第六章：错误处理

服务端错误

连接中断

from fastapi import FastAPI
from fastapi.responses import StreamingResponse
import asyncio

app = FastAPI()

async def robust_generator():
    try:
        count = 0
        while True:
            count += 1
            yield f"data: {json.dumps({'count': count})}\n\n"
            await asyncio.sleep(1)
    except asyncio.CancelledError:
        print("Client disconnected")
        # 清理资源
    except Exception as e:
        print(f"Error: {e}")
        yield f"event: error\ndata: {json.dumps({'error': str(e)})}\n\n"

@app.get("/robust-events")
async def robust_sse():
    return StreamingResponse(
        robust_generator(),
        media_type="text/event-stream"
    )

客户端错误处理

class RobustSSEClient {
    constructor(url) {
        this.url = url
        this.eventSource = null
        this.reconnectAttempts = 0
        this.maxReconnectAttempts = 5
        this.connect()
    }

    connect() {
        this.eventSource = new EventSource(this.url)

        this.eventSource.onopen = () => {
            console.log('Connected')
            this.reconnectAttempts = 0
        }

        this.eventSource.onerror = (error) => {
            console.error('Connection error:', error)

            if (this.eventSource.readyState === EventSource.CLOSED) {
                console.log('Connection closed')
                this.handleDisconnect()
            } else if (this.eventSource.readyState === EventSource.CONNECTING) {
                console.log('Reconnecting...')
            }
        }

        // 监听错误事件
        this.eventSource.addEventListener('error', (event) => {
            console.error('Server error:', event.data)
        })
    }

    handleDisconnect() {
        this.reconnectAttempts++

        if (this.reconnectAttempts <= this.maxReconnectAttempts) {
            const delay = Math.min(1000 * Math.pow(2, this.reconnectAttempts), 30000)
            console.log(`Reconnecting in ${delay}ms...`)
            setTimeout(() => this.connect(), delay)
        } else {
            console.error('Max reconnect attempts reached')
        }
    }

    close() {
        if (this.eventSource) {
            this.eventSource.close()
        }
    }
}

小结

错误处理要点：

• 服务端错误：try/except、资源清理
• 客户端错误：onerror、重连策略
• 指数退避：延迟重连

下一章我们将学习生产部署。