Server-Sent Events (SSE)

Real-time server-to-client event streaming and consumption for building AI agents, live dashboards, and real-time notifications

New in BoxLang 1.7.0 - Server-Sent Events (SSE) enable real-time, unidirectional event streaming over HTTP. BoxLang provides two powerful SSE capabilities:

1. SSE Creation (SSE() BIF) - Push events from your BoxLang server to clients

2. SSE Consumption (http() BIF / bx:http component) - Connect to and consume SSE streams from remote servers (New in BoxLang 1.8.0)

🌐 What are Server-Sent Events?

Server-Sent Events is a standard web technology that allows servers to push data to web clients over HTTP. Unlike WebSockets (which are bidirectional), SSE provides a simple, efficient one-way communication channel, perfect for:

• AI Agent Streaming - Stream AI responses token-by-token for better UX (creation & consumption)

• Live Dashboards - Push real-time metrics and updates to dashboards (creation & consumption)

• Progressive Loading - Load and display content as it becomes available (creation)

• Real-Time Notifications - Push notifications without polling (creation)

• Log Streaming - Stream server logs to browser console (creation)

• Status Updates - Track long-running processes in real-time (creation & consumption)

• Consuming Third-Party Streams - Connect to AI APIs (OpenAI, Claude), monitoring services, event feeds (consumption)

---

📋 Table of Contents

• What are Server-Sent Events?

• SSE Creation vs Consumption

• SSE() BIF - Creating Streams

• Usage Examples

• Client-Side JavaScript

• Implementation Features

• Best Practices

• Security Considerations

• Related Resources

• Additional Examples

• SSE Consumption - Connecting to Remote Streams

• Summary

🔄 SSE Creation vs Consumption

BoxLang provides both sides of the SSE equation:

SSE Creation - SSE() BIF

Create SSE streams that push events to web browsers and clients:

// Server endpoint: /api/stream
SSE( ( emitter ) => {
    emitter.send( "Hello from server!" );
    emitter.send( { status: "processing" }, "update" );
    emitter.close();
} );

Use cases:

• Push real-time updates to your web UI

• Stream AI responses from your BoxLang backend

• Build live dashboards

• Send notifications to connected clients

SSE Consumption - http() BIF / bx:http Component

New in BoxLang 1.8.0 - Consume SSE streams from remote servers:

// Connect to external SSE endpoint
http( "https://api.openai.com/v1/chat/completions" )
    .post()
    .sse( true )
    .onChunk( ( event, lastEventId ) => {
        println( "Received: " & event.data );
    } )
    .send();

Use cases:

• Consume AI streaming APIs (OpenAI, Claude, Gemini)

• Connect to real-time monitoring feeds

• Subscribe to third-party event streams

• Integrate with microservices using SSE

---

📋 SSE() BIF - Creating Streams

The SSE() function establishes a Server-Sent Events connection and streams data to the client.

Syntax

SSE(
    callback: function,
    async: boolean = false,
    retry: number = 0,
    keepAliveInterval: number = 0,
    timeout: number = 0,
    cors: string = ""
)

Parameters

Parameter	Type	Required	Default	Description
callback	function	Yes	-	Closure/lambda that receives the emitter object for sending events
async	boolean	No	false	Run callback in background thread (non-blocking)
retry	number	No	0	Client reconnect interval in milliseconds (0 = no reconnect)
keepAliveInterval	number	No	0	Auto-send keep-alive comments interval in milliseconds (0 = disabled)
timeout	number	No	0	Maximum execution time for async mode in milliseconds (0 = no timeout)
cors	string	No	""	CORS origin header (* for all origins, specific domain, or empty for none)

Emitter Methods

The callback function receives an emitter object with the following methods:

send( data, [event], [id] )

Send an SSE event to the client. Complex data is automatically serialized to JSON.

Parameters:

• data (required) - Data to send (string, number, struct, array, etc.)

