diff --git a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py index 8e473c1cb2..853208a538 100644 --- a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py +++ b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py @@ -50,7 +50,9 @@ from litellm.proxy._experimental.mcp_server.oauth2_token_cache import resolve_mc from litellm.proxy._experimental.mcp_server.utils import ( MCP_TOOL_PREFIX_SEPARATOR, add_server_prefix_to_name, + compute_short_server_prefix, get_server_prefix, + is_short_mcp_tool_prefix_enabled, is_tool_name_prefixed, iter_known_server_prefixes, merge_mcp_headers, @@ -365,6 +367,7 @@ class MCPServerManager: aws_session_name=server_config.get("aws_session_name", None), instructions=server_config.get("instructions", None), ) + self._assign_unique_short_prefix(new_server) self.config_mcp_servers[server_id] = new_server # Check if this is an OpenAPI-based server @@ -727,6 +730,7 @@ class MCPServerManager: try: if mcp_server.server_id not in self.registry: new_server = await self.build_mcp_server_from_table(mcp_server) + self._assign_unique_short_prefix(new_server) self.registry[mcp_server.server_id] = new_server await self._maybe_register_openapi_tools(new_server) verbose_logger.debug(f"Added MCP Server: {new_server.name}") @@ -739,6 +743,12 @@ class MCPServerManager: try: if mcp_server.server_id in self.registry: new_server = await self.build_mcp_server_from_table(mcp_server) + # Carry the previously-resolved short prefix across so the + # tool names stay stable for clients holding cached lists. + existing_prefix = self.registry[mcp_server.server_id].short_prefix + if existing_prefix and not new_server.short_prefix: + new_server.short_prefix = existing_prefix + self._assign_unique_short_prefix(new_server) self.registry[mcp_server.server_id] = new_server await self._maybe_register_openapi_tools(new_server) verbose_logger.debug(f"Updated MCP Server: {new_server.name}") @@ -1815,6 +1825,63 @@ class MCPServerManager: verbose_logger.warning(f"Error listing tools from {server_name}: {str(e)}") return [] + _SHORT_PREFIX_MAX_REHASH_ATTEMPTS = 1024 + + def _assign_unique_short_prefix(self, server: MCPServer) -> None: + """Resolve and cache a collision-free short tool prefix on ``server``. + + Called at registration time for every MCP server entering the + registry. Mutates ``server.short_prefix`` in place. No-ops when + ``LITELLM_USE_SHORT_MCP_TOOL_PREFIX`` is disabled, when the server + has no ``server_id`` (synthetic temp-server objects), or when a + prefix is already cached. + + Collision strategy: take the natural hash; if it's already used by + a *different* server in the combined registry, rehash with an + incrementing attempt counter until we find an unused slot. The + attempt counter is folded into the hash so the resulting prefix is + still deterministic for a given (server_id, set-of-other-server-ids) + pair within one process. + """ + if not is_short_mcp_tool_prefix_enabled(): + return + if server.short_prefix: + return + if not server.server_id: + return + + used: Dict[str, str] = {} + for other in self.get_registry().values(): + if other.server_id == server.server_id: + continue + if other.short_prefix: + used[other.short_prefix] = other.server_id + + for attempt in range(self._SHORT_PREFIX_MAX_REHASH_ATTEMPTS): + candidate = compute_short_server_prefix(server.server_id, attempt=attempt) + if candidate not in used: + server.short_prefix = candidate + if attempt > 0: + verbose_logger.info( + "MCP short-prefix collision resolved for server %s: " + "natural hash collided with %s, using rehashed prefix " + "%s (attempt=%d).", + server.server_id, + used.get( + compute_short_server_prefix(server.server_id, attempt=0), + "", + ), + candidate, + attempt, + ) + return + + raise RuntimeError( + f"Unable to assign a unique short MCP tool prefix for server " + f"{server.server_id} after {self._SHORT_PREFIX_MAX_REHASH_ATTEMPTS} " + "attempts; the 3-character prefix space is too crowded." + ) + def _create_prefixed_tools( self, tools: List[MCPTool], server: MCPServer, add_prefix: bool = True ) -> List[MCPTool]: @@ -2681,6 +2748,9 @@ class MCPServerManager: previous_registry = self.registry new_registry: Dict[str, MCPServer] = {} + # Stage one: build every server. Stage