Your Base64 string is not valid. It must be padded with =
characters to have
a length that is a multiple of 4. In your case: "eyJlbWFp....MTM3fQ=="
.
With this padding, initWithBase64EncodedString
decodes the Base64 string correctly.
質問
I'm implementing JSON Web Token authentication on the iOS (7) cient-side. It's working nicely. My app rceives tokens, and can make authenticated calls to my server with them.
Now, I want my client side code to check for an expiration date on the token so it can know when to re-authenticate. Checking for the expiration date on a JWT auth token is straightforward. The authorization token is 3 base64 encoded JSON blobs, separated by a '.' - The expiration timestamp is in the middle blob, in a field called ext
. It's seconds since unix epoch.
So my code's looking like so:
- (NSDate*) expirationDate
{
if ( !_tokenAppearsValid ) return nil;
if ( !_parsedExpirationDate )
{
//
// Token is three base64 encoded payloads separated by '.'
// The payload we want is the middle one, which is a JSON dict, with
// 'exp' being the unix seconds timestamp of the expiration date
// Returning nil is appropriate if no 'exp' is findable
//
NSArray *components = [self.token componentsSeparatedByString:@"."];
NSString *payload = components[1];
NSData* payloadJsonData = [[NSData alloc]
initWithBase64EncodedString:payload
options:NSDataBase64DecodingIgnoreUnknownCharacters];
NSError* jsonError = nil;
NSDictionary* payloadJson = [NSJSONSerialization JSONObjectWithData:payloadJsonData options:0 error:&jsonError];
if ( payloadJson )
{
if ( payloadJson[@"exp"] )
{
NSTimeInterval timestampSeconds = [payloadJson[@"exp"] doubleValue];
_expirationDate = [NSDate dateWithTimeIntervalSince1970:timestampSeconds];
}
}
_parsedExpirationDate = YES;
}
return _expirationDate;
}
The problem is simple. The middle base64 blob, when parsed by NSData -initWithBase64EncodedString is nil
- and that's bad.
I've checked the base64 blob and it seems to be valid. My server's returning dummy data for the moment so here's an example blob:
eyJlbWFpbCI6ImZvb0BiYXIuYmF6IiwiYWNjb3VudElkIjoiMTIzNDUtNjc4OTAtYmFyLWJheiIsImV4cCI6MTM5MDkxNTAzNywiaWF0IjoxMzkwOTE0MTM3fQ
It decodes to:
{"email":"foo@bar.baz","accountId":"12345-67890-bar-baz","exp":1390915037,"iat":1390914137}
I tested it here: http://www.base64decode.org
I've used NSData's base64 methods elswhere in my app with success - I don't think I'm doing anything particularly broken here. But I'm all ears! Any ideas?
解決
Your Base64 string is not valid. It must be padded with =
characters to have
a length that is a multiple of 4. In your case: "eyJlbWFp....MTM3fQ=="
.
With this padding, initWithBase64EncodedString
decodes the Base64 string correctly.
他のヒント
Although Martin's answer is correct, here is a quick and correct(!) way to fix the problem:
NSString *base64String = @"<the token>";
NSUInteger paddedLength = base64String.length + (4 - (base64String.length % 4));
NSString* correctBase64String = [base64String stringByPaddingToLength:paddedLength withString:@"=" startingAtIndex:0];
Here is a solution that pads the Base-64 string appropriately and works in iOS 4+:
NSData+Base64.h
@interface NSData (Base64)
/**
Returns a data object initialized with the given Base-64 encoded string.
@param base64String A Base-64 encoded NSString
@returns A data object built by Base-64 decoding the provided string. Returns nil if the data object could not be decoded.
*/
- (instancetype) initWithBase64EncodedString:(NSString *)base64String;
/**
Create a Base-64 encoded NSString from the receiver's contents
@returns A Base-64 encoded NSString
*/
- (NSString *) base64EncodedString;
@end
NSData+Base64.m
@interface NSString (Base64)
- (NSString *) stringPaddedForBase64;
@end
@implementation NSString (Base64)
- (NSString *) stringPaddedForBase64 {
NSUInteger paddedLength = self.length + (self.length % 3);
return [self stringByPaddingToLength:paddedLength withString:@"=" startingAtIndex:0];
}
@end
@implementation NSData (Base64)
- (instancetype) initWithBase64EncodedString:(NSString *)base64String {
return [self initWithBase64Encoding:[base64String stringPaddedForBase64]];
}
- (NSString *) base64EncodedString {
return [self base64Encoding];
}
@end
A Swift version of Paul's answer
func paddedBase64EncodedString(encodedString: String) -> String
{
let encodedStringLength = encodedString.characters.count
let paddedLength = encodedStringLength + (4 - (encodedStringLength % 4))
let paddedBase64String = encodedString.stringByPaddingToLength(paddedLength,
withString: "=",
startingAtIndex: 0)
return paddedBase64String
}
I faced the same issue, but resolved it by adding ==
at end of string
base64UserStr = NSString(format: "%@%@", base64UserStr,"==") as String
let decodedData = NSData(base64EncodedString: base64UserStr, options: NSDataBase64DecodingOptions.init(rawValue: 0))
if (decodedData != nil)
{
let decodedString = NSString(data: decodedData!, encoding: NSUTF8StringEncoding)
print("Base 64 decode string is \(decodedString)")
}
This will definitely work.