offset)
+TEST_DECLARE   (fs_file_pos_after_op_with_offset)
 TEST_DECLARE   (threadpool_queue_work_simple)
 TEST_DECLARE   (threadpool_queue_work_einval)
 TEST_DECLARE   (threadpool_multiple_event_loops)
@@ -793,6 +794,7 @@ TASK_LIST_START
   TEST_ENTRY  (fs_write_alotof_bufs)
   TEST_ENTRY  (fs_write_alotof_bufs_with_offset)
   TEST_ENTRY  (fs_read_write_null_arguments)
+  TEST_ENTRY  (fs_file_pos_after_op_with_offset)
   TEST_ENTRY  (get_osfhandle_valid_handle)
   TEST_ENTRY  (threadpool_queue_work_simple)
   TEST_ENTRY  (threadpool_queue_work_einval)