Convert error codes to text in iOS - ios

Question

I have a wrapper for encrypting and decrypting using CommonCryptor. Occasionally the decryption process will fail, in which case I fill an error like so:
if (result == kCCSuccess) {
cipherData.length = outLength;
} else {
if (error) {
*error = [NSError errorWithDomain:kBridgeEncryptorErrorDomain
code:result
userInfo:nil];
}
return nil;
}
And then I log the error like this:
if (error != nil) {
DDLogError(#"Decrypt fail %i, %#", [error code], [error localizedDescription]);
}
However, this ends up generating strings like:
2013-01-09 09:15:19.753 [BridgeEncrypter decryptDataFromData:] [Line 83] E: Decrypt fail -4304, The operation couldn’t be completed. (com.***.bridgecrypt error -4304.)
Where the -4304 could be any of the error codes in CommonCryptor.h (-4300 to -4305). Is there a good way to map the error codes to their string values, or do I need to have a switch statement that adjusts the string by hand? If I do have to depend on a switch, would best practice be to put it where the issue is logged or where the error is generated?

Answer 1

I'm not sure what you're looking for here. I'm not familiar with CommonCryptor or how error messages are handled in it.
I can recommend that you lean on NSError and it's userInfo and NSLocalized*Key feature.
For example, if you set a NSLocalizedDescriptionKey in the userInfo dictionary, error:
NSDictionary userInfo = #{
NSLocalizedDescriptionKey : #"This is the error message I want users to see"
};
*error = [NSError errorWithDomain:kBridgeEncryptorErrorDomain
code:result
userInfo:userInfo];
Then This is the error message I want users to see is the string returned by -localizedDescription. Then the calling code can use the string to display a message to the user without needing to reinterpret it.
As to the question of how to link error codes to messages you want users to see, there could be a CommonCryptor function that converts error codes to human readable string. If not, then you could write your own. I would recommend using a switch.
NSString *MyCodeToLocalizedDescription(CCCryptorStatus cryptorStatus)
{
switch(cryptorStatus) {
case kCCDecodeError: return #"This is the error message I want users to see";
…
default: return #"Oh noes, unknown error";
}
}
At that point setting the error is:
NSDictionary userInfo = #{
NSLocalizedDescriptionKey : MyCodeToLocalizedDescription(result)
};
*error = [NSError errorWithDomain:kBridgeEncryptorErrorDomain
code:result
userInfo:userInfo];