feat: add support for structured content for MCP

[hallvictoria]

fixes: Azure/azure-functions-python-worker#1825, Azure/azure-functions-python-worker#1836, Azure-Samples/remote-mcp-functions-python#38

Examples:

import base64
import json
from datetime import datetime
from enum import Enum
from typing import List, Optional, Dict
from uuid import UUID

import azure.functions as func


app = func.FunctionApp()


# Enum example (matching .NET JobType)
class JobType(Enum):
    FULL_TIME = "FullTime"
    PART_TIME = "PartTime"
    CONTRACT = "Contract"
    INTERNSHIP = "Internship"
    TEMPORARY = "Temporary"
    FREELANCE = "Freelance"
    UNEMPLOYED = "Unemployed"


# ============================================================================
# Scenario 1: Single ResourceLinkBlock return
# Matches: GetFunctionsLogo in .NET
# ============================================================================
@app.mcp_tool()
def get_functions_logo() -> func.ResourceLinkBlock:
    """Returns the Azure Functions logo as a resource link."""
    return func.ResourceLinkBlock(
        uri="file://logo.png",
        name="Azure Functions Logo",
        mime_type="image/png"
    )

# ============================================================================
# Scenario 3: Multiple content blocks (List[ContentBlock])
# Matches: MultiContentTypeFunction in .NET
# ============================================================================
@app.mcp_tool()
def multi_content_type_function(
    data: str,
    mime_type: Optional[str] = None
) -> List[func.ContentBlock]:
    """Responds to user with multiple content blocks."""
    return [
        func.TextContentBlock(text="Here is an image for you!"),
        func.ResourceLinkBlock(
            name="example",
            uri="https://www.google.com/",
            description="Image Information"
        ),
        func.ImageContentBlock(
            data=data,
            mime_type=mime_type or "image/jpeg"
        )
    ]


# ============================================================================
# Scenario 4: Single ImageContentBlock return
# Matches: RenderImage in .NET
# ============================================================================
@app.mcp_tool()
def render_image(
    data: str,
    mime_type: Optional[str] = None
) -> func.ImageContentBlock:
    """Responds to user with an image."""
    return func.ImageContentBlock(
        data=data,
        mime_type=mime_type or "image/jpeg"
    )

# ============================================================================
# Scenario 8: @mcp_content decorated dataclass
# Matches: GetSnippet returning [McpContent] Snippet in .NET
# ============================================================================
@func.mcp_content
class Snippet:
    """Snippet class that will be serialized as structured content."""
    def __init__(self, name: str, content: Optional[str] = None):
        self.name = name
        self.content = content


# In-memory snippet cache
snippets_cache: Dict[str, str] = {
    "hello": "print('Hello, World!')",
    "loop": "for i in range(10):\n    print(i)"
}


@app.mcp_tool()
def get_snippet(name: str) -> Optional[Snippet]:
    """Gets a code snippet by name."""
    if name in snippets_cache:
        return Snippet(name=name, content=snippets_cache[name])
    return None


# ============================================================================
# Scenario 9: Complex object as parameter
# Matches: SaveSnippet in .NET
# ============================================================================
@app.mcp_tool()
def save_snippet(name: str, content: str) -> str:
    """Saves a code snippet."""
    snippets_cache[name] = content
    return f"Snippet '{name}' saved successfully"


# ============================================================================
# Scenario 10: Complex request/response objects
# Matches: SearchSnippets in .NET
# ============================================================================
@func.mcp_content
class SnippetSearchRequest:
    """Search request for snippets."""
    def __init__(self, pattern: str, case_sensitive: bool = False):
        self.pattern = pattern
        self.case_sensitive = case_sensitive


@app.mcp_tool()
def search_snippets(pattern: str, case_sensitive: bool = False) -> Dict[str, str]:
    """Searches for snippets matching a pattern."""
    results = {}
    for key, value in snippets_cache.items():
        if case_sensitive:
            if pattern in key:
                results[key] = value
        else:
            if pattern.lower() in key.lower():
                results[key] = value
    return results


# ============================================================================
# Scenario 11: CallToolResult with explicit content and structured content
# Matches: GetImageWithMetadata in .NET
# ============================================================================
@app.mcp_tool()
def get_image_with_metadata() -> func.CallToolResult:
    """Returns an image with metadata as structured content."""
    # Metadata object
    metadata = {
        "ImageId": "logo",
        "Format": "png",
        "CreatedAt": datetime.utcnow().isoformat(),
        "Tags": ["functions", "azure", "serverless"]
    }
    
    # Read image file (or use a tiny test image)
    # For demo, using a 10x10 red pixel PNG (larger version of the 1x1)
    import zlib
    import struct
    
    # PNG signature
    png_data = b'\x89PNG\r\n\x1a\n'
    
    def make_chunk(chunk_type, data):
        """Create a PNG chunk with proper CRC."""
        chunk_data = chunk_type + data
        crc = zlib.crc32(chunk_data) & 0xffffffff
        return struct.pack('>I', len(data)) + chunk_data + struct.pack('>I', crc)
    
    # IHDR: 10x10, 8-bit RGB
    width, height = 10, 10
    ihdr_data = struct.pack('>IIBBBBB', width, height, 8, 2, 0, 0, 0)
    png_data += make_chunk(b'IHDR', ihdr_data)
    
    # IDAT: image data (10x10 red pixels)
    raw_data = b''
    for y in range(height):
        raw_data += b'\x00'  # Filter type: None
        for x in range(width):
            raw_data += b'\xff\x00\x00'  # RGB: Red
    
    compressed = zlib.compress(raw_data, 9)
    png_data += make_chunk(b'IDAT', compressed)
    
    # IEND
    png_data += make_chunk(b'IEND', b'')
    
    base64_image = base64.b64encode(png_data).decode('utf-8')
    
    # Construct CallToolResult with both content blocks and structured content
    return func.CallToolResult(
        content=[
            func.TextContentBlock(text=json.dumps(metadata)),  # JSON representation
            func.ImageContentBlock(
                data=base64_image,
                mime_type="image/png"
            )
        ],
        structured_content=metadata  # Structured data for parsing
    )


# ============================================================================
# Additional scenario: use_result_schema parameter
# ============================================================================
@app.mcp_tool(use_result_schema=True)
def get_structured_data(query: str) -> Snippet:
    """Returns structured data using @mcp_content decorated class."""
    return Snippet(
        name="result",
        content=f"Query result for: {query}"
    )

[gavin-aguiar]

Here if arg is CallToolResult, you're setting is_content_block = True instead of is_call_tool_result = True..
Lets break this into 2 if conditions
if issubclass(arg, ContentBlock):
...
elif issubclass(arg, CallToolResult):
...

[gavin-aguiar]

This will return "None" . Maybe return ""

[gavin-aguiar]

These imports will happen at every call. Can we move this to the top?

[gavin-aguiar]

NIT: bool is a subclass of int so its just a redundant check. (str, int, float) should be enough

[gavin-aguiar]

Should we add a check for this ?
if isinstance(obj, (dict, list)):
return False