Use index rather than telldir/seekdir to represent fd_readdir cookie

src/uvwasi.c

@@ -1396,6 +1396,7 @@ uvwasi_errno_t uvwasi_fd_readdir(uvwasi_t* uvwasi,
 #if defined(UVWASI_FD_READDIR_SUPPORTED)
   /* TODO(cjihrig): Avoid opening and closing the directory on each call. */
   struct uvwasi_fd_wrap_t* wrap;
+  uvwasi_dircookie_t cur_cookie;
   uvwasi_dirent_t dirent;
   uv_dirent_t dirents[UVWASI__READDIR_NUM_ENTRIES];
   uv_dir_t* dir;
@@ -1404,7 +1405,6 @@ uvwasi_errno_t uvwasi_fd_readdir(uvwasi_t* uvwasi,
   size_t name_len;
   size_t available;
   size_t size_to_cp;
-  long tell;
   int i;
   int r;
 #endif /* defined(UVWASI_FD_READDIR_SUPPORTED) */
@@ -1444,8 +1444,22 @@ uvwasi_errno_t uvwasi_fd_readdir(uvwasi_t* uvwasi,
   uv_fs_req_cleanup(&req);
 
   /* Seek to the proper location in the directory. */
-  if (cookie != UVWASI_DIRCOOKIE_START)
-    seekdir(dir->dir, cookie);
+  cur_cookie = 0;
+  while (cur_cookie < cookie) {
+    r = uv_fs_readdir(NULL, &req, dir, NULL);
+    if (r < 0) {
+      err = uvwasi__translate_uv_error(r);
+      uv_fs_req_cleanup(&req);
+      goto exit;
+    }
+
+    cur_cookie += (uvwasi_dircookie_t)r;
+    uv_fs_req_cleanup(&req);
+
+    if (r == 0) {
+      break;
+    }
+  }
 
   /* Read the directory entries into the provided buffer. */
   err = UVWASI_ESUCCESS;
@@ -1460,15 +1474,9 @@ uvwasi_errno_t uvwasi_fd_readdir(uvwasi_t* uvwasi,
     available = 0;
 
     for (i = 0; i < r; i++) {
-      tell = telldir(dir->dir);
-      if (tell < 0) {
-        err = uvwasi__translate_uv_error(uv_translate_sys_error(errno));
-        uv_fs_req_cleanup(&req);
-        goto exit;
-      }
-
+      cur_cookie++;
       name_len = strlen(dirents[i].name);
-      dirent.d_next = (uvwasi_dircookie_t) tell;
+      dirent.d_next = (uvwasi_dircookie_t) cur_cookie;
       /* TODO(cjihrig): libuv doesn't provide d_ino, and d_type is not
                         supported on all platforms. Use stat()? */
       dirent.d_ino = 0;

test/test-fd-readdir-cookie.c

@@ -0,0 +1,101 @@
+#include "test-common.h"
+#include "uv.h"
+#include "uvwasi.h"
+#include "wasi_serdes.h"
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define TEST_TMP_DIR "./out/tmp"
+#define TEST_PATH_READDIR TEST_TMP_DIR "/test_readdir_cookie"
+
+#if !defined(_WIN32) && !defined(__ANDROID__)
+static void touch_file(const char *name) {
+  uv_fs_t req;
+  int r;
+
+  r = uv_fs_open(NULL, &req, name, O_WRONLY | O_CREAT | O_TRUNC,
+                 S_IWUSR | S_IRUSR, NULL);
+  uv_fs_req_cleanup(&req);
+  assert(r >= 0);
+  r = uv_fs_close(NULL, &req, r, NULL);
+  uv_fs_req_cleanup(&req);
+  assert(r == 0);
+}
+#endif /* !defined(_WIN32) && !defined(__ANDROID__) */
+
+/*
+ * This is a test case for https://github.com/nodejs/node/issues/47193.
+ */
+
+int main(void) {
+#if !defined(_WIN32) && !defined(__ANDROID__)
+  uvwasi_t uvwasi;
+  uvwasi_options_t init_options;
+  uvwasi_dircookie_t cookie;
+  uvwasi_dirent_t dirent;
+  uvwasi_size_t buf_size;
+  uvwasi_size_t buf_used;
+  uvwasi_errno_t err;
+  uv_fs_t req;
+  uvwasi_fd_t tmp_fd = 3;
+  char buf[64];
+  int r;
+  int cnt;
+
+  setup_test_environment();
+
+  r = uv_fs_mkdir(NULL, &req, TEST_TMP_DIR, 0777, NULL);
+  uv_fs_req_cleanup(&req);
+  assert(r == 0 || r == UV_EEXIST);
+
+  r = uv_fs_mkdir(NULL, &req, TEST_PATH_READDIR, 0777, NULL);
+  uv_fs_req_cleanup(&req);
+  assert(r == 0 || r == UV_EEXIST);
+
+  for (int i = 0; i < 10; i++) {
+    const char *format = TEST_PATH_READDIR "/test_file_"
+                                           "%d";
+    int len = strlen(format) + 3;
+    char file_name[len];
+    snprintf(file_name, len, format, i);
+    touch_file(file_name);
+  }
+
+  uvwasi_options_init(&init_options);
+  init_options.preopenc = 1;
+  init_options.preopens = calloc(1, sizeof(uvwasi_preopen_t));
+  init_options.preopens[0].mapped_path = "/var";
+  init_options.preopens[0].real_path = TEST_PATH_READDIR;
+
+  err = uvwasi_init(&uvwasi, &init_options);
+  assert(err == 0);
+
+  buf_size = 64;
+  memset(buf, 0, buf_size);
+  buf_used = -1;
+  cookie = UVWASI_DIRCOOKIE_START;
+  cnt = 0;
+
+  // For simplicity, we read entries one by one
+  while (buf_used == -1 || buf_used == buf_size) {
+    memset(buf, 0, buf_size);
+    err = uvwasi_fd_readdir(&uvwasi, tmp_fd, &buf, buf_size, cookie, &buf_used);
+    uvwasi_serdes_read_dirent_t(buf, 0, &dirent);
+    assert(err == UVWASI_ESUCCESS);
+
+    cookie = dirent.d_next;
+    cnt += 1;
+
+    // There are only 10 files
+    assert(cnt <= 10);
+  }
+
+  assert(cnt == 10);
+  uvwasi_destroy(&uvwasi);
+  free(init_options.preopens);
+
+#endif /* !defined(_WIN32) && !defined(__ANDROID__) */
+  return 0;
+}