A Weird Imagination

Deleting deeply nested OPFS directories

Posted in Web
file system api javascript opfs recursion

The problem#

The straightforward OPFS API for deleting a directory

await parentDir.removeEntry(name, {recursive: true});

doesn't work if the directory contains too many (several hundred) levels of nested directories. The sensible workaround is never create such a directory structure and wipe the OPFS storage entirely if you ever do by accident, but as discussed previously, I did get in that situation due to a bug and wrote some helpers to deal with it.

The solution#

For any reasonable real-world case, what you actually want is probably removeEntry():

await parentDir.removeEntry(name, {recursive: true});

or to delete everything from the root directory:

const root = await navigator.storage.getDirectory();
for await (const handle of root.values()) {
  await root.removeEntry(handle.name, {recursive: true});
}

or possibly to simply use your browser's settings to delete all site data, which should include OPFS data.

In case you do still want to delete a directory in OPFS without worrying about how deeply nested the directory structure is, you can use

async function removeDirectoryFast(dir) {
  const toDelete = [];
  let i = 0;
  let maxDepth = 0;
  for await (const fileHandle
             of getFilesNonRecursively(dir)) {
    maxDepth = Math.max(maxDepth, fileHandle.depth);
    toDelete.push(fileHandle);
  }
  async function deleteAtDepth(depth) {
    for (const f of toDelete) {
      if (f.depth === depth) {
        await f.parentDir.removeEntry(f.name,
                            {recursive: true});
      }
    }
  }
  const increment = 500; // Works empirically in Firefox.
  for (let depth = maxDepth; depth > 1; depth -= increment) {
    await deleteAtDepth(depth);
  }
  await deleteAtDepth(1);
}

This depends on the getFilesNonRecursively() helper from my previous blog post.

The details#

Read more…

Debugging OPFS

Posted in Web
chromium debugging file system api firefox javascript opfs privacy recursion sqlite

The problem#

While the web developer tools in Firefox and Chrome provide a Storage/Application tab for inspecting the local data stored by a web app, neither shows OPFS files there, making it difficult to tell what's going wrong when you have a bug (which was a problem when writting my recent blog posts about OPFS). There's open Firefox and Chromium bugs about the missing feature, so if it's been a while since this was posted when you're reading this, hopefully this is no longer a problem.

Additionally, the tools I did find all use recursion, resulting in them failing to work on the deeply nested directory tree I created by accident.

The solution#

If you don't have several hundred levels deep of nested directories, you can just use this Chrome extension or this script (or probably this web component, although I couldn't get it to install), all named "opfs-explorer".

The following AsyncIterator returns all of the files in OPFS without using recursion and adds properties to include their full path and parent directory:

async function* getFilesNonRecursively(dir) {
  const stack = [[dir, "", undefined, 0]];
  while (stack.length) {
    const [current, prefix, parentDir] = stack.pop();
    current.relativePath = prefix + current.name;
    current.parentDir = parentDir;
    current.depth = depth;
    yield current;

    if (current.kind === "directory") {
      for await (const handle of current.values()) {
        stack.push([handle,
                    prefix + current.name + "/",
                    current,
                    depth + 1]);
      }
    }
  }
}

And here's the simple HTML display function I've been using that calls that (you will likely want to modify this to your preferences):

async function displayOPFSFileList() {
  const existing = document.getElementById("opfs-file-list");
  const l = document.createElement('ol');
  l.id = "opfs-file-list";
  if (existing) existing.replaceWith(l);
  else document.body.appendChild(l);

  const root = await navigator.storage.getDirectory();
  for await (const fileHandle
             of getFilesNonRecursively(root)) {
    const i = document.createElement("li");
    i.innerText = fileHandle.kind + ": "
                  + (fileHandle.relativePath ?? "(root)");
    if (fileHandle.kind === "file") {
      const content = await fileHandle.getFile();
      const contentStr = content.type.length === 0
                      || content.type.startsWith("text/")
        ? ("\"" + (await content.slice(0, 100).text()).trim()
          + "\"")
        : content.type;
      i.innerText += ": (" + content.size + " bytes) "
                     + contentStr;
    }
    l.appendChild(i);
  }
}

The details#

Read more…