• event (optional) - Event type/name for client-side filtering

• id (optional) - Event ID for client-side tracking

emitter.send( "Simple message" );
emitter.send( { status: "processing", progress: 50 }, "update" );
emitter.send( { complete: true }, "done", 123 );

comment( text )

Send an SSE comment (not visible to client, used for keep-alive).

emitter.comment( "Connection alive" );

close()

Gracefully close the SSE stream.

emitter.close();

isClosed()

Check if the client has disconnected.

if ( emitter.isClosed() ) {
    // Stop processing
    break;
}

💡 Usage Examples

Basic Synchronous Streaming

SSE( ( emitter ) => {
    emitter.send( "Hello from server!" );
    emitter.send( { status: "processing", progress: 25 }, "update" );
    emitter.send( { status: "processing", progress: 50 }, "update" );
    emitter.send( { status: "processing", progress: 75 }, "update" );
    emitter.send( { complete: true }, "done" );
    emitter.close();
} );

AI Streaming with Async Execution

// Stream AI responses token-by-token (non-blocking)
SSE(
    callback: ( emitter ) => {
        var response = openAI.chat( prompt: request.prompt );

        while ( !emitter.isClosed() && response.hasMoreTokens() ) {
            var token = response.getNextToken();
            emitter.send( token, "token" );

            // Optional: Add small delay for better client rendering
            sleep( 10 );
        }

        emitter.send( { complete: true, total: response.getTotalTokens() }, "done" );
    },
    async: true,
    keepAliveInterval: 30000,  // Keep-alive every 30s
    timeout: 300000            // 5 minute max timeout
);

Cross-Origin Streaming

// Enable CORS for cross-domain requests
SSE(
    callback: ( emitter ) => {
        emitter.send( { message: "Hello from API" }, "greeting", 1 );
        emitter.send( { data: "Cross-origin data" }, "data", 2 );
        emitter.close();
    },
    cors: "*"  // Allow all origins
);

// Or specify specific origin
SSE(
    callback: ( emitter ) => {
        emitter.send( { secure: "data" }, "secure" );
    },
    cors: "https://app.example.com"
);

Live Dashboard Updates

SSE(
    callback: ( emitter ) => {
        var startTime = now();
        var maxDuration = 3600000; // 1 hour

        while ( !emitter.isClosed() && ( now() - startTime ) < maxDuration ) {
            // Fetch current metrics
            var metrics = {
                cpu: getCPUUsage(),
                memory: getMemoryUsage(),
                requests: getRequestCount(),
                timestamp: now()
            };

            emitter.send( metrics, "metrics" );

            // Update every 5 seconds
            sleep( 5000 );
        }

        emitter.close();
    },
    async: true,
    keepAliveInterval: 30000,
    timeout: 3600000
);

Progress Tracking

SSE(
    callback: ( emitter ) => {
        var tasks = [ "Initialize", "Load Data", "Process", "Validate", "Complete" ];
        var totalTasks = tasks.len();

        tasks.each( ( task, index ) => {
            if ( emitter.isClosed() ) {
                return; // Client disconnected
            }

            emitter.send( {
                task: task,
                progress: ( index / totalTasks ) * 100,
                step: index,
                total: totalTasks
            }, "progress" );

            // Simulate task execution
            performTask( task );
        } );

        emitter.send( { complete: true }, "done" );
        emitter.close();
    },
    async: true
);

Log Streaming

SSE(
    callback: ( emitter ) => {
        var logFile = "/var/logs/app.log";
        var lastPosition = 0;

        while ( !emitter.isClosed() ) {
            // Read new log entries
            var newLogs = readLogsSince( logFile, lastPosition );

            if ( newLogs.len() > 0 ) {
                newLogs.each( ( logEntry ) => {
                    emitter.send( {
                        level: logEntry.level,
                        message: logEntry.message,
                        timestamp: logEntry.timestamp
                    }, "log" );
                } );

                lastPosition = getFilePosition( logFile );
            }

            // Check every second
            sleep( 1000 );
        }
    },
    async: true,
    keepAliveInterval: 15000,
    timeout: 0 // No timeout - keep streaming until client disconnects
);

Real-Time Notifications

SSE(
    callback: ( emitter ) => {
        var userId = session.userId;
        var lastCheck = now();

        while ( !emitter.isClosed() ) {
            // Check for new notifications
            var notifications = getNotificationsForUser( userId, lastCheck );

            notifications.each( ( notification ) => {
                emitter.send( {
                    id: notification.id,
                    type: notification.type,
                    title: notification.title,
                    message: notification.message,
                    timestamp: notification.created
                }, "notification" );
            } );

            lastCheck = now();

            // Check every 10 seconds
            sleep( 10000 );
        }
    },
    async: true,
    keepAliveInterval: 30000
);

🎨 Client-Side JavaScript

Basic EventSource Usage

// Connect to SSE endpoint
const eventSource = new EventSource('/api/sse/stream');

// Listen for default message events
eventSource.onmessage = function(event) {
    console.log('Received:', event.data);
    const data = JSON.parse(event.data);
    // Handle data
};

