mcp-python-sdk/tests/server/fastmcp/test_server.py

import base64
from pathlib import Path
from typing import TYPE_CHECKING, Union

import pytest
from mcp.shared.exceptions import McpError
from mcp.shared.memory import (
    create_connected_server_and_client_session as client_session,
)
from mcp.types import (
    ImageContent,
    TextContent,
    TextResourceContents,
    BlobResourceContents,
)
from pydantic import AnyUrl

from mcp.server.fastmcp import Context, FastMCP
from mcp.server.fastmcp.prompts.base import EmbeddedResource, Message, UserMessage
from mcp.server.fastmcp.resources import FileResource, FunctionResource
from mcp.server.fastmcp.utilities.types import Image

if TYPE_CHECKING:
    from mcp.server.fastmcp import Context


class TestServer:
    async def test_create_server(self):
        mcp = FastMCP()
        assert mcp.name == "FastMCP"

    async def test_add_tool_decorator(self):
        mcp = FastMCP()

        @mcp.tool()
        def add(x: int, y: int) -> int:
            return x + y

        assert len(mcp._tool_manager.list_tools()) == 1

    async def test_add_tool_decorator_incorrect_usage(self):
        mcp = FastMCP()

        with pytest.raises(TypeError, match="The @tool decorator was used incorrectly"):

            @mcp.tool  # Missing parentheses #type: ignore
            def add(x: int, y: int) -> int:
                return x + y

    async def test_add_resource_decorator(self):
        mcp = FastMCP()

        @mcp.resource("r://{x}")
        def get_data(x: str) -> str:
            return f"Data: {x}"

        assert len(mcp._resource_manager._templates) == 1

    async def test_add_resource_decorator_incorrect_usage(self):
        mcp = FastMCP()

        with pytest.raises(
            TypeError, match="The @resource decorator was used incorrectly"
        ):

            @mcp.resource  # Missing parentheses #type: ignore
            def get_data(x: str) -> str:
                return f"Data: {x}"


def tool_fn(x: int, y: int) -> int:
    return x + y


def error_tool_fn() -> None:
    raise ValueError("Test error")


def image_tool_fn(path: str) -> Image:
    return Image(path)


def mixed_content_tool_fn() -> list[Union[TextContent, ImageContent]]:
    return [
        TextContent(type="text", text="Hello"),
        ImageContent(type="image", data="abc", mimeType="image/png"),
    ]


class TestServerTools:
    async def test_add_tool(self):
        mcp = FastMCP()
        mcp.add_tool(tool_fn)
        mcp.add_tool(tool_fn)
        assert len(mcp._tool_manager.list_tools()) == 1

    async def test_list_tools(self):
        mcp = FastMCP()
        mcp.add_tool(tool_fn)
        async with client_session(mcp._mcp_server) as client:
            tools = await client.list_tools()
            assert len(tools.tools) == 1

    async def test_call_tool(self):
        mcp = FastMCP()
        mcp.add_tool(tool_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("my_tool", {"arg1": "value"})
            assert not hasattr(result, "error")
            assert len(result.content) > 0

    async def test_tool_exception_handling(self):
        mcp = FastMCP()
        mcp.add_tool(error_tool_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("error_tool_fn", {})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert "Test error" in content.text
            assert result.isError is True

    async def test_tool_error_handling(self):
        mcp = FastMCP()
        mcp.add_tool(error_tool_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("error_tool_fn", {})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert "Test error" in content.text
            assert result.isError is True

    async def test_tool_error_details(self):
        """Test that exception details are properly formatted in the response"""
        mcp = FastMCP()
        mcp.add_tool(error_tool_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("error_tool_fn", {})
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert isinstance(content.text, str)
            assert "Test error" in content.text
            assert result.isError is True

    async def test_tool_return_value_conversion(self):
        mcp = FastMCP()
        mcp.add_tool(tool_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("tool_fn", {"x": 1, "y": 2})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert content.text == "3"

    async def test_tool_image_helper(self, tmp_path: Path):
        # Create a test image
        image_path = tmp_path / "test.png"
        image_path.write_bytes(b"fake png data")

        mcp = FastMCP()
        mcp.add_tool(image_tool_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("image_tool_fn", {"path": str(image_path)})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, ImageContent)
            assert content.type == "image"
            assert content.mimeType == "image/png"
            # Verify base64 encoding
            decoded = base64.b64decode(content.data)
            assert decoded == b"fake png data"

    async def test_tool_mixed_content(self):
        mcp = FastMCP()
        mcp.add_tool(mixed_content_tool_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("mixed_content_tool_fn", {})
            assert len(result.content) == 2
            content1 = result.content[0]
            content2 = result.content[1]
            assert isinstance(content1, TextContent)
            assert content1.text == "Hello"
            assert isinstance(content2, ImageContent)
            assert content2.mimeType == "image/png"
            assert content2.data == "abc"

