mastodon_vk_reposter/bin/server.dart

import 'dart:convert';
import 'dart:io';

import 'package:shelf/shelf.dart';
import 'package:shelf/shelf_io.dart';
import 'package:shelf_router/shelf_router.dart';

import 'package:dio/dio.dart' as dio_lib;

var dio = dio_lib.Dio();

// Load confirmation token from env
final confirmationToken = Platform.environment['CONFIRMATION_TOKEN'];
// Load secret key from env
final secretKey = Platform.environment['SECRET_KEY'];
// Load mastodon instance url from env
final instanceUrl = Platform.environment['INSTANCE_URL'];
// Load mastodon auth token from env
final authToken = Platform.environment['MASTODON_TOKEN'];

// Configure routes.
final _router = Router()
  ..get('/', _rootHandler)
  ..post('/vk', _vkHandler);

Response _rootHandler(Request req) {
  return Response.ok('Hello, World!\n');
}

Future<Response> _vkHandler(Request req) async {
  // POST request should contain a JSON body.
  // JSON must contain a 'type' field.
  // The value of the 'type' field must be one of the following:
  //   'confirmation'
  //   'wall_post_new'
  // If we recieve a 'confirmation' request, we should respond with a confirmationToken.
  // If we recieve a 'wall_post_new' request, we should validate if 'secret' field equals
  // secretKey and respond with an 'ok' string, printing request in the console.

  final requestBody = await req.readAsString();
  final requestJson = json.decode(requestBody);
  final requestType = requestJson['type'];

  if (requestType == 'confirmation') {
    return Response.ok(confirmationToken);
  } else if (requestType == 'wall_post_new') {
    if (requestJson['secret'] == secretKey) {
      print(requestBody);
      _postOnMastodon(requestJson);
      return Response.ok('ok');
    } else {
      return Response.ok('invalid secret');
    }
  } else {
    return Response.ok('invalid request type');
  }
}

Future<void> _postOnMastodon(reqJson) async {
  // Called to repost the post on Mastodon on vk.
  // reqJson contains the 'object' field of the VK post.
  // This object has the 'text' field with the post text.
  // Also it contains the 'attachments' field with the attachments.
  // The attachments field is an array of objects.
  // Each object has the 'type' field with the attachment type.
  // We only want to post photos.
  // The 'photo' type is 'photo'.
  // The 'photo' type has the 'sizes' field with an array of objects.
  // Each object has the 'url', 'height' and 'width' fields.
  // We want to post the largest photo.
  // The 'url' field is the url of the photo.
  // The 'height' and 'width' fields are the height and width of the photo.
  // We download all pictures with dio into a temporary directory.

  // Make sure post text is 500 characters or less.
  String postText = reqJson['object']['text'];
  if (postText.length > 500) {
    postText.substring(0, 500);
  }

  final attachments = reqJson['object']['attachments'] ?? [];

  var photos = attachments.where((attachment) => attachment['type'] == 'photo');

  List<String> photoUrls = [];

  for (final photo in photos) {
    final photoUrl = photo['photo']['sizes'].last['url'];
    // Generate a random filename.
    // Add the extension '.jpg'.
    final photoFilename =
        '${DateTime.now().millisecondsSinceEpoch}-${photoUrl.split('/').last.split('?').first.substring(0, 10)}.jpg';
    final photoPath = '${Directory.systemTemp.path}/$photoFilename';
    await dio.download(photoUrl, photoPath);
    photoUrls.add(photoPath);
  }

  // If there are more than four photos, move other photos to another array to be posted in the thread.
  List<String> otherPhotos = [];
  if (photoUrls.length > 4) {
    otherPhotos = photoUrls.sublist(4);
    photoUrls = photoUrls.sublist(0, 4);
  }

  print('photoUrls: $photoUrls');
  print('otherPhotos: $otherPhotos');

  // Post the post on Mastodon.
  // First we upload all photos with dio.
  // Then we post the post with the uploaded photos and the text.
  // We delete the photos after posting.
  // Photos are uploaded to POST <instanceUrl>/api/v1/media in the 'file' form data field.
  // We take the 'id' field of the response and add it to the post's 'media_ids' field.
  // The 'media_ids' field is an array of media ids.
  // We post the post with the media ids and the text in the 'status' field.
  // Endpoint: POST <instanceUrl>/api/v1/statuses
  // Headers: Authorization: Bearer <authToken>
  // We use auth on all requests.

  // if there are no photos, we don't fetch them
  if (photos.isEmpty) {
    await dio.post('$instanceUrl/api/v1/statuses',
        data: {'status': postText},
        options:
            dio_lib.Options(headers: {'Authorization': 'Bearer $authToken'}));
  } else {
    var mediaIds = [];

    for (final photoUrl in photoUrls) {
      final resp = await dio.post('$instanceUrl/api/v1/media',
          data: dio_lib.FormData.fromMap(
              {'file': dio_lib.MultipartFile.fromFileSync(photoUrl)}),
          options:
              dio_lib.Options(headers: {'Authorization': 'Bearer $authToken'}));
      mediaIds.add(resp.data['id']);
    }

    var postResponse = await dio.post('$instanceUrl/api/v1/statuses',
        data: {'status': postText, 'media_ids': mediaIds},
        options:
            dio_lib.Options(headers: {'Authorization': 'Bearer $authToken'}));

    await Future.wait(photoUrls.map((photoUrl) => File(photoUrl).delete()));

    // If there are other photos, post them in a thread.
    while (otherPhotos.isNotEmpty) {
      mediaIds = [];
      if (otherPhotos.length > 4) {
        otherPhotos = photoUrls.sublist(4);
        photoUrls = photoUrls.sublist(0, 4);
      } else {
        photoUrls = otherPhotos;
        otherPhotos = [];
      }

      print('photoUrls: $photoUrls');
      print('otherPhotos: $otherPhotos');

      for (final photoUrl in photoUrls) {
        final resp = await dio.post('$instanceUrl/api/v1/media',
            data: dio_lib.FormData.fromMap(
                {'file': dio_lib.MultipartFile.fromFileSync(photoUrl)}),
            options: dio_lib.Options(
                headers: {'Authorization': 'Bearer $authToken'}));
        mediaIds.add(resp.data['id']);
      }

      postResponse = await dio.post('$instanceUrl/api/v1/statuses',
          data: {
            'in_reply_to_id': postResponse.data['id'],
            'media_ids': mediaIds
          },
          options:
              dio_lib.Options(headers: {'Authorization': 'Bearer $authToken'}));

      await Future.wait(photoUrls.map((photoUrl) => File(photoUrl).delete()));
    }
  }
}

void main(List<String> args) async {
  // Use any available host or container IP (usually `0.0.0.0`).
  final ip = InternetAddress.anyIPv4;

  // Configure a pipeline that logs requests.
  final _handler = Pipeline().addMiddleware(logRequests()).addHandler(_router);

  // For running in containers, we respect the PORT environment variable.
  final port = int.parse(Platform.environment['PORT'] ?? '8080');
  final server = await serve(_handler, ip, port);
  print('Server listening on port ${server.port}');
}