How to pass header in another response in flutter - flutter

Question

I have response.header in header. I want to pass that header to another response.
so, my approach is to save the header in shared preference and then retrieve it.
final prefs = await SharedPreferences.getInstance();
prefs.setString('header', response.headers.toString());
and then retrieve it
final prefs = await SharedPreferences.getInstance();
String? head = prefs.getString('header');
Map<String, String> authHeaders = jsonDecode(head!);
but authHeders is giving me an error.
Unhandled Exception: FormatException: Unexpected character (at character 2)
header before saving to SharedPreferences.
{connection: keep-alive, set-cookie: XSRF-TOKEN=nBYdTZyY2FrQUl0RitDemxmdnNVMVRacC9XcENyV3pJankiLCJtYWMiOiJkOTRmZWMwYjYyMDdjMjAwNjBmZTJmZDYyNGYzYzI0YTVjMDNmN2VjZjc3MzZkM2UzNzc1MTk2ZjViOGE0MGMyIiwidGFnIjoiIn0%3D; expires=Mon, 01-Aug-2022 08:56:00 GMT; Max-Age=7200; path=/; samesite=lax,laravel_session=eyJpdiI6Iko1U1ZkejhNWVo3b0twb0pwdS9QMVE9PSIsInZhbHVlIjoiVUxyTFVmMm9XSG95VHd6cGxCVThqSExvSzJQWmQ2WWRMRGpoT0xsVjExdHl1M0xnZ2xGZjd2WDRVdHRqa1J4TU4rRjByakFoSUNHT2lPTGVUb0Z4aHNhWjRleTM0TnBjakRPRzc4WkZVWDMvTzdqNlpoVTBCRWRsOTlwcHIvNFQiLCJtYWMiOiI0MTRhMjRkNGY3Njg0ZDI4NjU1MzFmZjI2M2FkOTA5NDc4ZWJhYzhiZTA5MTFkZTQ2ZmJlY2UxNzBlZjc3MTc3IiwidGFnIjoiIn0%3D; path=/; httponly; samesite=lax, cache-control: no-cache, private, date: Mon, 01 Aug 2022 06:56:00 GMT, vary: Accept-Encoding, content-encoding: gzip, cf-cache-status: DYNAMIC, report-to: {"endpoint .......
header after retrieving it.
{connection: keep-alive, set-cookie: XSRF-TOKEN=nBYdTZyY2FrQUl0RitDemxmdnNVMVRacC9XcENyV3pJankiLCJtYWMiOiJkOTRmZWMwYjYyMDdjMjAwNjBmZTJmZDYyNGYzYzI0YTVjMDNmN2VjZjc3MzZkM2UzNzc1MTk2ZjViOGE0MGMyIiwidGFnIjoiIn0%3D; expires=Mon, 01-Aug-2022 08:56:00 GMT; Max-Age=7200; path=/; samesite=lax,laravel_session=eyJpdiI6Iko1U1ZkejhNWVo3b0twb0pwdS9QMVE9PSIsInZhbHVlIjoiVUxyTFVmMm9XSG95VHd6cGxCVThqSExvSzJQWmQ2WWRMRGpoT0xsVjExdHl1M0xnZ2xGZjd2WDRVdHRqa1J4TU4rRjByakFoSUNHT2lPTGVUb0Z4aHNhWjRleTM0TnBjakRPRzc4WkZVWDMvTzdqNlpoVTBCRWRsOTlwcHIvNFQiLCJtYWMiOiI0MTRhMjRkNGY3Njg0ZDI4NjU1MzFmZjI2M2FkOTA5NDc4ZWJhYzhiZTA5MTFkZTQ2ZmJlY2UxNzBlZjc3MTc3IiwidGFnIjoiIn0%3D; path=/; httponly; samesite=lax, cache-control: no-cache, private, date: Mon, 01 Aug 2022 06:56:00 GMT, vary: Accept-Encoding, content-encoding: gzip, cf-cache-status: DYNAMIC, report-to: {"endpoint .......
Yes, both are same.
This is how I am saving header.
login(String phn, String password) async {
final prefs = await SharedPreferences.getInstance();
await getLocation();
String uri = "$baseUrl/User_Login";
try {
http.Response response = await http.post(Uri.parse(uri), headers: {
'Accept': 'application/json'
}, body: {
"number": phn,
"password": password,
"long": long,
"lati": lati
});
print(response.headers);
prefs.setString('header', response.headers.toString());
return json.decode(response.body);
} catch (e) {
return e;
}
}
This is how I am retrieving it and passing it to another response.
getData() async {
final prefs = await SharedPreferences.getInstance();
String? head = prefs.getString('header');
print("headers");
print(head);
Map<String, String> authHeaders = jsonDecode($head!);
// print("authHeaders");
// print(authHeaders.toString());
String uri = "$baseUrlUser/user_bal";
try {
http.Response response =
await http.get(Uri.parse(uri), headers: authHeaders);
return json.decode(response.body);
} catch (e) {
return e;
}
}

Answer 1

The common issue in Flutter when parsing Json data is about the type of request and it's encoding.
Even if you may post the complete source code, at least, the relevant one to your problem, like how you're performing the request, your error probably comes on how you ask for data to the remote.
If you're trying to parse the response as Json, you must specifically add the application/json;charset=UTF-8 in your headers.
But, if you read this line in your source code:
prefs.setString('header', response.headers.toString());
you're saving the headers as string in the header key. This means, that the headers are usually represented in most standars as Map datastructures, so you're asking for retrive as a String in decode(...) a probably bad formatted data.
The solution it's pretty straightfoward. Save the header(s) that your interested one by one, and then retrieve them by key, and the format should be ok to use the jsonDecode.
Edit:
getting directly your code to exemplify as requested by the OP how to get them individually. We will take the Accept header as example, as it's also the unique provide in the example code.
login(String phn, String password) async {
final prefs = await SharedPreferences.getInstance();
await getLocation();
String uri = "$baseUrl/User_Login";
try {
http.Response response = await http.post(Uri.parse(uri), headers: {
'Accept': 'application/json'
}, body: {
"number": phn,
"password": password,
"long": long,
"lati": lati
});
prefs.setString('header', response.headers.get('Accept'));
return json.decode(response.body);
} catch (e) {
return e;
}
}
Then, you only must retrieve it by key:
getData() async {
final prefs = await SharedPreferences.getInstance();
String? head = prefs.getString('Accept');
Map<String, String> authHeaders = new Map();
authHeaders['Accept'] = head!;
String uri = "$baseUrlUser/user_bal";
try {
http.Response response =
await http.get(Uri.parse(uri), headers: authHeaders);
return json.decode(response.body);
} catch (e) {
return e;
}
}
The unique difference is that you're not storing a completly Map as a String as you do in the example, you're saving the keys that you desire as what they are, Strings. Parsing JSON it's alwaya a quite sensible action, so the more granularity over the pieces you take, the best results.