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Stream events let you react to agent activity - update UI, log activity, or integrate with other systems.

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Quick Start

1

Create Stream Events

use praisonai::{StreamEvent, StreamEventType};

// Create a text delta event
let event = StreamEvent::delta_text("Hello, ");

// Create events for different stages
let start = StreamEvent::request_start();
let first = StreamEvent::first_token("The");
let end = StreamEvent::stream_end();
2

Handle Events

use praisonai::{StreamEvent, StreamEventType};

fn handle_event(event: &StreamEvent) {
    match event.event_type {
        StreamEventType::RequestStart => println!("Starting..."),
        StreamEventType::FirstToken => println!("First token: {:?}", event.content),
        StreamEventType::DeltaText => print!("{}", event.content.as_deref().unwrap_or("")),
        StreamEventType::ToolCallEnd => println!("Tool complete"),
        StreamEventType::StreamEnd => println!("\nDone!"),
        StreamEventType::Error => eprintln!("Error: {:?}", event.error),
        _ => {}
    }
}
3

Track Metrics

use praisonai::StreamMetrics;

let mut metrics = StreamMetrics::new();
metrics.start();

// ... process stream ...

metrics.end();
println!("Time to First Token: {:?}ms", metrics.time_to_first_token());
println!("Total Tokens: {}", metrics.total_tokens());

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StreamEventType

Events emitted during streaming. 
pub enum StreamEventType {
    RequestStart,    // Before API call
    HeadersReceived, // HTTP headers arrived
    FirstToken,      // First content (TTFT marker)
    DeltaText,       // Text content chunk
    DeltaToolCall,   // Tool call in progress
    ToolCallEnd,     // Tool call complete
    LastToken,       // Final content chunk
    StreamEnd,       // Stream completed
    Error,           // Error occurred
}
EventWhen Triggered
RequestStartBefore API call
HeadersReceivedHTTP headers received
FirstTokenFirst token arrives
DeltaTextEach text chunk
DeltaToolCallTool call delta
ToolCallEndTool execution done
LastTokenFinal token
StreamEndStream finishes
ErrorError occurs

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StreamEvent

Structure for streaming events. 
pub struct StreamEvent {
    pub event_type: StreamEventType,
    pub content: Option<String>,
    pub tool_call: Option<ToolCallData>,
    pub error: Option<String>,
    pub timestamp: DateTime<Utc>,
    // ... more fields
}

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Factory Methods

MethodDescription
request_start()Create start event
first_token(content)Create first token event
delta_text(content)Create text delta event
stream_end()Create end event
error_event(msg)Create error event

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Builder Methods

MethodDescription
.content(text)Set content
.tool_call(data)Set tool call data
.error(msg)Set error
.agent_id(id)Set agent ID
.session_id(id)Set session ID
.metadata(k, v)Add metadata

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Best Practices

Process events quickly - avoid blocking the stream.
Great for logging, metrics, progress updates, and debugging.
Use FirstToken event to measure Time To First Token.

Hooks

Intercept and modify behavior

Streaming

Enable response streaming