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279 lines
10 KiB
Python
279 lines
10 KiB
Python
2 years ago
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import re
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from typing import AnyStr, cast, List, overload, Sequence, Tuple, TYPE_CHECKING, Union
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from ._abnf import field_name, field_value
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from ._util import bytesify, LocalProtocolError, validate
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if TYPE_CHECKING:
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from ._events import Request
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try:
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from typing import Literal
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except ImportError:
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from typing_extensions import Literal # type: ignore
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# Facts
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# -----
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#
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# Headers are:
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# keys: case-insensitive ascii
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# values: mixture of ascii and raw bytes
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#
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# "Historically, HTTP has allowed field content with text in the ISO-8859-1
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# charset [ISO-8859-1], supporting other charsets only through use of
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# [RFC2047] encoding. In practice, most HTTP header field values use only a
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# subset of the US-ASCII charset [USASCII]. Newly defined header fields SHOULD
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# limit their field values to US-ASCII octets. A recipient SHOULD treat other
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# octets in field content (obs-text) as opaque data."
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# And it deprecates all non-ascii values
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#
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# Leading/trailing whitespace in header names is forbidden
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#
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# Values get leading/trailing whitespace stripped
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#
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# Content-Disposition actually needs to contain unicode semantically; to
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# accomplish this it has a terrifically weird way of encoding the filename
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# itself as ascii (and even this still has lots of cross-browser
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# incompatibilities)
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#
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# Order is important:
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# "a proxy MUST NOT change the order of these field values when forwarding a
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# message"
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# (and there are several headers where the order indicates a preference)
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#
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# Multiple occurences of the same header:
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# "A sender MUST NOT generate multiple header fields with the same field name
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# in a message unless either the entire field value for that header field is
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# defined as a comma-separated list [or the header is Set-Cookie which gets a
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# special exception]" - RFC 7230. (cookies are in RFC 6265)
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#
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# So every header aside from Set-Cookie can be merged by b", ".join if it
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# occurs repeatedly. But, of course, they can't necessarily be split by
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# .split(b","), because quoting.
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#
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# Given all this mess (case insensitive, duplicates allowed, order is
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# important, ...), there doesn't appear to be any standard way to handle
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# headers in Python -- they're almost like dicts, but... actually just
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# aren't. For now we punt and just use a super simple representation: headers
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# are a list of pairs
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#
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# [(name1, value1), (name2, value2), ...]
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#
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# where all entries are bytestrings, names are lowercase and have no
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# leading/trailing whitespace, and values are bytestrings with no
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# leading/trailing whitespace. Searching and updating are done via naive O(n)
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# methods.
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#
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# Maybe a dict-of-lists would be better?
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_content_length_re = re.compile(rb"[0-9]+")
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_field_name_re = re.compile(field_name.encode("ascii"))
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_field_value_re = re.compile(field_value.encode("ascii"))
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class Headers(Sequence[Tuple[bytes, bytes]]):
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"""
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A list-like interface that allows iterating over headers as byte-pairs
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of (lowercased-name, value).
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Internally we actually store the representation as three-tuples,
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including both the raw original casing, in order to preserve casing
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over-the-wire, and the lowercased name, for case-insensitive comparisions.
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r = Request(
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method="GET",
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target="/",
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headers=[("Host", "example.org"), ("Connection", "keep-alive")],
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http_version="1.1",
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)
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assert r.headers == [
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(b"host", b"example.org"),
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(b"connection", b"keep-alive")
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]
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assert r.headers.raw_items() == [
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(b"Host", b"example.org"),
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(b"Connection", b"keep-alive")
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]
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"""
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__slots__ = "_full_items"
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def __init__(self, full_items: List[Tuple[bytes, bytes, bytes]]) -> None:
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self._full_items = full_items
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def __bool__(self) -> bool:
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return bool(self._full_items)
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def __eq__(self, other: object) -> bool:
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return list(self) == list(other) # type: ignore
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def __len__(self) -> int:
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return len(self._full_items)
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def __repr__(self) -> str:
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return "<Headers(%s)>" % repr(list(self))
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def __getitem__(self, idx: int) -> Tuple[bytes, bytes]: # type: ignore[override]
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_, name, value = self._full_items[idx]
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return (name, value)
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def raw_items(self) -> List[Tuple[bytes, bytes]]:
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return [(raw_name, value) for raw_name, _, value in self._full_items]
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HeaderTypes = Union[
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List[Tuple[bytes, bytes]],
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List[Tuple[bytes, str]],
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List[Tuple[str, bytes]],
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List[Tuple[str, str]],
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]
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@overload
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def normalize_and_validate(headers: Headers, _parsed: Literal[True]) -> Headers:
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...
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@overload
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def normalize_and_validate(headers: HeaderTypes, _parsed: Literal[False]) -> Headers:
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...
