Multipart files tweaks

[yeraydiazdiaz]

Fixeshttps://github.com/encode/httpx/issues/481

The tuple values of the files dictionary passed to multipart_encode now support:

• None filenames, the header will not include the filename section
• str objects as the contents, as opposed to file-like objects

I wasn't sure about adding docs about it as requests seems to not include it and it seemed more of an implementation detail that doesn't quite fit in the quickstart guide. But I'm happy to include it if we think it's worth it.

[florimondmanca]

Nice work @yeraydiazdiaz! I might be in favor of a files section in the advanced docs. :)

[sethmlarson]

Looks good to me, thanks @yeraydiazdiaz!

[florimondmanca]

LGTM as well, just a minor typo nit. :)

[yeraydiazdiaz]

Thanks all! 💚

[lovelydinosaur]

I'm a bit confused by this example - wouldn't we expect the item to be in "files" here?

[yeraydiazdiaz]

I was confused about that too.

That's the actual output of httpbin, the headers we send are correct as shown in the tests and I verified requests gets the same output from httpbin so I left it as is.

It's a bit confusing for the docs, maybe we should show the request headers instead of the response from httpbin?

[lovelydinosaur]

I'd probably just omit that example, since:

1. We can't really walk the user through "btw the server appears to have a weird implementation where it puts files into "form" if they're unnamed.
2. Sending unnamed files isn't a prefered usage.

I guess you could verify the behavior against say, Starlette, just to check that we really are doing the right thing, but not fussed if that's too onerous, since we're checking in our tests.