Asynchronous actions

Processing a chat event from user blocks other event from same user until the processing is finnished. It's very important for choosing right approach.

There are two approches to drive asynchronous actions:

• blocking: Other Messenger events are waiting for limited time until the asynchronous operation is completed
• non blocking: Bot can process other chat events while asynchronous operation is in progress

Blocking is important for keeping conversation state consistent.

Blocking Asynchronous actions

For fast async operations you can use blocking approach. You can simply return a Promise or make function async. This approach is not recommended for production environments.

const { Router } = require('wingbot');
const bot = new Router();

function asyncAction () {
    return new Promise(r => setTimeout(() => r(Math.rand()), 100));
}

bot.use(async (req, res) => {
    try {
        res.typingOn();
        const result = await asyncAction();

        res.text('Complete!')
                .setState({ result });
    } catch (e) {
        res.text('Async action failed');
    }
});

module.exports = bot;

It's not good to block messaging event processing with async actions, when action takes more then timeout (Processor option), it can lead to overwriting state, when concurrent request arrives.

Non blocking asynchronous actions

For non blocking approach is good to know, that only postBack can be called after an action is resolved. Any other calls, like setState() will have no effect. This is the only right way to make non-blocking asynchronous operations.

const { Router } = require('wingbot');
const bot = new Router();

function asyncAction () {
    return new Promise(r => setTimeout(() => Math.rand(), 100));
}

bot.use('/asyncComplete', (req, res) => {
    const { result, err } = req.actionData();
    if (err) {
        res.text('Async action failed');
    } else {
        res.text('Complete!')
                .setState({ result });
    }
});

bot.use((req, res, postBack) => {
    res.typingOn();
    postBack('asyncComplete', async () => {
        try {
            const result = await asyncAction();
            return { result };
        } catch (err) {
            return err;
        }
    });
});

module.exports = bot;

Loading Attachments to Buffer

Most simpliest way to upload attachments is converting them to base64 buffer:

const { Router, bufferloader } = require('wingbot');
const bot = new Router();

function asyncAction () {
    return new Promise(r => setTimeout(() => Math.rand(), 100));
}

bot.use('/uploadComplete', (req, res) => {
    const { result, err } =
    if (!err) {
        res.text('Complete!')
                .setState({ result });
    } else if (err.code === 400) {
        res.text('Upload size exceeded');
    } else {
        res.text('Async action failed');
    }
});

bot.use((req, res, postBack) => {
    // wait method is usefull for testing
    if (!req.isAttachment()) {
        return Router.CONTINUE;
    }
    res.typingOn();
    postBack('uploadComplete', async () => {
        try {
            const buf = bufferloader(req.attachmentUrl(), 1024);
            return { result: buf.toString('base64') };
        } catch (err) {
            return { err };
        }
    });
});

module.exports = bot;