HTMLReader

A WHATWG-compliant HTML parser with CSS selectors in Objective-C and Foundation. It parses HTML just like a browser.

Usage

@import HTMLReader;

// Parse a string and find an element.
NSString *markup = @"<p><b>Ahoy there sailor!</b></p>";
HTMLDocument *document = [HTMLDocument documentWithString:markup];
NSLog(@"%@", [document firstNodeMatchingSelector:@"b"].textContent);
// => Ahoy there sailor!

// Wrap one element in another.
HTMLElement *b = [document firstNodeMatchingSelector:@"b"];
NSMutableOrderedSet *children = [b.parentNode mutableChildren];
HTMLElement *wrapper = [[HTMLElement alloc] initWithTagName:@"div"
                                                 attributes:@{@"class": @"special"}];
[children insertObject:wrapper atIndex:[children indexOfObject:b]];
b.parentNode = wrapper;
NSLog(@"%@", [document.rootElement serializedFragment]);
// => <html><head></head><body><p><div class="special"> \
      <b>Ahoy there sailor!</b></div></p></body></html>

// Load a web page.
NSURL *URL = [NSURL URLWithString:@"https://github.com/nolanw/HTMLReader"];
NSURLSession *session = [NSURLSession sharedSession];
[[session dataTaskWithURL:URL completionHandler:
  ^(NSData *data, NSURLResponse *response, NSError *error) {
    NSString *contentType = nil;
    if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
        NSDictionary *headers = [(NSHTTPURLResponse *)response allHeaderFields];
        contentType = headers[@"Content-Type"];
    }
    HTMLDocument *home = [HTMLDocument documentWithData:data
                                      contentTypeHeader:contentType];
    HTMLElement *div = [home firstNodeMatchingSelector:@".repository-meta-content"];
    NSCharacterSet *whitespace = [NSCharacterSet whitespaceAndNewlineCharacterSet];
    NSLog(@"%@", [div.textContent stringByTrimmingCharactersInSet:whitespace]);
    // => A WHATWG-compliant HTML parser in Objective-C.
}] resume];

Installation

You have choices:

Copy the files in the Sources folder into your project.
Add the following line to your Cartfile:

github "nolanw/HTMLReader"
Add the following line to your Podfile:

pod "HTMLReader"
Add the following line to your Package.swift:

.Package(url: "https://github.com/nolanw/HTMLReader", majorVersion: 2)

You'll need to invoke swift package with an extra option like so: swift package [command] -Xcc -fobjc-arc.
Clone this repository (perhaps add it as a submodule) and add HTMLReader.xcodeproj to your project/workspace. Then add HTMLReader.framework to your app target. (Or, if you're targeting iOS earlier than 8.0: add libHTMLReader.a to your app target and "$(SYMROOT)/include" to your app target's Header Search Paths.)

HTMLReader has no dependencies other than Foundation.

Why HTMLReader?

I needed to scrape HTML like a browser. I couldn't find a good choice for iOS.

The Alternatives

libxml2 ships with iOS. It parses a variant of HTML 4 and does not handle broken markup like a modern browser.

Other Objective-C libraries I came across (e.g. hpple and Ono) use libxml2 and inherit its shortcomings.

There are C libraries such as Gumbo or Hubbub, but you need to shuffle data to and from Objective-C. (Also Gumbo wasn't publicly announced until after HTMLReader was far enough along.)

WebKit ships with iOS, but its HTML parsing abilities are considered private API. I consider a round-trip through a web view inappropriate for parsing HTML. And I didn't make it very far into building my own copy of WebCore.

Google Toolbox for Mac will escape and unescape strings for HTML (e.g. & ⇔ &) but, again, not like a modern browser. For example, GTM will not unescape &#65 (note the missing semicolon).

CFStringTransform does numeric entities via (the reversible) kCFStringTransformToXMLHex, but that rules out named entities.

Does it work?

HTMLReader continually runs html5lib's tokenization and tree construction tests, ignoring the tests for <template> (which HTMLReader does not implement). Note that you need to check out the HTMLReaderTests/html5lib Git submodule in order to actually run these tests.

HTMLReader is continually built and tested on iOS versions 8.4, 9.3, and 10.3; built and tested on macOS versions 10.9, 10.10, 10.11, and 10.12; built and tested on tvOS versions 9.2 and 10.2; and built on watchOS versions 2.2 and 3.2. It should work on down to iOS 5, macOS 10.7, tvOS 9.0, and watchOS 2.0, but there is no automated testing there (it's ok to file an issue though!).

Given all that:

HTMLReader is used by at least one shipping app.

How fast is it?

I'm not sure.

Included in the project is a utility called Benchmarker. It knows how to run three tests:

Parsing a large HTML file. In this case, the 7MB single-page HTML specification.
Escaping and unescaping entities in the large HTML file.
Running a bunch of CSS selectors. Basically copied from a WebKit performance test.

Changes to HTMLReader should not cause these benchmarks to run slower. Ideally changes make them run faster!

Bugs and Feature Requests

Bugs can be reported, and features can be requested, using the issue tracker. Or get in touch directly if you'd prefer.

License

HTMLReader is in the public domain.

Acknowledgements

HTMLReader is developed by Nolan Waite.

Thanks to Chris Williams for contributing the implementation of CSS selectors.

kepeifeng/HTMLReader