modelcontextprotocol--python-sdk/tests/server/mcpserver/test_elicitation.py

"""Test the elicitation feature over the in-memory client transport."""

from typing import Any, Literal

import mcp_types as types
import pytest
from mcp_types import ElicitRequestParams, ElicitResult, TextContent
from pydantic import BaseModel, Field

from mcp import Client
from mcp.client import ClientRequestContext
from mcp.client.session import ElicitationFnT
from mcp.server.mcpserver import Context, MCPServer


# Shared schema for basic tests
class AnswerSchema(BaseModel):
    answer: str = Field(description="The user's answer to the question")


def create_ask_user_tool(mcp: MCPServer):
    """Create a standard ask_user tool that handles all elicitation responses."""

    @mcp.tool(description="A tool that uses elicitation")
    async def ask_user(prompt: str, ctx: Context) -> str:
        result = await ctx.elicit(message=f"Tool wants to ask: {prompt}", schema=AnswerSchema)

        if result.action == "accept" and result.data:
            return f"User answered: {result.data.answer}"
        elif result.action == "decline":
            return "User declined to answer"
        else:  # pragma: no cover
            return "User cancelled"

    return ask_user


async def call_tool_and_assert(
    mcp: MCPServer,
    elicitation_callback: ElicitationFnT,
    tool_name: str,
    args: dict[str, Any],
    expected_text: str | None = None,
    text_contains: list[str] | None = None,
):
    """Helper to create session, call tool, and assert result."""
    async with Client(mcp, mode="legacy", elicitation_callback=elicitation_callback) as client:
        result = await client.call_tool(tool_name, args)
        assert len(result.content) == 1
        assert isinstance(result.content[0], TextContent)

        if expected_text is not None:
            assert result.content[0].text == expected_text
        elif text_contains is not None:  # pragma: no branch
            for substring in text_contains:
                assert substring in result.content[0].text

        return result


@pytest.mark.anyio
async def test_elicitation_accept_returns_the_users_answer_to_the_tool():
    """An accepted elicitation delivers the user's content back to the requesting tool."""
    mcp = MCPServer(name="ElicitationServer")
    create_ask_user_tool(mcp)

    # Create a custom handler for elicitation requests
    async def elicitation_callback(context: ClientRequestContext, params: ElicitRequestParams):
        if params.message == "Tool wants to ask: What is your name?":
            return ElicitResult(action="accept", content={"answer": "Test User"})
        else:  # pragma: no cover
            raise ValueError(f"Unexpected elicitation message: {params.message}")

    await call_tool_and_assert(
        mcp, elicitation_callback, "ask_user", {"prompt": "What is your name?"}, "User answered: Test User"
    )


@pytest.mark.anyio
async def test_elicitation_decline_reaches_the_tool_without_content():
    """A declined elicitation reports the decline to the tool, with no content attached."""
    mcp = MCPServer(name="ElicitationDeclineServer")
    create_ask_user_tool(mcp)

    async def elicitation_callback(context: ClientRequestContext, params: ElicitRequestParams):
        return ElicitResult(action="decline")

    await call_tool_and_assert(
        mcp, elicitation_callback, "ask_user", {"prompt": "What is your name?"}, "User declined to answer"
    )


@pytest.mark.anyio
async def test_elicitation_schema_validation():
    """Test that elicitation schemas must only contain primitive types."""
    mcp = MCPServer(name="ValidationTestServer")

    def create_validation_tool(name: str, schema_class: type[BaseModel]):
        @mcp.tool(name=name, description=f"Tool testing {name}")
        async def tool(ctx: Context) -> str:
            try:
                await ctx.elicit(message="This should fail validation", schema=schema_class)
                return "Should not reach here"  # pragma: no cover
            except TypeError as e:
                return f"Validation failed as expected: {str(e)}"

        return tool

    # Test cases for invalid schemas
    class InvalidListSchema(BaseModel):
        numbers: list[int] = Field(description="List of numbers")

    class NestedModel(BaseModel):
        value: str

    class InvalidNestedSchema(BaseModel):
        nested: NestedModel = Field(description="Nested model")

    create_validation_tool("invalid_list", InvalidListSchema)
    create_validation_tool("nested_model", InvalidNestedSchema)