two assigns short prefixes + # against the *full* set so dedup is deterministic regardless of + # iteration order. for server in db_mcp_servers: existing_server = previous_registry.get(server.server_id) @@ -2704,10 +2774,18 @@ class MCPServerManager: f"Building server from DB: {server.server_id} ({server.server_name})" ) new_server = await self.build_mcp_server_from_table(server) + # Carry the cached short_prefix from the previous registry entry + # (if any) so the prefix is stable across reloads. + if existing_server is not None and existing_server.short_prefix: + new_server.short_prefix = existing_server.short_prefix new_registry[server.server_id] = new_server await self._maybe_register_openapi_tools(new_server) + # Swap in the new registry first so _assign_unique_short_prefix + # sees the complete set when checking for collisions. self.registry = new_registry + for new_server in new_registry.values(): + self._assign_unique_short_prefix(new_server) verbose_logger.debug( "MCP registry refreshed (%s servers in registry)", len(new_registry) diff --git a/litellm/proxy/_experimental/mcp_server/utils.py b/litellm/proxy/_experimental/mcp_server/utils.py index 42910cc790..a0c278b906 100644 --- a/litellm/proxy/_experimental/mcp_server/utils.py +++ b/litellm/proxy/_experimental/mcp_server/utils.py @@ -54,17 +54,22 @@ def is_short_mcp_tool_prefix_enabled() -> bool: return raw.strip().lower() in ("1", "true", "yes", "on") -def compute_short_server_prefix(server_id: str) -> str: +def compute_short_server_prefix(server_id: str, attempt: int = 0) -> str: """Derive the deterministic three-character base62 prefix for a server. - Uses SHA-256 of the server_id and folds the first eight bytes into a - base62 string. An empty server_id raises ValueError — short prefixes - require a stable identifier to be deterministic. + Uses SHA-256 of ``f"{server_id}#{attempt}"`` and folds the first eight + bytes into a base62 string. Pass ``attempt > 0`` to rehash to a + different prefix when the natural hash collides with a prefix already + assigned to another server (see + ``MCPServerManager._assign_unique_short_prefix``). An empty server_id + raises ValueError — short prefixes require a stable identifier to be + deterministic. """ if not server_id: raise ValueError("compute_short_server_prefix requires a non-empty server_id") - digest = hashlib.sha256(server_id.encode("utf-8")).digest() + seed = server_id if attempt == 0 else f"{server_id}#{attempt}" + digest = hashlib.sha256(seed.encode("utf-8")).digest() value = int.from_bytes(digest[:8], "big") chars = [] for _ in range(SHORT_MCP_TOOL_PREFIX_LENGTH): @@ -143,11 +148,18 @@ def get_server_prefix(server: Any) -> str: """Return the prefix for a server. When the short-prefix mode is enabled (``LITELLM_USE_SHORT_MCP_TOOL_PREFIX``) - a deterministic three-character base62 ID derived from ``server_id`` is - returned. Otherwise we fall back to the historical behaviour: alias if - present, else server_name, else server_id. + a three-character base62 ID is returned. We prefer the cached + ``server.short_prefix`` value when set — that field is populated at + registration time by ``MCPServerManager._assign_unique_short_prefix`` + and resolves natural-hash collisions deterministically — and only fall + back to the natural hash for ad-hoc / temp-server objects without a + cached value. In default mode the historical behaviour is preserved: + alias if present, else server_name, else server_id. """ if is_short_mcp_tool_prefix_enabled(): + cached = getattr(server, "short_prefix", None) + if cached: + return cached server_id = getattr(server, "server_id", None) if server_id: return compute_short_server_prefix(server_id) @@ -177,6 +189,7 @@ def iter_known_server_prefixes(server: Any) -> Iterator[str]: yield value yield from _emit(get_server_prefix(server)) + yield from _emit(getattr(server, "short_prefix", None)) server_id = getattr(server, "server_id", None) if server_id: diff --git a/litellm/types/mcp_server/mcp_server_manager.py b/litellm/types/mcp_server/mcp_server_manager.py index ace8c8a418..8f8673b0a7 100644 --- a/litellm/types/mcp_server/mcp_server_manager.py +++ b/litellm/types/mcp_server/mcp_server_manager.py @@ -81,6 +81,12 @@ class MCPServer(BaseModel): # Defaults