Web Scraping with Objective C: A Comprehensive Guide

Web scraping is the process of automatically extracting data and content from websites. It allows you to gather information from across the web at scale, without having to manually browse and copy/paste. While web scraping is often done using Python, JavaScript, or other languages, it‘s also possible to leverage the power of Objective C and native macOS/iOS libraries to build robust web scrapers.

In this in-depth guide, we‘ll walk through how to scrape both static and dynamic web pages using Objective C. Whether you‘re new to web scraping or an experienced developer, you‘ll learn the tools, techniques and best practices to efficiently extract the web data you need. Let‘s get started!

Setting Up Your Objective C Web Scraping Project

We‘ll use Xcode to create a macOS command-line tool project for our web scraper. Open Xcode and select File > New > Project. Choose macOS and Command Line Tool.

Name the project something like "WebScraper", choose Objective C for language, and save it to your desired location.

Next, you‘ll want to add a few useful libraries to help with HTML parsing and web requests. We recommend:

• HTMLReader – A standards-compliant HTML parser
• AFNetworking – A networking framework for iOS and macOS

You can add these as dependencies to your project using Swift Package Manager or CocoaPods. For HTMLReader, select File > Swift Packages > Add Package Dependency and enter the GitHub URL. For AFNetworking, create a Podfile with:

target ‘WebScraper‘ do
  pod ‘AFNetworking‘, ‘~> 4.0‘
end

Then run pod install to set up the CocoaPods dependencies. Open the .xcworkspace file going forward.

Basic Scraping of Static Web Pages

Many websites serve static HTML content that can be loaded and parsed without executing JavaScript. Scraping static pages is relatively straightforward. The typical steps are:

1. Send an HTTP request to fetch the HTML content of a URL
2. Parse the returned HTML string into a document object
3. Locate the desired elements in the parsed document using selectors
4. Extract the text, attributes, or HTML of each matched element
5. (Optional) Follow hyperlinks to other pages and repeat the process

Here‘s a simplified example of performing those steps in Objective C using HTMLReader and AFNetworking:

#import "HTMLDocument.h" 
#import <AFNetworking/AFNetworking.h>

- (void)scrapePage:(NSString*)urlString {

  NSURL *url = [NSURL URLWithString:urlString];

  AFHTTPSessionManager *manager = [AFHTTPSessionManager manager];
  [manager GET:url.absoluteString parameters:nil headers:nil progress:nil 
    success:^(NSURLSessionTask *task, NSString *responseObject) {

      HTMLDocument *doc = [HTMLDocument documentWithString:responseObject];

      NSArray<HTMLElement *> *titles = 
        [doc querySelectorAll:@"h1, h2, h3"];

      for (HTMLElement *title in titles) {
        NSLog(@"%@", title.textContent);
      }

  } failure:^(NSURLSessionTask *operation, NSError *error) {
    NSLog(@"Error: %@", error);
  }];

}

This sends a GET request to the specified URL, parses the response HTML using HTMLReader, finds all the <h1>, <h2>, <h3> elements using querySelectorAll, and prints out their text content.

The CSS selector syntax is very powerful for locating specific elements. Some other examples:

• div.info – all <div> elements with class="info"
• #main img – all <img> tags that are descendants of the element with id="main"
• a[href^="https://"] – all <a> tags whose href attribute starts with "https://"
• ul > li – all <li> elements that are direct children of a <ul> element

HTMLReader also supports XPath selectors if you prefer those to CSS selectors.

To extract other data from matched elements, access their properties:

element.textContent; // inner text
element.innerHTML; // inner HTML
element[@"src"]; // src attribute
[element attr:@"class"]; // class attribute

To follow and scrape links, you can select the <a href="..."> elements, extract their URLs, and recursively call scrapePage for each one. Just be mindful of circular references and restrict the recursion depth to avoid infinite loops.

Advanced Scraping of Dynamic Pages with Selenium

Some websites heavily rely on JavaScript and don‘t serve full HTML upfront. The content is dynamically loaded and rendered by the browser. Scraping such single-page apps and JS-heavy sites is trickier, as you need to fully load the pages in an actual browser environment.

We can automate this using Selenium, a popular browser automation tool originally designed for testing. It allows programmatically controlling a real web browser like Safari, Chrome or Firefox.

Setting up Selenium

First, ensure you have a compatible WebDriver executable for your browser of choice:

• Safari: /usr/bin/safaridriver (builtin)
• Chrome: ChromeDriver
• Firefox: geckodriver

The Selenium client bindings for Objective C are a bit outdated. For the smoothest experience, we recommend controlling the browser via the Selenium WebDriver HTTP API. You can set up a Selenium server Grid that receives API requests and passes them to the browser driver.

Download the latest Selenium Server JAR from https://www.selenium.dev/downloads/. Launch the server, specifying the browser driver path if needed:

java -jar selenium-server-<version>.jar standalone \
  --driver-executable-path <path/to/driver>

This starts the Selenium Grid server listening on port 4444 by default. You can verify it‘s working at http://localhost:4444.

Controlling the Browser with Objective C

Now we‘re ready to write Objective C code that will talk to the Selenium Grid API, tell it what page to load and what elements to find. We‘ll use the AFNetworking library to make the HTTP requests to the API.

