How to read file from an imported library

Question

I have two packages: webserver and utils which provides assets to webserver.

The webserver needs access to static files inside uti

Answer 1

I tend to use Platform.script or mirrors to find the main package top folder (i.e. where pubspec.yaml is present) and find imported packages exported assets. I agree this is not a perfect solution but it works

import 'dart:io';
import 'package:path/path.dart';

String getProjectTopPath(String resolverPath) {
  String dirPath = normalize(absolute(resolverPath));

  while (true) {
    // Find the project root path
    if (new File(join(dirPath, "pubspec.yaml")).existsSync()) {
      return dirPath;
    }
    String newDirPath = dirname(dirPath);

    if (newDirPath == dirPath) {
      throw new Exception("No project found for path '$resolverPath");
    }
    dirPath = newDirPath;
  }
}

String getPackagesPath(String resolverPath) {
  return join(getProjectTopPath(resolverPath), 'packages');
}

class _TestUtils {}

main(List<String> arguments) {
  // User Platform.script - does not work in unit test
  String currentScriptPath = Platform.script.toFilePath();
  String packagesPath = getPackagesPath(currentScriptPath);
  // Get your file using the package name and its relative path from the lib folder
  String filePath = join(packagesPath, "utils", "static.html");
  print(filePath);

  // use mirror to find this file path
  String thisFilePath =  (reflectClass(_TestUtils).owner as LibraryMirror).uri.toString();
  packagesPath = getPackagesPath(thisFilePath);
  filePath = join(packagesPath, "utils", "static.html");
  print(filePath);
}

To note that since recently Platform.script is not reliable in unit test when using the new test package so you might use the mirror tricks that I propose above and explained here: https://github.com/dart-lang/test/issues/110

Answer 2

Use the Resource class, a new class in Dart SDK 1.12.

Usage example:

var resource = new Resource('package:myapp/myfile.txt');
var contents = await resource.loadAsString();
print(contents);

This works on the VM, as of 1.12.

However, this doesn't directly address your need to get to the actual File entity, from a package: URI. Given the Resource class today, you'd have to route the bytes from loadAsString() into the HTTP server's Response object.