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