// Listen for specific event types
eventSource.addEventListener('update', function(event) {
    const data = JSON.parse(event.data);
    console.log('Update:', data);
});

eventSource.addEventListener('done', function(event) {
    console.log('Stream complete');
    eventSource.close();
});

// Handle errors
eventSource.onerror = function(error) {
    console.error('SSE Error:', error);
    eventSource.close();
};

AI Streaming Example

const eventSource = new EventSource('/api/ai/stream?prompt=' + encodeURIComponent(prompt));
let fullResponse = '';

eventSource.addEventListener('token', function(event) {
    const token = event.data;
    fullResponse += token;
    document.getElementById('response').textContent = fullResponse;
});

eventSource.addEventListener('done', function(event) {
    const data = JSON.parse(event.data);
    console.log('Complete! Total tokens:', data.total);
    eventSource.close();
});

Dashboard Updates Example

const eventSource = new EventSource('/api/metrics/stream');

eventSource.addEventListener('metrics', function(event) {
    const metrics = JSON.parse(event.data);

    // Update dashboard
    document.getElementById('cpu').textContent = metrics.cpu + '%';
    document.getElementById('memory').textContent = metrics.memory + 'MB';
    document.getElementById('requests').textContent = metrics.requests;
});

⚙️ Implementation Features

Automatic First-Byte Flush

BoxLang's SSE implementation automatically flushes the first byte to establish the connection quickly, ensuring minimal latency before streaming begins.

Large Data Chunking

Data larger than 32KB is automatically split into properly formatted SSE chunks, ensuring reliable delivery of large payloads.

Multi-Line Data Support

Complex data with newlines is automatically formatted according to SSE specification with proper data: line prefixing.

Client Disconnect Detection

The emitter automatically detects when clients disconnect, allowing your callback to gracefully stop processing with emitter.isClosed().

Proxy/Nginx Compatibility

Response headers are automatically configured to disable buffering in proxies (nginx, Apache) for true real-time delivery:

X-Accel-Buffering: no
Cache-Control: no-cache

Keep-Alive Support

Configure automatic keep-alive comments to keep connections alive through proxies and firewalls:

SSE(
    callback: ( emitter ) => {
        // Your streaming logic
    },
    keepAliveInterval: 30000 // Send keep-alive every 30s
);

🎯 Best Practices

When to Use SSE:

• AI response streaming for better user experience

• Real-time dashboard updates

• Live log streaming

• Progress tracking for long-running operations

• Real-time notifications and alerts

• One-way server-to-client communication (server pushes data)

Performance Tips:

• Use async: true for long-running streams to avoid blocking request threads

• Set appropriate timeout values for async streams to prevent resource leaks

• Use keepAliveInterval for long-lived connections (30-60 seconds recommended)

• Check emitter.isClosed() frequently in loops to detect disconnects early

• Implement proper error handling in callback functions

• Consider rate limiting for high-frequency updates

• Use event types to allow client-side filtering

Important Considerations:

• Browser Compatibility: SSE is supported in all modern browsers (not IE11)

• Connection Limits: Browsers limit concurrent SSE connections (typically 6 per domain)

• Reconnection: Clients automatically reconnect - use retry parameter to control interval

• Async Mode: Always use async: true for streams lasting more than a few seconds

• Resource Management: Set timeout for async streams to prevent orphaned threads

• Proxy Buffering: Ensure proxies/CDNs don't buffer SSE responses (headers handled automatically)

• Memory Usage: Long-running streams consume server resources - monitor and limit as needed

• Security: Implement authentication/authorization before establishing SSE connections

🔒 Security Considerations

Authentication

Always authenticate users before establishing SSE connections:

// Check authentication first
if ( !session.isAuthenticated() ) {
    header statuscode="401" statustext="Unauthorized";
    writeOutput( "Not authenticated" );
    abort;
}

// Then establish SSE
SSE( callback: ( emitter ) => {
    var userId = session.userId;
    // Stream user-specific data
} );

Authorization

Verify user permissions for the requested data stream:

if ( !hasPermission( session.userId, "view_metrics" ) ) {
    header statuscode="403" statustext="Forbidden";
    writeOutput( "Access denied" );
    abort;
}

SSE( callback: ( emitter ) => {
    // Stream authorized metrics
} );

CORS Configuration

Be specific with CORS origins in production:

// Development: Allow all origins
SSE( callback: ( emitter ) => {
    // ...
}, cors: "*" );

