URL Loading System Programming Guide - Apple Developer

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Encoding URL Data To URL-encode strings, use the Core Foundation functions CFURLCreateStringByAddingPercentEscapes and CFURLCreateStringByReplacingPercentEscapesUsingEncoding. These functions allow you to specify a list of characters to encode in addition to high-ASCII (0x80–0xff) and nonprintable characters. According to RFC 3986, the reserved characters in a URL are: reserved = gen-delims / sub-delims gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@" sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "=" Therefore, to properly URL-encode a UTF-8 string for inclusion in a URL, you should do the following: CFStringRef originalString = ... CFStringRef encodedString = CFURLCreateStringByAddingPercentEscapes( kCFAllocatorDefault, originalString, NULL, CFSTR(":/?#[]@!$&'()*+,;="), kCFStringEncodingUTF8); If you want to decode a URL fragment, you must first split the URL string into its constituent parts (fields and path parts). If you do not decode it, you will be unable to tell the difference (for example) between an encoded ampersand that was originally part of the contents of a field and a bare ampersand that indicated the end of the field. After you have broken the URL into parts, you can decode each part as follows: 2013-10-22 | Copyright © 2003, 2013 Apple Inc. All Rights Reserved. 48
Encoding URL Data CFStringRef decodedString = CFURLCreateStringByReplacingPercentEscapesUsingEncoding( kCFAllocatorDefault, encodedString, CFSTR(""), kCFStringEncodingUTF8); Important: Although the NSString class provides built-in methods for adding percent escapes, you usually should not use them. These methods assume you are passing them a string containing a series of ampersand-separated values, and as a result, you cannot use them to properly URL-encode any string that contains an ampersand. If you try to use them for something that does, your code could be vulnerable to a URL string injection attack (security hole), depending on how the software at the other end handles the malformed URL. 2013-10-22 | Copyright © 2003, 2013 Apple Inc. All Rights Reserved. 49
Page 1 and 2: URL Loading System Programming Guid
Page 3 and 4: Contents Making a POST Request 36 R
Page 5 and 6: Listings Understanding Cache Access
Page 7 and 8: About the URL Loading System At a G
Page 13 and 14: About the URL Loading System How to
Page 15 and 16: Using NSURLSession The NSURLSession
Page 17 and 18: Using NSURLSession Understanding UR
Page 19 and 20: Using NSURLSession Creating and Con
Page 21 and 22: Using NSURLSession Creating and Con
Page 23 and 24: Using NSURLSession Fetching Data Us
Page 25 and 26: Using NSURLSession Downloading File
Page 27 and 28: Using NSURLSession Uploading Body C
Page 29 and 30: Using NSURLSession Handling iOS Bac
Page 31 and 32: Using NSURLSession Handling iOS Bac
Page 33 and 34: Using NSURLConnection Creating a Co
Page 35 and 36: Using NSURLConnection Creating a Co
Page 37 and 38: Using NSURLConnection Making a POST
Page 39 and 40: Using NSURLConnection Retrieving Da
Page 41 and 42: Using NSURLDownload Downloading to
Page 43 and 44: Using NSURLDownload Downloading a F
Page 45 and 46: Using NSURLDownload Displaying Down
Page 47: Using NSURLDownload Decoding Encode
Page 51 and 52: Handling Redirects and Other Reques
Page 53 and 54: Authentication Challenges and TLS C
Page 59 and 60: Understanding Cache Access Cache Us
Page 61 and 62: Understanding Cache Access Controll
Page 63 and 64: Cookies and Custom Protocols Protoc
Page 65 and 66: Life Cycle of a URL Session Life Cy
Page 71 and 72: Document Revision History Date 2003

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