MCP servers, over streamable HTTP
A server is a row with a URL; its tools are discovered by a button and cached, then offered beside the built-in ones. Written by hand rather than taken from the reference SDK, because that SDK's transport does its own connecting -- and the one thing that must not be bypassed is check_url on every hop. Owning the transport is the point; the framing beside it is the small part. Sessions are per call: initialize, initialized, the call, a best-effort DELETE. Caching one wants an owner, a TTL, eviction, a lock and a shutdown hook, and the server may expire it under all of that anyway -- ToolContext is a session-free snapshot precisely so nothing in a tool holds live state. A server's names and descriptions reach the model as instructions and are bounded before they do; what it returns is escaped preformatted text, never markdown. Tools are namespaced per server, so two servers exposing "search" do not collide and neither shadows a built-in. Also: a round's calls now run together under a semaphore, results indexed so each tool turn stays paired with its call, and generation.status names what is running -- a remote tool is latency-bound, and a silent pause is what a hang looks like. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Jaroslav Beneš
@@ -31,11 +31,15 @@ from lembas.db.models import (
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SECRET_PLACEMENTS,
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CustomTool,
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Group,
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McpServer,
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)
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from lembas.services import custom_tools
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from lembas.services import prompts as prompts_service
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from lembas.services import tools as tools_service
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from lembas.services.crypto import UNCHANGED_SENTINEL, decrypt, keep_or_replace, mask
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from lembas.services.fetch import FetchError, check_url
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from lembas.services.mcp import client as mcp_client
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from lembas.services.mcp import registry as mcp_registry
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from lembas.web.templating import render
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log = logging.getLogger(__name__)
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@@ -413,3 +417,245 @@ async def update_tool(request: Request, db: Db, user: AdminUser, tool_id: str) -
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log.info("%s updated custom tool %s", user.email, tool.slug)
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return _back(f"Saved {tool.name}.")
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# --- MCP servers -------------------------------------------------------------
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MCP_SLUG_PATTERN = re.compile(r"^[a-z0-9][a-z0-9_-]{0,23}$")
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def _server(db: Db, server_id: str) -> McpServer:
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server = db.get(McpServer, server_id)
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if server is None:
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raise HTTPException(status.HTTP_404_NOT_FOUND, "That server no longer exists.")
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return server
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def _mcp_back(message: str = "") -> Response:
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target = f"/admin/mcp?saved={message}" if message else "/admin/mcp"
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return RedirectResponse(target, status_code=status.HTTP_303_SEE_OTHER)
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def _populate_server(server: McpServer, form) -> None:
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server.name = str(form.get("name") or "").strip()[:120]
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server.url = str(form.get("url") or "").strip()[:1000]
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server.guidance = str(form.get("guidance") or "").replace("\r\n", "\n").strip()
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server.headers_json = _parse_headers(str(form.get("headers") or ""))
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placement = str(form.get("secret_placement") or SECRET_NONE)
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server.secret_placement = placement if placement in SECRET_PLACEMENTS else SECRET_NONE
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server.secret_name = str(form.get("secret_name") or "Authorization").strip()[:120]
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server.timeout = _number(
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form.get("timeout"), default=30, low=mcp_client.MIN_TIMEOUT, high=mcp_client.MAX_TIMEOUT
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)
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server.max_chars = _number(
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form.get("max_chars"), default=8000, low=mcp_client.MIN_CHARS, high=mcp_client.MAX_CHARS
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)
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server.position = _number(form.get("position"), default=server.position or 0, low=0, high=999)
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server.allow_private = "allow_private" in form
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server.enabled = "enabled" in form
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server.public = "public" in form
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# One checkbox per advertised tool, so an unticked one is absent. The
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# stored map holds only the refusals; absent means on.
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if "tool_choices" in form:
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offered = set(form.getlist("tool_names"))
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chosen = set(form.getlist("tool_names_on"))
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server.tool_overrides_json = dict.fromkeys(offered - chosen, False)
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def _server_problem(db: Db, server: McpServer, form, *, existing_id: str = "") -> str:
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if not server.name:
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return "A server needs a name."
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slug = str(form.get("slug") or "").strip().lower()
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if not MCP_SLUG_PATTERN.match(slug):
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return (
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"The identifier must be lowercase letters, digits, hyphens or "
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"underscores, and at most 24 characters. It prefixes every tool "
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"name this server offers."
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)
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clash = db.scalar(select(McpServer).where(McpServer.slug == slug))
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if clash is not None and clash.id != existing_id:
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return f"There is already a server called “{slug}”."
