feat: publish Hermes Nextcloud calendar MCP under AGPL-3.0

src/hermes_caldav_mcp/transport.py

@@ -0,0 +1,282 @@
+"""Constrain every authenticated request before constructing its headers."""
+
+import base64
+import re
+import ssl
+from urllib.parse import quote, unquote, urlsplit
+
+import httpx
+
+from .types import MAX_DAV_BYTES, ErrorCode, HTTPResult, SafeError
+
+
+def path(value: str) -> str:
+    if (
+        not isinstance(value, str)
+        or not value.startswith("/")
+        or value.startswith("//")
+    ):
+        raise SafeError(ErrorCode.INVALID_INPUT)
+    if re.search(r"[\x00-\x1f\x7f\\?#]", value) or re.search(
+        r"%(?![0-9a-fA-F]{2})", value
+    ):
+        raise SafeError(ErrorCode.INVALID_INPUT)
+    segments = value.split("/")[1:]
+    normalized = []
+    for i, segment in enumerate(segments):
+        try:
+            decoded = unquote(segment, encoding="utf-8", errors="strict")
+        except UnicodeError:
+            raise SafeError(ErrorCode.INVALID_INPUT) from None
+        if decoded in (".", "..") or re.search(r"[%/\\\x00-\x1f\x7f]", decoded):
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        if not decoded and i != len(segments) - 1:
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        normalized.append(quote(decoded, safe="-._~"))
+    return "/" + "/".join(normalized)
+
+
+def strong_etag(value: str | None) -> bool:
+    return (
+        isinstance(value, str)
+        and len(value) <= 256
+        and bool(re.fullmatch(r'"[\x21\x23-\x7e]*"', value))
+    )
+
+
+def event_id(calendar, href: str) -> str:
+    resource = path(href)
+    root = path(calendar.href)
+    if not root.endswith("/") or not resource.startswith(root):
+        raise SafeError(ErrorCode.INVALID_INPUT)
+    filename = resource[len(root) :]
+    if not filename or "/" in filename:
+        raise SafeError(ErrorCode.INVALID_INPUT)
+    return base64.urlsafe_b64encode(filename.encode()).decode().rstrip("=")
+
+
+def event_href(calendar, identifier: str) -> str:
+    if not isinstance(identifier, str) or not re.fullmatch(
+        r"[A-Za-z0-9_-]{1,2048}", identifier
+    ):
+        raise SafeError(ErrorCode.INVALID_INPUT)
+    try:
+        filename = base64.b64decode(
+            identifier + "=" * (-len(identifier) % 4), altchars=b"-_", validate=True
+        ).decode()
+        href = path(calendar.href) + filename
+        if event_id(calendar, href) != identifier:
+            raise ValueError("noncanonical")
+        return href
+    except (ValueError, UnicodeError):
+        raise SafeError(ErrorCode.INVALID_INPUT) from None
+
+
+def endpoint(value: str):
+    if not isinstance(value, str) or re.search(r"[\x00-\x20\x7f\\]", value):
+        raise SafeError(ErrorCode.INVALID_INPUT)
+    try:
+        parts = urlsplit(value)
+        if (
+            parts.scheme != "https"
+            or not parts.hostname
+            or parts.username is not None
+            or parts.password is not None
+            or parts.query
+            or parts.fragment
+            or "?" in value
+            or "#" in value
+        ):
+            raise ValueError("url")
+        host = parts.hostname.encode("idna").decode().lower()
+        if "%" in host:
+            raise ValueError("host")
+        port = parts.port or 443
+        if not 1 <= port <= 65535:
+            raise ValueError("port")
+        host_url = f"[{host}]" if ":" in host else host
+        origin = f"https://{host_url}" + (f":{port}" if port != 443 else "")
+        return origin, path(parts.path or "/"), (host, port)
+    except (ValueError, UnicodeError):
+        raise SafeError(ErrorCode.INVALID_INPUT) from None
+
+
+class CalDAVClient:
+    def __init__(self, profile, *, transport=None, discovery=False):
+        self.write_started = False
+        self.profile = profile
+        self.discovery = discovery
+        self.origin, base, self.authority = endpoint(profile.base_url)
+        self.home = path(profile.calendar_home)
+        if not self.home.startswith(
+            base.rstrip("/") + "/remote.php/dav/calendars/"
+        ) or not self.home.endswith("/"):
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        self.roots = tuple(path(c.href) for c in profile.calendars)
+        if any(
+            not root.startswith(self.home)
+            or not root.endswith("/")
+            or "/" in root[len(self.home) : -1]
+            or root == self.home
+            for root in self.roots
+        ):
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        if (
+            not profile.username
+            or ":" in profile.username
+            or any(ord(c) < 32 for c in profile.username)
+        ):
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        try:
+            self.ssl_context = ssl.create_default_context(cafile=profile.ca_bundle)
+        except (OSError, ssl.SSLError):
+            raise SafeError(ErrorCode.NETWORK_ERROR) from None
+        self.http = httpx.AsyncClient(
+            verify=self.ssl_context,
+            trust_env=False,
+            follow_redirects=False,
+            transport=transport,
+            timeout=httpx.Timeout(20, connect=10),
+            limits=httpx.Limits(max_connections=2, max_keepalive_connections=0),
+        )
+
+    async def __aenter__(self):
+        return self
+
+    async def __aexit__(self, *args):
+        await self.http.aclose()
+
+    def validated_href(self, href: str, *, discovered=False) -> str:
+        if href.startswith("https://"):
+            origin, resource, authority = endpoint(href)
+            if authority != self.authority or origin != self.origin:
