How to encode + into %2B with NSURLComponents

Question

I'm using NSURLComponents and I can't seem to get the query values to encode correctly. I need the final URL to represent a + as %2B.

let baseUrl = NSURL(string: "http://www.example.com")    
let components = NSURLComponents(URL: baseUrl, resolvingAgainstBaseURL: true)
components.queryItems = [ NSURLQueryItem(name: "name", value: "abc+def") ]
XCTAssertEqual(components!.string!, "http://www.example.com?connectionToken=abc%2Bdef")

Failed!

Output equals:

http://www.example.com?connectionToken=abc+def 

NOT

http://www.example.com?connectionToken=abc%2Bdef

I've tried several variations and I just can't seem to get it to output %2B at all.

Answer 1

My answer from Radar 24076063 with an explanation of why it works the way it does (with a little cleanup of the text):

The '+' character is legal in the query component so it does not need to be percent-encoded.

Some systems use the '+' as a space and require '+' the plus character to be percent-encoded. However, that kind of two stage encoding (converting plus sign to %2B and then converting space to plus sign) is prone to errors because it easily leads to encoding problems. It also breaks if the URL is normalized (syntax normalization of URLs includes the removal of all unnecessary percent-encoding — see rfc3986 section 6.2.2.2).

So, if you need that behavior because of the server your code is talking to, you'll handle the extra transformation(s) yourself. Here's a snippet of code that shows what you need to do both ways:

NSURLComponents *components = [[NSURLComponents alloc] init];
NSArray *items = [NSArray arrayWithObjects:[NSURLQueryItem queryItemWithName:@"name" value:@"Value +"], nil];
components.queryItems = items;
NSLog(@"URL queryItems: %@", [components queryItems]);
NSLog(@"URL string before: %@", [components string]);

// Replace all "+" in the percentEncodedQuery with "%2B" (a percent-encoded +) and then replace all "%20" (a percent-encoded space) with "+"
components.percentEncodedQuery = [[components.percentEncodedQuery stringByReplacingOccurrencesOfString:@"+" withString:@"%2B"] stringByReplacingOccurrencesOfString:@"%20" withString:@"+"];
NSLog(@"URL string after: %@", [components string]);

// This is the reverse if you receive a URL with a query in that form and want to parse it with queryItems
components.percentEncodedQuery = [[components.percentEncodedQuery stringByReplacingOccurrencesOfString:@"+" withString:@"%20"] stringByReplacingOccurrencesOfString:@"%2B" withString:@"+"];
NSLog(@"URL string back: %@", [components string]);
NSLog(@"URL queryItems: %@", [components queryItems]);

The output is:

URL queryItems: (
    "<NSURLQueryItem 0x100502460> {name = name, value = Value +}"
)

URL string before: ?name=Value%20+

URL string after: ?name=Value+%2B

URL string back: ?name=Value%20+

URL queryItems: (
    "<NSURLQueryItem 0x1002073e0> {name = name, value = Value +}"
)

Answer 2

As the other answers mention, "+" isn't encoded on iOS by default. But if your server requires that to be encoded, here's how to do it:

var comps = URLComponents(url: self, resolvingAgainstBaseURL: true)
// a local var is needed to fix a swift warning about "overlapping accesses" caused by writing to the same property that's being read.
var compsCopy = comps
compsCopy?.queryItems = [URLQueryItem(name: "name", value: "abc+def")]
comps?.percentEncodedQuery = compsCopy?.percentEncodedQuery?.replacingOccurrences(of: "+", with: "%2B")