    async def test_tool_mixed_list_with_image(self, tmp_path: Path):
        """Test that lists containing Image objects and other types are handled correctly"""
        # Create a test image
        image_path = tmp_path / "test.png"
        image_path.write_bytes(b"test image data")

        def mixed_list_fn() -> list:
            return [
                "text message",
                Image(image_path),
                {"key": "value"},
                TextContent(type="text", text="direct content"),
            ]

        mcp = FastMCP()
        mcp.add_tool(mixed_list_fn)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("mixed_list_fn", {})
            assert len(result.content) == 4
            # Check text conversion
            content1 = result.content[0]
            assert isinstance(content1, TextContent)
            assert content1.text == "text message"
            # Check image conversion
            content2 = result.content[1]
            assert isinstance(content2, ImageContent)
            assert content2.mimeType == "image/png"
            assert base64.b64decode(content2.data) == b"test image data"
            # Check dict conversion
            content3 = result.content[2]
            assert isinstance(content3, TextContent)
            assert '"key": "value"' in content3.text
            # Check direct TextContent
            content4 = result.content[3]
            assert isinstance(content4, TextContent)
            assert content4.text == "direct content"


class TestServerResources:
    async def test_text_resource(self):
        mcp = FastMCP()

        def get_text():
            return "Hello, world!"

        resource = FunctionResource(
            uri=AnyUrl("resource://test"), name="test", fn=get_text
        )
        mcp.add_resource(resource)

        async with client_session(mcp._mcp_server) as client:
            result = await client.read_resource(AnyUrl("resource://test"))
            assert isinstance(result.contents[0], TextResourceContents)
            assert result.contents[0].text == "Hello, world!"

    async def test_binary_resource(self):
        mcp = FastMCP()

        def get_binary():
            return b"Binary data"

        resource = FunctionResource(
            uri=AnyUrl("resource://binary"),
            name="binary",
            fn=get_binary,
            mime_type="application/octet-stream",
        )
        mcp.add_resource(resource)

        async with client_session(mcp._mcp_server) as client:
            result = await client.read_resource(AnyUrl("resource://binary"))
            assert isinstance(result.contents[0], BlobResourceContents)
            assert result.contents[0].blob == base64.b64encode(b"Binary data").decode()

    async def test_file_resource_text(self, tmp_path: Path):
        mcp = FastMCP()

        # Create a text file
        text_file = tmp_path / "test.txt"
        text_file.write_text("Hello from file!")

        resource = FileResource(
            uri=AnyUrl("file://test.txt"), name="test.txt", path=text_file
        )
        mcp.add_resource(resource)

        async with client_session(mcp._mcp_server) as client:
            result = await client.read_resource(AnyUrl("file://test.txt"))
            assert isinstance(result.contents[0], TextResourceContents)
            assert result.contents[0].text == "Hello from file!"

    async def test_file_resource_binary(self, tmp_path: Path):
        mcp = FastMCP()

        # Create a binary file
        binary_file = tmp_path / "test.bin"
        binary_file.write_bytes(b"Binary file data")

        resource = FileResource(
            uri=AnyUrl("file://test.bin"),
            name="test.bin",
            path=binary_file,
            mime_type="application/octet-stream",
        )
        mcp.add_resource(resource)

        async with client_session(mcp._mcp_server) as client:
            result = await client.read_resource(AnyUrl("file://test.bin"))
            assert isinstance(result.contents[0], BlobResourceContents)
            assert (
                result.contents[0].blob
                == base64.b64encode(b"Binary file data").decode()
            )


class TestServerResourceTemplates:
    async def test_resource_with_params(self):
        """Test that a resource with function parameters raises an error if the URI
        parameters don't match"""
        mcp = FastMCP()

        with pytest.raises(ValueError, match="Mismatch between URI parameters"):

            @mcp.resource("resource://data")
            def get_data_fn(param: str) -> str:
                return f"Data: {param}"

    async def test_resource_with_uri_params(self):
        """Test that a resource with URI parameters is automatically a template"""
        mcp = FastMCP()

        with pytest.raises(ValueError, match="Mismatch between URI parameters"):

            @mcp.resource("resource://{param}")
            def get_data() -> str:
                return "Data"

    async def test_resource_with_untyped_params(self):
        """Test that a resource with untyped parameters raises an error"""
        mcp = FastMCP()

        @mcp.resource("resource://{param}")
        def get_data(param) -> str:
            return "Data"

    async def test_resource_matching_params(self):
        """Test that a resource with matching URI and function parameters works"""
        mcp = FastMCP()

