How to encode a URL in Swift [duplicate]

Question

Swift 4.2

var urlString = originalString.addingPercentEncoding(withAllowedCharacters: .urlQueryAllowed)

Swift 3.0

var address = "American Tourister, Abids Road, Bogulkunta, Hyderabad, Andhra Pradesh, India"
let escapedAddress = address.addingPercentEncoding(withAllowedCharacters: CharacterSet.urlQueryAllowed)
let urlpath = String(format: "http://maps.googleapis.com/maps/api/geocode/json?address=\(escapedAddress)")

Use stringByAddingPercentEncodingWithAllowedCharacters:

var escapedAddress = address.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLQueryAllowedCharacterSet())

---

Use stringByAddingPercentEscapesUsingEncoding: Deprecated in iOS 9 and OS X v10.11

var address = "American Tourister, Abids Road, Bogulkunta, Hyderabad, Andhra Pradesh, India"
var escapedAddress = address.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)
let urlpath = NSString(format: "http://maps.googleapis.com/maps/api/geocode/json?address=\(escapedAddress)")

If it's possible that the value that you're adding to your URL can have reserved characters (as defined by section 2 of RFC 3986), you might have to refine your percent-escaping. Notably, while & and + are valid characters in a URL, they're not valid within a URL query parameter value (because & is used as delimiter between query parameters which would prematurely terminate your value, and + is translated to a space character). Unfortunately, the standard percent-escaping leaves those delimiters unescaped.

Thus, you might want to percent escape all characters that are not within RFC 3986's list of unreserved characters:

Characters that are allowed in a URI but do not have a reserved purpose are called unreserved. These include uppercase and lowercase letters, decimal digits, hyphen, period, underscore, and tilde.

     unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"

Later, in section 3.4, the RFC further contemplates adding ? and / to the list of allowed characters within a query:

The characters slash ("/") and question mark ("?") may represent data within the query component. Beware that some older, erroneous implementations may not handle such data correctly when it is used as the base URI for relative references (Section 5.1), apparently because they fail to distinguish query data from path data when looking for hierarchical separators. However, as query components are often used to carry identifying information in the form of "key=value" pairs and one frequently used value is a reference to another URI, it is sometimes better for usability to avoid percent- encoding those characters.

Nowadays, you'd generally use URLComponents to percent escape the query value:

var address = "American Tourister, Abids Road, Bogulkunta, Hyderabad, Andhra Pradesh, India"
var components = URLComponents(string: "http://maps.googleapis.com/maps/api/geocode/json")!
components.queryItems = [URLQueryItem(name: "address", value: address)]
let url = components.url!

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By the way, while it's not contemplated in the aforementioned RFC, section 5.2, URL-encoded form data, of the W3C HTML spec says that application/x-www-form-urlencoded requests should also replace space characters with + characters (and includes the asterisk in the characters that should not be escaped). And, unfortunately, URLComponents won't properly percent escape this, so Apple advises that you manually percent escape it before retrieving the url property of the URLComponents object:

// configure `components` as shown above, and then:

components.percentEncodedQuery = components.percentEncodedQuery?.replacingOccurrences(of: "+", with: "%2B")
let url = components.url!

For Swift 2 rendition, where I manually do all of this percent escaping myself, see the previous revision of this answer.

Swift 3:

let escapedString = originalString.addingPercentEncoding(withAllowedCharacters:NSCharacterSet.urlQueryAllowed)

Swift 2.0

let needsLove = "string needin some URL love"
let safeURL = needsLove.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLQueryAllowedCharacterSet())!

Helpful Progamming Tips and Hacks

URLQueryAllowedCharacterSet should not be used for URL encoding of query parameters because this charset includes &, ?, / etc. which serve as delimiters in a URL query, e.g.

/?paramname=paramvalue&paramname=paramvalue

These characters are allowed in URL queries as a whole but not in parameter values.

RFC 3986 specifically talks about unreserved characters, which are different from allowed:

2.3. Unreserved Characters

Characters that are allowed in a URI but do not have a reserved
purpose are called unreserved. These include uppercase and lowercase letters, decimal digits, hyphen, period, underscore, and tilde.

  unreserved  = ALPHA / DIGIT / "-" / "." / "_" / "~"

Accordingly:

extension String {
    var URLEncoded:String {

        let unreservedChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~"
        let unreservedCharsSet: CharacterSet = CharacterSet(charactersIn: unreservedChars)
        let encodedString = self.addingPercentEncoding(withAllowedCharacters: unreservedCharsSet)!
        return encodedString
    }
}

The code above doesn't make a call to alphanumericCharacterSet because of the enormous size of the charset it returns (103806 characters). And in view of how many Unicode characters alphanumericCharacterSet allows for, using it for the purpose of URL encoding would be simply erroneous.

Usage:

let URLEncodedString = myString.URLEncoded