How do I make an http request using cookies on flutter?

I have improved the Richard Heap's solution to be capable to process multiple 'Set-cookies' and multiple cookies.

In my case, the server returns multiples 'Set-cookies'. The http package concatenate all the set-cookies headers in one header and separate it by comma (',').

class NetworkService {

  final JsonDecoder _decoder = new JsonDecoder();
  final JsonEncoder _encoder = new JsonEncoder();

  Map<String, String> headers = {"content-type": "text/json"};
  Map<String, String> cookies = {};

  void _updateCookie(http.Response response) {
    String allSetCookie = response.headers['set-cookie'];

    if (allSetCookie != null) {

      var setCookies = allSetCookie.split(',');

      for (var setCookie in setCookies) {
        var cookies = setCookie.split(';');

        for (var cookie in cookies) {
          _setCookie(cookie);
        }
      }

      headers['cookie'] = _generateCookieHeader();
    }
  }

  void _setCookie(String rawCookie) {
    if (rawCookie.length > 0) {
      var keyValue = rawCookie.split('=');
      if (keyValue.length == 2) {
        var key = keyValue[0].trim();
        var value = keyValue[1];

        // ignore keys that aren't cookies
        if (key == 'path' || key == 'expires')
          return;

        this.cookies[key] = value;
      }
    }
  }

  String _generateCookieHeader() {
    String cookie = "";

    for (var key in cookies.keys) {
      if (cookie.length > 0)
        cookie += ";";
      cookie += key + "=" + cookies[key];
    }

    return cookie;
  }

  Future<dynamic> get(String url) {
    return http.get(url, headers: headers).then((http.Response response) {
      final String res = response.body;
      final int statusCode = response.statusCode;

      _updateCookie(response);

      if (statusCode < 200 || statusCode > 400 || json == null) {
        throw new Exception("Error while fetching data");
      }
      return _decoder.convert(res);
    });
  }

  Future<dynamic> post(String url, {body, encoding}) {
    return http
        .post(url, body: _encoder.convert(body), headers: headers, encoding: encoding)
        .then((http.Response response) {
      final String res = response.body;
      final int statusCode = response.statusCode;

      _updateCookie(response);

      if (statusCode < 200 || statusCode > 400 || json == null) {
        throw new Exception("Error while fetching data");
      }
      return _decoder.convert(res);
    });
  }
}

I've published a small flutter library called requests to assist with cookie-aware http requests.

dependencies:
  requests: ^3.0.1

Usage:

import 'package:requests/requests.dart';

// ...

// this will persist cookies
var r1 = await Requests.post("https://example.com/api/v1/login", json: {"username":"...", "password":"..."} ); 
r1.raiseForStatus();

// this will re-use the persisted cookies
var r2 = await Requests.get("https://example.com/api/v1/stuff"); 
r2.raiseForStatus();
print(r2.json()['id'])

find out more about requests

Here's an example of how to grab a session cookie and return it on subsequent requests. You could easily adapt it to return multiple cookies. Make a Session class and route all your GETs and POSTs through it.

class Session {
  Map<String, String> headers = {};

  Future<Map> get(String url) async {
    http.Response response = await http.get(url, headers: headers);
    updateCookie(response);
    return json.decode(response.body);
  }

  Future<Map> post(String url, dynamic data) async {
    http.Response response = await http.post(url, body: data, headers: headers);
    updateCookie(response);
    return json.decode(response.body);
  }

  void updateCookie(http.Response response) {
    String rawCookie = response.headers['set-cookie'];
    if (rawCookie != null) {
      int index = rawCookie.indexOf(';');
      headers['cookie'] =
          (index == -1) ? rawCookie : rawCookie.substring(0, index);
    }
  }
}