Ios – Convert UTF-8 encoded NSData to NSString

iosnsdatansstring

I have UTF-8 encoded NSData from windows server and I want to convert it to NSString for iPhone. Since data contains characters (like a degree symbol) which have different values on both platforms, how do I convert data to string?

Best Answer

If the data is not null-terminated, you should use -initWithData:encoding:

NSString* newStr = [[NSString alloc] initWithData:theData encoding:NSUTF8StringEncoding];

If the data is null-terminated, you should instead use -stringWithUTF8String: to avoid the extra \0 at the end.

NSString* newStr = [NSString stringWithUTF8String:[theData bytes]];

(Note that if the input is not properly UTF-8-encoded, you will get nil.)

Swift variant:

let newStr = String(data: data, encoding: .utf8)
// note that `newStr` is a `String?`, not a `String`.

If the data is null-terminated, you could go though the safe way which is remove the that null character, or the unsafe way similar to the Objective-C version above.

// safe way, provided data is \0-terminated
let newStr1 = String(data: data.subdata(in: 0 ..< data.count - 1), encoding: .utf8)
// unsafe way, provided data is \0-terminated
let newStr2 = data.withUnsafeBytes(String.init(utf8String:))

Related Solutions

Ios – How to convert an NSString value to NSData

NSString* str = @"teststring";
NSData* data = [str dataUsingEncoding:NSUTF8StringEncoding];

Objective-c – Encrypted NSData to NSString in obj-c

First off, DO NOT use -[NSData description] to create an NSString for such purposes. (It's best to treat -description as debugging output. I apologize if my previous answer misled you, I was merely printing the description to demonstrate that the NSData can be encrypted and decrypted.) Instead, use NSString's -dataUsingEncoding: and -initWithData:encoding: methods to convert between NSData and NSString. Even with these, note that AES-encrypted data will probably not translate well into strings as-is — some byte sequences just won't play nicely, so it's a good idea to encode the data before creating the string.

I'd suggest you try Base64 encoding the NSData, since Base64 data can always be represented as an ASCII string. (Of course, when you do that, you'll have to decode from Base64 before decrypting.)

Here are some helpful resources...

Colloquy has some code that does encoding/decoding on NSData (header and implementation)
Google Toolbox for Mac has similar functionality (header and implementation)
A Cocoa With Love blog post on the topic.
A CocoaDev.com wiki page on the topic.

Edit: I was assuming you'd combine this with my answer to your previous question on AES encryption of NSString objects. Encoding data as Base64 doesn't place any restrictions on the data itself — it can certainly be AES-enrypted data itself. Here's what to do if you just want string input and output:

Encryption
- Provide the NSString to be encrypted, and the passphrase to use for encrypting.
- Convert the string to an NSData and perform AES encryption on it (see previous question).
- Base64-encode the NSData, then create and return and NSString of the encoded output.
Decryption
- Provide the encrypted and encoded string, and the passphrase to use for decrypting.
- Create an NSData from the first string, then Base64-decode the data.
- Perform AES decryption on the data, then create and return an NSString.

It's really just a matter of chaining the two parts together and performing them in reverse on the way out. From my previous answer, you can modify encryptString:withKey: to perform the last step and return a string, and change decryptData:withKey: to be decryptString:withKey: and accept two strings. It's pretty straightforward.

Best Answer

Swift variant:

Related Solutions

Ios – How to convert an NSString value to NSData

Objective-c – Encrypted NSData to NSString in obj-c

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