to the token's expires_in minus the expiry buffer, or # MCP_PER_USER_TOKEN_DEFAULT_TTL when expires_in is absent. token_storage_ttl_seconds: Optional[int] = None + # Resolved short-ID tool prefix when LITELLM_USE_SHORT_MCP_TOOL_PREFIX is + # enabled. Set by ``MCPServerManager._assign_unique_short_prefix`` at + # registration time so that natural-hash collisions between two + # different ``server_id`` values are bumped deterministically. Left + # ``None`` in default-prefix mode. + short_prefix: Optional[str] = None model_config = ConfigDict(arbitrary_types_allowed=True) @property diff --git a/tests/test_litellm/proxy/_experimental/mcp_server/test_short_mcp_tool_prefix.py b/tests/test_litellm/proxy/_experimental/mcp_server/test_short_mcp_tool_prefix.py index aef6546c81..cdaecfb227 100644 --- a/tests/test_litellm/proxy/_experimental/mcp_server/test_short_mcp_tool_prefix.py +++ b/tests/test_litellm/proxy/_experimental/mcp_server/test_short_mcp_tool_prefix.py @@ -205,3 +205,84 @@ class TestManagerShortPrefix: prefix = get_server_prefix(server) full = add_server_prefix_to_name("get_repo", prefix) assert len(full) < 60 + + +# --------------------------------------------------------------------------- +# Collision-resolution at registration time +# --------------------------------------------------------------------------- + + +class TestShortPrefixCollisionResolution: + """``_assign_unique_short_prefix`` must rehash on collision. + + The dedup path is exercised by forcing two distinct ``server_id`` + values to both hash to the same natural prefix via a monkeypatched + ``compute_short_server_prefix``. + """ + + def test_no_op_when_flag_off(self): + manager = MCPServerManager() + server = _make_server(server_id="abc") + manager._assign_unique_short_prefix(server) + assert server.short_prefix is None + + def test_assigns_natural_hash_when_no_collision(self, monkeypatch): + from litellm.proxy._experimental.mcp_server import utils as mcp_utils + + monkeypatch.setenv("LITELLM_USE_SHORT_MCP_TOOL_PREFIX", "true") + manager = MCPServerManager() + server = _make_server(server_id="abc") + manager._assign_unique_short_prefix(server) + + assert server.short_prefix == mcp_utils.compute_short_server_prefix("abc") + + def test_rehashes_when_natural_hash_collides(self, monkeypatch): + """Two server_ids that natural-hash to the same prefix get + deterministic, distinct short prefixes.""" + monkeypatch.setenv("LITELLM_USE_SHORT_MCP_TOOL_PREFIX", "true") + + # Force every attempt=0 hash to "AAA" and attempt=1 to "AAB". + # That way the second server registered must rehash to "AAB". + from litellm.proxy._experimental.mcp_server import utils as mcp_utils + + def _fake_hash(server_id: str, attempt: int = 0) -> str: + return "AAA" if attempt == 0 else f"AA{chr(ord('A') + attempt)}" + + monkeypatch.setattr(mcp_utils, "compute_short_server_prefix", _fake_hash) + # Also patch the symbol that the manager imported at module load. + from litellm.proxy._experimental.mcp_server import ( + mcp_server_manager as mgr_module, + ) + + monkeypatch.setattr(mgr_module, "compute_short_server_prefix", _fake_hash) + + manager = MCPServerManager() + first = _make_server(server_id="server-1", alias="srv1") + second = _make_server(server_id="server-2", alias="srv2") + + # Pretend both are already in the registry so dedup sees both. + manager.registry[first.server_id] = first + manager._assign_unique_short_prefix(first) + manager.registry[second.server_id] = second + manager._assign_unique_short_prefix(second) + + assert first.short_prefix == "AAA" + assert second.short_prefix == "AAB" + assert first.short_prefix != second.short_prefix + + def test_cached_prefix_is_reused(self, monkeypatch): + monkeypatch.setenv("LITELLM_USE_SHORT_MCP_TOOL_PREFIX", "true") + manager = MCPServerManager() + server = _make_server(server_id="abc") + server.short_prefix = "ZZZ" # pretend a previous registration set this + + manager._assign_unique_short_prefix(server) + + assert server.short_prefix == "ZZZ" + + def test_get_server_prefix_prefers_cached(self, monkeypatch): + monkeypatch.setenv("LITELLM_USE_SHORT_MCP_TOOL_PREFIX", "true") + server = _make_server(server_id="abc") + server.short_prefix = "Q9q" + + assert get_server_prefix(server) == "Q9q"