Ashton (AttributedStringHTMLTransformation) is an iOS, macOS, and visionOS library for fast conversion of NSAttributedStrings into HTML, and back. Ashton is battle-tested and used in MindNode, for persisting formatted strings.

The latest release is a complete rewrite in Swift focusing on improved performance and functional backwards compatibility to Ashton 1.x. The new codebase has a comprehensive test suite with a test coverage of > 90% and additional tests against the legacy 1.0 output.

Find out more about the launch of Ashton 2.0 in our Blog Post.

The following NSAttributedString.Key attributes are supported, when converting to HTML:

• .backgroundColor (persisted as RGBA)
• .foregroundColor (persisted as RGBA)
• .underlineStyle (single, double, thick)
• .underlineColor (persisted as RGBA)
• .strikethroughColor (persisted as RGBA)
• .strikethroughStyle (single, double, thick)
• .font
• .paragraphStyle (text alignment)
• .baselineOffset
• NSSuperScript
• .link

As Ashton supports only tags which are necessary to persist the attributes mentioned above, not all HTML tags are supported when converting HTML --> AttributedString. Basically, Ashton converts an AttributedString into a concatenation of span, p and a tags with style attributes.

Supported HTML Tags:

• span
• p
• a
• em
• strong

The following style attribute keys are supported:

• background-color
• color
• text-decoration
• font
• text-align
• vertical-align
• Additional custom attributes (-cocoa-strikethrough-color, -cocoa-underline-color, -cocoa-baseline-offset, -cocoa-vertical-align, -cocoa-font-postscriptname, -cocoa-underline, -cocoa-strikethrough, -cocoa-fontFeatures)

Colors have to be formatted as rgba like rgba(0, 0, 0, 1.000000).

Add this line to your Cartfile.

github "IdeasOnCanvas/Ashton"

The Swift Package Manager is a dependency manager integrated with the Swift build system. To learn how to use the Swift Package Manager for your project, please read the official documentation.
To add Ashton as a dependency, you have to add it to the dependencies of your Package.swift file and refer to that dependency in your target.

// swift-tools-version:5.1
import PackageDescription
let package = Package(
    name: "<Your Product Name>",
    dependencies: [
		.package(url: "https://github.com/IdeasOnCanvas/Ashton/", .upToNextMajor(from: "2.0.0"))
    ],
    targets: [
        .target(
		name: "<Your Target Name>",
		dependencies: ["Ashton"]),
    ]
)

After adding the dependency, you can fetch the library with:

$ swift package resolve

let htmlString = Ashton.encode(attributedString)

let attributedString = Ashton.decode(htmlString)

An example app can be found in the /Example directory. It can be used to test NSAttributedString -> HTML -> NSAttributedString roundtrips and also to extract the HTML representation of an `NSAttributedString.

Ashton is brought to you by IdeasOnCanvas GmbH, the creator of MindNode for iOS, macOS & watchOS.