With Data (not NSData), in fact how actually do yo

问题:

Exactly as explained here, https://stackoverflow.com/a/30624755/294884

[It is a mistake to think that] the JPEG representation of an image is a UTF-8-encoded string. It's not. It's arbitrary binary data. UTF-8 strings aren't arbitrary sequences of bytes; there are rules about what bytes can follow other bytes.

In fact, how do you best make a utf8 data from an image, in the Data era?

The everyday use case is in a http form.

I do something like this,

    formData.append( "Content-Disposition etc".(using: .utf8)! )
    formData.append( "Content type etc".(using: .utf8)! )

    // now let's add a #@@%$%$% image

    let trueBinary = UIImageJPEGRepresentation(i, 0.10)!
    print("the size seems to be \(trueBinary.count)")

    let mystere = trueBinary.base64EncodedString(
                  options: .lineLength76Characters)

    formData.append( mystere.data(using: .utf8)! )

But

A, that seems poxy, and probably doesn't work anyway.

B, the "lineLength" concept means nothing to me, so I just guess stuff, and type something in there.

Note that, incredibly confusingly, if you have a Data x and you add to x a few strings as utf8 using append ..... And then you add a 'real' binary data, such as a jpeg representation to x ...... in fact it nils "x" - ouch! (It doesn't just "not add the binary one", it scratches x to nothing.)

回答1:

This line has a problem:

let mystere = trueBinary.count.base64EncodedString(
              options: .lineLength76Characters)

The problem is that trueBinary is a Data, and trueBinary.count is an Int, and Int doesn't have a base64EncodedString method. You want this:

let mystere = trueBinary.base64EncodedString(
              options: .lineLength76Characters)

As for ‘the "lineLength" concept’: you don't have to specify a line length option if you don't want to. Arguably I shouldn't have specified one in the answer you referenced in your question, because HTTP requests are not strictly MIME messages and are not subject to the MIME line length limit. You can do this instead:

let mystere = trueBinary.base64EncodedString()