+                raise SafeError(ErrorCode.INVALID_INPUT)
+        else:
+            resource = path(href)
+        if discovered:
+            if resource == self.home:
+                return resource
+            if (
+                resource.startswith(self.home)
+                and resource.endswith("/")
+                and "/" not in resource[len(self.home) : -1]
+                and resource != self.home
+            ):
+                return resource
+        for root in self.roots:
+            if resource == root or (
+                resource.startswith(root)
+                and resource[len(root) :]
+                and "/" not in resource[len(root) :]
+            ):
+                return resource
+        raise SafeError(ErrorCode.INVALID_INPUT)
+
+    async def request(
+        self,
+        method: str,
+        href: str,
+        *,
+        body=None,
+        expected_revision=None,
+        create=False,
+        max_bytes=MAX_DAV_BYTES,
+    ) -> HTTPResult:
+        if (
+            method not in {"PROPFIND", "REPORT", "GET", "PUT"}
+            or not 1 <= max_bytes <= MAX_DAV_BYTES
+        ):
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        resource = self.validated_href(href, discovered=self.discovery)
+        if self.discovery:
+            if method != "PROPFIND" or resource != self.home:
+                raise SafeError(ErrorCode.INVALID_INPUT)
+        elif (method in {"REPORT", "PROPFIND"}) != resource.endswith("/"):
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        if method != "PUT" and (create or expected_revision is not None):
+            raise SafeError(ErrorCode.INVALID_INPUT)
+        headers = {"Accept-Encoding": "identity"}
+        if method == "PROPFIND":
+            headers.update(
+                {
+                    "Depth": "1" if self.discovery else "0",
+                    "Content-Type": "application/xml; charset=utf-8",
+                }
+            )
+        elif method == "REPORT":
+            headers.update(
+                {"Depth": "1", "Content-Type": "application/xml; charset=utf-8"}
+            )
+        elif method == "PUT":
+            if create == (expected_revision is not None) or (
+                expected_revision is not None and not strong_etag(expected_revision)
+            ):
+                raise SafeError(ErrorCode.INVALID_INPUT)
+            headers["Content-Type"] = "text/calendar; charset=utf-8"
+            headers["If-None-Match" if create else "If-Match"] = (
+                "*" if create else expected_revision
+            )
+        try:
+            if method == "PUT":
+                self.write_started = True
+            async with self.http.stream(
+                method,
+                self.origin + resource,
+                headers=headers,
+                content=body,
+                auth=httpx.BasicAuth(self.profile.username, self.profile.password),
+            ) as response:
+                status = response.status_code
+                failures = {
+                    401: ErrorCode.AUTH_FAILED,
+                    403: ErrorCode.PERMISSION_DENIED,
+                    404: ErrorCode.NOT_FOUND,
+                    412: ErrorCode.CONFLICT,
+                }
+                if status in failures:
+                    raise SafeError(failures[status])
+                allowed = {
+                    "PROPFIND": {207},
+                    "REPORT": {207},
+                    "GET": {200},
+                    "PUT": {200, 201, 204},
+                }
+                if status not in allowed[method]:
+                    if method == "PUT" and status >= 500:
+                        raise SafeError(ErrorCode.UNKNOWN_WRITE_OUTCOME)
+                    raise SafeError(ErrorCode.BAD_RESPONSE)
+                etag = response.headers.get("ETag")
+                if method == "PUT":
+                    # Status and ETag suffice. Consuming an unused response body
+                    # could turn an acknowledged write into a false failure.
+                    return HTTPResult(status, b"", etag if strong_etag(etag) else None)
+                # Reject compressed responses to bound decompression memory as well as bytes.
+                if (
+                    response.headers.get("Content-Encoding", "identity").lower()
+                    != "identity"
+                ):
+                    raise SafeError(ErrorCode.BAD_RESPONSE)
+                length = response.headers.get("Content-Length")
+                if length is not None:
+                    try:
+                        if int(length) < 0:
+                            raise ValueError("length")
+                        if int(length) > max_bytes:
+                            raise SafeError(ErrorCode.LIMIT_EXCEEDED)
+                    except ValueError:
+                        raise SafeError(ErrorCode.BAD_RESPONSE) from None
+                data = bytearray()
+                async for chunk in response.aiter_bytes():
+                    if len(data) + len(chunk) > max_bytes:
+                        raise SafeError(ErrorCode.LIMIT_EXCEEDED)
+                    data.extend(chunk)
+                etag = response.headers.get("ETag")
+                return HTTPResult(
+                    status, bytes(data), etag if strong_etag(etag) else None
+                )
+        except httpx.HTTPError:
+            raise SafeError(
+                ErrorCode.UNKNOWN_WRITE_OUTCOME
+                if method == "PUT"
+                else ErrorCode.NETWORK_ERROR
+            ) from None