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server.slug = slug
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try:
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check_url(server.url, allow_private=True)
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except FetchError as exc:
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return exc.message
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return ""
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def _server_detail(
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request: Request, db: Db, server: McpServer, *, is_new: bool, error: str = "", **extra
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):
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key = f"tool.mcp_{server.slug}" if server.slug else ""
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overrides = server.tool_overrides_json or {}
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return render(
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request,
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"admin/mcp_detail.html",
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{
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"server": server,
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"is_new": is_new,
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"error": error,
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"groups": list(db.scalars(select(Group).order_by(Group.name))),
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"selected_groups": extra.pop(
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"selected_groups", {group.id for group in (server.groups if server.id else [])}
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),
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"headers_text": extra.pop("headers_text", _headers_text(server.headers_json)),
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"tools": [
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{**entry, "on": overrides.get(entry.get("name"), True)}
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for entry in (server.tools_json or [])
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if isinstance(entry, dict)
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],
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"masked": mask(decrypt(server.secret_encrypted)) if server.secret_encrypted else "",
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"unchanged": UNCHANGED_SENTINEL,
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"secret_placements": SECRET_LABELS,
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"prompt_key": key,
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"prompt_overridden": key in prompts_service.stored(db),
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**extra,
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},
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)
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@router.get("/admin/mcp")
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async def mcp_page(request: Request, db: Db, user: AdminUser, saved: str = ""):
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servers = list(db.scalars(select(McpServer).order_by(McpServer.position, McpServer.slug)))
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return render(
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request,
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"admin/mcp.html",
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{
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"servers": servers,
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"counts": {server.id: len(server.tools_json or []) for server in servers},
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"saved": saved,
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},
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)
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# Registered before /{server_id}, for the reason given above.
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@router.get("/admin/mcp/new")
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async def new_server_page(request: Request, db: Db, user: AdminUser):
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draft = McpServer(
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name="",
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slug="",
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url="https://",
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secret_placement=SECRET_NONE,
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timeout=30,
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max_chars=8000,
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enabled=True,
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public=True,
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position=0,
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tools_json=[],
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tool_overrides_json={},
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)
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return _server_detail(request, db, draft, is_new=True)
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@router.post("/admin/mcp")
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async def create_server(request: Request, db: Db, user: AdminUser) -> Response:
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form = await request.form()
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draft = McpServer(headers_json={}, tools_json=[], tool_overrides_json={})
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_populate_server(draft, form)
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draft.position = db.scalar(select(func.coalesce(func.max(McpServer.position), -1))) + 1
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problem = _server_problem(db, draft, form)
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if problem:
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return _server_detail(
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request,
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db,
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draft,
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is_new=True,
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error=problem,
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headers_text=str(form.get("headers") or ""),
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selected_groups=set(form.getlist("group_ids")),
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)
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draft.secret_encrypted = keep_or_replace(str(form.get("secret") or ""), "")
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draft.groups = _chosen_groups(db, form, public=draft.public)
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db.add(draft)
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db.commit()
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# Discovered immediately, the way a new connection's models are: an
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# administrator who has just typed a URL wants to know whether it answered.
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count, error = await mcp_registry.refresh(db, draft)
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log.info("%s added MCP server %s (%d tools)", user.email, draft.slug, count)
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if error:
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return _mcp_back(f"Added {draft.name}, but it could not be reached: {error}")
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return _mcp_back(f"Added {draft.name} — {count} tool(s).")
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@router.get("/admin/mcp/{server_id}/edit")
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async def edit_server_page(request: Request, db: Db, user: AdminUser, server_id: str):
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return _server_detail(request, db, _server(db, server_id), is_new=False)
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@router.post("/admin/mcp/{server_id}/test")
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async def test_server(request: Request, db: Db, user: AdminUser, server_id: str):
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"""Contact the server and cache what it advertises.
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Returns the row fragment, swapped in place, exactly as "Test & refresh"
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does for a connection.
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"""
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server = _server(db, server_id)
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count, error = await mcp_registry.refresh(db, server)
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message = (
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f"{server.name}: {error}"
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if error
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else f"{server.name}: found {count} tool{'s' if count != 1 else ''}."
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)
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return render(
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request,
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"admin/_mcp_row.html",
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{
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"server": server,
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"tool_count": len(server.tools_json or []),
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"message": message,
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"message_kind": "error" if error else "success",
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},
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)
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@router.post("/admin/mcp/{server_id}/delete")
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async def delete_server(db: Db, user: AdminUser, server_id: str) -> Response:
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server = _server(db, server_id)
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name = server.name
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db.delete(server)
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db.commit()
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log.info("%s deleted MCP server %s", user.email, name)
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return _mcp_back(f"Deleted {name}.")
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@router.post("/admin/mcp/{server_id}")
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async def update_server(request: Request, db: Db, user: AdminUser, server_id: str) -> Response:
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server = _server(db, server_id)
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form = await request.form()
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draft = McpServer(headers_json={}, tools_json=[], position=server.position)
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_populate_server(draft, form)
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problem = _server_problem(db, draft, form, existing_id=server.id)
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if problem:
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draft.id = server.id
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draft.secret_encrypted = server.secret_encrypted
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draft.tools_json = server.tools_json
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return _server_detail(
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request,
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db,
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draft,
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is_new=False,
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error=problem,
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headers_text=str(form.get("headers") or ""),
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selected_groups=set(form.getlist("group_ids")),
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)
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_populate_server(server, form)
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server.slug = draft.slug
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server.secret_encrypted = keep_or_replace(
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str(form.get("secret") or ""), server.secret_encrypted
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)
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server.groups = _chosen_groups(db, form, public=server.public)
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db.commit()
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log.info("%s updated MCP server %s", user.email, server.slug)
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return _mcp_back(f"Saved {server.name}.")
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