A single "|" character in the URL breaks loading contents of URL - objective-c

Question

I'm trying to load an article in JSON format from the Wikipedia API and I get these errors:
nil host used in call to allowsSpecificHTTPSCertificateForHost
nil host used in call to allowsAnyHTTPSCertificateForHost:
NSURLConnection finished with error - code -1002
error when trying to fetch from URL (null) - The file couldn’t be opened.
I get these errors only when the URL string includes the character "|"
The URL for an article with id=1 (pageids=1) is:
https://en.wikipedia.org/w/api.php?action=query&format=json&pageids=1&prop=extracts&exintro&explaintext
The URL above doesn't contain the character "I" so it works just fine.
In the wikipedia API you can ask for multiple articles by seperating their ids with the "|" character
The URL for the articles with ids=1,2 and 3 (pageids=1|2|3) is:
https://en.wikipedia.org/w/api.php?action=query&format=json&pageids=1|2|3&prop=extracts&exintro&explaintext
The URL above contains the "|" character and everything fails.
I use this snippet I found in another post just to catch the errors:
NSError *error = NULL;
NSStringEncoding actualEncoding;
NSString *string = [[NSString alloc] initWithContentsOfURL:url usedEncoding:&actualEncoding error:&error];
if(string)
{
NSLog( #"hey, I actually got a result of %#", string);
if(actualEncoding != NSUTF8StringEncoding)
{
NSLog( #"and look at that, the actual encoding wasn't NSUTF8StringEncoding");
}
} else {
NSLog( #"error when trying to fetch from URL %# - %#", [url absoluteString], [error localizedDescription]);
}
If you go through the code, url.absoluteString returns null when there's a "|" character in it.

Answer 1

The pipe (|) is a special character. You have to encode the URL by adding appropriate percent encoding.
This has nothing to do with the text encoding of a string.
NSString * string = #"https://en.wikipedia.org/w/api.php?action=query&format=json&pageids=1|2|3&prop=extracts&exintro&explaintext";
NSURL *url = [NSURL URLWithString:[string stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]]];