iPhone - finalizing Apple's vague "VerificationController.m" - iphone

Question

I am trying to implement the new VerificationController.m class that Apple released to fix the in-app purchase fraud problem.
As everything released by Apple, this is one more vague, incomplete and bad explained document with a lot of voids and unknowns that cannot be circumvented/understood by everyone.
I am trying to implement that, but at the end of the code we see these four methods:
- (NSString *)encodeBase64:(const uint8_t *)input length:(NSInteger)length
{
#warning Replace this method.
return nil;
}
- (NSString *)decodeBase64:(NSString *)input length:(NSInteger *)length
{
#warning Replace this method.
return nil;
}
#warning Implement this function.
char* base64_encode(const void* buf, size_t size)
{ return NULL; }
#warning Implement this function.
void * base64_decode(const char* s, size_t * data_len)
{ return NULL; }
You can see that Apple was lazy to implement the C functions at the end of the code. As my C/C++ abilities stink, I see I need to implement these two functions in C/C++ and that they must return char and void (???). Other people have posted routines to do that on SO, but they are either in Objective-C or not returning chars and void (??).
NOTE: this is another problem I have: how can a method return void if it is used by Apple in this form?
uint8_t *purchase_info_bytes = base64_decode([purchase_info_string cStringUsingEncoding:NSASCIIStringEncoding], &purchase_info_length);
shouldn't it be returning uint8_t?
NOTE2: another problem I have is that apple says base64_encode is required but it is not being used on the code provided by them. I think they are smoking bad stuff or my C/C++ knowledge really stink.
So, returning to my first question. Can someone post/point a method that can do the job that follows the requirements of the declared methods base64_encode and base64_decode? Please refrain from posting objective-c methods that are not compatible with these requirements imposed by Apple.
Thanks.

Answer 1

This solution should be pretty straight forward, which includes all the methods to populate the missing information. Tested and functional within the sandbox.
// single base64 character conversion
static int POS(char c)
{
if (c>='A' && c<='Z') return c - 'A';
if (c>='a' && c<='z') return c - 'a' + 26;
if (c>='0' && c<='9') return c - '0' + 52;
if (c == '+') return 62;
if (c == '/') return 63;
if (c == '=') return -1;
[NSException raise:#"invalid BASE64 encoding" format:#"Invalid BASE64 encoding"];
return 0;
}
- (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;
}
char* base64_encode(const void* buf, size_t size)
{
static const char base64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
char* str = (char*) malloc((size+3)*4/3 + 1);
char* p = str;
unsigned char* q = (unsigned char*) buf;
size_t i = 0;
while(i < size) {
int c = q[i++];
c *= 256;
if (i < size) c += q[i];
i++;
c *= 256;
if (i < size) c += q[i];
i++;
*p++ = base64[(c & 0x00fc0000) >> 18];
*p++ = base64[(c & 0x0003f000) >> 12];
if (i > size + 1)
*p++ = '=';
else
*p++ = base64[(c & 0x00000fc0) >> 6];
if (i > size)
*p++ = '=';
else
*p++ = base64[c & 0x0000003f];
}
*p = 0;
return str;
}
void* base64_decode(const char* s, size_t* data_len_ptr)
{
size_t len = strlen(s);
if (len % 4)
[NSException raise:#"Invalid input in base64_decode" format:#"%d is an invalid length for an input string for BASE64 decoding", len];
unsigned char* data = (unsigned char*) malloc(len/4*3);
int n[4];
unsigned char* q = (unsigned char*) data;
for(const char*p=s; *p; )
{
n[0] = POS(*p++);
n[1] = POS(*p++);
n[2] = POS(*p++);
n[3] = POS(*p++);
if (n[0]==-1 || n[1]==-1)
[NSException raise:#"Invalid input in base64_decode" format:#"Invalid BASE64 encoding"];
if (n[2]==-1 && n[3]!=-1)
[NSException raise:#"Invalid input in base64_decode" format:#"Invalid BASE64 encoding"];
q[0] = (n[0] << 2) + (n[1] >> 4);
if (n[2] != -1) q[1] = ((n[1] & 15) << 4) + (n[2] >> 2);
if (n[3] != -1) q[2] = ((n[2] & 3) << 6) + n[3];
q += 3;
}
// make sure that data_len_ptr is not null
if (!data_len_ptr)
[NSException raise:#"Invalid input in base64_decode" format:#"Invalid destination for output string length"];
*data_len_ptr = q-data - (n[2]==-1) - (n[3]==-1);
return data;
}

