File.Url

Summary#

File.Url(path) builds the URL a browser uses to fetch an app file — it prepends the app-file serving route to an app-relative path. File.Url("public/products/latte.png") returns /_osy/files/public/products/latte.png.

It is pure (it touches no storage — it just formats a string), which is what lets it appear directly in a render argument, unlike the File.* read/write effects. The canonical use is a photo on a page:

Image(src: File.Url(item.ImagePath), alt: item.Name);

Like the rest of the File.* surface it is gated on using Osyrin.Storage; — an app that hasn't opted into storage gets a compile error, not a silently-built URL.

Signature#

using Osyrin.Storage;

string File.Url(string path)

Description#

File.Url is the display half of the file story. You write a file to the app-file store under a public/ path (with a File.WriteAllBytes("public/…", bytes) effect, or via an upload), keep that path on a record (CatalogItem.ImagePath = "public/products/latte.png"), and render it with Image(src: File.Url(item.ImagePath)).

Two things make it safe on a public, anonymous page:

• Only public/ files are servable anonymously. A browser <img> sends no auth, so the serving endpoint returns only files written under public/ (every other path is a 404). Build your URLs from public/ paths.
• It's a pure value, evaluated where it's needed. In a [Render(CSR)] page the URL is built on the client as the image renders; in a server-rendered page it's built on the server. Either way there's no round-trip and no data read — it's string formatting.

File.Url does not check that the file exists — it only formats the path. A missing file simply 404s when the browser fetches it, exactly like any other broken image URL.

Examples#

A public product catalog — each item's stored public/ path becomes an <img src>:

using Osyrin.Storage;

entity CatalogItem {
  string Name;
  string ImagePath;              // e.g. "public/products/latte.png"
  security { allow read when IsAuthenticated || IsAnonymous; }        // anonymous read — a public catalog
}

[Page("/catalog")]
[AllowAnonymous]
[Render(CSR)]
component CatalogPage() {
  var items = CatalogItem.ToList();      // bound to a field, so the render has an answer to "when again?"
  render {
    Stack {
      foreach (var item in items) {
        Image(src: File.Url(item.ImagePath), alt: item.Name);
      }
    }
  }
}

Writing the file first (an admin action), then saving its path on the record:

using Osyrin.Storage;

string SavePhoto(string sku, byte[] photo) {
  var path = "public/products/" + sku + ".png";
  File.WriteAllBytes(path, photo);
  return path;                    // store this on CatalogItem.ImagePath
}

See also#

• [Searchable] — the other capability-gated surface (using Osyrin.Memory; — searchable text)
• style props — styling the image and its container