// Production: Specify exact origin
SSE( callback: ( emitter ) => {
    // ...
}, cors: "https://app.example.com" );

Rate Limiting

Implement rate limiting to prevent abuse:

if ( !checkRateLimit( session.userId, "sse_connections" ) ) {
    header statuscode="429" statustext="Too Many Requests";
    writeOutput( "Rate limit exceeded" );
    abort;
}

SSE( callback: ( emitter ) => {
    // Stream data
} );

🔗 Related Resources

• HTTP/S Calls

• Asynchronous Programming

• BoxLang Web Runtime

• Release Notes 1.7.0

📚 Additional Examples

Multi-Channel Chat Streaming

SSE(
    callback: ( emitter ) => {
        var channels = session.subscribedChannels;
        var lastMessageId = 0;

        while ( !emitter.isClosed() ) {
            // Fetch new messages across all subscribed channels
            var messages = getNewMessages( channels, lastMessageId );

            messages.each( ( message ) => {
                emitter.send( {
                    channel: message.channel,
                    user: message.user,
                    text: message.text,
                    timestamp: message.created
                }, "message", message.id );

                lastMessageId = max( lastMessageId, message.id );
            } );

            sleep( 1000 );
        }
    },
    async: true,
    keepAliveInterval: 30000,
    timeout: 7200000 // 2 hour max
);

Stock Price Updates

SSE(
    callback: ( emitter ) => {
        var symbols = url.symbols.listToArray(); // ["AAPL", "GOOGL", "MSFT"]

        while ( !emitter.isClosed() ) {
            symbols.each( ( symbol ) => {
                var price = getStockPrice( symbol );
                emitter.send( {
                    symbol: symbol,
                    price: price.current,
                    change: price.change,
                    percentChange: price.percentChange,
                    timestamp: now()
                }, "quote" );
            } );

            // Update every 5 seconds
            sleep( 5000 );
        }
    },
    async: true,
    keepAliveInterval: 30000
);

---

📥 SSE Consumption - Connecting to Remote Streams

New in BoxLang 1.8.0 - BoxLang now provides built-in support for consuming Server-Sent Events from remote servers using the http() BIF or bx:http component.

Why Consume SSE?

SSE consumption allows you to connect to external SSE endpoints and process events in real-time:

• 🤖 AI Streaming APIs - Consume token-by-token responses from OpenAI, Claude, Gemini, and other AI services

• 📊 Real-Time Data Feeds - Connect to stock tickers, weather updates, sports scores

• 🔔 Event Notifications - Subscribe to third-party notification services

• 📈 Monitoring Services - Receive alerts and metrics from monitoring platforms

• 🔄 Microservices - Integrate with SSE-based microservices architecture

Basic SSE Consumption

Using the http() BIF

// Connect to SSE endpoint
http( "https://api.example.com/events" )
    .sse( true )
    .onChunk( ( event, lastEventId, httpResult, httpClient, response ) => {
        // Process each SSE event as it arrives
        println( "Event Type: " & event.event );
        println( "Event Data: " & event.data );
        println( "Event ID: " & event.id );
        println( "Last Event ID: " & lastEventId );
    } )
    .send();

Using the bx:http Component

// Define callback function
function handleSSEEvent( event, lastEventId, httpResult, httpClient, response ) {
    println( "Received: " & event.event & " - " & event.data );
}

// Use component with SSE
bx:http
    url="https://api.example.com/events"
    sse=true
    onChunk=handleSSEEvent
    result="result";

SSE Event Structure

Each event received in the onChunk callback contains:

{
    data: "Event payload content",
    event: "message",              // Event type (default: "message")
    id: "123",                     // Event ID for reconnection
    retry: 3000                    // Retry interval in ms (optional)
}

Callback Parameters

The onChunk callback receives five parameters:

Parameter	Type	Description
event	struct	The SSE event (data, event, id, retry)
lastEventId	string	Most recent event ID (for reconnection)
httpResult	struct	HTTP result structure
httpClient	object	BoxHttpClient instance
response	object	Raw Java HttpResponse

Real-World SSE Consumption Examples

OpenAI Streaming Chat

// Stream AI responses token-by-token
fullResponse = "";

http( "https://api.openai.com/v1/chat/completions" )
    .post()
    .header( "Authorization", "Bearer " & apiKey )
    .header( "Content-Type", "application/json" )
    .jsonBody( '{
        "model": "gpt-4",
        "messages": [
            {"role": "system", "content": "You are a helpful assistant."},
            {"role": "user", "content": "' & userPrompt & '"}
        ],
        "stream": true
    }' )
    .sse( true )
    .onChunk( ( event, lastEventId ) => {
        // OpenAI sends "[DONE]" when stream completes
        if ( event.data == "[DONE]" ) {
            return;
        }

        try {
            chunk = deserializeJSON( event.data );
            if ( structKeyExists( chunk.choices[1].delta, "content" ) ) {
                token = chunk.choices[1].delta.content;
                fullResponse &= token;

