Message Structure

{
  "role": "user",
  "parts": [{
    "content_type": "text/plain",
    "content": "Hello, world!"
  }]
}

{
  "role": "agent/assistant",
  "parts": [{
    "content_type": "text/plain",
    "content": "Hello! How can I help you today?"
  }]
}

{
  "role": "agent/image-analyzer",
  "parts": [
    {
      "content_type": "text/plain",
      "content": "This is a cute cat:"
    },
    {
      "content_type": "image/png",
      "content_url": "https://s3.example.com/12345678901234567890/image.png"
    },
    {
      "content_type": "text/plain",
      "content": "Would you like me to send more images of cats?"
    },
    {
      "name": "/sources/1.url",
      "content_type": "text/url",
      "content": "https://example.com/cat-facts"
    }
  ]
}

{
  "role": "agent/report-generator",
  "parts": [
    {
      "content_type": "text/plain",
      "content": "Here's the report you requested:"
    },
    {
      "name": "/report.pdf",
      "content_type": "application/pdf",
      "content_url": "https://example.com/report.pdf"
    }
  ]
}

{
  "role": "user",
  "parts": [{
    "content_type": "text/plain",
    "content": "Direct text content",
    "content_encoding": "plain" // Default if omitted
  }]
}

{
  "role": "agent/file-processor",
  "parts": [{
    "content_type": "image/jpeg",
    "content_url": "https://example.com/image.jpg"
  }]
}

{
  "role": "agent/image-processor",
  "parts": [{
    "content_type": "image/png",
    "content": "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==",
    "content_encoding": "base64"
  }]
}

class MessagePart(BaseModel):
    name: Optional[str] = None
    content_type: str
    content: Optional[str] = None
    content_encoding: Optional[Literal["plain", "base64"]] = "plain"
    content_url: Optional[AnyUrl] = None
    metadata: Optional[CitationMetadata | TrajectoryMetadata] = None

    # Validation ensures either content or content_url is provided, but not both

class Artifact(MessagePart):
    name: str  # Name is required for Artifacts

class Message(BaseModel):
    role: Literal["user"] | Literal["agent"] | str  # str must match pattern "^(user|agent(\/[a-zA-Z0-9_\-]+)?)$"
    parts: list[MessagePart]