    # Dummy callback (won't be called due to validation failure)
    async def elicitation_callback(context: ClientRequestContext, params: ElicitRequestParams):  # pragma: no cover
        return ElicitResult(action="accept", content={})

    async with Client(mcp, mode="legacy", elicitation_callback=elicitation_callback) as client:
        # Test both invalid schemas
        for tool_name, field_name in [("invalid_list", "numbers"), ("nested_model", "nested")]:
            result = await client.call_tool(tool_name, {})
            assert len(result.content) == 1
            assert isinstance(result.content[0], TextContent)
            assert "Validation failed as expected" in result.content[0].text
            assert field_name in result.content[0].text


@pytest.mark.anyio
async def test_elicitation_with_optional_fields():
    """Test that Optional fields work correctly in elicitation schemas."""
    mcp = MCPServer(name="OptionalFieldServer")

    class OptionalSchema(BaseModel):
        required_name: str = Field(description="Your name (required)")
        optional_age: int | None = Field(default=None, description="Your age (optional)")
        optional_email: str | None = Field(default=None, description="Your email (optional)")
        subscribe: bool | None = Field(default=False, description="Subscribe to newsletter?")

    @mcp.tool(description="Tool with optional fields")
    async def optional_tool(ctx: Context) -> str:
        result = await ctx.elicit(message="Please provide your information", schema=OptionalSchema)

        if result.action == "accept" and result.data:
            info = [f"Name: {result.data.required_name}"]
            if result.data.optional_age is not None:
                info.append(f"Age: {result.data.optional_age}")
            if result.data.optional_email is not None:
                info.append(f"Email: {result.data.optional_email}")
            info.append(f"Subscribe: {result.data.subscribe}")
            return ", ".join(info)
        else:  # pragma: no cover
            return f"User {result.action}"

    # Test cases with different field combinations
    test_cases: list[tuple[dict[str, Any], str]] = [
        (
            # All fields provided
            {"required_name": "John Doe", "optional_age": 30, "optional_email": "john@example.com", "subscribe": True},
            "Name: John Doe, Age: 30, Email: john@example.com, Subscribe: True",
        ),
        (
            # Only required fields
            {"required_name": "Jane Smith"},
            "Name: Jane Smith, Subscribe: False",
        ),
    ]

    for content, expected in test_cases:

        async def callback(context: ClientRequestContext, params: ElicitRequestParams):
            assert isinstance(params, types.ElicitRequestFormParams)
            # Optional fields render as the bare primitive (no anyOf), absent from `required`.
            assert params.requested_schema["properties"]["optional_age"] == {
                "type": "integer",
                "title": "Optional Age",
                "description": "Your age (optional)",
            }
            assert params.requested_schema["required"] == ["required_name"]
            return ElicitResult(action="accept", content=content)

        await call_tool_and_assert(mcp, callback, "optional_tool", {}, expected)

    # Test invalid optional field
    class InvalidOptionalSchema(BaseModel):
        name: str = Field(description="Name")
        optional_list: list[int] | None = Field(default=None, description="Invalid optional list")

    @mcp.tool(description="Tool with invalid optional field")
    async def invalid_optional_tool(ctx: Context) -> str:
        try:
            await ctx.elicit(message="This should fail", schema=InvalidOptionalSchema)
            return "Should not reach here"  # pragma: no cover
        except TypeError as e:
            return f"Validation failed: {str(e)}"

    async def elicitation_callback(context: ClientRequestContext, params: ElicitRequestParams):  # pragma: no cover
        return ElicitResult(action="accept", content={})

    await call_tool_and_assert(
        mcp,
        elicitation_callback,
        "invalid_optional_tool",
        {},
        text_contains=["Validation failed:", "optional_list"],
    )