        @mcp.resource("resource://{name}/data")
        def get_data(name: str) -> str:
            return f"Data for {name}"

        async with client_session(mcp._mcp_server) as client:
            result = await client.read_resource(AnyUrl("resource://test/data"))
            assert isinstance(result.contents[0], TextResourceContents)
            assert result.contents[0].text == "Data for test"

    async def test_resource_mismatched_params(self):
        """Test that mismatched parameters raise an error"""
        mcp = FastMCP()

        with pytest.raises(ValueError, match="Mismatch between URI parameters"):

            @mcp.resource("resource://{name}/data")
            def get_data(user: str) -> str:
                return f"Data for {user}"

    async def test_resource_multiple_params(self):
        """Test that multiple parameters work correctly"""
        mcp = FastMCP()

        @mcp.resource("resource://{org}/{repo}/data")
        def get_data(org: str, repo: str) -> str:
            return f"Data for {org}/{repo}"

        async with client_session(mcp._mcp_server) as client:
            result = await client.read_resource(
                AnyUrl("resource://cursor/fastmcp/data")
            )
            assert isinstance(result.contents[0], TextResourceContents)
            assert result.contents[0].text == "Data for cursor/fastmcp"

    async def test_resource_multiple_mismatched_params(self):
        """Test that mismatched parameters raise an error"""
        mcp = FastMCP()

        with pytest.raises(ValueError, match="Mismatch between URI parameters"):

            @mcp.resource("resource://{org}/{repo}/data")
            def get_data_mismatched(org: str, repo_2: str) -> str:
                return f"Data for {org}"

        """Test that a resource with no parameters works as a regular resource"""
        mcp = FastMCP()

        @mcp.resource("resource://static")
        def get_static_data() -> str:
            return "Static data"

        async with client_session(mcp._mcp_server) as client:
            result = await client.read_resource(AnyUrl("resource://static"))
            assert isinstance(result.contents[0], TextResourceContents)
            assert result.contents[0].text == "Static data"

    async def test_template_to_resource_conversion(self):
        """Test that templates are properly converted to resources when accessed"""
        mcp = FastMCP()

        @mcp.resource("resource://{name}/data")
        def get_data(name: str) -> str:
            return f"Data for {name}"

        # Should be registered as a template
        assert len(mcp._resource_manager._templates) == 1
        assert len(await mcp.list_resources()) == 0

        # When accessed, should create a concrete resource
        resource = await mcp._resource_manager.get_resource("resource://test/data")
        assert isinstance(resource, FunctionResource)
        result = await resource.read()
        assert result == "Data for test"


class TestContextInjection:
    """Test context injection in tools."""

    async def test_context_detection(self):
        """Test that context parameters are properly detected."""
        mcp = FastMCP()

        def tool_with_context(x: int, ctx: Context) -> str:
            return f"Request {ctx.request_id}: {x}"

        tool = mcp._tool_manager.add_tool(tool_with_context)
        assert tool.context_kwarg == "ctx"

    async def test_context_injection(self):
        """Test that context is properly injected into tool calls."""
        mcp = FastMCP()

        def tool_with_context(x: int, ctx: Context) -> str:
            assert ctx.request_id is not None
            return f"Request {ctx.request_id}: {x}"

        mcp.add_tool(tool_with_context)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("tool_with_context", {"x": 42})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert "Request" in content.text
            assert "42" in content.text

    async def test_async_context(self):
        """Test that context works in async functions."""
        mcp = FastMCP()

        async def async_tool(x: int, ctx: Context) -> str:
            assert ctx.request_id is not None
            return f"Async request {ctx.request_id}: {x}"

        mcp.add_tool(async_tool)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("async_tool", {"x": 42})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert "Async request" in content.text
            assert "42" in content.text

    async def test_context_logging(self):
        """Test that context logging methods work."""
        mcp = FastMCP()

        def logging_tool(msg: str, ctx: Context) -> str:
            ctx.debug("Debug message")
            ctx.info("Info message")
            ctx.warning("Warning message")
            ctx.error("Error message")
            return f"Logged messages for {msg}"

        mcp.add_tool(logging_tool)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("logging_tool", {"msg": "test"})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert "Logged messages for test" in content.text

    async def test_optional_context(self):
        """Test that context is optional."""
        mcp = FastMCP()

        def no_context(x: int) -> int:
            return x * 2

        mcp.add_tool(no_context)
        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("no_context", {"x": 21})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert content.text == "42"

    async def test_context_resource_access(self):
        """Test that context can access resources."""
        mcp = FastMCP()

        @mcp.resource("test://data")
        def test_resource() -> str:
            return "resource data"

