Fix encoding error with non-prettified encoded responses (#1168)

* Fix encoding error with non-prettified encoded responses

Removed `--format-option response.as` an promote `--response-as`: using
the format option would be misleading as it is now also used by non-prettified
responses.

* Encoding refactoring

* split --response-as into --response-mime and --response-charset
* add support for Content-Type charset for requests printed to terminal
* add support charset detection for requests printed to terminal without a Content-Type charset
* etc.

* `test_unicode.py` → `test_encoding.py`

* Drop sequence length check

* Clean-up tests

* [skip ci] Tweaks

* Use the compatible release clause for `charset_normalizer` requirement

Cf. https://www.python.org/dev/peps/pep-0440/#version-specifiers

* Clean-up

* Partially revert d52a4833e4

* Changelog

* Tweak tests

* [skip ci] Better test name

* Cleanup tests and add request body charset detection

* More test suite cleanups

* Cleanup

* Fix code style in test

* Improve detect_encoding() docstring

* Uniformize pytest.mark.parametrize() calls

* [skip ci] Comment out TODOs (will be tackled in a specific PR)

Co-authored-by: Jakub Roztocil <jakub@roztocil.co>

httpie/models.py

@@ -1,34 +1,33 @@
-from abc import ABCMeta, abstractmethod
-from typing import Iterable, Optional
+from typing import Iterable
 from urllib.parse import urlsplit
 
-from .constants import UTF8
-from .utils import split_cookies
+from .utils import split_cookies, parse_content_type_header
+from .compat import cached_property
 
 
-class HTTPMessage(metaclass=ABCMeta):
+class HTTPMessage:
     """Abstract class for HTTP messages."""
 
     def __init__(self, orig):
         self._orig = orig
 
-    @abstractmethod
     def iter_body(self, chunk_size: int) -> Iterable[bytes]:
         """Return an iterator over the body."""
+        raise NotImplementedError
 
-    @abstractmethod
     def iter_lines(self, chunk_size: int) -> Iterable[bytes]:
         """Return an iterator over the body yielding (`line`, `line_feed`)."""
+        raise NotImplementedError
 
     @property
-    @abstractmethod
     def headers(self) -> str:
         """Return a `str` with the message's headers."""
+        raise NotImplementedError
 
-    @property
-    @abstractmethod
-    def encoding(self) -> Optional[str]:
-        """Return a `str` with the message's encoding, if known."""
+    @cached_property
+    def encoding(self) -> str:
+        ct, params = parse_content_type_header(self.content_type)
+        return params.get('charset', '')
 
     @property
     def content_type(self) -> str:
@@ -77,10 +76,6 @@ class HTTPResponse(HTTPMessage):
         )
         return '\r\n'.join(headers)
 
-    @property
-    def encoding(self):
-        return self._orig.encoding or UTF8
-
 
 class HTTPRequest(HTTPMessage):
     """A :class:`requests.models.Request` wrapper."""
@@ -114,10 +109,6 @@ class HTTPRequest(HTTPMessage):
         headers = '\r\n'.join(headers).strip()
         return headers
 
-    @property
-    def encoding(self):
-        return UTF8
-
     @property
     def body(self):
         body = self._orig.body