Percent escaping query url strings - ios

Question

I am getting NSString as given http://maps.apple.com/maps?saddr=41.447910,-74.357881&daddr=719 Old Route 9 North, Wappingers Falls, NY 12590
However i need to covert the above string into this one given for showing location in map
http://maps.apple.com/maps?saddr=41.447910,-74.357881&daddr=719+Old%20Route+9+North%2CWappingers+Falls%2CNY+12590
Please let me know.

Answer 1

You can do this with the following...
NSString *theOrigString = #"http://maps.apple.com/maps?saddr=41.447910,-74.357881&daddr=719 Old Route 9 North, Wappingers Falls, NY 12590";
NSString *formattedString = [theOrigString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
NSLog(#"%#", formattedString);
Output
http://maps.apple.com/maps?saddr=41.447910,-74.357881&daddr=719%20Old%20Route%2‌​09%20North,%20Wappingers%20Falls,%20NY%2012590
This will replace spaces with %20 and so on.
You can then use this as a url string.

Answer 2

An old question but this is what you need:
-(NSString*) encodeToPercentEscapeString:(NSString *)string {
return (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL,
(CFStringRef) string,
NULL,
(CFStringRef) #"!*'();:#&=+$,/?%#[]",
kCFStringEncodingUTF8)); }
-(NSString*) decodeFromPercentEscapeString:(NSString *)string {
return (NSString *)CFBridgingRelease(CFURLCreateStringByReplacingPercentEscapesUsingEncoding(NULL,
(CFStringRef) string,
CFSTR(""),
kCFStringEncodingUTF8)); }

Answer 3

Take a look at NSString's stringByAddingPercentEscapesUsingEncoding:
NSString *urlString = #"http://maps.apple.com/maps?saddr=41.447910,-74.357881&daddr=719 Old Route 9 North, Wappingers Falls, NY 12590";
NSString *encodedString = [urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]

Answer 4

The reason behind the percent encoding simply comes down from the RFC 3986. In a nutshell, you should percent escape values of your URI query params to escape the reserved characters ("!*'();:#&=+$,/?%#[]"). Doing so it is possible to properly decoding the encoded URI - supposing for the sake of simplicity same encoding on the both sides.
As pointed out by Duncan and Fogmeister, Apple's stringByAddingPercentEscapesUsingEncoding is very friendly but, in general, wrong - or, at least, say, not compliant with RFC 3986 - since doesn't percent escape chars like "/:&%?".
A more general and robust solution would be something like
NSString * HKObjectToString(id object) {
return [NSString stringWithFormat:#"%#", object];
}
NSString * HKPercentEscapedString(id object, CFStringEncoding encoding) {
NSString *string = HKObjectToString(object);
return ((NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL, (__bridge CFStringRef) string, NULL,
CFSTR("!*'();:#&=+$,/?%#[]"),
encoding)));
}
...
#implementation NSDictionary (URLAdditions)
...
- (NSString *)percentEscapedQueryStringWithEncoding:(CFStringEncoding)encoding
{
NSMutableArray *queryParts = [[NSMutableArray alloc] init];
for (NSString *key in [self allKeys]) {
NSString *part = [NSString stringWithFormat:#"%#=%#", HKPercentEscapedString(key, encoding), HKPercentEscapedString(HKObjectToString(self[key]), encoding)];
[queryParts addObject:part];
}
return [queryParts componentsJoinedByString:#"&"];
}
...
#end
...
#implementation NSString (StringHelper)
...
+ (NSString *)URIEncodedWithStringURI:(NSString *)baseURI queryParameters:(NSDictionary *)queryParams URIEncoding:(CFStringEncoding)encoding
{
return [NSString stringWithFormat:#"%#?%#", baseURI, [queryParams percentEscapedQueryStringWithEncoding:encoding]];
}
...
#end
For more details try to give a look at this public repo on github.

Answer 5

This question is problematic because the input data is damaged. At some earlier point in the code, this URL got decoded as a single string. You should never do that, because it can lead to situations where the distinction between different parts of the URL is lost and can never be recovered. For example, suppose I have this URL:
http://www.example.com/folder/this%2Fthat.html
When decoded, this becomes
http://www.example.com/folder/this/that.html
and there's no way to turn that back into the original, because there's no way to know which of those slashes is real and which should be encoded as %2F. The distinction is simply lost.
For this reason, when you work with URLs, it is important to always preserve them in their original form whenever possible, and when you have to decode a URL, to do so piecewise—that is, to start by splitting apart all of the path components, the query string, and so on, then pulling apart the fields in the query string (where applicable), and finally decoding each part individually.
After that, you would need to reencode each part by using CFURLCreateStringByReplacingPercentEscapesUsingEncoding, because the NSString method above doesn't do percent encoding of slashes, ampersands, and other special URL characters.
But in your case, your best bet is to find the code that is decoding the URL, and rip it out so that you have the original, undamaged URL. If and only if that is not possible, the stringByAddingPercentEscapesUsingEncoding: method can make a "best guess" about what to encode, so long as you understand that for arbitrary URLs, that solution won't necessarily work.

Answer 6

Edited:
Sulthan has a point. You can't percent encode the whole URL if the string portion (like the address in this case) might contain reserved URL characters ("/", ":", "&", "%", "?", etc.)
The stringByAddingPercentEscapesUsingEncoding method encodes spaces, but not slashes, colons, etc. Thus if the address string contains any of those, the receiver of the URL can't tell what's part of the syntax of the URL and what's data.
I have a category of NSString that escapes these characters as well:
The header
#import <Foundation/Foundation.h>
#interface NSString (URLEncoding)
- (NSString *)stringByAddingPercentEscapes;
- (NSString *)stringByReplacingPercentEscapes;
#end
NSString *mapURLStringTemplate =
#"http://maps.apple.com/maps?saddr=%f,%f&daddr=%#";
The body:
#import "StringCategory.h"
CFStringRef charsToEscape = CFSTR(":/&=");
#implementation NSString (URLEncoding)
- (NSString *)stringByAddingPercentEscapes
{
return (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL,
(CFStringRef)self, NULL, charsToEscape,
CFStringConvertNSStringEncodingToEncoding(NSUTF8StringEncoding)));
}
- (NSString *)stringByReplacingPercentEscapes
{
return (NSString *)CFBridgingRelease(CFURLCreateStringByReplacingPercentEscapes(kCFAllocatorDefault,(CFStringRef)self, CFSTR("")));
}
#end
And to use it:
NSString *escapedAddressString =
[addressString stringByAddingPercentEscapes];
NSString *mapURLString =
[NSString stringWithFormat: mapURLStringTemplate,
latitude,
longitude,
escapedAddressString];