BoundaryML/baml · error · io::Error

{}: {error}

Error message

{}: {error}

What it means

read_to_string in the WASM VFS reads a file via vfs_read_file and maps any backend error to io::Error::other('{path}: {error:?}'); it then separately maps UTF-8 decode failures to InvalidData '{path}: {error}'. So this message means either the virtual file could not be read (backend error string appended) or its bytes are not valid UTF-8.

Source

Thrown at baml_language/crates/bridge_wasm/src/wasm_vfs.rs:259

                    frontier.push(child);
                } else if child.extension().is_some_and(|ext| ext == "baml") {
                    files.push(child);
                }
            }
        }
        files.sort();
        files
    }
}

impl ProjectFs for WasmProjectFs {
    fn read_to_string(&self, path: &Path) -> std::io::Result<String> {
        let bytes = self
            .vfs()
            .vfs_read_file(&path.to_string_lossy())
            .map_err(|error| std::io::Error::other(format!("{}: {error:?}", path.display())))?;
        String::from_utf8(bytes.to_vec()).map_err(|error| {
            std::io::Error::new(
                std::io::ErrorKind::InvalidData,
                format!("{}: {error}", path.display()),
            )
        })
    }

    fn discover_roots(&self, folder: &Path) -> Vec<DiscoveredRoot> {
        let mut roots = Vec::new();
        // The folder itself may sit inside a project (the host opened
        // `baml_src/`, or a subdirectory of it).
        roots.extend(
            baml_db::project_resolution::find_baml_project_root_from_ancestors(
                folder.ancestors().map(Path::to_path_buf),
                |dir| self.is_file(&dir.join(baml_db::project_resolution::BAML_TOML)),
                |dir| self.is_dir(&dir.join(baml_db::project_resolution::BAML_SRC_DIR)),
            ),
        );
        roots.extend(self.marked_roots(folder));

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Verify the path exists in the VFS (write/upload it) before reading
2. Use a bytes/read_file API for binary content and only call read_to_string for UTF-8 text
3. Log the mapped error's trailing backend message to identify the underlying vfs_read_file failure
4. Normalize the path (absolute, no duplicate slashes) as the VFS keys on exact strings

Example fix

// before
const text = vfs.read_to_string('/assets/logo.png'); // InvalidData
// after
const bytes = vfs.read_file('/assets/logo.png');
const text = isTextual(path) ? new TextDecoder().decode(bytes) : null;

function fileExistsInVfs(vfs, path) {
  return vfs.vfs_list_dir(dirname(path)).includes(basename(path));
}

function isVfsReadError(e) {
  return e instanceof Error && /: /.test(e.message) && (e.name === 'Error' || e.name === 'NotFoundError' || e.name === 'InvalidData');
}

try {
  text = vfs.read_to_string(path);
} catch (e) {
  if (String(e.message).includes('stream did not contain valid UTF-8')) {
    const bytes = vfs.vfs_read_file(path); // handle as binary
  } else {
    throw new Error(`VFS read failed for ${path}: ${e.message}`);
  }
}

When it happens

Trigger: Calling read_to_string on a path missing from the in-memory VFS, a backend I/O failure, or on binary (non-UTF-8) files that must not be read as strings.

Common situations: Loading BAML sources from a browser-injected VFS where the file was never registered, or accidentally reading .bmx/binary assets with read_to_string instead of a bytes API.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• WASM history boundary {} was not begun
• WASM history boundary {} was not found
• diagnostic message style code is a valid Unicode variation s
• no filesystem is attached to this server ({})
• native path is not valid Unicode: {0:?}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/67d43937e17201d3. Report an issue: GitHub.