How do I decode HTML entities in Swift?
I am pulling a JSON file from a site and one of the strings received is:
The Weeknd ‘King Of The Fall’ [Video Premiere] | @TheWeeknd | #SoPhi
How can I convert things like ‘ into the correct characters?
I've made a Xcode Playground to demonstrate it:
import UIKit
var error: NSError?
let blogUrl: NSURL = NSURL.URLWithString("http://sophisticatedignorance.net/api/get_recent_summary/")
let jsonData = NSData(contentsOfURL: blogUrl)
let dataDictionary = NSJSONSerialization.JSONObjectWithData(jsonData, options: nil, error: &error) as NSDictionary
var a = dataDictionary["posts"] as NSArray
println(a[0]["title"])
This answer was last revised for Swift 5.2 and iOS 13.4 SDK.
There's no straightforward way to do that, but you can use NSAttributedString magic to make this process as painless as possible (be warned that this method will strip all HTML tags as well).
Remember to initialize NSAttributedString from main thread only. It uses WebKit to parse HTML underneath, thus the requirement.
// This is a[0]["title"] in your case
let htmlEncodedString = "The Weeknd <em>‘King Of The Fall’</em>"
guard let data = htmlEncodedString.data(using: .utf8) else {
return
}
let options: [NSAttributedString.DocumentReadingOptionKey: Any] = [
.documentType: NSAttributedString.DocumentType.html,
.characterEncoding: String.Encoding.utf8.rawValue
]
guard let attributedString = try? NSAttributedString(data: data, options: options, documentAttributes: nil) else {
return
}
// The Weeknd ‘King Of The Fall’
let decodedString = attributedString.string
extension String {
init?(htmlEncodedString: String) {
guard let data = htmlEncodedString.data(using: .utf8) else {
return nil
}
let options: [NSAttributedString.DocumentReadingOptionKey: Any] = [
.documentType: NSAttributedString.DocumentType.html,
.characterEncoding: String.Encoding.utf8.rawValue
]
guard let attributedString = try? NSAttributedString(data: data, options: options, documentAttributes: nil) else {
return nil
}
self.init(attributedString.string)
}
}
let encodedString = "The Weeknd <em>‘King Of The Fall’</em>"
let decodedString = String(htmlEncodedString: encodedString)
@akashivskyy's answer is great and demonstrates how to utilize NSAttributedString to decode HTML entities. One possible disadvantage
(as he stated) is that all HTML markup is removed as well, so
<strong> 4 < 5 & 3 > 2</strong>
becomes
4 < 5 & 3 > 2
On OS X there is CFXMLCreateStringByUnescapingEntities() which does the job:
let encoded = "<strong> 4 < 5 & 3 > 2 .</strong> Price: 12 €. @ "
let decoded = CFXMLCreateStringByUnescapingEntities(nil, encoded, nil) as String
println(decoded)
// <strong> 4 < 5 & 3 > 2 .</strong> Price: 12 €. @
but this is not available on iOS.
Here is a pure Swift implementation. It decodes character entities
references like < using a dictionary, and all numeric character
entities like @ or €. (Note that I did not list all
252 HTML entities explicitly.)
Swift 4:
// Mapping from XML/HTML character entity reference to character
// From http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references
private let characterEntities : [ Substring : Character ] = [
// XML predefined entities:
""" : "\"",
"&" : "&",
"'" : "'",
"<" : "<",
">" : ">",
// HTML character entity references:
" " : "\u{00a0}",
// ...
"♦" : "♦",
]
extension String {
/// Returns a new string made by replacing in the `String`
/// all HTML character entity references with the corresponding
/// character.
var stringByDecodingHTMLEntities : String {
// ===== 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("@") --> "@"
// decode("€") --> "€"
// decode("<") --> "<"
// 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
}
}
Example:
let encoded = "<strong> 4 < 5 & 3 > 2 .</strong> Price: 12 €. @ "
let decoded = encoded.stringByDecodingHTMLEntities
print(decoded)
// <strong> 4 < 5 & 3 > 2 .</strong> Price: 12 €. @
Swift 3:
// Mapping from XML/HTML character entity reference to character
// From http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references
private let characterEntities : [ String : Character ] = [
// XML predefined entities:
""" : "\"",
"&" : "&",
"'" : "'",
"<" : "<",
">" : ">",
// HTML character entity references:
" " : "\u{00a0}",
// ...
"♦" : "♦",
]
extension String {
/// Returns a new string made by replacing in the `String`
/// all HTML character entity references with the corresponding
/// character.
var stringByDecodingHTMLEntities : String {
// ===== Utility functions =====
// Convert the number in the string to the corresponding
// Unicode character, e.g.
