Enum AssistantMessageEvent 

#[non_exhaustive]
pub enum AssistantMessageEvent {
    Start,
    TextStart {
        content_index: usize,
    },
    TextDelta {
        content_index: usize,
        delta: String,
    },
    TextEnd {
        content_index: usize,
    },
    ThinkingStart {
        content_index: usize,
    },
    ThinkingDelta {
        content_index: usize,
        delta: String,
    },
    ThinkingEnd {
        content_index: usize,
        signature: Option<String>,
    },
    ToolCallStart {
        content_index: usize,
        id: String,
        name: String,
    },
    ToolCallDelta {
        content_index: usize,
        delta: String,
    },
    ToolCallEnd {
        content_index: usize,
    },
    Done {
        stop_reason: StopReason,
        usage: Usage,
        cost: Cost,
    },
    Error {
        stop_reason: StopReason,
        error_message: String,
        usage: Option<Usage>,
        error_kind: Option<StreamErrorKind>,
    },
}

An incremental event emitted by a StreamFn implementation.

Events follow a strict start/delta/end protocol per content block. Each block carries a content_index that identifies its position in the final message’s content vec.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Start

The stream has opened.

TextStart

A new text content block is starting at content_index.

Fields

content_index: usize

TextDelta

An incremental text fragment for the block at content_index.

Fields

content_index: usize

delta: String

TextEnd

The text block at content_index is complete.

Fields

content_index: usize

ThinkingStart

A new thinking content block is starting at content_index.

Fields

content_index: usize

ThinkingDelta

An incremental thinking fragment for the block at content_index.

Fields

content_index: usize

delta: String

ThinkingEnd

The thinking block at content_index is complete, with an optional provider verification signature.

Fields

content_index: usize

signature: Option<String>

ToolCallStart

A new tool call content block is starting at content_index.

Fields

content_index: usize

id: String

name: String

ToolCallDelta

An incremental JSON argument fragment for the tool call at content_index.

Fields

content_index: usize

delta: String

ToolCallEnd

The tool call at content_index is complete.

Fields

content_index: usize

Done

The stream completed successfully.

Fields

stop_reason: StopReason

usage: Usage

cost: Cost

Error

The stream ended with an error.

Fields

stop_reason: StopReason

error_message: String

usage: Option<Usage>

error_kind: Option<StreamErrorKind>

Optional structured error classification.

When set, the agent loop uses this to classify the error without falling back to string matching on error_message.

Implementations

impl AssistantMessageEvent

pub fn error(message: impl Into<String>) -> Self

Create a stream error event with no structured classification.

Convenience constructor used by adapters when the stream encounters an error condition. The error_kind is set to None, so the agent loop will fall back to string-based classification.

pub fn error_throttled(message: impl Into<String>) -> Self

Create a throttle/rate-limit error event.

Sets StreamErrorKind::Throttled so the agent loop can classify the error structurally.

pub fn error_context_overflow(message: impl Into<String>) -> Self

Create a context-window overflow error event.

Sets StreamErrorKind::ContextWindowExceeded so the agent loop can trigger context compaction.

pub fn error_auth(message: impl Into<String>) -> Self

Create an authentication error event.

Sets StreamErrorKind::Auth so the agent loop can treat this as a non-retryable failure.

pub fn error_network(message: impl Into<String>) -> Self

Create a network/server error event.

Sets StreamErrorKind::Network so the agent loop can classify the error as retryable.

pub fn error_content_filtered(message: impl Into<String>) -> Self

Create a content-filtered error event.

Sets StreamErrorKind::ContentFiltered so the agent loop can treat this as a non-retryable safety policy violation.

pub fn text_response(text: &str) -> Vec<Self>

Build a complete single-text-block response event sequence.

Useful for testing and mock StreamFn implementations. Returns the five events needed for a valid text-only response: Start, TextStart, TextDelta, TextEnd, and Done.

Trait Implementations

impl Clone for AssistantMessageEvent

fn clone(&self) -> AssistantMessageEvent

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for AssistantMessageEvent

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

Formats the value using the given formatter.