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HTMLString.swift
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194 lines (146 loc) · 5.61 KB
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import Foundation
// MARK: Escaping
public extension String {
///
/// Returns a new string made from the `String` by replacing 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) |
///
/// **Complexity**: `O(N)` where `N` is the number of characters in the string.
///
public var addingUnicodeEntities: String {
return unicodeScalars.reduce("") { $0 + $1.escapingIfNeeded }
}
///
/// Returns a new string made from the `String` by replacing every character
/// incompatible with HTML ASCII encoding 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 `escapingForUnicodeHTML` instead
/// as it is faster, and produces less bloated and more readable HTML (as long as you are using
/// a unicode compliant HTML reader).
///
/// **Complexity**: `O(N)` where `N` is the number of characters in the string.
///
public var addingASCIIEntities: String {
return unicodeScalars.reduce("") { $0 + $1.escapingForASCII }
}
}
// MARK: - Unescaping
extension String {
///
/// Returns a new string made from the `String` by replacing every HTML entity
/// 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 |
///
/// **Complexity**: `O(N)` where `N` is the number of characters in the string.
///
public var removingHTMLEntities: String {
guard self.contains("&") else {
return self
}
var result = String()
var idx = startIndex
while let delimiterRange = range(of: "&", range: idx ..< endIndex) {
// Avoid unnecessary operations
let head = self[idx ..< delimiterRange.lowerBound]
result += head
guard let semicolonRange = range(of: ";", range: delimiterRange.upperBound ..< endIndex) else {
result += "&"
idx = delimiterRange.upperBound
break
}
let escapableContent = self[delimiterRange.upperBound ..< semicolonRange.lowerBound]
let replacementString: String
if escapableContent.hasPrefix("#") {
guard let unescapedNumber = escapableContent.unescapeAsNumber() else {
result += self[delimiterRange.lowerBound ..< semicolonRange.upperBound]
idx = semicolonRange.upperBound
continue
}
replacementString = unescapedNumber
} else {
guard let unescapedCharacter = HTMLTables.unescapingTable[escapableContent] else {
result += self[delimiterRange.lowerBound ..< semicolonRange.upperBound]
idx = semicolonRange.upperBound
continue
}
replacementString = unescapedCharacter
}
result += replacementString
idx = semicolonRange.upperBound
}
// Append unprocessed data, if unprocessed data there is
let tail = self[idx ..< endIndex]
result += tail
return result
}
private func unescapeAsNumber() -> String? {
let isHexadecimal = self.hasPrefix("#X") || self.hasPrefix("#x")
let numberStartIndexOffset = isHexadecimal ? 2 : 1
let numberString = self [ index(startIndex, offsetBy: numberStartIndexOffset) ..< endIndex ]
let radix = isHexadecimal ? 16 : 10
guard let codePoint = UInt32(numberString, radix: radix),
let scalar = UnicodeScalar(codePoint) else {
return nil
}
return String(scalar)
}
}
// MARK: - UnicodeScalar+Escape
extension UnicodeScalar {
///
/// Returns the decimal HTML entity of the Unicode scalar.
///
/// This allows you to perform custom escaping.
///
public var htmlEscaped: String {
return "&#" + String(value) + ";"
}
///
/// The scalar escaped for ASCII encoding.
///
fileprivate var escapingForASCII: String {
return isASCII ? escapingIfNeeded : htmlEscaped
}
///
/// Escapes the scalar only if it needs to be escaped for Unicode pages.
///
/// [Reference](http://wonko.com/post/html-escaping)
///
fileprivate var escapingIfNeeded: String {
switch value {
case 33, 34, 36, 37, 38, 39, 43, 44, 60, 61, 62, 64, 91, 93, 96, 123, 125: return htmlEscaped
default: return String(self)
}
}
}