    # Bare `list[str]` renders without enum items and so is not a spec MultiSelectEnumSchema.
    class BareListSchema(BaseModel):
        name: str = Field(description="Name")
        tags: list[str] = Field(description="Tags")

    def make_reject_tool(tool_name: str, schema_cls: type[BaseModel]) -> None:
        @mcp.tool(name=tool_name, description="Tool with a rejected field")
        async def _tool(ctx: Context) -> str:
            try:
                await ctx.elicit(message="Provide value", schema=schema_cls)
            except TypeError as e:
                return f"Validation failed: {str(e)}"
            raise NotImplementedError

    make_reject_tool("bare_list_tool", BareListSchema)
    await call_tool_and_assert(
        mcp, elicitation_callback, "bare_list_tool", {}, text_contains=["Validation failed:", "tags"]
    )

    # A union of two primitives renders as `anyOf`, outside `PrimitiveSchemaDefinition`.
    class MultiPrimitiveSchema(BaseModel):
        value: int | str = Field(description="Value")

    make_reject_tool("multi_primitive_tool", MultiPrimitiveSchema)
    await call_tool_and_assert(
        mcp, elicitation_callback, "multi_primitive_tool", {}, text_contains=["Validation failed:", "value"]
    )


@pytest.mark.anyio
async def test_elicitation_with_default_values():
    """Test that default values work correctly in elicitation schemas and are included in JSON."""
    mcp = MCPServer(name="DefaultValuesServer")

    class DefaultsSchema(BaseModel):
        name: str = Field(default="Guest", description="User name")
        age: int = Field(default=18, description="User age")
        subscribe: bool = Field(default=True, description="Subscribe to newsletter")
        email: str = Field(description="Email address (required)")

    @mcp.tool(description="Tool with default values")
    async def defaults_tool(ctx: Context) -> str:
        result = await ctx.elicit(message="Please provide your information", schema=DefaultsSchema)

        if result.action == "accept" and result.data:
            return (
                f"Name: {result.data.name}, Age: {result.data.age}, "
                f"Subscribe: {result.data.subscribe}, Email: {result.data.email}"
            )
        else:  # pragma: no cover
            return f"User {result.action}"

    # First verify that defaults are present in the JSON schema sent to clients
    async def callback_schema_verify(context: ClientRequestContext, params: ElicitRequestParams):
        # Verify the schema includes defaults
        assert isinstance(params, types.ElicitRequestFormParams), "Expected form mode elicitation"
        schema = params.requested_schema
        props = schema["properties"]

        assert props["name"]["default"] == "Guest"
        assert props["age"]["default"] == 18
        assert props["subscribe"]["default"] is True
        assert "default" not in props["email"]  # Required field has no default

        return ElicitResult(action="accept", content={"email": "test@example.com"})

    await call_tool_and_assert(
        mcp,
        callback_schema_verify,
        "defaults_tool",
        {},
        "Name: Guest, Age: 18, Subscribe: True, Email: test@example.com",
    )

    # Test overriding defaults
    async def callback_override(context: ClientRequestContext, params: ElicitRequestParams):
        return ElicitResult(
            action="accept", content={"email": "john@example.com", "name": "John", "age": 25, "subscribe": False}
        )

    await call_tool_and_assert(
        mcp, callback_override, "defaults_tool", {}, "Name: John, Age: 25, Subscribe: False, Email: john@example.com"
    )


@pytest.mark.anyio
async def test_elicitation_with_enum_titles():
    """Test elicitation with enum schemas using oneOf/anyOf for titles."""
    mcp = MCPServer(name="ColorPreferencesApp")

    # Test single-select with titles using oneOf
    class FavoriteColorSchema(BaseModel):
        user_name: str = Field(description="Your name")
        favorite_color: str = Field(
            description="Select your favorite color",
            json_schema_extra={
                "oneOf": [
                    {"const": "red", "title": "Red"},
                    {"const": "green", "title": "Green"},
                    {"const": "blue", "title": "Blue"},
                    {"const": "yellow", "title": "Yellow"},
                ]
            },
        )

