withUnsafeBytes Data API confusion

Using Swift
6

How about this?

func md5DigestA(of data: Data) -> Data {
    precondition(!data.isEmpty)
    var result = [UInt8](repeating: 0, count: Int(CC_MD5_DIGEST_LENGTH))
    data.withUnsafeBytes { buffer in
        _ = CC_MD5(buffer.baseAddress!, CC_LONG(buffer.count), &result)
    }
    return Data(result)
}

If you want to handle the empty data case [1], remove the precondition check on line 2 and the force unwrap on line 5. This works because CC_MD5 will handle a NULL parameter if the count is 0.

If you want to handle the empty data case and you’re dealing with a C function that doesn’t allow a NULL pointer when the count is 0, things get more complex (-:

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Quinn “The Eskimo!” @ DTS @ Apple

[1] A question that deserves serious consideration, at least in a crypto context.

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