Added string extension method to decode html entities

Sources/OpenGraph/Extension/String.swift

@@ -26,4 +26,85 @@ extension String {
 
  self.init(data: data, encoding: encoding)
  }
+
+ //Retreived from: https://stackoverflow.com/a/30141700
+ /// Returns a new string made by replacing in the `String`
+ /// all HTML character entity references with the corresponding
+ /// character.
+ var stringByDecodingHTMLEntities : String {
+ // Mapping from XML/HTML character entity reference to character
+ // From http:https://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references
+ let characterEntities : [ Substring : Character ] = [
+ // XML predefined entities:
+ """ : "\"",
+ "&" : "&",
+ "'" : "'",
+ "&lt;" : "<",
+ "&gt;" : ">",
+
+ // HTML character entity references:
+ "&nbsp;" : "\u{00a0}",
+ // ...
+ "&diams;" : "♦",
+ ]
+
+ // ===== Utility functions =====
+
+ // Convert the number in the string to the corresponding
+ // Unicode character, e.g.
+ // decodeNumeric("64", 10) --> "@"
+ // decodeNumeric("20ac", 16) --> "€"
+ func decodeNumeric(_ string : Substring, base : Int) -> Character? {
+ guard let code = UInt32(string, radix: base),
+ let uniScalar = UnicodeScalar(code) else { return nil }
+ return Character(uniScalar)
+ }
+
+ // Decode the HTML character entity to the corresponding
+ // Unicode character, return `nil` for invalid input.
+ // decode("&#64;") --> "@"
+ // decode("&#x20ac;") --> "€"
+ // decode("&lt;") --> "<"
+ // decode("&foo;") --> nil
+ func decode(_ entity : Substring) -> Character? {
+
+ if entity.hasPrefix("&#x") || entity.hasPrefix("&#X") {
+ return decodeNumeric(entity.dropFirst(3).dropLast(), base: 16)
+ } else if entity.hasPrefix("&#") {
+ return decodeNumeric(entity.dropFirst(2).dropLast(), base: 10)
+ } else {
+ return characterEntities[entity]
+ }
+ }
+
+ // ===== Method starts here =====
+
+ var result = ""
+ var position = startIndex
+
+ // Find the next '&' and copy the characters preceding it to `result`:
+ while let ampRange = self[position...].range(of: "&") {
+ result.append(contentsOf: self[position ..< ampRange.lowerBound])
+ position = ampRange.lowerBound
+
+ // Find the next ';' and copy everything from '&' to ';' into `entity`
+ guard let semiRange = self[position...].range(of: ";") else {
+ // No matching ';'.
+ break
+ }
+ let entity = self[position ..< semiRange.upperBound]
+ position = semiRange.upperBound
+
+ if let decoded = decode(entity) {
+ // Replace by decoded character:
+ result.append(decoded)
+ } else {
+ // Invalid entity, copy verbatim:
+ result.append(contentsOf: entity)
+ }
+ }
+ // Copy remaining characters to `result`:
+ result.append(contentsOf: self[position...])
+ return result
+ }
 }