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HTMLString.swift
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238 lines (200 loc) · 8.89 KB
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import Foundation
// MARK: Escaping
extension String {
///
/// Returns a copy of the current `String` where every character incompatible with HTML Unicode
/// encoding (UTF-16 or UTF-8) is replaced by a decimal HTML entity.
///
/// ### Examples
///
/// | String | Result | Format |
/// |--------|--------|--------|
/// | `&` | `&` | Decimal entity (part of the Unicode special characters) |
/// | `Σ` | `Σ` | Not escaped (Unicode compliant) |
/// | `🇺🇸` | `🇺🇸` | Not escaped (Unicode compliant) |
/// | `a` | `a` | Not escaped (alphanumerical) |
///
public var addingUnicodeEntities: String {
var copy = self
copy.addUnicodeEntities()
return copy
}
///
/// Replaces every character incompatible with HTML Unicode encoding (UTF-16 or UTF-8) by a decimal HTML entity.
///
/// ### Examples
///
/// | String | Result | Format |
/// |--------|--------|--------|
/// | `&` | `&` | Decimal entity (part of the Unicode special characters) |
/// | `Σ` | `Σ` | Not escaped (Unicode compliant) |
/// | `🇺🇸` | `🇺🇸` | Not escaped (Unicode compliant) |
/// | `a` | `a` | Not escaped (alphanumerical) |
///
public mutating func addUnicodeEntities() {
var position: String.Index? = startIndex
let requiredEscapes: Set<Character> = ["!", "\"", "$", "%", "&", "'", "+", ",", "<", "=", ">", "@", "[", "]", "`", "{", "}"]
while let cursorPosition = position {
guard cursorPosition != endIndex else { break }
let character = self[cursorPosition]
if requiredEscapes.contains(character) {
// One of the required escapes for security reasons
let escape = "&#\(character.asciiValue!);" // required escapes can can only be ASCII
position = positionAfterReplacingCharacter(at: cursorPosition, with: escape)
} else {
// Not a required escape, no need to replace the character
position = index(cursorPosition, offsetBy: 1, limitedBy: endIndex)
}
}
}
///
/// Returns a copy of the current `String` where every character incompatible with HTML ASCII
/// encoding is replaced by a decimal HTML entity.
///
/// ### Examples
///
/// | String | Result | Format |
/// |--------|--------|--------|
/// | `&` | `&` | Decimal entity |
/// | `Σ` | `Σ` | Decimal entity |
/// | `🇺🇸` | `🇺🇸` | Combined decimal entities (extented grapheme cluster) |
/// | `a` | `a` | Not escaped (alphanumerical) |
///
/// ### Performance
///
/// If your webpage is unicode encoded (UTF-16 or UTF-8) use `addingUnicodeEntities` instead,
/// as it is faster and produces a less bloated and more readable HTML.
///
public var addingASCIIEntities: String {
var copy = self
copy.addASCIIEntities()
return copy
}
///
/// Replaces every character incompatible with HTML Unicode (UTF-16 or UTF-8) with a decimal HTML entity.
///
/// ### Examples
///
/// | String | Result | Format |
/// |--------|--------|--------|
/// | `&` | `&` | Decimal entity (part of the Unicode special characters) |
/// | `Σ` | `Σ` | Not escaped (Unicode compliant) |
/// | `🇺🇸` | `🇺🇸` | Not escaped (Unicode compliant) |
/// | `a` | `a` | Not escaped (alphanumerical) |
///
public mutating func addASCIIEntities() {
var position: String.Index? = startIndex
let requiredEscapes: Set<Character> = ["!", "\"", "$", "%", "&", "'", "+", ",", "<", "=", ">", "@", "[", "]", "`", "{", "}"]
while let cursorPosition = position {
guard cursorPosition != endIndex else { break }
let character = self[cursorPosition]
if let asciiiValue = character.asciiValue {
if requiredEscapes.contains(character) {
// One of the required escapes for security reasons
let escape = "&#\(asciiiValue);"
position = positionAfterReplacingCharacter(at: cursorPosition, with: escape)
} else {
// Not a required escape, no need to replace the character
position = index(cursorPosition, offsetBy: 1, limitedBy: endIndex)
}
} else {
// Not an ASCII Character, we need to escape.
let escape = character.unicodeScalars.reduce(into: "") { $0 += "&#\($1.value);" }
position = positionAfterReplacingCharacter(at: cursorPosition, with: escape)
}
}
}
}
// MARK: - Unescaping
extension String {
///
/// Replaces every HTML entity in the receiver with the matching Unicode character.
