Struct Message 

pub struct Message {
    pub role: Role,
    pub content: String,
    pub reasoning: Option<String>,
    pub reasoning_details: ReasoningDetails,
    pub tool_calls: Option<Vec<ToolCall>>,
    pub tool_call_id: Option<String>,
    pub parts: Option<Vec<ContentPart>>,
    pub timestamp: DateTime<Utc>,
}

A single message in the LLM API request / response payload.

For tool results set tool_call_id in addition to content (which holds the tool’s output).

Fields

role: Role

Message role (system, user, assistant, developer, tool).

content: String

Text content of the message.

reasoning: Option<String>

Reasoning retained for providers that require it on later tool turns.

reasoning_details: ReasoningDetails

Complete provider reasoning blocks for replay on subsequent tool turns.

tool_calls: Option<Vec<ToolCall>>

Tool calls requested by the assistant (only on assistant messages).

tool_call_id: Option<String>

ID of the tool call this is a result for (only on tool messages).

parts: Option<Vec<ContentPart>>

Multimodal content parts (images, documents, audio). When present, content is also included as a text part.

timestamp: DateTime<Utc>

Timestamp when the message was created.

Implementations

impl Message

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

Create a plain-text user message.

pub fn assistant(content: impl Into<String>) -> Self

Create an assistant text message (no tool calls).

pub fn assistant_with_tool_calls( content: impl Into<String>, tool_calls: Vec<ToolCall>, ) -> Self

Create an assistant message that includes tool call requests.

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

Create a system prompt message.

pub fn developer(content: impl Into<String>) -> Self

Create a developer message (system-level instructions using the developer role).

pub fn tool_result( tool_call_id: impl Into<String>, content: impl Into<String>, ) -> Self

Create a tool-result message linked to a prior ToolCall.id.

pub fn user_with_parts( content: impl Into<String>, parts: Vec<ContentPart>, ) -> Self

Create a multimodal user message with inline attachments.

pub fn strip_binary_data(&self) -> Self

Replace binary content parts (image, document, video, audio) with text placeholders so the message can be sent to models that don’t support those modalities.

Example:

• Image { media_type: "image/jpeg", .. } → Text { text: "[Image: image/jpeg]" }

Trait Implementations

impl Clone for Message

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Message

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Message

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for Message

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.