@moleculer/channels

Reliable messages for Moleculer services via external queue/channel/topic. Unlike moleculer built-in events, this is not a fire-and-forget solution. It's a persistent, durable and reliable message sending solution. The module uses an external message queue/streaming server that stores messages until they are successfully processed. It supports consumer groups, which means that you can run multiple instances of consumer services, incoming messages will be balanced between them.

Features

reliable messages with acknowledgement.
multiple adapters (Redis, RabbitMQ, NATS JetStream, Kafka).
plugable adapters.
configurable max-in-flight.
retry messages.
dead-letter topic function.
can receive messages from 3rd party services.
graceful stopping with active message tracking.

Install

npm i @moleculer/channels

Communication diagram

Native Communication

Integration With A Third-Party System

Note: If you want to send messages to moleculer-services via channels from an external system, you must use the same serialization format as defined in the adapter options (default is JSON). Otherwise, the services won't be able to parse the incoming messages.

Usage

Register middleware in broker options

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

module.exports = {
    logger: true,

    middlewares: [
        ChannelsMiddleware({
            adapter: "redis://localhost:6379"
        })
    ]
};

By default, the middleware will add a sendToChannel(<topic-name>, { payload }) method and channelAdapter property to the broker instance. Moreover, it will register handlers located in channels of a service schema.

Consuming messages in Moleculer services

module.exports = {
    name: "payments",

    actions: {
        /*...*/
    },

    channels: {
        // Shorthand format
        // In this case the consumer group is the service full name
        async "order.created"(payload) {
            // Do something with the payload
            // You should throw error if you want to NACK the message processing.
        },

        "payment.processed": {
            // Using custom consumer-group
            group: "other",
            async handler(payload) {
                // Do something with the payload
                // You should throw error if you want to NACK the message processing.
            }
        }
    },

    methods: {
        /*...*/
    }
};

The received payload doesn't contain any Moleculer-specific data. It means you can use it to get messages from 3rd party topics/channels, as well.

Producing messages

broker.sendToChannel("order.created", {
    id: 1234,
    items: [
        /*...*/
    ]
});

The sent message doesn't contain any Moleculer-specific data. It means you can use it to produce messages to 3rd party topics/channels, as well.

Multiple adapters

Registering multiple adapters

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

// moleculer.config.js
module.exports = {
    logger: true,
    logLevel: "error",
    middlewares: [
        // Default options
        ChannelsMiddleware({
            adapter: {
                type: "Kafka",
                options: {}
            }
        }),
        ChannelsMiddleware({
            adapter: "Redis",
            schemaProperty: "redisChannels",
            sendMethodName: "sendToRedisChannel",
            adapterPropertyName: "redisAdapter"
        }),
        ChannelsMiddleware({
            adapter: "AMQP",
            schemaProperty: "amqpChannels",
            sendMethodName: "sendToAMQPChannel",
            adapterPropertyName: "amqpAdapter"
        })
    ]
};

Using multiple adapters in a service

module.exports = {
    name: "payments",

    actions: {
        /*...*/
    },

    channels: {
        "default.options.topic": {
            group: "mygroup",
            async handler(payload) {
                /*...*/
            }
        }
    },
    redisChannels: {
        "redis.topic": {
            group: "mygroup",
            async handler(payload) {
                /*...*/
            }
        }
    },
    amqpChannels: {
        "amqp.topic": {
            group: "mygroup",
            async handler(payload) {
                /*...*/
            }
        }
    }
};

Middleware options

Name	Type	Default value	Description
`adapter`	`String`, `Object`	`null`	Adapter definition. It can be a `String` as name of the adapter or a connection string or an adapter definition `Object`. More info
`schemaProperty`	`String`	`"channels"`	Name of the property in service schema.
`sendMethodName`	`String`	`"sendToChannel"`	Name of the method in ServiceBroker to send message to the channels.
`adapterPropertyName`	`String`	`"channelAdapter"`	Name of the property in ServiceBroker to access the `Adapter` instance directly.
`context`	`boolean`	`false`	Using Moleculer context in channel handlers by default.

Examples

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

module.exports = {
    logger: true,

    middlewares: [
        ChannelsMiddleware({
            adapter: "redis://localhost:6379",
            sendMethodName: "sendToChannel",
            adapterPropertyName: "channelAdapter",
            schemaProperty: "channels"
        })
    ]
};

