Question

My C++ knowledge stinks. I have a code provided by Apple where they, as usually, provided an incomplete solution.

On this code they provide two empty methods headers:

- (NSString *)encodeBase64:(const uint8_t *)input length:(NSInteger)length
- (NSString *)decodeBase64:(NSString *)input length:(NSInteger *)length

These methods, in theory, should call two C++ style functions, but as my C++ knowledge stinks infinity squared plus one, please fill the ???

- (NSString *)encodeBase64:(const uint8_t *)input length:(NSInteger)length
{
   // I need to call base64_encode and return its results as string... is this correct?

   return [NSString stringWithUTF8String:
       base64_encode(input, ???)];
    // ??? I need to pass a NSInteger to a size_t... how do I do that?
}


- (NSString *)decodeBase64:(NSString *)input length:(NSInteger *)length
{

// ??? = this method receives a NSInteger *length variable. How do I pass that
// to a size_t * variable required by base64_decode?

    NSString *st = [[NSString alloc] initWithBytes:
                    base64_decode([input UTF8String], ???)
                                            length:&length
                                          encoding: NSUTF8StringEncoding];

    return st;
}

these 2 methods call these C++ functions

char* base64_encode(const void* buf, size_t size)
{
   // bla bla bla
}

void* base64_decode(const char* s, size_t* data_len_ptr)
{
    // bla bla bla
}

thanks.

Answer 1

First, if you want to do base64 encode/decode you will find it easier to start with a properly worked out example for how to do so. Matt Gallagher gives easy recipes for doing this in Base64 encoding options on the Mac and iPhone.

If you really want to flesh out your example, keep in mind that NSInteger is a long and size_t is an unsigned long. You could replace the lines in question with the following:

- (NSString *)encodeBase64:(const uint8_t *)input length:(NSInteger)length
{
    return [NSString stringWithUTF8String:base64_encode(input, (size_t)length)];
}

- (NSString *)decodeBase64:(NSString *)input length:(NSInteger *)length
{
    size_t retLen;
    uint8_t *retStr = base64_decode([input UTF8String], &retLen);
    if (length)
        *length = (NSInteger)retLen;
    NSString *st = [[[NSString alloc] initWithBytes:retStr
                                        length:retLen
                                      encoding:NSUTF8StringEncoding] autorelease];
    free(retStr);    // If base64_decode returns dynamically allocated memory
    return st;
}

(Remove the autorelease if you are compiling under ARC.)

Note that an arbitrary sequence of bytes is not guaranteed to be a valid UTF-8 string. This API allows you to send in arbitrary bytes but assumes it will decode to a valid UTF-8 string, which is not necessarily true.