        @mcp.tool()
        async def tool_with_resource(ctx: Context) -> str:
            data = await ctx.read_resource("test://data")
            return f"Read resource: {data}"

        async with client_session(mcp._mcp_server) as client:
            result = await client.call_tool("tool_with_resource", {})
            assert len(result.content) == 1
            content = result.content[0]
            assert isinstance(content, TextContent)
            assert "Read resource: resource data" in content.text


class TestServerPrompts:
    """Test prompt functionality in FastMCP server."""

    async def test_prompt_decorator(self):
        """Test that the prompt decorator registers prompts correctly."""
        mcp = FastMCP()

        @mcp.prompt()
        def fn() -> str:
            return "Hello, world!"

        prompts = mcp._prompt_manager.list_prompts()
        assert len(prompts) == 1
        assert prompts[0].name == "fn"
        # Don't compare functions directly since validate_call wraps them
        content = await prompts[0].render()
        assert isinstance(content[0].content, TextContent)
        assert content[0].content.text == "Hello, world!"

    async def test_prompt_decorator_with_name(self):
        """Test prompt decorator with custom name."""
        mcp = FastMCP()

        @mcp.prompt(name="custom_name")
        def fn() -> str:
            return "Hello, world!"

        prompts = mcp._prompt_manager.list_prompts()
        assert len(prompts) == 1
        assert prompts[0].name == "custom_name"
        content = await prompts[0].render()
        assert isinstance(content[0].content, TextContent)
        assert content[0].content.text == "Hello, world!"

    async def test_prompt_decorator_with_description(self):
        """Test prompt decorator with custom description."""
        mcp = FastMCP()

        @mcp.prompt(description="A custom description")
        def fn() -> str:
            return "Hello, world!"

        prompts = mcp._prompt_manager.list_prompts()
        assert len(prompts) == 1
        assert prompts[0].description == "A custom description"
        content = await prompts[0].render()
        assert isinstance(content[0].content, TextContent)
        assert content[0].content.text == "Hello, world!"

    def test_prompt_decorator_error(self):
        """Test error when decorator is used incorrectly."""
        mcp = FastMCP()
        with pytest.raises(TypeError, match="decorator was used incorrectly"):

            @mcp.prompt  # type: ignore
            def fn() -> str:
                return "Hello, world!"

    async def test_list_prompts(self):
        """Test listing prompts through MCP protocol."""
        mcp = FastMCP()

        @mcp.prompt()
        def fn(name: str, optional: str = "default") -> str:
            return f"Hello, {name}!"

        async with client_session(mcp._mcp_server) as client:
            result = await client.list_prompts()
            assert result.prompts is not None
            assert len(result.prompts) == 1
            prompt = result.prompts[0]
            assert prompt.name == "fn"
            assert prompt.arguments is not None
            assert len(prompt.arguments) == 2
            assert prompt.arguments[0].name == "name"
            assert prompt.arguments[0].required is True
            assert prompt.arguments[1].name == "optional"
            assert prompt.arguments[1].required is False

    async def test_get_prompt(self):
        """Test getting a prompt through MCP protocol."""
        mcp = FastMCP()

        @mcp.prompt()
        def fn(name: str) -> str:
            return f"Hello, {name}!"

        async with client_session(mcp._mcp_server) as client:
            result = await client.get_prompt("fn", {"name": "World"})
            assert len(result.messages) == 1
            message = result.messages[0]
            assert message.role == "user"
            content = message.content
            assert isinstance(content, TextContent)
            assert content.text == "Hello, World!"

    async def test_get_prompt_with_resource(self):
        """Test getting a prompt that returns resource content."""
        mcp = FastMCP()

        @mcp.prompt()
        def fn() -> Message:
            return UserMessage(
                content=EmbeddedResource(
                    type="resource",
                    resource=TextResourceContents(
                        uri=AnyUrl("file://file.txt"),
                        text="File contents",
                        mimeType="text/plain",
                    ),
                )
            )

        async with client_session(mcp._mcp_server) as client:
            result = await client.get_prompt("fn")
            assert len(result.messages) == 1
            message = result.messages[0]
            assert message.role == "user"
            content = message.content
            assert isinstance(content, EmbeddedResource)
            resource = content.resource
            assert isinstance(resource, TextResourceContents)
            assert resource.text == "File contents"
            assert resource.mimeType == "text/plain"

    async def test_get_unknown_prompt(self):
        """Test error when getting unknown prompt."""
        mcp = FastMCP()
        async with client_session(mcp._mcp_server) as client:
            with pytest.raises(McpError, match="Unknown prompt"):
                await client.get_prompt("unknown")

    async def test_get_prompt_missing_args(self):
        """Test error when required arguments are missing."""
        mcp = FastMCP()

        @mcp.prompt()
        def prompt_fn(name: str) -> str:
            return f"Hello, {name}!"

        async with client_session(mcp._mcp_server) as client:
            with pytest.raises(McpError, match="Missing required arguments"):
                await client.get_prompt("prompt_fn")