Converting file to Base64 URL safe encoding format in iOS

I am supposed to convert a file in to Base64 and add that String to a JSON which I am appending to a URL. The files that I am having are a .zip file and a text file with .info extension. The .info file is uploading correctly but with .zip file I am getting “Incorrect Padding” error as response from the server.

Below is my work;

- (void)uploadingData: (NSString *)fileName {

    NSArray *directoryPathsArray = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [directoryPathsArray objectAtIndex:0];

    NSString *absoluteFilePath = [NSString stringWithFormat:@"%@/%@/%@", documentsDirectory, baseDirName, fileName];

    NSInputStream *inputStream = [NSInputStream inputStreamWithFileAtPath:absoluteFilePath];
    [inputStream open];

    uint8_t buffer[1024];

    int len;

    NSMutableString *total = [[NSMutableString alloc] init];

    while ([inputStream hasBytesAvailable]) {
        len = [inputStream read:buffer maxLength:sizeof(buffer)];

        if (len > 0) {
             [total appendString: [[NSString alloc] initWithBytes:buffer length:len encoding:NSASCIIStringEncoding]];

    NSData *plainData = [total dataUsingEncoding:NSUTF8StringEncoding];
    NSString *base64String = [plainData base64EncodedStringWithOptions:0];

// Adding to JSON and upload goes here.

Where I have done the mistake?

Additionally, is there a way I can check the converted string is exactly according to Base64, before it append to JSON and upload to server?


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try this..

+ (NSString *)base64String:(NSString *)str
    NSData *theData = [str dataUsingEncoding: NSASCIIStringEncoding];
    const uint8_t* input = (const uint8_t*)[theData bytes];
    NSInteger length = [theData length];

    static char table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

    NSMutableData* data = [NSMutableData dataWithLength:((length + 2) / 3) * 4];
    uint8_t* output = (uint8_t*)data.mutableBytes;

    NSInteger i;
    for (i=0; i < length; i += 3) {
        NSInteger value = 0;
        NSInteger j;
        for (j = i; j < (i + 3); j++) {
            value <<= 8;

            if (j < length) {
                value |= (0xFF & input[j]);

        NSInteger theIndex = (i / 3) * 4;
        output[theIndex + 0] =                    table[(value >> 18) & 0x3F];
        output[theIndex + 1] =                    table[(value >> 12) & 0x3F];
        output[theIndex + 2] = (i + 1) < length ? table[(value >> 6)  & 0x3F] : '=';
        output[theIndex + 3] = (i + 2) < length ? table[(value >> 0)  & 0x3F] : '=';

    return [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];

I have found the mistakes as well as the answer. I do not need to convert the .zip file in to NSInputStream and I haven’t applied URL safe methods to the encoded string. Following is the way I have tackled it.

- (void)uploadingData: (NSString *)fileName {

    NSArray *directoryPathsArray = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [directoryPathsArray objectAtIndex:0];

    NSString *absoluteFilePath = [NSString stringWithFormat:@"%@/%@/%@", documentsDirectory, baseDirName, fileName];

    NSData *zipFileData = [NSData dataWithContentsOfFile:absoluteFilePath];

    NSString *base64String = [zipFileData base64EncodedStringWithOptions:0];

    base64String = [base64String stringByReplacingOccurrencesOfString:@"/"

    base64String = [base64String stringByReplacingOccurrencesOfString:@"+"

// Adding to JSON and upload goes here.

In Android there is a way to do both Base64 encoding and URL safe formatting with a single function.

byte[] bytes = Files.toByteArray(new File(sFileName));
byte[] encoded = Base64.encodeBase64URLSafe(bytes);

I have no idea whether there is a similar kind of easy way of doing it with iOS too.