import re from typing import Callable, Generator, NamedTuple, Optional from .datastructures import Headers from .exceptions import SecurityError MAX_HEADERS = 256 MAX_LINE = 4110 def d(value: bytes) -> str: """ Decode a bytestring for interpolating into an error message. """ return value.decode(errors="backslashreplace") # See https://tools.ietf.org/html/rfc7230#appendix-B. # Regex for validating header names. _token_re = re.compile(rb"[-!#$%&\'*+.^_`|~0-9a-zA-Z]+") # Regex for validating header values. # We don't attempt to support obsolete line folding. # Include HTAB (\x09), SP (\x20), VCHAR (\x21-\x7e), obs-text (\x80-\xff). # The ABNF is complicated because it attempts to express that optional # whitespace is ignored. We strip whitespace and don't revalidate that. # See also https://www.rfc-editor.org/errata_search.php?rfc=7230&eid=4189 _value_re = re.compile(rb"[\x09\x20-\x7e\x80-\xff]*") # Consider converting to dataclasses when dropping support for Python < 3.7. class Request(NamedTuple): """ WebSocket handshake request. :param path: path and optional query :param headers: """ path: str headers: Headers # body isn't useful is the context of this library @classmethod def parse( cls, read_line: Callable[[], Generator[None, None, bytes]] ) -> Generator[None, None, "Request"]: """ Parse an HTTP/1.1 GET request and return ``(path, headers)``. ``path`` isn't URL-decoded or validated in any way. ``path`` and ``headers`` are expected to contain only ASCII characters. Other characters are represented with surrogate escapes. :func:`parse_request` doesn't attempt to read the request body because WebSocket handshake requests don't have one. If the request contains a body, it may be read from ``stream`` after this coroutine returns. :param read_line: generator-based coroutine that reads a LF-terminated line or raises an exception if there isn't enough data :raises EOFError: if the connection is closed without a full HTTP request :raises SecurityError: if the request exceeds a security limit :raises ValueError: if the request isn't well formatted """ # https://tools.ietf.org/html/rfc7230#section-3.1.1 # Parsing is simple because fixed values are expected for method and # version and because path isn't checked. Since WebSocket software tends # to implement HTTP/1.1 strictly, there's little need for lenient parsing. try: request_line = yield from parse_line(read_line) except EOFError as exc: raise EOFError("connection closed while reading HTTP request line") from exc try: method, raw_path, version = request_line.split(b" ", 2) except ValueError: # not enough values to unpack (expected 3, got 1-2) raise ValueError(f"invalid HTTP request line: {d(request_line)}") from None if method != b"GET": raise ValueError(f"unsupported HTTP method: {d(method)}") if version != b"HTTP/1.1": raise ValueError(f"unsupported HTTP version: {d(version)}") path = raw_path.decode("ascii", "surrogateescape") headers = yield from parse_headers(read_line) return cls(path, headers) def serialize(self) -> bytes: """ Serialize an HTTP/1.1 GET request. """ # Since the path and headers only contain ASCII characters, # we can keep this simple. request = f"GET {self.path} HTTP/1.1\r\n".encode() request += self.headers.serialize() return request # Consider converting to dataclasses when dropping support for Python < 3.7. class Response(NamedTuple): """ WebSocket handshake response. """ status_code: int reason_phrase: str headers: Headers body: Optional[bytes] = None # If processing the response triggers an exception, it's stored here. exception: Optional[Exception] = None @classmethod def parse( cls, read_line: Callable[[], Generator[None, None, bytes]], read_exact: Callable[[int], Generator[None, None, bytes]], read_to_eof: Callable[[], Generator[None, None, bytes]], ) -> Generator[None, None, "Response"]: """ Parse an HTTP/1.1 response and return ``(status_code, reason, headers)``. ``reason`` and ``headers`` are expected to contain only ASCII characters. Other characters are represented with surrogate escapes. :func:`parse_request` doesn't attempt to read the response body because WebSocket handshake responses don't have one. If the response contains a body, it may be read from ``stream`` after this coroutine returns. :param read_line: generator-based coroutine that reads a LF-terminated line or raises an exception if there isn't enough data :param read_exact: generator-based coroutine that reads the requested number of bytes or raises an exception if there isn't enough