Issues with post request in Flutter/Dart frontend with Go backend - post

Question

I am new to Flutter/Dart, Go and mobile development in general. I am currently coding a login authentication page in flutter that connects to a backend written in go. To check if everything worked I wanted to print out the cookie that my backend sends back in the console. Unfortunately I am getting errors not sure what to do.
EDIT: I have been able to read the cookie, should I save the cookie in this format "session=UUID" or just the "UUID"? I want to send this cookie back in the header for future get requests. My Go code will check for the cookie name "session",but I'm not sure if sending it back in that format is correct.
Flutter code (I read on another stackoverflow post to use 10.0.2.2 as localhost when using an android emulator):
EDIT: After playing around with the code I was able to read the cookie in the header but it has the name as well not just the UUID.
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
class Login extends StatefulWidget {
#override
State<StatefulWidget> createState(){
return new LoginState();
}
}
class LoginState extends State <Login> {
final formKey = GlobalKey<FormState>();
String _email, _password;
String cookie;
void loginApi(){
var form = formKey.currentState;
var url = "http://10.0.2.2:8080";
if (form.validate()) {
form.save();
var body = { "Email":_email, "Pass":_password};
http.post(url,body:json.encode(body)).then((response){
print(response.headers['set-cookie']);
});
}
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text("Login"),
backgroundColor: Colors.white,
),
body: new Container(
alignment: Alignment.center,
child: Form(
key: formKey,
child: Column(
children: <Widget>[
TextFormField(
autocorrect: false,
decoration: InputDecoration(
labelText: "Email:",
),
validator: (str) =>
!str.contains('#') ? "Not a Valid Email!" : null,
onSaved: (str) => _email = str,
),
TextFormField(
autocorrect: false,
decoration: InputDecoration(
labelText: "Password:",
),
validator: (str) =>
str.length <= 7 ? "Not a Valid Password!" : null,
onSaved: (str) => _password = str,
obscureText: false,
),
RaisedButton(
child: Text("Submit"),
onPressed:loginApi,
),
],
)
),
),
);
}
}
Golang code (EDIT: Inserted a missing curly bracket after the panic error and deleted the curly bracket at the end of the code):
package main
import (
"encoding/json"
"html/template"
"net/http"
uuid "github.com/satori/go.uuid"
"golang.org/x/crypto/bcrypt"
)
type user struct {
UserName string //Same as email
Password []byte
}
type logindata struct {
Email string
Pass string
}
var tpl *template.Template
var dbUsers = map[string]user{}
var dbSess = map[string]string{}
func init() {
bs, _ := bcrypt.GenerateFromPassword([]byte("password"), bcrypt.MinCost)
dbUsers["test#test.com"] = user{"test#test.com", bs}
}
func main() {
http.HandleFunc("/", login)
http.Handle("/favicon.ico", http.NotFoundHandler()) //Don't have favicon
http.ListenAndServe(":8080", nil)
}
func login(w http.ResponseWriter, req *http.Request) {
var data logindata
decoder := json.NewDecoder(req.Body)
err_decode := decoder.Decode(&data)
if err_decode != nil {
panic(err_decode)
}
u, ok := dbUsers[data.Email]
if !ok {
http.Error(w, "Username and/or password do not match", http.StatusForbidden)
return
}
err_compare := bcrypt.CompareHashAndPassword(u.Password, []byte(data.Pass))
if err_compare != nil {
http.Error(w, "Username and/or password do not match", http.StatusForbidden)
return
}
// create session
sID, _ := uuid.NewV4()
c := &http.Cookie{
Name: "session",
Value: sID.String(),
}
http.SetCookie(w, c)
dbSess[c.Value] = data.Email
return
}
Output from console for flutter code (after I put in username and password and click submit, username is "test#test.com" password is "password"):