Channel options

Name	Type	Supported adapters	Description
`group`	`String`	*	Group name. It's used as a consumer group in adapter. By default, it's the full name of service (with version)
`maxInFlight`	`Number`	Redis	Max number of messages under processing at the same time.
`maxRetries`	`Number`	*	Maximum number of retries before sending the message to dead-letter-queue or drop.
`deadLettering.enabled`	`Boolean`	*	Enable "Dead-lettering" feature.
`deadLettering.queueName`	`String`	*	Name of dead-letter queue.
`deadLettering.errorInfoTTL`	`Number`	*	[Redis adapter only] TTL (in seconds) of error info messages stored in a separate hash. Default is `86400` (1 day).
`deadLettering.transformErrorToHeaders`	`Function`	*	Function to parse error instance to a plain object which will be stored in message headers.
`deadLettering.transformHeadersToErrorData`	`Function`	*	Function to parse plain error info object back to original data types
`context`	`boolean`	*	Using Moleculer context in channel handlers.
`tracing`	`Object`	*	Tracing options same as action tracing options. It works only with `context: true`.
`handler`	`Function(payload: any, rawMessage: any)`	*	Channel handler function. It receives the payload at first parameter. The second parameter is a raw message which depends on the adapter.
`redis.startID`	`String`	Redis	Starting point when consumers fetch data from the consumer group. By default equals to `$`, i.e., consumers will only see new elements arriving in the stream. More info here
`redis.minIdleTime`	`Number`	Redis	Time (in milliseconds) after which pending messages are considered NACKed and should be claimed. Defaults to 1 hour.
`redis.claimInterval`	`Number`	Redis	Interval (in milliseconds) between message claims
`redis.readTimeoutInterval`	`Number`	Redis	Maximum time (in milliseconds) while waiting for new messages. By default equals to 0, i.e., never timeout. More info here
`redis.processingAttemptsInterval`	`Number`	Redis	Interval (in milliseconds) between message transfer into `FAILED_MESSAGES` channel
`amqp.queueOptions`	`Object`	AMQP	AMQP lib queue configuration. More info here.
`amqp.exchangeOptions`	`Object`	AMQP	AMQP lib exchange configuration. More info here.
`amqp.consumerOptions`	`Object`	AMQP	AMQP lib consume configuration. More info here.
`nats.consumerOptions`	`Object`	NATS	NATS JetStream consumer configuration. More info here.
`nats.streamConfig`	`Object`	NATS	NATS JetStream storage configuration. More info here.
`kafka.fromBeginning`	`Boolean`	Kafka	Kafka consumer `fromBeginning` option. More info here.
`kafka.partitionsConsumedConcurrently`	`Number`	Kafka	Kafka consumer `partitionsConsumedConcurrently` option. More info here.

Failed message

If the service is not able to process a message, it should throw an Error inside the handler function. In case of error and if maxRetries option is a positive number, the adapter will redeliver the message to one of all consumers. When the number of redelivering reaches the maxRetries, it will drop the message to avoid the 'retry-loop' effect. If the dead-lettering feature is enabled with deadLettering.enabled: true option then the adapter will move the message into the deadLettering.queueName queue/topic.

The dead-lettered message will contain the original payload and additional error information in the ctx.headers (for Moleculer version >= 0.15.x only) and in the raw message headers. Note that depending on the adapter, the raw message structure may differ (e.g, Map or Object, Buffer or String). The error information includes details about the original error that caused the message to be dead-lettered, such as the error message, stack trace, code, type, data, name, retryable status, and a timestamp indicating when the error occurred.

You can customize the error information that will be stored in the message headers by providing a custom transformErrorToHeaders function in the deadLettering options. By default, the parser stores the message, stack, code, type, data, name and retryable properties of the error object (if they exist) in the headers as plain string, except for stack and data properties which are stored as base64 encoded strings. Encoding is necessary to handle special characters, as some message brokers (like NATS JetStream) do not support characters like \n or \r in headers.

You can also provide a custom transformHeadersToErrorData function in the deadLettering options to parse the error information from the message headers back to their original data types when consuming dead-lettered messages in ctx.headers.

Also note that, for Redis adapter it's not possible to update the original message with error info, to overcome this limitation the adapter will store error info in a separate hash with the message ID as the key. You can customize the TTL of these error info message by setting deadLettering.errorInfoTTL, which defaults to 1 day. When Redis adapter moves a message to the dead-letter queue, it will merge the original message with the error info from the hash.

Default error to headers parser

/**
 * Converts Error object to a plain object
 * @param {any} err
 * @returns {Record<string, string>|null}
 */
const transformErrorToHeaders = err => {
    if (!err) return null;

    let errorHeaders = {
        // primitive properties
        ...(err.message ? { [HEADER_ERROR_MESSAGE]: err.message.toString() } : {}),
        ...(err.code ? { [HEADER_ERROR_CODE]: err.code.toString() } : {}),
        ...(err.type ? { [HEADER_ERROR_TYPE]: err.type.toString() } : {}),
        ...(err.name ? { [HEADER_ERROR_NAME]: err.name.toString() } : {}),
        ...(typeof err.retryable === "boolean"
            ? { [HEADER_ERROR_RETRYABLE]: err.retryable.toString() }
            : {}),

