Quickie: URL Form Decoding

Here’s a little utility function I use to decode application/x-www-form-urlencoded strings on the iPhone:

- (NSDictionary*)extractArguments:(NSString*)raw
{
	NSArray* args = [raw componentsSeparatedByString:@"&"];
	
	NSMutableDictionary* rv = [NSMutableDictionary dictionaryWithCapacity:[args count]];
	for (NSString* sPair in args)
	{
		NSArray* aPair = [sPair componentsSeparatedByString:@"="];
		
		NSString* k = [aPair count]>0?[aPair objectAtIndex:0]:@"";
		NSString* v = [aPair count]>1?[aPair objectAtIndex:1]:@"";
		
		k = [[k stringByReplacingOccurrencesOfString:@"+" withString:@" "] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
		v = [[v stringByReplacingOccurrencesOfString:@"+" withString:@" "] stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
		
		if ([k length])
		{
			NSMutableArray* vs = [rv objectForKey:k];
			if (vs)
			{
				[vs addObject:v];
			}
			else
			{
				[rv setObject:[NSMutableArray arrayWithObject:v] forKey:k];
			}
		}
	}
	return rv;
}

The return value is an NSDictionary that maps NSString keys to NSArray values. The values are NSArrays because under form encoding more than one value may be associated with a key. The value NSArrays contain NSStrings.