use separate helper for macOS to optimize bundle size

cef-helper/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "tauri-cef-helper"
+version = "0.1.0"
+edition = "2021"
+license = "Apache-2.0 OR MIT"
+publish = false
+
+[dependencies]
+cef = { version = "142.2.1", default-features = false }
+
+[features]
+default = ["sandbox"]
+# Mirrors `tauri-runtime-cef` default feature to enable CEF sandbox support on macOS.
+sandbox = ["cef/sandbox"]
+
+# Ensure this crate is NOT treated as part of the repo workspace.
+[workspace]
+
+

cef-helper/src/main.rs

@@ -0,0 +1,27 @@
+use cef::{args::Args, *};
+
+fn main() {
+  let args = Args::new();
+
+  #[cfg(all(target_os = "macos", feature = "sandbox"))]
+  let _sandbox = {
+    let mut sandbox = cef::sandbox::Sandbox::new();
+    sandbox.initialize(args.as_main_args());
+    sandbox
+  };
+
+  #[cfg(target_os = "macos")]
+  let _loader = {
+    let loader = library_loader::LibraryLoader::new(&std::env::current_exe().unwrap(), true);
+    assert!(loader.load());
+    loader
+  };
+
+  execute_process(
+    Some(args.as_main_args()),
+    None::<&mut App>,
+    std::ptr::null_mut(),
+  );
+}
+
+

crates/tauri-bundler/build.rs

@@ -0,0 +1,109 @@
+// Copyright 2019-2025 Tauri Programme within The Commons Conservancy
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-License-Identifier: MIT
+
+use std::{
+  env, fs,
+  path::{Path, PathBuf},
+  process::Command,
+};
+
+fn main() {
+  let target = env::var("TARGET").unwrap_or_default();
+  let host = env::var("HOST").unwrap_or_default();
+
+  // Only build/embed the CEF helper when compiling `tauri-bundler` for macOS.
+  if !target.contains("apple-darwin") {
+    return;
+  }
+
+  // We need `lipo` and a functioning macOS toolchain to produce a universal Mach-O.
+  if !host.contains("apple-darwin") {
+    panic!(
+      "Building tauri-bundler for macOS requires a macOS host to build/embed the CEF helper binary"
+    );
+  }
+
+  let out_dir = PathBuf::from(env::var("OUT_DIR").expect("OUT_DIR not set"));
+  let bundler_manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
+
+  let helper_root = bundler_manifest_dir
+    .parent() // crates/
+    .and_then(|p| p.parent()) // repo root
+    .map(|p| p.join("cef-helper"))
+    .expect("failed to compute cef-helper path");
+
+  let helper_manifest = helper_root.join("Cargo.toml");
+  let helper_main = helper_root.join("src").join("main.rs");
+
+  // Rebuild if the helper crate changes.
+  println!("cargo:rerun-if-changed={}", helper_manifest.display());
+  println!("cargo:rerun-if-changed={}", helper_main.display());
+
+  // Copy the helper crate sources into OUT_DIR so any generated files (Cargo.lock, target dir)
+  // stay out of the repo checkout.
+  let helper_src_dir = out_dir.join("cef-helper-src");
+  let helper_src_manifest = helper_src_dir.join("Cargo.toml");
+  let helper_src_main = helper_src_dir.join("src").join("main.rs");
+  fs::create_dir_all(helper_src_main.parent().unwrap())
+    .expect("failed to create cef-helper-src directory");
+  fs::copy(&helper_manifest, &helper_src_manifest).expect("failed to copy cef-helper Cargo.toml");
+  fs::copy(&helper_main, &helper_src_main).expect("failed to copy cef-helper main.rs");
+
+  let cargo = env::var("CARGO").unwrap_or_else(|_| "cargo".into());
+
+  let helper_target_dir = out_dir.join("cef-helper-target");
+  let aarch64 = build_helper(
+    &cargo,
+    &helper_src_manifest,
+    &helper_target_dir,
+    "aarch64-apple-darwin",
+    "tauri-cef-helper",
+  );
+  let x86_64 = build_helper(
+    &cargo,
+    &helper_src_manifest,
+    &helper_target_dir,
+    "x86_64-apple-darwin",
+    "tauri-cef-helper",
+  );
+
+  // Generate a small rust shim that exposes the embedded helper bytes.
+  let shim_path = out_dir.join("cef_helpers.rs");
+  let shim = format!(
+    "pub const CEF_HELPER_AARCH64: &[u8] = include_bytes!(r#\"{}\"#);\n\
+pub const CEF_HELPER_X86_64: &[u8] = include_bytes!(r#\"{}\"#);\n",
+    aarch64.display(),
+    x86_64.display()
+  );
+  fs::write(&shim_path, shim).expect("failed to write cef_helpers.rs");
+}
+
+fn build_helper(
+  cargo: &str,
+  manifest_path: &Path,
+  target_dir: &Path,
+  target: &str,
+  bin_name: &str,
+) -> PathBuf {
+  let mut cmd = Command::new(cargo);
+  cmd
+    .arg("build")
+    .arg("--release")
+    .arg("--manifest-path")
+    .arg(manifest_path)
+    .arg("--bin")
+    .arg(bin_name)
+    .arg("--target")
+    .arg(target)
+    .env("CARGO_TARGET_DIR", target_dir);
+
+  let status = cmd
+    .status()
+    .expect("failed to spawn cargo build for CEF helper");
+  if !status.success() {
+    panic!("failed to build CEF helper for target {target}");
+  }
+
+  target_dir.join(target).join("release").join(bin_name)
+}