// decodeNumeric("64", 10) --> "@"
// decodeNumeric("20ac", 16) --> "€"
func decodeNumeric(_ string : String, 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("@") --> "@"
// decode("€") --> "€"
// decode("<") --> "<"
// decode("&foo;") --> nil
func decode(_ entity : String) -> Character? {
if entity.hasPrefix("&#x") || entity.hasPrefix("&#X"){
return decodeNumeric(entity.substring(with: entity.index(entity.startIndex, offsetBy: 3) ..< entity.index(entity.endIndex, offsetBy: -1)), base: 16)
} else if entity.hasPrefix("&#") {
return decodeNumeric(entity.substring(with: entity.index(entity.startIndex, offsetBy: 2) ..< entity.index(entity.endIndex, offsetBy: -1)), 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.range(of: "&", range: position ..< endIndex) {
result.append(self[position ..< ampRange.lowerBound])
position = ampRange.lowerBound
// Find the next ';' and copy everything from '&' to ';' into `entity`
if let semiRange = self.range(of: ";", range: position ..< endIndex) {
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(entity)
}
} else {
// No matching ';'.
break
}
}
// Copy remaining characters to `result`:
result.append(self[position ..< endIndex])
return result
}
}
Swift 2:
// Mapping from XML/HTML character entity reference to character
// From http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references
private let characterEntities : [ String : Character ] = [
// XML predefined entities:
""" : "\"",
"&" : "&",
"'" : "'",
"<" : "<",
">" : ">",
// HTML character entity references:
" " : "\u{00a0}",
// ...
"♦" : "♦",
]
extension String {
/// Returns a new string made by replacing in the `String`
/// all HTML character entity references with the corresponding
/// character.
var stringByDecodingHTMLEntities : String {
// ===== Utility functions =====
// Convert the number in the string to the corresponding
// Unicode character, e.g.
// decodeNumeric("64", 10) --> "@"
// decodeNumeric("20ac", 16) --> "€"
func decodeNumeric(string : String, base : Int32) -> Character? {
let code = UInt32(strtoul(string, nil, base))
return Character(UnicodeScalar(code))
}
// Decode the HTML character entity to the corresponding
// Unicode character, return `nil` for invalid input.
// decode("@") --> "@"
// decode("€") --> "€"
// decode("<") --> "<"
// decode("&foo;") --> nil
func decode(entity : String) -> Character? {
if entity.hasPrefix("&#x") || entity.hasPrefix("&#X"){
return decodeNumeric(entity.substringFromIndex(entity.startIndex.advancedBy(3)), base: 16)
} else if entity.hasPrefix("&#") {
return decodeNumeric(entity.substringFromIndex(entity.startIndex.advancedBy(2)), 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.rangeOfString("&", range: position ..< endIndex) {
result.appendContentsOf(self[position ..< ampRange.startIndex])
position = ampRange.startIndex
// Find the next ';' and copy everything from '&' to ';' into `entity`
if let semiRange = self.rangeOfString(";", range: position ..< endIndex) {
let entity = self[position ..< semiRange.endIndex]
position = semiRange.endIndex
if let decoded = decode(entity) {
// Replace by decoded character:
result.append(decoded)
} else {
// Invalid entity, copy verbatim:
result.appendContentsOf(entity)
}
} else {
// No matching ';'.
break
}
}
// Copy remaining characters to `result`:
result.appendContentsOf(self[position ..< endIndex])
return result
}
}
Swift 4
- String extension computed variable
- Without extra guard, do, catch, etc...
- Returns the original strings if decoding fails
extension String {
var htmlDecoded: String {
let decoded = try? NSAttributedString(data: Data(utf8), options: [
.documentType: NSAttributedString.DocumentType.html,
.characterEncoding: String.Encoding.utf8.rawValue
], documentAttributes: nil).string
return decoded ?? self
}
}
Swift 3 version of @akashivskyy's extension,
extension String {
init(htmlEncodedString: String) {
self.init()
guard let encodedData = htmlEncodedString.data(using: .utf8) else {
self = htmlEncodedString
return
}
let attributedOptions: [String : Any] = [
NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType,
NSCharacterEncodingDocumentAttribute: String.Encoding.utf8.rawValue
]
do {
let attributedString = try NSAttributedString(data: encodedData, options: attributedOptions, documentAttributes: nil)
self = attributedString.string
} catch {
print("Error: \(error)")
self = htmlEncodedString
}
}
}