///
/// ### Examples
///
/// | String | Result | Format |
/// |--------|--------|--------|
/// | `&` | `&` | Keyword entity |
/// | `Σ` | `Σ` | Decimal entity |
/// | `č` | `č` | Hexadecimal entity |
/// | `🇺🇸` | `🇺🇸` | Combined decimal entities (extented grapheme cluster) |
/// | `a` | `a` | Not an entity |
/// | `&` | `&` | Not an entity |
///
public mutating func removeHTMLEntities() {
var cursorPosition = startIndex
while let delimiterRange = range(of: "&", range: cursorPosition ..< endIndex) {
// Avoid unnecessary operations
guard let semicolonRange = range(of: ";", range: delimiterRange.upperBound ..< endIndex) else {
cursorPosition = delimiterRange.upperBound
break
}
let escapableRange = delimiterRange.upperBound ..< semicolonRange.lowerBound
let replaceableRange = delimiterRange.lowerBound ..< semicolonRange.upperBound
let escapableContent = self[escapableRange]
if let unescapedNumber = escapableContent.unescapeAsNumber() {
self.replaceSubrange(replaceableRange, with: unescapedNumber)
cursorPosition = self.index(delimiterRange.lowerBound, offsetBy: unescapedNumber.count)
} else if let unescapedCharacter = HTMLStringMappings.shared.unescapingTable[String(escapableContent)] {
self.replaceSubrange(replaceableRange, with: unescapedCharacter)
cursorPosition = self.index(delimiterRange.lowerBound, offsetBy: unescapedCharacter.count)
} else {
cursorPosition = semicolonRange.upperBound
}
}
}
///
/// Returns a copy of the current `String` where every HTML entity is replaced with the matching
/// Unicode character.
///
/// ### Examples
///
/// | String | Result | Format |
/// |--------|--------|--------|
/// | `&` | `&` | Keyword entity |
/// | `Σ` | `Σ` | Decimal entity |
/// | `č` | `č` | Hexadecimal entity |
/// | `🇺🇸` | `🇺🇸` | Combined decimal entities (extented grapheme cluster) |
/// | `a` | `a` | Not an entity |
/// | `&` | `&` | Not an entity |
///
public var removingHTMLEntities: String {
var copy = self
copy.removeHTMLEntities()
return copy
}
}
// MARK: - Helpers
extension StringProtocol {
/// Unescapes the receives as a number if possible.
fileprivate func unescapeAsNumber() -> String? {
guard hasPrefix("#") else { return nil }
let unescapableContent = self.dropFirst()
let isHexadecimal = unescapableContent.hasPrefix("x") || hasPrefix("X")
let radix = isHexadecimal ? 16 : 10
guard let numberStartIndex = unescapableContent.index(unescapableContent.startIndex, offsetBy: isHexadecimal ? 1 : 0, limitedBy: unescapableContent.endIndex) else {
return nil
}
let numberString = unescapableContent[numberStartIndex ..< endIndex]
guard let codePoint = UInt32(numberString, radix: radix), let scalar = UnicodeScalar(codePoint) else {
return nil
}
return String(scalar)
}
}
extension String {
/// Replaces the character at the given position with the escape and returns the new position.
fileprivate mutating func positionAfterReplacingCharacter(at position: String.Index, with escape: String) -> String.Index? {
let nextIndex = index(position, offsetBy: 1)
if let fittingPosition = index(position, offsetBy: escape.count, limitedBy: endIndex) {
// Check if we can fit the whole escape in the receiver
replaceSubrange(position ..< nextIndex, with: escape)
return fittingPosition
} else {
// If we can't, remove the character and insert the escape to make it fit.
remove(at: position)
insert(contentsOf: escape, at: position)
return index(position, offsetBy: escape.count, limitedBy: endIndex)
}
}
}