    @mcp.tool(description="Single color selection")
    async def select_favorite_color(ctx: Context) -> str:
        result = await ctx.elicit(message="Select your favorite color", schema=FavoriteColorSchema)
        if result.action == "accept" and result.data:
            return f"User: {result.data.user_name}, Favorite: {result.data.favorite_color}"
        return f"User {result.action}"  # pragma: no cover

    # Test legacy enumNames format
    class LegacyColorSchema(BaseModel):
        user_name: str = Field(description="Your name")
        color: str = Field(
            description="Select a color",
            json_schema_extra={"enum": ["red", "green", "blue"], "enumNames": ["Red", "Green", "Blue"]},
        )

    @mcp.tool(description="Legacy enum format")
    async def select_color_legacy(ctx: Context) -> str:
        result = await ctx.elicit(message="Select a color (legacy format)", schema=LegacyColorSchema)
        if result.action == "accept" and result.data:
            return f"User: {result.data.user_name}, Color: {result.data.color}"
        return f"User {result.action}"  # pragma: no cover

    # Test multi-select with titles using items.anyOf
    class FavoriteColorsSchema(BaseModel):
        user_name: str = Field(description="Your name")
        favorite_colors: list[str] = Field(
            description="Select your favorite colors",
            json_schema_extra={
                "items": {
                    "anyOf": [
                        {"const": "red", "title": "Red"},
                        {"const": "green", "title": "Green"},
                        {"const": "blue", "title": "Blue"},
                        {"const": "yellow", "title": "Yellow"},
                    ]
                }
            },
        )

    @mcp.tool(description="Multiple color selection")
    async def select_favorite_colors(ctx: Context) -> str:
        result = await ctx.elicit(message="Select your favorite colors", schema=FavoriteColorsSchema)
        if result.action == "accept" and result.data:
            return f"User: {result.data.user_name}, Colors: {', '.join(result.data.favorite_colors)}"
        raise NotImplementedError

    async def enum_callback(context: ClientRequestContext, params: ElicitRequestParams):
        if "colors" in params.message:
            return ElicitResult(action="accept", content={"user_name": "Bob", "favorite_colors": ["red", "green"]})
        if "legacy" in params.message:
            return ElicitResult(action="accept", content={"user_name": "Charlie", "color": "green"})
        return ElicitResult(action="accept", content={"user_name": "Alice", "favorite_color": "blue"})

    # Test single-select with titles
    await call_tool_and_assert(mcp, enum_callback, "select_favorite_color", {}, "User: Alice, Favorite: blue")

    # Test multi-select with titles
    await call_tool_and_assert(mcp, enum_callback, "select_favorite_colors", {}, "User: Bob, Colors: red, green")

    # Test legacy enumNames format
    await call_tool_and_assert(mcp, enum_callback, "select_color_legacy", {}, "User: Charlie, Color: green")


@pytest.mark.anyio
async def test_elicitation_literal_field_renders_as_a_spec_enum_schema():
    """`Literal[...]` and `list[Literal[...]]` render as the spec's enum schemas and pass the gate."""
    mcp = MCPServer(name="LiteralServer")

    class LiteralSchema(BaseModel):
        size: Literal["s", "m", "l"] = Field(description="Size")
        extras: list[Literal["a", "b"]] = Field(description="Extras")

    @mcp.tool(description="Literal selection")
    async def pick(ctx: Context) -> str:
        result = await ctx.elicit(message="Pick", schema=LiteralSchema)
        if result.action == "accept" and result.data:
            return f"{result.data.size}:{','.join(result.data.extras)}"
        raise NotImplementedError

    async def callback(context: ClientRequestContext, params: ElicitRequestParams):
        assert isinstance(params, types.ElicitRequestFormParams)
        assert params.requested_schema["properties"]["size"]["enum"] == ["s", "m", "l"]
        assert params.requested_schema["properties"]["extras"]["items"]["enum"] == ["a", "b"]
        return ElicitResult(action="accept", content={"size": "m", "extras": ["a"]})

    await call_tool_and_assert(mcp, callback, "pick", {}, "m:a")