Interest in implementing in a bundler & dev server (subresource loading)

For apps with ~15 MB of JavaScript dependencies (3,185 modules & 295 npm packages), the metadata loads in ~0.15ms on my laptop

The file starts with #!/usr/bin/env bun\n, followed by a byte offset to the start of the metadata, then the bundled code for each file, and at the end, the metadata.

// This is the top-level type loaded from disk
message JavascriptBundleContainer {
  uint32 bundle_format_version = 1;

  // These fields are specific to Bun and probably not other bundlers
  LoadedRouteConfig routes = 3;
  LoadedFramework framework = 2;

  JavascriptBundle bundle = 4;

  // Don't technically need to store this, but it may be helpful as a sanity check
  uint32 code_length = 5;
}

struct StringPointer {
  uint32 offset;
  uint32 length;
}

struct JavascriptBundledModule {
  // package-relative path including file extension
  StringPointer path;

  // Source code
  StringPointer code;

  // index into JavascriptBundle.packages
  uint32 package_id;

  // The ESM export is this id ("$" + number.toString(16))
  uint32 id;

  // This lets us efficiently compare strings ignoring the extension
  byte path_extname_length;
}

struct JavascriptBundledPackage {
  StringPointer name;
  StringPointer version;
  uint32 hash;

  uint32 modules_offset;
  uint32 modules_length;
}

struct JavascriptBundle {
  // These are sorted alphabetically so you can do binary search
  JavascriptBundledModule[] modules;
  JavascriptBundledPackage[] packages;
  
  byte[] etag;

  uint32 generated_at;
  
  // generated by hashing all ${name}@${version} in sorted order
  byte[] app_package_json_dependencies_hash;

  byte[] import_from_name;

  // This is what StringPointer refers to 
  byte[] manifest_string;
}

Eventually, this will include exports & imports of each module.