Always rewind files on multipart uploads.

[tomchristie]

Raised in #2064

• Failing test case.
• Implement rewind fix.

[tomchristie]

Waiting on a release of httpcore with encode/httpcore#502 in order to fix the test suite.
Once we've got that I'll re-run the suite to demo that the test currently fails, and then push the fix.

Edit Okay, done.

Test suite prior to the fix fails with this...

=================================== FAILURES ===================================
[50](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:50)
_________________________ test_multipart_rewinds_files _________________________
[51](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:51)

[52](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:52)
    def test_multipart_rewinds_files():
[53](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:53)
        with tempfile.TemporaryFile() as upload:
[54](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:54)
            upload.write(b"Hello, world!")
[55](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:55)
    
[56](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:56)
            transport = httpx.MockTransport(echo_request_content)
[57](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:57)
            client = httpx.Client(transport=transport)
[58](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:58)
    
[59](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:59)
            files = {"file": upload}
[60](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:60)
            response = client.post("http://127.0.0.1:8000/", files=files)
[61](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:61)
            assert response.status_code == 200
[62](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:62)
>           assert b"\r\nHello, world!\r\n" in response.content
[63](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:63)
E           assert b'\r\nHello, world!\r\n' in b'--[64](https://github.com/encode/httpx/runs/5066317760?check_suite_focus=true#step:7:64)703278012ba578d5eea2ebfafab695\r\nContent-Disposition: form-data; name="file"; filename="20"\r\nContent-Type: application/octet-stream\r\n\r\n\r\n--64703278012ba578d5eea2ebfafab695--\r\n'
64
E            +  where b'--64703278012ba578d5eea2ebfafab695\r\nContent-Disposition: form-data; name="file"; filename="20"\r\nContent-Type: application/octet-stream\r\n\r\n\r\n--64703278012ba578d5eea2ebfafab695--\r\n' = <Response [200 OK]>.content

[aminalaee]

This is more of a question, so we do seek for the first file upload too, right?

[tomchristie]

Yup

[ShivangKakkar]

It works like charm now! Thanks