Here‘s a function to create a new Selenium browser session with desired capabilities:

- (NSDictionary*)createSeleniumSession {

  NSDictionary *caps = @{
    @"browserName": @"chrome",
    @"platformName": @"mac"
  };

  AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc]
    initWithBaseURL:[NSURL URLWithString:@"http://localhost:4444"]];
  manager.requestSerializer = [AFJSONRequestSerializer serializer];

  __block NSDictionary *session;
  [manager POST:@"/session" parameters:@{@"desiredCapabilities": caps} headers:nil
    progress:nil success:^(NSURLSessionDataTask *task, id responseObject) {

    session = (NSDictionary*)responseObject;

  } failure:^(NSURLSessionDataTask *task, NSError *error) {
    NSLog(@"Error starting Selenium session: %@", error);
  }];

  return session;
}

This starts a new Selenium session using Chrome browser on macOS. The responseObject will contain a sessionId we‘ll need for future requests that control this automated browser instance.

We can now write a function to tell Selenium to load a URL and extract elements from the page:

- (void)scrapeWithSelenium:(NSString*)url sessionId:(NSString*)sessionId {

  AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc] 
    initWithBaseURL:[NSURL URLWithString:@"http://localhost:4444/session"]];

  NSString *urlPath = [NSString stringWithFormat:@"/%@/url", sessionId]; 
  [manager POST:urlPath parameters:@{@"url": url} headers:nil 
    progress:nil success:^(NSURLSessionTask *task, NSDictionary *responseObject) {

    NSString *elemPath = [NSString stringWithFormat:@"/%@/elements", sessionId];
    [manager POST:elemPath parameters:@{
        @"using": @"css selector",
        @"value": @".result"
      } success:^(NSURLSessionTask *task, NSArray *elements) {

      for (NSDictionary *element in elements) {
        NSString *elemId = element[@"element-6066-11e4-a52e-4f735466cecf"];
        NSString *textPath = [NSString stringWithFormat:@"/%@/element/%@/text", 
          sessionId, elemId];

        [manager GET:textPath parameters:nil headers:nil progress:nil
          success:^(NSURLSessionTask *task, NSString *text) {

          NSLog(@"%@", text);

        } failure:nil];
      }
    } failure:nil];

  } failure:nil];
}

Let‘s break this down:

1. We create a new AFHTTPSessionManager pointing to the base Selenium session URL
2. POST a request to {session}/url to tell the browser to load the target page URL
3. Once that‘s loaded, POST to {session}/elements to find elements matching the CSS selector .result
4. For each matched element, extract its unique element ID
5. GET request to {session}/element/{elementId}/text to retrieve the text content of that element
6. Log the extracted text strings

The Selenium WebDriver protocol supports a wide variety of commands for finding elements, extracting their attributes, states, and values, clicking, typing, executing JS, and more. Refer to the documentation for details.

It‘s a good idea to clean up and quit the automated browser when done scraping:

- (void)quitSession:(NSString*)sessionId {
  [[AFHTTPSessionManager alloc] initWithBaseURL:
    [NSURL URLWithString:@"http://localhost:4444/session"]];

  NSString *quitPath = [NSString stringWithFormat:@"/%@", sessionId]; 
  [manager DELETE:quitPath parameters:nil headers:nil
    success:nil failure:nil];
}

Avoiding Detection

Some websites attempt to block web scraping by detecting automated access. They may look for signs like missing human behaviors (mouse movements, scrolling, typing cadence), known bot user agents, or IP addresses associated with cloud hosting providers.

To avoid detection and bans, try the following:

• Randomize the user agent string to impersonate different desktop and mobile browsers
• Use IP rotation with proxies to distribute requests across many IP addresses
• Introduce random delays between requests to avoid high-frequency access patterns
• Disable features that aren‘t typically available in real browsers, like headless mode
• Inject human-like behaviors with Selenium: mouse movements, scrolling, clicking

Here‘s how to set a custom user agent when creating the Selenium session:

NSDictionary *caps = @{
  @"browserName": @"chrome", 
  @"platformName": @"mac",
  @"goog:chromeOptions": @{
    @"args": @[@"--user-agent=Mozilla/5.0 My Custom UA String"]
  }
};

To route browser traffic through a proxy for IP rotation:

NSDictionary *caps = @{
  @"browserName": @"chrome",
  @"platformName": @"mac", 
  @"proxy": @{
    @"proxyType": @"manual",
    @"httpProxy": @"myproxy.com:8080"
  }
};

Tips and Gotchas

Some additional advice for Objective C web scraping:

• Debug and test CSS/XPath selectors in the browser first before attempting to use them in code. Browsers‘ developer tools make it easy to test selectors on the currently loaded page.
• Start with hardcoded URLs and selectors, then generalize and parameterize your code as needed to handle different pages and websites.
• Check response status codes and handle errors gracefully. Some requests may fail due to network issues, bot detection, etc. Log the errors to investigate later.
• Respect website terms of service and robots.txt restrictions on scraping. Some sites may ask you not to scrape them or to throttle request rates. Be a good web citizen!
• Consider headless browsers like PhantomJS as lightweight alternatives to Selenium. They can be easier to install and configure.
• For large scale scraping jobs, consider splitting work across many machines/threads and saving the extracted data to a shared database for aggregation.
• If you hit roadblocks, consider
  professional scraping solutions like ScrapingBee or ScrapingBot to outsource the work. They manage the scrapers, proxies, browsers, and CAPTCHAs for you.

Conclusion

Web scraping with Objective C is very doable, if not quite as straightforward as with scripting languages. We walked through the process of setting up an Xcode project with HTML parsing and networking libraries, scraping static pages with CSS selectors, and automating dynamic pages with Selenium WebDriver. By following the tips and best practices, you can build robust, efficient, and responsible Objective C web scrapers.

Of course, if you get stuck or want to save development time, give ScrapingBee‘s API a try to let them handle the scraping infrastructure for you. Either way, you‘re now well on your way to gathering web data using the power of Objective C and native Apple operating systems. Happy scraping!