crates/tauri-bundler/src/bundle/macos/app.rs

@@ -52,6 +52,23 @@ const NESTED_CODE_FOLDER: [&str; 6] = [
 
 const CEF_FRAMEWORK: &str = "Chromium Embedded Framework.framework";
 
+mod embedded_cef_helper {
+  // Generated by `crates/tauri-bundler/build.rs` when compiling on macOS.
+  include!(concat!(env!("OUT_DIR"), "/cef_helpers.rs"));
+}
+
+fn lipo_create_universal(output: &Path, aarch64: &Path, x86_64: &Path) -> crate::Result<()> {
+  Command::new("lipo")
+    .arg("-create")
+    .arg("-output")
+    .arg(output)
+    .arg(aarch64)
+    .arg(x86_64)
+    .output_ok()
+    .with_context(|| "failed to create universal CEF helper binary using lipo")?;
+  Ok(())
+}
+
 /// Bundles the project.
 /// Returns a vector of PathBuf that shows where the .app was created.
 pub fn bundle_project(settings: &Settings) -> crate::Result<Vec<PathBuf>> {
@@ -650,6 +667,8 @@ fn create_cef_helpers(
     frameworks_dir.to_path_buf(),
   )?;
 
+  let arch = settings.binary_arch();
+
   // Create helper .app bundles
   let helpers = vec![
     format!("{} Helper (GPU)", exec_name),
@@ -659,7 +678,33 @@ fn create_cef_helpers(
     format!("{} Helper", exec_name),
   ];
 
-  let main_binary_path = bundle_directory.join("MacOS").join(exec_name);
+  // If building an universal app bundle, create a universal helper binary once (outside the loop),
+  // then copy it into each helper .app.
+  let universal_helper: Option<(tempfile::TempDir, PathBuf)> =
+    if arch == crate::bundle::settings::Arch::Universal {
+      let tmp = tempfile::tempdir().map_err(|e| {
+        crate::Error::GenericError(format!(
+          "failed to create temp dir for CEF helper lipo: {e}"
+        ))
+      })?;
+      let aarch64 = tmp.path().join("tauri-cef-helper.aarch64");
+      let x86_64 = tmp.path().join("tauri-cef-helper.x86_64");
+      let universal = tmp.path().join("tauri-cef-helper.universal");
+
+      fs::write(&aarch64, embedded_cef_helper::CEF_HELPER_AARCH64).fs_context(
+        "failed to write embedded CEF helper (aarch64)",
+        aarch64.clone(),
+      )?;
+      fs::write(&x86_64, embedded_cef_helper::CEF_HELPER_X86_64).fs_context(
+        "failed to write embedded CEF helper (x86_64)",
+        x86_64.clone(),
+      )?;
+
+      lipo_create_universal(&universal, &aarch64, &x86_64)?;
+      Some((tmp, universal))
+    } else {
+      None
+    };
 
   for helper_name in helpers {
     let helper_app = frameworks_dir.join(format!("{helper_name}.app"));
@@ -709,10 +754,31 @@ fn create_cef_helpers(
 
     let helper_exec = helper_macos.join(&helper_name);
 
-    std::fs::copy(&main_binary_path, &helper_exec).fs_context(
-      "failed to copy main binary to CEF helper",
-      helper_exec.clone(),
-    )?;
+    match arch {
+      crate::bundle::settings::Arch::AArch64 => {
+        fs::write(&helper_exec, embedded_cef_helper::CEF_HELPER_AARCH64).fs_context(
+          "failed to write embedded CEF helper executable",
+          helper_exec.clone(),
+        )?;
+      }
+      crate::bundle::settings::Arch::X86_64 => {
+        fs::write(&helper_exec, embedded_cef_helper::CEF_HELPER_X86_64).fs_context(
+          "failed to write embedded CEF helper executable",
+          helper_exec.clone(),
+        )?;
+      }
+      crate::bundle::settings::Arch::Universal => {
+        let (_temp_dir, universal_path) = universal_helper
+          .as_ref()
+          .expect("universal helper binary was not generated");
+        fs_utils::copy_file(universal_path, &helper_exec)?;
+      }
+      other => {
+        return Err(GenericError(format!(
+          "CEF helper embedding is only supported for aarch64, x86_64, and universal on macOS (got {other:?})"
+        )));
+      }
+    }
 
     #[cfg(unix)]
     {