                // Stream to client in real-time
                writeOutput( token );
                flush;
            }
        } catch ( any e ) {
            // Handle parsing errors
            logger.error( "Error parsing SSE chunk", e );
        }
    } )
    .onComplete( ( httpResult ) => {
        logger.info( "Stream complete. Tokens received: " & len( fullResponse ) );
    } )
    .onError( ( error, httpResult ) => {
        logger.error( "SSE stream error: " & error.message );
    } )
    .send();

println( "\n\nComplete response: " & fullResponse );

Claude AI Streaming

// Consume Claude streaming API
fullResponse = "";

http( "https://api.anthropic.com/v1/messages" )
    .post()
    .header( "x-api-key", claudeApiKey )
    .header( "anthropic-version", "2023-06-01" )
    .header( "content-type", "application/json" )
    .jsonBody( '{
        "model": "claude-3-opus-20240229",
        "messages": [
            {"role": "user", "content": "' & userPrompt & '"}
        ],
        "max_tokens": 1024,
        "stream": true
    }' )
    .sse( true )
    .onChunk( ( event, lastEventId ) => {
        if ( event.event == "content_block_delta" ) {
            data = deserializeJSON( event.data );
            token = data.delta.text;
            fullResponse &= token;
            writeOutput( token );
            flush;
        }
    } )
    .send();

Real-Time Stock Quotes

// Consume live stock price feed
http( "https://stockstream.example.com/quotes?symbols=AAPL,GOOGL,MSFT" )
    .header( "Authorization", "Bearer " & stockAPIKey )
    .sse( true )
    .onChunk( ( event, lastEventId, httpResult ) => {
        if ( event.event == "quote" ) {
            quote = deserializeJSON( event.data );

            // Update database or cache
            cacheSet(
                "stock_" & quote.symbol,
                quote,
                createTimeSpan( 0, 0, 0, 10 ) // 10 seconds
            );

            // Broadcast to connected WebSocket clients
            broadcastStockUpdate( {
                symbol: quote.symbol,
                price: quote.price,
                change: quote.change,
                percentChange: quote.percentChange,
                timestamp: quote.timestamp
            } );
        }
    } )
    .onError( ( error, httpResult ) => {
        logger.error( "Stock stream disconnected, reconnecting..." );
        reconnectStockStream();
    } )
    .send();

Server Monitoring Feed

// Consume monitoring metrics stream
http( "https://monitoring.example.com/metrics/stream" )
    .header( "X-API-Key", monitoringAPIKey )
    .sse( true )
    .onChunk( ( event, lastEventId ) => {
        switch ( event.event ) {
            case "metric":
                metric = deserializeJSON( event.data );

                // Store in time-series database
                influxDB.write( {
                    measurement: metric.name,
                    tags: metric.tags,
                    fields: { value: metric.value },
                    timestamp: metric.timestamp
                } );

                // Check thresholds
                if ( metric.value > metric.threshold ) {
                    sendAlert( "Metric " & metric.name & " exceeded threshold" );
                }
                break;

            case "alert":
                alert = deserializeJSON( event.data );
                handleAlert( alert );
                break;

            case "heartbeat":
                // Update last seen timestamp
                session.lastHeartbeat = now();
                break;
        }
    } )
    .onComplete( ( httpResult ) => {
        logger.info( "Monitoring stream closed" );
    } )
    .send();

GitHub Events Stream

// Monitor GitHub repository events
http( "https://api.github.com/repos/ortus-boxlang/boxlang/events" )
    .header( "Accept", "text/event-stream" )
    .header( "Authorization", "Bearer " & githubToken )
    .sse( true )
    .onChunk( ( event, lastEventId ) => {
        if ( event.event == "push" ) {
            pushEvent = deserializeJSON( event.data );

            // Notify team
            slackNotify( {
                channel: "#github",
                message: "New push to " & pushEvent.ref & " by " & pushEvent.pusher.name,
                commits: pushEvent.commits.len()
            } );

            // Trigger CI/CD
            if ( pushEvent.ref == "refs/heads/main" ) {
                triggerBuild( pushEvent.after );
            }
        }
    } )
    .send();

