Struct Message

Source

pub struct Message {
    pub role: MessageRole,
    pub content: Vec<ContentBlock>,
}

Expand description

A complete message in a conversation.

Messages are the primary unit of communication in the agent system. Each message has a role (who sent it) and content (what it contains). Content is structured as a vector of blocks to support multi-modal communication.

§Structure

role: Who sent the message (MessageRole)
content: What the message contains (one or more ContentBlocks)

§Message Patterns

§Simple Text Message

use open_agent::Message;

let msg = Message::user("What's the weather?");

§Assistant Response with Tool Call

use open_agent::{Message, ContentBlock, TextBlock, ToolUseBlock};
use serde_json::json;

let msg = Message::assistant(vec![
    ContentBlock::Text(TextBlock::new("Let me check that for you.")),
    ContentBlock::ToolUse(ToolUseBlock::new(
        "call_123",
        "get_weather",
        json!({"location": "San Francisco"})
    ))
]);

§Tool Result

use open_agent::{Message, ContentBlock, ToolResultBlock};
use serde_json::json;

let msg = Message::user_with_blocks(vec![
    ContentBlock::ToolResult(ToolResultBlock::new(
        "call_123",
        json!({"temp": 72, "conditions": "sunny"})
    ))
]);

Fields§

§role: MessageRole

The role/sender of this message.

§content: Vec<ContentBlock>

The content blocks that make up this message.

A message can contain multiple blocks of different types. For example, an assistant message might have both text and tool use blocks.

Implementations§

Source §

impl Message

Source

pub fn new(role: MessageRole, content: Vec<ContentBlock>) -> Self

Creates a new message with the specified role and content.

This is the most general constructor. For convenience, use the role-specific constructors like user(), assistant(), etc.

§Example

use open_agent::{Message, MessageRole, ContentBlock, TextBlock};

let msg = Message::new(
    MessageRole::User,
    vec![ContentBlock::Text(TextBlock::new("Hello"))]
);

Source

pub fn user(text: impl Into<String>) -> Self

Creates a user message with simple text content.

This is the most common way to create user messages. For more complex content with multiple blocks, use user_with_blocks().

§Example

use open_agent::Message;

let msg = Message::user("What is 2+2?");

Source

pub fn assistant(content: Vec<ContentBlock>) -> Self

Creates an assistant message with the specified content blocks.

Assistant messages often contain multiple content blocks (text + tool use). This method takes a vector of blocks for maximum flexibility.

§Example

use open_agent::{Message, ContentBlock, TextBlock};

let msg = Message::assistant(vec![
    ContentBlock::Text(TextBlock::new("The answer is 4"))
]);

Source

pub fn system(text: impl Into<String>) -> Self

Creates a system message with simple text content.

System messages establish the agent’s behavior and context. They’re typically sent at the start of a conversation.

§Example

use open_agent::Message;

let msg = Message::system("You are a helpful assistant. Be concise.");

Source

pub fn user_with_blocks(content: Vec<ContentBlock>) -> Self

Creates a user message with custom content blocks.

Use this when you need to send structured content beyond simple text, such as tool results. For simple text messages, prefer user().

§Example

use open_agent::{Message, ContentBlock, ToolResultBlock};
use serde_json::json;

let msg = Message::user_with_blocks(vec![
    ContentBlock::ToolResult(ToolResultBlock::new(
        "call_123",
        json!({"result": "success"})
    ))
]);

Source

pub fn user_with_image( text: impl Into<String>, image_url: impl Into<String>, ) -> Result<Self>

Creates a user message with text and an image from a URL.

This is a convenience method for the common pattern of sending text with an image. The image uses ImageDetail::Auto by default. For more control over detail level, use user_with_image_detail().

§Arguments

text - The text prompt
image_url - URL of the image (http/https or data URI)

§Errors

Returns Error::InvalidInput if the image URL is invalid (empty, wrong scheme, etc.)

§Example

use open_agent::Message;

let msg = Message::user_with_image(
    "What's in this image?",
    "https://example.com/photo.jpg"
)?;

Source

pub fn user_with_image_detail( text: impl Into<String>, image_url: impl Into<String>, detail: ImageDetail, ) -> Result<Self>

Creates a user message with text and an image with specified detail level.

Use this when you need control over the image detail level for token cost management. On OpenAI’s Vision API: ImageDetail::Low uses ~85 tokens, ImageDetail::High uses more tokens based on image dimensions, and ImageDetail::Auto lets the model decide. Local models may have very different token costs.

§Arguments

text - The text prompt
image_url - URL of the image (http/https or data URI)
detail - Detail level (Low, High, or Auto)

§Errors

Returns Error::InvalidInput if the image URL is invalid (empty, wrong scheme, etc.)

§Example

use open_agent::{Message, ImageDetail};

let msg = Message::user_with_image_detail(
    "Analyze this diagram in detail",
    "https://example.com/diagram.png",
    ImageDetail::High
)?;

Source

pub fn user_with_base64_image( text: impl Into<String>, base64_data: impl AsRef<str>, mime_type: impl AsRef<str>, ) -> Result<Self>

Creates a user message with text and a base64-encoded image.

This is useful when you have image data in memory and want to send it without uploading to a URL first. The image will be encoded as a data URI.

§Arguments

text - The text prompt
base64_data - Base64-encoded image data
mime_type - MIME type (e.g., “image/png”, “image/jpeg”)

§Errors

Returns Error::InvalidInput if the base64 data or MIME type is invalid

§Example

use open_agent::Message;

// Use properly formatted base64 (length divisible by 4, valid chars)
let base64_data = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==";
let msg = Message::user_with_base64_image(
    "What's this image?",
    base64_data,
    "image/png"
)?;