# URL extraction for hostname, domain, subdomain and tld in Swift

How difficult can it be to parse an HTTP link to identify and extract individual components like its subdomain or top-level domain?

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690138494907/8c8347bc-c398-478b-a494-4933e77595df.png align="center")

Giving the example `http://super.duper.domain.co.uk` how would you know that `super.duper` is the subdomain and `co.uk` is the top-level domain?

You won't solve this with a regular expression.

You need to parse the URL manually, but more importantly, you need to know which top-level domains exist.

Mozilla initiated an open-source catalog of effective top-level domains called the [Public Suffix List](https://publicsuffix.org/). The list is maintained as a community resource, and updates can occur as often as every few days.

Kojiro Futamura created `TLDExtract` to solve the problem within Swift projects. A Swift library that bundles the Public Suffix List (PSL), understands [Punycode](https://en.wikipedia.org/wiki/Punycode), and therefore makes extracting information a breeze.

```swift
import TLDExtract

let extractor = TLDExtract()

let urlString: String = "http://super.duper.domain.co.uk"
guard let result: TLDResult = extractor.parse(urlString) else { return }

print(result.rootDomain)        // Optional("domain.co.uk")
print(result.topLevelDomain)    // Optional("co.uk")
print(result.secondLevelDomain) // Optional("domain")
print(result.subDomain)         // Optional("super.duper")
```

The code base of `TLDExtract` is very good, but the bundled PSL is outdated as the project stopped releasing updates.

The code allowed you to fetch PSL updates from within your app, but what if your app is mainly operating offline? Also, the implementation used synchronous `Data(contentsOf: url)` API, which is a blocking operation.

I decided to create a [fork](https://github.com/MarcoEidinger/TLDExtractSwift) to keep this project up-to-date. My key focus is:

* **Always up-to-date**
    
    * leveraging GitHub actions to regularly create new package versions bundling the latest [Public Suffix List](http://www.publicsuffix.org/) (PSL) - perfect for offline use
        
    * modern `async` function to invoke a network request fetching the latest PSL from the remote server ad-hoc.
        
* **Swift Package Manager** (SPM) as the **exclusive distribution channel**
    
* No package dependencies
    

%[https://github.com/MarcoEidinger/TLDExtractSwift] 

I hope this helps the Swift community. Let me know if you have suggestions to improve the project further.