Performing hot reload...
Reloaded 0 of 489 libraries in 544ms.
I/flutter ( 3778): session=db3690d6-db6e-4658-8b5b-5f2d3f908a65
I also went to localhost:8080 on my browser expecting to show a blank page but it displayed "page not working" and my terminal outputted the following error I guess because I was accessing it with a browser and I wasn't sending in JSON data, not sure:
2018/05/24 23:29:38 http: panic serving [::1]:40010: EOF
goroutine 6 [running]:
net/http.(*conn).serve.func1(0xc82001a280)
/usr/lib/go-1.6/src/net/http/server.go:1389 +0xc1
panic(0x76c6c0, 0xc82000a160)
/usr/lib/go-1.6/src/runtime/panic.go:443 +0x4e9
main.login(0x7f96c9a848b8, 0xc82012c000, 0xc8201121c0)
/home/daniel/Desktop/Workspace/Genesis/main.go:43 +0x176
net/http.HandlerFunc.ServeHTTP(0x8a8688, 0x7f96c9a848b8, 0xc82012c000, 0xc8201121c0)
/usr/lib/go-1.6/src/net/http/server.go:1618 +0x3a
net/http.(*ServeMux).ServeHTTP(0xc820013020, 0x7f96c9a848b8, 0xc82012c000, 0xc8201121c0)
/usr/lib/go-1.6/src/net/http/server.go:1910 +0x17d
net/http.serverHandler.ServeHTTP(0xc82001a100, 0x7f96c9a848b8, 0xc82012c000, 0xc8201121c0)
/usr/lib/go-1.6/src/net/http/server.go:2081 +0x19e
net/http.(*conn).serve(0xc82001a280)
/usr/lib/go-1.6/src/net/http/server.go:1472 +0xf2e
created by net/http.(*Server).Serve
/usr/lib/go-1.6/src/net/http/server.go:2137 +0x44e
2018/05/24 23:29:38 http: panic serving [::1]:40012: EOF
goroutine 18 [running]:
net/http.(*conn).serve.func1(0xc82011c080)
/usr/lib/go-1.6/src/net/http/server.go:1389 +0xc1
panic(0x76c6c0, 0xc82000a160)
/usr/lib/go-1.6/src/runtime/panic.go:443 +0x4e9
main.login(0x7f96c9a848b8, 0xc8201161a0, 0xc820154000)
/home/daniel/Desktop/Workspace/Genesis/main.go:43 +0x176
net/http.HandlerFunc.ServeHTTP(0x8a8688, 0x7f96c9a848b8, 0xc8201161a0, 0xc820154000)
/usr/lib/go-1.6/src/net/http/server.go:1618 +0x3a
net/http.(*ServeMux).ServeHTTP(0xc820013020, 0x7f96c9a848b8, 0xc8201161a0, 0xc820154000)
/usr/lib/go-1.6/src/net/http/server.go:1910 +0x17d
net/http.serverHandler.ServeHTTP(0xc82001a100, 0x7f96c9a848b8, 0xc8201161a0, 0xc820154000)
/usr/lib/go-1.6/src/net/http/server.go:2081 +0x19e
net/http.(*conn).serve(0xc82011c080)
/usr/lib/go-1.6/src/net/http/server.go:1472 +0xf2e
created by net/http.(*Server).Serve
/usr/lib/go-1.6/src/net/http/server.go:2137 +0x44e
2018/05/24 23:29:43 http: panic serving [::1]:40016: EOF
goroutine 7 [running]:
net/http.(*conn).serve.func1(0xc82001a380)
/usr/lib/go-1.6/src/net/http/server.go:1389 +0xc1
panic(0x76c6c0, 0xc82000a160)
/usr/lib/go-1.6/src/runtime/panic.go:443 +0x4e9
main.login(0x7f96c9a848b8, 0xc82012c1a0, 0xc8201122a0)
/home/daniel/Desktop/Workspace/Genesis/main.go:43 +0x176
net/http.HandlerFunc.ServeHTTP(0x8a8688, 0x7f96c9a848b8, 0xc82012c1a0, 0xc8201122a0)
/usr/lib/go-1.6/src/net/http/server.go:1618 +0x3a
net/http.(*ServeMux).ServeHTTP(0xc820013020, 0x7f96c9a848b8, 0xc82012c1a0, 0xc8201122a0)
/usr/lib/go-1.6/src/net/http/server.go:1910 +0x17d
net/http.serverHandler.ServeHTTP(0xc82001a100, 0x7f96c9a848b8, 0xc82012c1a0, 0xc8201122a0)
/usr/lib/go-1.6/src/net/http/server.go:2081 +0x19e
net/http.(*conn).serve(0xc82001a380)
/usr/lib/go-1.6/src/net/http/server.go:1472 +0xf2e
created by net/http.(*Server).Serve
/usr/lib/go-1.6/src/net/http/server.go:2137 +0x44e

Answer 1

In your code
http.post(url,body:json.encode(body)).then((http.Response response){
cookie = response.headers['session'];
});
debugPrint(cookie);
the line
debugPrint(cookie);
is executed before
cookie = response.headers['session'];
so it is expected that cookie is null when you print it. For some weird reason debugPrint(null) throws an exception about "slit on null"
Try instead
http.post(url,body:json.encode(body)).then((http.Response response){
cookie = response.headers['session'];
debugPrint(cookie);
});