gistfile1.m

- (NSString *)signatureBaseStringForMethod:(NSString *)aMethod
									   url:(NSURL *)aURL
								parameters:(NSDictionary *)aParameterDict {
	NSMutableDictionary *parameters = [aParameterDict mutableCopy];

	if ([aURL query]) {
		NSArray *parameterItems = [[aURL query] componentsSeparatedByString:@"&"];
		for(NSString *parameterItem in parameterItems) {
			NSMutableArray *parameterItemParts = (NSMutableArray *)[parameterItem componentsSeparatedByString:@"="];

			NSString *parameter = [[parameterItemParts objectAtIndex:0] retain];
			[parameterItemParts removeObjectAtIndex:0];

			NSString *value = [parameterItemParts componentsJoinedByString:@"="];

			[parameters setValue:value forKey:parameter]; // todo: urldecode?
		}
	}
	
	NSMutableArray *normalizedParameter = [[NSMutableArray alloc] init];
	NSArray *sortedKeys = [[parameters allKeys] sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)];
	for(NSString *key in sortedKeys) {
		[normalizedParameter addObject:[NSString stringWithFormat:@"%@=%@", key, [parameters valueForKey:key]]];
	}
	
	NSMutableString *normalizedUrl = [[NSMutableString alloc] initWithFormat:@"%@://%@", [aURL.scheme lowercaseString], [aURL.host lowercaseString]];
	if (aURL.port && (([aURL.scheme isEqual:@"https"] && aURL.port != [NSNumber numberWithInt:443]) || ([aURL.scheme isEqual:@"http"] && aURL.port != [NSNumber numberWithInt:80]))) {
		[normalizedUrl appendFormat:@":%d", aURL.port];
	}
	[normalizedUrl appendString:aURL.path];
	
	NSString *normalizedBaseString = [NSString stringWithFormat:@"%@&%@&%@", [aURL.scheme uppercaseString], normalizedUrl, [normalizedParameter componentsJoinedByString:@"&"]];

	[parameters release];
	[normalizedParameter release];
	[normalizedUrl release];
	
	return normalizedBaseString;
}