Sample to create own server working with iOS app on rest api

HTTPService.h

//
//  HTTPService.h
//  Tutorials
//
//  Created by Linh on 6/7/17.
//  Copyright © 2017 Linh. All rights reserved.
//

#import <Foundation/Foundation.h>

typedef void (^onComplete)(NSArray * __nullable dataArray, NSString* __nullable errMsg);

@interface HTTPService : NSObject

+ (id)instance;
- (void)getTutorials:(nullable onComplete)completionHandler;
- (void)postCommentsWithComment:(nonnull NSDictionary*)comment :(nullable onComplete)completionHandler;

@end

HttpService.m

//
//  HTTPService.m
//  Tutorials
//
//  Created by Linh on 6/7/17.
//  Copyright © 2017 Linh. All rights reserved.
//

#import "HTTPService.h"

#define URL_BASE "http://localhost:6069"
#define URL_TUTORIAL "/tutorials" // get
#define URL_COMMENT "/comments" // post

@implementation HTTPService

+ (id)instance {
    static HTTPService *shared = nil;
    
    @synchronized (self) {
        if (shared == nil) {
            shared = [[self alloc] init];
        }
        
        return shared;
    }
}

- (void)getTutorials:(nullable onComplete)completionHandler {
    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%s%s", URL_BASE, URL_TUTORIAL]];
    NSURLSession *session = [NSURLSession sharedSession];
    
    [[session dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        if (data != nil) {
            NSError *err;
            NSArray *json = [NSJSONSerialization JSONObjectWithData:data options:0 error:&err];
            
            if (err == nil) {
//                NSLog(@"JSON: %@", json.debugDescription);
                completionHandler(json, nil);
            } else {
                completionHandler(nil, err.debugDescription);
            }
        } else {
            NSLog(@"NETWORK ERR: %@", error.debugDescription);
            completionHandler(nil, @"Problem connecting to the server");
        }
    }] resume];
    
}

- (void)postCommentsWithComment:(nonnull NSDictionary*)comment :(nullable onComplete)completionHandler {
    NSLog(@"postCommentsWithComment");
    
    NSError *error;
    NSURLSession *session = [NSURLSession sharedSession];
    NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:@"%s%s", URL_BASE, URL_COMMENT]];
    
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request addValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
    [request addValue:@"application/json" forHTTPHeaderField:@"Accept"];
    [request setHTTPMethod:@"POST"];
    
    NSData *postData = [NSJSONSerialization dataWithJSONObject:comment options:0 error:&error];
    [request setHTTPBody:postData];
    
    NSURLSessionDataTask *postDataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        NSLog(@"postCommentsWithComment received data!");
         if (data != nil) {
            NSError *err;
            NSString *strData = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
            NSMutableArray *arr = [[NSMutableArray alloc] init];
            [arr addObject:strData];
            NSLog(@"valid data: %@", strData.debugDescription);
            
            if (err == nil) {
//                NSLog(@"JSON: %@", json.debugDescription);
                completionHandler([NSArray arrayWithArray:arr], nil);
            } else {
                completionHandler(nil, err.debugDescription);
            }
        } else {
            NSLog(@"NETWORK ERR: %@", error.debugDescription);
            completionHandler(nil, @"Problem connecting to the server");
        }
    }];
    
    [postDataTask resume];
}

@end

server.js

var express = require('express');
var bodyParser = require('body-parser');
var app = express();

app.all('/*', function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "X-Requested-With", "Content-Type, Accept");
  res.header("Access-Control-Allow-Methods", "POST", "GET");
  next();
});

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: false}));

var tutorials = [
  {
    id: 1,
    title: "Android Studio Tutorial for Beginners",
    description: "Learn how to install AS",
    iframe: '<div class="container"><iframe class="video" src="https://www.youtube.com/embed/nfs8NYg7yQM" frameborder="0" allowfullscreen></iframe></div>',
    thumbnail: "https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQAaGEkWCL2oB8rMoa7aj8azJNGj_-HZvCWDbLOUP1XN18vBFrH"

  },
  {
    id: 1,
    title: "Android Kotlin Tutorial",
    description: "Learn how to learn Kotlin",
    iframe: '<div class="container"><iframe class="video" src="https://www.youtube.com/embed/nfs8NYg7yQM" frameborder="0" allowfullscreen></iframe></div>',
    thumbnail: "https://s-media-cache-ak0.pinimg.com/originals/c5/7e/a0/c57ea04f0b2cbdeab1d94a1d0352dfbc.jpg"
  }
];

var comments = [
    {
        username: "linhtruong",
        comment: "This is very cool practice deloying my own server"
    }
];

/*
app.put('/comments', function(req, res) {
    var someObj = req.body;
    var id = someObj.uniqueId;

    // talk to database, find the record by the id
    // then replace the existing record with req.body
    res.send("Successfully update");
});
*/

app.post('/comments', function(req, res) {
    console.log("POST to server");
    var comment = req.body;
    if (comment) {
        if (comment.username &&  comment.comment) {
            comments.push(comment);
            console.log(comments);
        } else {
            res.send("You posted invalid data!");
        }
    } else {
        res.send("Your post has no body!");
    }

    res.send("You successfully posted a comment!");
});

app.get('/tutorials', function(req, res) {
    console.log("GET from server");
    res.send(tutorials);
});

app.listen(6069);