Advanced SSE Consumption Patterns

Reconnection with Last Event ID

// Store last event ID for reconnection
application.lastEventId = "";

function connectToSSE() {
    request = http( "https://api.example.com/events" );

    // Resume from last event if we have one
    if ( len( application.lastEventId ) ) {
        request.header( "Last-Event-ID", application.lastEventId );
    }

    request
        .sse( true )
        .onChunk( ( event, lastEventId ) => {
            // Store last event ID
            application.lastEventId = lastEventId;

            // Process event
            processEvent( event );
        } )
        .onError( ( error, httpResult ) => {
            logger.error( "Connection lost, reconnecting in 5 seconds..." );
            sleep( 5000 );
            connectToSSE();  // Reconnect with Last-Event-ID
        } )
        .send();
}

// Start connection
connectToSSE();

Multiple Event Types

// Handle different event types
http( "https://api.example.com/events" )
    .sse( true )
    .onChunk( ( event, lastEventId ) => {
        switch ( event.event ) {
            case "message":
                handleMessage( deserializeJSON( event.data ) );
                break;

            case "notification":
                handleNotification( deserializeJSON( event.data ) );
                break;

            case "update":
                handleUpdate( deserializeJSON( event.data ) );
                break;

            case "ping":
                // Keep-alive ping, do nothing
                break;

            default:
                logger.warn( "Unknown event type: " & event.event );
        }
    } )
    .send();

Timeout and Error Handling

// Robust SSE connection with comprehensive error handling
http( "https://api.example.com/events" )
    .timeout( 300 )  // 5 minute timeout
    .sse( true )
    .onRequestStart( () => {
        logger.info( "Connecting to SSE stream..." );
    } )
    .onChunk( ( event, lastEventId, httpResult ) => {
        try {
            processEvent( event );
        } catch ( any e ) {
            logger.error( "Error processing event", e );
            // Don't let one bad event break the stream
        }
    } )
    .onError( ( error, httpResult ) => {
        logger.error( "SSE error: " & error.message );

        // Decide whether to retry based on error type
        if ( httpResult.statusCode == 429 ) {
            // Rate limited, wait before retry
            sleep( 60000 );
            retryConnection();
        } else if ( httpResult.statusCode >= 500 ) {
            // Server error, retry with exponential backoff
            sleep( retryDelay );
            retryDelay *= 2;  // Double delay each time
            retryConnection();
        } else {
            // Client error, don't retry
            logger.error( "Client error, not retrying: " & httpResult.statusCode );
        }
    } )
    .onComplete( ( httpResult ) => {
        logger.info( "SSE stream completed normally" );
    } )
    .send();

SSE Consumption Best Practices

Best Practices for SSE Consumption:

1. Always handle errors - Network failures will interrupt streams

2. Store lastEventId - Use it to reconnect and resume from last event

3. Implement reconnection logic - Connections will drop, be ready to reconnect

4. Parse event types - Different event types require different handling

5. Handle stream termination signals - Look for [DONE], empty data, or specific event types

6. Set appropriate timeouts - Long-lived streams need longer timeouts

7. Use try-catch for parsing - JSON parsing can fail on malformed data

8. Log connection state - Track connects, disconnects, and errors

9. Implement exponential backoff - Don't hammer failing endpoints

10. Monitor memory usage - Accumulating data can grow quickly

Important Considerations:

• Unidirectional - SSE is server → client only (no client → server messages)

• Network sensitive - Interruptions terminate the stream

• Proxy buffering - Some proxies buffer responses (check your infrastructure)

• Browser connection limits - Browsers limit concurrent SSE connections (typically 6 per domain)

• Long-lived connections - Consumes server resources, monitor connection count

• Error handling is critical - Always implement robust retry logic

• Memory management - Process and discard events, don't accumulate indefinitely

• Authentication - Include proper API keys/tokens in headers

---

🎯 Summary

Server-Sent Events in BoxLang provides a powerful, standards-based way to build real-time web applications with minimal complexity:

• SSE Creation (SSE() BIF) - Push events from BoxLang to web clients with automatic connection management, keep-alive, and client disconnect detection

• SSE Consumption (http() BIF / bx:http component) - Connect to and consume SSE streams from remote servers with built-in event parsing, reconnection support, and error handling

Whether you're building real-time dashboards, streaming AI responses, or integrating with third-party event feeds, BoxLang's SSE support makes it easy to create robust streaming experiences.