Encoding handling in XML-RPC testing infrastructure seems to be broken on Python 3

[icemac]

ZopeTestTranport does a decode of the body with utf-8 to convert it from bytes to str:

zope.app.publisher/src/zope/app/publisher/xmlrpc/testing.py

Lines 79 to 81 in 19ee519

	if not isinstance(body, str):
	# Python 3
	body = body.decode("utf-8")

Later on FakeSocket converts the body str back to bytes using latin-1:

zope.app.publisher/src/zope/app/publisher/xmlrpc/testing.py

Lines 24 to 25 in 19ee519

	if not isinstance(data, bytes):
	data = data.encode('iso-8859-1')

This breaks inside the expat parser because it is not able to handle chars outside ASCII which are latin-1 encoded as the default encoding for XML-RPC seems to be utf-8.

I propose to omit converting of the HTTP body and instead using the raw data to feed the parser.

[d-maurer]

Michael Howitz wrote at 2020-4-17 00:57 -0700:

`ZopeTestTranport` does a decode of the body with `utf-8` to convert it from `bytes` to `str`: https://github.com/zopefoundation/zope.app.publisher/blob/19ee5193e1bd42e9e69dc144b76e11abfb4da773/src/zope/app/publisher/xmlrpc/testing.py#L79-L81 Later on `FakeSocket` converts the body `str` back to `bytes` using `latin-1`: https://github.com/zopefoundation/zope.app.publisher/blob/19ee5193e1bd42e9e69dc144b76e11abfb4da773/src/zope/app/publisher/xmlrpc/testing.py#L24-L25 This breaks inside the expat parser because it is not able to handle chars outside ASCII which are `latin-1` encoded as the default encoding for XML-RPC seems to be `utf-8`. I propose to omit converting of the HTTP body and instead using the raw data to feed the parser.

A byte (i.e. an integer between 0 and 255) is naturally represented by the unicode character with its value as unicode codepoint. Based on this representation, it is natuaral to convert a `bytes` object to `str` via `bytes.decode("latin1")` and revert the conversion via `str.encode("latin-1")`. Therefore, I think that it is `ZopeTestTransport` which does the wrong thing, not `FakeSocket`.