Convert characters to HTML Entities in Cocoa - cocoa

Question

I am currently trying to put together an URL where I specify some GET parameters. But I want to use japanese or other characters too in this URL.
Is there a way to convert a NSString to a string containing the HTML entities for the 'special' characters in my NSString?
I am currently using the following code, which seems to work, except for 'special characters' like chinese and japanese:
NSString* url = #"/translate_a/t?client=t&sl=auto&tl=";
url = [url stringByAppendingString:destinationLanguage];
url = [url stringByAppendingString:#"&text="];
url = [url stringByAppendingString:text];
NSURL* nsurl = [[NSURL alloc] initWithScheme:#"http" host:#"translate.google.com" path:url];
NSError* error;
NSString* returnValue = [[NSString alloc] initWithContentsOfURL:nsurl encoding:NSUTF8StringEncoding error:&error];

Answer 1

To properly URL encode your parameters, you need to convert each name and value to UTF-8, then URL encode each name and value separately, then join names with values using '=' and name-value pairs using '&'.
I generally find it easier to put all the parameters in an NSDictionary, then build the query string from the dictionary. Here's a category that I use for doing that:
// file NSDictionary+UrlEncoding.h
#import <Cocoa/Cocoa.h>
#interface NSDictionary (UrlEncoding)
-(NSString*) urlEncodedString;
#end
// file NSDictionary+UrlEncoding.m
#import "NSDictionary+UrlEncoding.h"
// private helper function to convert any object to its string representation
static NSString *toString(id object) {
return [NSString stringWithFormat: #"%#", object];
}
// private helper function to convert string to UTF-8 and URL encode it
static NSString *urlEncode(id object) {
NSString *string = toString(object);
return [string stringByAddingPercentEscapesUsingEncoding: NSUTF8StringEncoding];
}
#implementation NSDictionary (UrlEncoding)
-(NSString*) urlEncodedString {
NSMutableArray *parts = [NSMutableArray array];
for (id key in self) {
id value = [self objectForKey: key];
NSString *part = [NSString stringWithFormat: #"%#=%#",
urlEncode(key), urlEncode(value)];
[parts addObject: part];
}
return [parts componentsJoinedByString: #"&"];
}
#end
The method build an array of name-value pairs called parts by URL encoding each key and value, then joining them together with '='. Then the parts in the parts array are joined together with '&' characters.
So for your example:
#import "NSDictionary+UrlEncoding.h"
// ...
NSMutableDictionary *parameters = [NSMutableDictionary dictionary];
[parameters setValue: #"t" forKey: #"client"];
[parameters setValue: #"auto" forKey: #"sl"];
[parameters setValue: destinationLanguage forKey: #"tl"];
[parameters setValue: text forKey: #"text"];
NSString *urlString = [#"/translate_a/t?" stringByAppendingString: [parameters urlEncodedString]];

Answer 2

NSString has a method -stringByAddingPercentEscapesUsingEncoding:

Answer 3

Here's NSString extension you can find over internet
http://code.google.com/p/wimframework/source/browse/trunk/WimFramework/Classes/Helpers/WimAdditions.m
The decode part has some error in mapping array index to actual entity number. But since you only need encoding, it's fine to use it.

Answer 4

For simple URL encoding of strings, many of the solutions I have seen, while technically correct, look a lot less easy to use than I would like. So I came up with the following NSString category:
#interface NSString (MLExtensions)
- (NSString *)urlencode;
#end
NSString *_mlfilterChars = #";/?:#&=+$,";
#implementation NSString (MLExtensions)
- (NSString *)urlencode
{
return [[NSString stringWithString: (NSString *)
CFURLCreateStringByAddingPercentEscapes(
NULL,
(CFStringRef)self,
NULL,
(CFStringRef)_mlfilterChars,
kCFStringEncodingUTF8)]
stringByReplacingOccurrencesOfString: #"%20" withString: #"+"];
}
#end
I'm kind of in a hurry with some other stuff I'm working on, so I kind of cheated with the %20 => + conversion step, but it all seems to work great and I've been using it for a while now with a good number of URLs in my app.
Usage is blessfully easy:
- (NSString *)URLForSearch: (NSString *)searchFor
{
return [#"http://example.org/search?query="
stringByAppendingString: [searchFor urlencode]];
}