data :raises EOFError: if the connection is closed without a full HTTP response :raises SecurityError: if the response exceeds a security limit :raises LookupError: if the response isn't well formatted :raises ValueError: if the response isn't well formatted """ # https://tools.ietf.org/html/rfc7230#section-3.1.2 # As in parse_request, parsing is simple because a fixed value is expected # for version, status_code is a 3-digit number, and reason can be ignored. try: status_line = yield from parse_line(read_line) except EOFError as exc: raise EOFError("connection closed while reading HTTP status line") from exc try: version, raw_status_code, raw_reason = status_line.split(b" ", 2) except ValueError: # not enough values to unpack (expected 3, got 1-2) raise ValueError(f"invalid HTTP status line: {d(status_line)}") from None if version != b"HTTP/1.1": raise ValueError(f"unsupported HTTP version: {d(version)}") try: status_code = int(raw_status_code) except ValueError: # invalid literal for int() with base 10 raise ValueError( f"invalid HTTP status code: {d(raw_status_code)}" ) from None if not 100 <= status_code < 1000: raise ValueError(f"unsupported HTTP status code: {d(raw_status_code)}") if not _value_re.fullmatch(raw_reason): raise ValueError(f"invalid HTTP reason phrase: {d(raw_reason)}") reason = raw_reason.decode() headers = yield from parse_headers(read_line) # https://tools.ietf.org/html/rfc7230#section-3.3.3 if "Transfer-Encoding" in headers: raise NotImplementedError("transfer codings aren't supported") # Since websockets only does GET requests (no HEAD, no CONNECT), all # responses except 1xx, 204, and 304 include a message body. if 100 <= status_code < 200 or status_code == 204 or status_code == 304: body = None else: content_length: Optional[int] try: # MultipleValuesError is sufficiently unlikely that we don't # attempt to handle it. Instead we document that its parent # class, LookupError, may be raised. raw_content_length = headers["Content-Length"] except KeyError: content_length = None else: content_length = int(raw_content_length) if content_length is None: body = yield from read_to_eof() else: body = yield from read_exact(content_length) return cls(status_code, reason, headers, body) def serialize(self) -> bytes: """ Serialize an HTTP/1.1 GET response. """ # Since the status line and headers only contain ASCII characters, # we can keep this simple. response = f"HTTP/1.1 {self.status_code} {self.reason_phrase}\r\n".encode() response += self.headers.serialize() if self.body is not None: response += self.body return response def parse_headers( read_line: Callable[[], Generator[None, None, bytes]] ) -> Generator[None, None, Headers]: """ Parse HTTP headers. Non-ASCII characters are represented with surrogate escapes. :param read_line: generator-based coroutine that reads a LF-terminated line or raises an exception if there isn't enough data """ # https://tools.ietf.org/html/rfc7230#section-3.2 # We don't attempt to support obsolete line folding. headers = Headers() for _ in range(MAX_HEADERS + 1): try: line = yield from parse_line(read_line) except EOFError as exc: raise EOFError("connection closed while reading HTTP headers") from exc if line == b"": break try: raw_name, raw_value = line.split(b":", 1) except ValueError: # not enough values to unpack (expected 2, got 1) raise ValueError(f"invalid HTTP header line: {d(line)}") from None if not _token_re.fullmatch(raw_name): raise ValueError(f"invalid HTTP header name: {d(raw_name)}") raw_value = raw_value.strip(b" \t") if not _value_re.fullmatch(raw_value): raise ValueError(f"invalid HTTP header value: {d(raw_value)}") name = raw_name.decode("ascii") # guaranteed to be ASCII at this point value = raw_value.decode("ascii", "surrogateescape") headers[name] = value else: raise SecurityError("too many HTTP headers") return headers def parse_line( read_line: Callable[[], Generator[None, None, bytes]] ) -> Generator[None, None, bytes]: """ Parse a single line. CRLF is stripped from the return value. :param read_line: generator-based coroutine that reads a LF-terminated line or raises an exception if there isn't enough data """ # Security: TODO: add a limit here line = yield from read_line() # Security: this guarantees header values are small (hard-coded = 4 KiB) if len(line) > MAX_LINE: raise SecurityError("line too long") # Not mandatory but safe - https://tools.ietf.org/html/rfc7230#section-3.5 if not line.endswith(b"\r\n"): raise EOFError("line without CRLF") return line[:-2]