refactor: standardize resource response format

Introduce ReadResourceContents type to properly handle MIME types in resource responses. Breaking change in FastMCP read_resource() return type.

Github-Issue:#152

tests/server/test_read_resource.py

@@ -0,0 +1,109 @@
+from pathlib import Path
+from tempfile import NamedTemporaryFile
+
+import pytest
+from pydantic import AnyUrl, FileUrl
+
+import mcp.types as types
+from mcp.server.lowlevel.server import ReadResourceContents, Server
+
+
+@pytest.fixture
+def temp_file():
+    """Create a temporary file for testing."""
+    with NamedTemporaryFile(mode="w", delete=False) as f:
+        f.write("test content")
+        path = Path(f.name).resolve()
+    yield path
+    try:
+        path.unlink()
+    except FileNotFoundError:
+        pass
+
+
+@pytest.mark.anyio
+async def test_read_resource_text(temp_file: Path):
+    server = Server("test")
+
+    @server.read_resource()
+    async def read_resource(uri: AnyUrl) -> ReadResourceContents:
+        return ReadResourceContents(content="Hello World", mime_type="text/plain")
+
+    # Get the handler directly from the server
+    handler = server.request_handlers[types.ReadResourceRequest]
+
+    # Create a request
+    request = types.ReadResourceRequest(
+        method="resources/read",
+        params=types.ReadResourceRequestParams(uri=FileUrl(temp_file.as_uri())),
+    )
+
+    # Call the handler
+    result = await handler(request)
+    assert isinstance(result.root, types.ReadResourceResult)
+    assert len(result.root.contents) == 1
+
+    content = result.root.contents[0]
+    assert isinstance(content, types.TextResourceContents)
+    assert content.text == "Hello World"
+    assert content.mimeType == "text/plain"
+
+
+@pytest.mark.anyio
+async def test_read_resource_binary(temp_file: Path):
+    server = Server("test")
+
+    @server.read_resource()
+    async def read_resource(uri: AnyUrl) -> ReadResourceContents:
+        return ReadResourceContents(
+            content=b"Hello World", mime_type="application/octet-stream"
+        )
+
+    # Get the handler directly from the server
+    handler = server.request_handlers[types.ReadResourceRequest]
+
+    # Create a request
+    request = types.ReadResourceRequest(
+        method="resources/read",
+        params=types.ReadResourceRequestParams(uri=FileUrl(temp_file.as_uri())),
+    )
+
+    # Call the handler
+    result = await handler(request)
+    assert isinstance(result.root, types.ReadResourceResult)
+    assert len(result.root.contents) == 1
+
+    content = result.root.contents[0]
+    assert isinstance(content, types.BlobResourceContents)
+    assert content.mimeType == "application/octet-stream"
+
+
+@pytest.mark.anyio
+async def test_read_resource_default_mime(temp_file: Path):
+    server = Server("test")
+
+    @server.read_resource()
+    async def read_resource(uri: AnyUrl) -> ReadResourceContents:
+        return ReadResourceContents(
+            content="Hello World",
+            # No mime_type specified, should default to text/plain
+        )
+
+    # Get the handler directly from the server
+    handler = server.request_handlers[types.ReadResourceRequest]
+
+    # Create a request
+    request = types.ReadResourceRequest(
+        method="resources/read",
+        params=types.ReadResourceRequestParams(uri=FileUrl(temp_file.as_uri())),
+    )
+
+    # Call the handler
+    result = await handler(request)
+    assert isinstance(result.root, types.ReadResourceResult)
+    assert len(result.root.contents) == 1
+
+    content = result.root.contents[0]
+    assert isinstance(content, types.TextResourceContents)
+    assert content.text == "Hello World"
+    assert content.mimeType == "text/plain"