Answer 2

Here is a base 64 encode function for NSString to NSString:
+(NSString *) encodeString:(NSString *)inString
{
NSData *data = [inString dataUsingEncoding:NSUTF8StringEncoding];
//Point to start of the data and set buffer sizes
int inLength = [data length];
int outLength = ((((inLength * 4)/3)/4)*4) + (((inLength * 4)/3)%4 ? 4 : 0);
const char *inputBuffer = [data bytes];
char *outputBuffer = malloc(outLength);
outputBuffer[outLength] = 0;
//64 digit code
static char Encode[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
//start the count
int cycle = 0;
int inpos = 0;
int outpos = 0;
char temp;
outputBuffer[outLength-1] = '=';
outputBuffer[outLength-2] = '=';
while (inpos < inLength){
switch (cycle) {
case 0:
outputBuffer[outpos++] = Encode[(inputBuffer[inpos]&0xFC)>>2];
cycle = 1;
break;
case 1:
temp = (inputBuffer[inpos++]&0x03)<<4;
outputBuffer[outpos] = Encode[temp];
cycle = 2;
break;
case 2:
outputBuffer[outpos++] = Encode[temp|(inputBuffer[inpos]&0xF0)>> 4];
temp = (inputBuffer[inpos++]&0x0F)<<2;
outputBuffer[outpos] = Encode[temp];
cycle = 3;
break;
case 3:
outputBuffer[outpos++] = Encode[temp|(inputBuffer[inpos]&0xC0)>>6];
cycle = 4;
break;
case 4:
outputBuffer[outpos++] = Encode[inputBuffer[inpos++]&0x3f];
cycle = 0;
break;
default:
cycle = 0;
break;
}
}
NSString *pictemp = [NSString stringWithUTF8String:outputBuffer];
free(outputBuffer);
return pictemp;
}
and Here is a base 64 decode function for NSString to NSString:
+(NSString *) decodeString:(NSString *)inString
{
const char* string = [inString cStringUsingEncoding:NSASCIIStringEncoding];
NSInteger inputLength = inString.length;
static char decodingTable[128];
static char encodingTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
for (NSInteger i = 0; i < 128; i++) {
decodingTable[encodingTable[i]] = i;
}
if ((string == NULL) || (inputLength % 4 != 0)) {
return nil;
}
while (inputLength > 0 && string[inputLength - 1] == '=') {
inputLength--;
}
NSInteger outputLength = inputLength * 3 / 4;
NSMutableData* data = [NSMutableData dataWithLength:outputLength];
uint8_t* output = data.mutableBytes;
NSInteger inputPoint = 0;
NSInteger outputPoint = 0;
while (inputPoint < inputLength) {
char i0 = string[inputPoint++];
char i1 = string[inputPoint++];
char i2 = inputPoint < inputLength ? string[inputPoint++] : 'A'; /* 'A' will decode to \0 */
char i3 = inputPoint < inputLength ? string[inputPoint++] : 'A';
output[outputPoint++] = (decodingTable[i0] << 2) | (decodingTable[i1] >> 4);
if (outputPoint < outputLength) {
output[outputPoint++] = ((decodingTable[i1] & 0xf) << 4) | (decodingTable[i2] >> 2);
}
if (outputPoint < outputLength) {
output[outputPoint++] = ((decodingTable[i2] & 0x3) << 6) | decodingTable[i3];
}
}
NSLog(#"%#",data);
NSString *finalString = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
return finalString;
}
These were pieced together from examples I found in various places on the internet when I was searching for them a while ago. They, may be easier for you to implement. I just created a Base64 class and placed these methods in it.

Answer 3

Here are the C wrappers around Justin's answer:
char* base64_encode(const void* buf, size_t size)
{
NSData* data = [NSData dataWithBytesNoCopy:(void*)buf length:size];
NSString* string = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];
return [[_Class_ encode:string] UTF8String];
}
void* base64_Decode (const char* s, size_t* data_len)
{
NSString* result = [_Class_ decode:[NSString stringWithCString:s encoding:NSASCIIStringEncoding]];
*data_len = result.length;
return [result UTF8String];
}
Where Class is the class that contains Justin's functions.