Context-based handlers

[icebob]

This PR adds Context-based functionality:

• transferring ctx.meta and tracing information from Context
• create a Context and pass to channel handlers where ctx.params contains the payload and ctx.meta contains the parent ctx.meta. The modified ctx.meta is not transferred back to the caller.

This functions works with all adapters.

Enable the function globally for all channel handlers

// moleculer.config.js
const ChannelsMiddleware = require("@moleculer/channels").Middleware;

module.exports = {
    logger: true,

    middlewares: [
        ChannelsMiddleware({
            adapter: "redis://localhost:6379",
            // Enable context in all channel handlers 
            context: true
        })
    ]
};

Call with context:

broker.createService({
    name: "publisher",
    actions: {
        async publish(ctx) {
            await broker.sendToChannel("my.topic", { a: 5, b: "John" }, {
                ctx,
                headers: { myHeader: "123" }
            });
        }
    }
});

Context in handler

The Context is always created regardless of whether it was passed at sendToChannel

module.exports = {
    name: "sub1",
    channels: {
        "my.topic": {
            context: true, // Unless not enabled it globally
            async handler(ctx, raw) {
                // Original `msg` in `ctx.params`
                this.logger.info("Processing...", ctx.params, ctx.meta);
            }
        }
    }
}

Tracing

Register channel tracing middleware

//moleculer.config.js
const TracingMiddleware = require("@moleculer/channels").Tracing;

module.exports = {
    logger: true,

    middlewares: [
        ChannelsMiddleware({
            adapter: "redis://localhost:6379",
            // Enable context in all channel handlers 
            context: true
        }),
        TracingMiddleware()
    ]
};

You can fine-tuning tracing tags and span name in tracing channel property similar to actions.

Customize tags and span name

broker.createService({
    name: "sub1",
    channels: {
        "my.topic": {
            context: true,
            tracing: {
                spanName: ctx => `My custom span: ${ctx.params.id}`
                tags: {
                    params: true,
                    meta: true
                }
            },
            async handler(ctx, raw) {
                // ...
            }
        }
    }
});