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@overload
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def normalize_and_validate(
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headers: Union[Headers, HeaderTypes], _parsed: bool = False
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) -> Headers:
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...
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def normalize_and_validate(
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headers: Union[Headers, HeaderTypes], _parsed: bool = False
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) -> Headers:
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new_headers = []
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seen_content_length = None
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saw_transfer_encoding = False
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for name, value in headers:
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# For headers coming out of the parser, we can safely skip some steps,
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# because it always returns bytes and has already run these regexes
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# over the data:
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if not _parsed:
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name = bytesify(name)
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value = bytesify(value)
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validate(_field_name_re, name, "Illegal header name {!r}", name)
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validate(_field_value_re, value, "Illegal header value {!r}", value)
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assert isinstance(name, bytes)
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assert isinstance(value, bytes)
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raw_name = name
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name = name.lower()
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if name == b"content-length":
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lengths = {length.strip() for length in value.split(b",")}
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if len(lengths) != 1:
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raise LocalProtocolError("conflicting Content-Length headers")
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value = lengths.pop()
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validate(_content_length_re, value, "bad Content-Length")
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if seen_content_length is None:
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seen_content_length = value
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new_headers.append((raw_name, name, value))
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elif seen_content_length != value:
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raise LocalProtocolError("conflicting Content-Length headers")
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elif name == b"transfer-encoding":
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# "A server that receives a request message with a transfer coding
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# it does not understand SHOULD respond with 501 (Not
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# Implemented)."
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# https://tools.ietf.org/html/rfc7230#section-3.3.1
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if saw_transfer_encoding:
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raise LocalProtocolError(
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"multiple Transfer-Encoding headers", error_status_hint=501
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)
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# "All transfer-coding names are case-insensitive"
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# -- https://tools.ietf.org/html/rfc7230#section-4
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value = value.lower()
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if value != b"chunked":
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raise LocalProtocolError(
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"Only Transfer-Encoding: chunked is supported",
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error_status_hint=501,
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)
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saw_transfer_encoding = True
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new_headers.append((raw_name, name, value))
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else:
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new_headers.append((raw_name, name, value))
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return Headers(new_headers)
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def get_comma_header(headers: Headers, name: bytes) -> List[bytes]:
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# Should only be used for headers whose value is a list of
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# comma-separated, case-insensitive values.
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#
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# The header name `name` is expected to be lower-case bytes.
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#
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# Connection: meets these criteria (including cast insensitivity).
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#
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# Content-Length: technically is just a single value (1*DIGIT), but the
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# standard makes reference to implementations that do multiple values, and
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# using this doesn't hurt. Ditto, case insensitivity doesn't things either
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# way.
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#
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# Transfer-Encoding: is more complex (allows for quoted strings), so
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# splitting on , is actually wrong. For example, this is legal:
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#
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# Transfer-Encoding: foo; options="1,2", chunked
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#
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# and should be parsed as
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#
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# foo; options="1,2"
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# chunked
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#
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# but this naive function will parse it as
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#
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# foo; options="1
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# 2"
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# chunked
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#
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# However, this is okay because the only thing we are going to do with
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# any Transfer-Encoding is reject ones that aren't just "chunked", so
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# both of these will be treated the same anyway.
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#
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# Expect: the only legal value is the literal string
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# "100-continue". Splitting on commas is harmless. Case insensitive.
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#
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out: List[bytes] = []
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for _, found_name, found_raw_value in headers._full_items:
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if found_name == name:
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found_raw_value = found_raw_value.lower()
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for found_split_value in found_raw_value.split(b","):
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found_split_value = found_split_value.strip()
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if found_split_value:
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out.append(found_split_value)
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return out
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def set_comma_header(headers: Headers, name: bytes, new_values: List[bytes]) -> Headers:
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# The header name `name` is expected to be lower-case bytes.
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#
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# Note that when we store the header we use title casing for the header
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# names, in order to match the conventional HTTP header style.
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#
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# Simply calling `.title()` is a blunt approach, but it's correct
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# here given the cases where we're using `set_comma_header`...
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#
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# Connection, Content-Length, Transfer-Encoding.
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new_headers: List[Tuple[bytes, bytes]] = []
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for found_raw_name, found_name, found_raw_value in headers._full_items:
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if found_name != name:
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new_headers.append((found_raw_name, found_raw_value))
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for new_value in new_values:
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new_headers.append((name.title(), new_value))
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return normalize_and_validate(new_headers)
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def has_expect_100_continue(request: "Request") -> bool:
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# https://tools.ietf.org/html/rfc7231#section-5.1.1
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# "A server that receives a 100-continue expectation in an HTTP/1.0 request
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# MUST ignore that expectation."
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if request.http_version < b"1.1":
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return False
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expect = get_comma_header(request.headers, b"expect")
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return b"100-continue" in expect
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