Swift 4, reading byte data - objective-c

Question

so I recently update my IMAC and Xcode, after updating part of my code wasn't running as its supposed to it. Here is where I originally check messages.
func checkForMessages() {
while true {
if inputBuffer.length < 4 {
return
}
var msgLength = (inputBuffer.bytes).load(as: UInt32.self)
msgLength = UInt32(bigEndian: msgLength)
print("msgLength = \(msgLength)")
print("inputBuffer Length = \(inputBuffer.length)")
print("inputBuffer = \(inputBuffer)")
if inputBuffer.length < msgLength {
return
}
//print("data = \(inputBuffer.subdata(with: NSRange(location: 4, length: Int(msgLength))))")
if inputBuffer.length < msgLength + 4 {
return
}
let message: Data? = inputBuffer.subdata(with: NSRange(location: 4, length: Int(msgLength)))
processMessage(message!)
let amtRemaining: Int = inputBuffer.length - Int(msgLength) - 4
if amtRemaining == 0 {
inputBuffer = NSMutableData()
}
else {
print("Creating input buffer of length \(amtRemaining)")
inputBuffer = NSMutableData(bytes: inputBuffer.bytes + 4 + Int(msgLength), length: amtRemaining)
}
}
}
and then the process message function
func processMessage(_ data: Data) {
let reader = MessageReader(data: data)
print("this is the message data\(data)")
let msgType = reader?.readByte().hashValue
}
and then the actually MessageReader, its in Objective C, since I pulled it off the internet a while ago. Its been working fine for me ever since. Until now.
#import "MessageReader.h"
#implementation MessageReader
- (id)initWithData:(NSData *)data {
if ((self = [super init])) {
_data = data;
_offset = 0;
}
return self;
}
- (unsigned char)readByte {
unsigned char retval = *((unsigned char *) (_data.bytes + _offset));
_offset += sizeof(unsigned char);
return retval;
}
- (int)readInt {
int retval = *((unsigned int *) (_data.bytes + _offset));
retval = ntohl(retval);
_offset += sizeof(unsigned int);
return retval;
}
- (NSString *)readString {
int strLen = [self readInt];
NSString *retval = [NSString stringWithCString:_data.bytes + _offset encoding:NSUTF8StringEncoding];
_offset += strLen;
return retval;
}
- (void)dealloc {
}
#end
Now the issue is that instead of returning the number for say “1” or “2”, “30”, etc. its returning some huge number like 1836718193728. I believe the issue lies in the messageReader, readByte function.

Answer 1

From your comment, reader?.readByte().hasValue is returning a huge number. (I believe hasValue is just a typo and its hashValue.)
That's a possible behavior of hashValue.
Are you using hashValue as if it's a UInt8 to Int conversion tool?
It's wrong. The property hashValue is (and should be) implemented to return some Int value which fulfills one axiom:
where a == b, a.hashValue == b.hashValue
In older versions of Swift, UInt8.hashValue may have returned the same value of type Int, but you should not rely on such an implementation detail that is not documented. A slight change of implementation would lead to different results.
And in fact, Swift 4.2 has changed the implementation of hashValue drastically.
SE-0206 Hashable Enhancements
You may need to fix all parts of your project using hashValue.
Usually, you use Int.init(_:) to convert UInt8 to Int.
In a context like Optional Chaining as shown in your let msgType, you may need to write something like this.
let msgType = (reader?.getByte()).map{Int($0)}
If you have many parts using hashValue wrongly, better write an extension:
extension UInt8 {
var integerValue: Int {
return Int(self)
}
}
let msgType = reader?.getByte().integerValue
Generally, you should better not include such wrong hacks in your project.