        // complex properties
        // Encode to base64 because of special characters For example, NATS JetStream does not support \n or \r in headers
        ...(err.stack ? { [HEADER_ERROR_STACK]: toBase64(err.stack) } : {}),
        ...(err.data ? { [HEADER_ERROR_DATA]: toBase64(err.data) } : {})
    };

    if (Object.keys(errorHeaders).length === 0) return null;

    errorHeaders[HEADER_ERROR_TIMESTAMP] = Date.now().toString();

    return errorHeaders;
};

Default headers to error info parser

/**
 * Parses error info from headers and attempts to reconstruct original data types
 *
 * @param {Record<string, string>} headers
 * @returns {Record<string, any>}
 */
const transformHeadersToErrorData = headers => {
    if (!headers || typeof headers !== "object") return null;

    const complexPropertiesList = [HEADER_ERROR_STACK, HEADER_ERROR_DATA];

    let errorInfo = {};

    for (let key in headers) {
        if (!key.startsWith(HEADER_ERROR_PREFIX)) continue;

        errorInfo[key] = complexPropertiesList.includes(key)
            ? parseBase64(headers[key])
            : (errorInfo[key] = parseStringData(headers[key]));
    }

    return errorInfo;
};

Dead-Letter Logic

Graceful stopping

The adapters track the messages that are being processed. This means that when a service or the broker is stopping the adapter will block the process and wait until all active messages are processed.

Publishing

Use the broker.sendToChannel(channelName, payload, opts) method to send a message to a channel. The payload should be a serializable data.

Method options

Name	Type	Supported adapters	Description
`raw`	`Boolean`	*	If truthy, the payload won't be serialized.
`persistent`	`Boolean`	AMQP	If truthy, the message will survive broker restarts provided it’s in a queue that also survives restarts.
`ttl`	`Number`	AMQP	If supplied, the message will be discarded from a queue once it’s been there longer than the given number of milliseconds.
`priority`	`Number`	AMQP	Priority of the message.
`correlationId`	`String`	AMQP	Request identifier.
`headers`	`Object`	AMQP, JetStream, Kafka, Redis	Application specific headers to be carried along with the message content.
`routingKey`	`Object`	AMQP	The AMQP `publish` method's second argument. If you want to send the message into an external queue instead of exchange, set the `channelName` to `""` and set the queue name to `routingKey`
`publishAssertExchange.enabled`	`Boolean`	AMQP	Enable/disable calling once `channel.assertExchange()` before first publishing in new exchange by `sendToChannel()`
`publishAssertExchange.exchangeOptions`	`Object`	AMQP	AMQP lib exchange configuration when publishAssertExchange enabled
`key`	`String`	Kafka	Key of Kafka message.
`partition`	`String`	Kafka	Partition of Kafka message.
`acks`	`Number`	Kafka	Control the number of required acks.
`timeout`	`Number`	Kafka	The time to await a response in ms. Default: `30000`
`compression`	`any`	Kafka	Compression codec. Default: `CompressionTypes.None`
`xaddMaxLen`	`Number` or `String`	Redis	Define `MAXLEN` for `XADD` command

Middleware hooks

It is possible to wrap the handlers and the send method in Moleculer middleware. The module defines two hooks to cover it. The localChannel hook is similar to localAction but it wraps the channel handlers in service schema. The sendToChannel hook is similar to emit or broadcast but it wraps the broker.sendToChannel publisher method.

Example

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

const MyMiddleware = {
    name: "MyMiddleware",

    // Wrap the channel handlers
    localChannel(next, chan) {
        return async (msg, raw) => {
            this.logger.info(kleur.magenta(`  Before localChannel for '${chan.name}'`), msg);
            await next(msg, raw);
            this.logger.info(kleur.magenta(`  After localChannel for '${chan.name}'`), msg);
        };
    },

    // Wrap the `broker.sendToChannel` method
    sendToChannel(next) {
        return async (channelName, payload, opts) => {
            this.logger.info(kleur.yellow(`Before sendToChannel for '${channelName}'`), payload);
            await next(channelName, payload, opts);
            this.logger.info(kleur.yellow(`After sendToChannel for '${channelName}'`), payload);
        };
    }
};

module.exports = {
    logger: true,

    middlewares: [
        MyMiddleware,
        ChannelsMiddleware({
            adapter: "redis://localhost:6379"
        })
    ]
};

Context-based messages

In order to use Moleculer Context in handlers (transferring ctx.meta and tracing information) you should set the context: true option in channel definition object or in middleware options to enable it for all channel handlers.

Example to enable context for all 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
        })
    ]
};

Using Context in handlers

module.exports = {
    name: "payments",

    actions: {
        /*...*/
    },

    channels: {
        "default.options.topic": {
            context: true, // Unless not enabled it globally
            async handler(ctx /*, raw*/) {
                // The `ctx` is a regular Moleculer Context
                if (ctx.meta.loggedInUser) {
                    // The `ctx.params` contains the original payload of the message
                    await ctx.call("some.action", ctx.params);
                }
            }
        }
    }
};

Send message with parent Context

In this case the ctx.meta and other tracing information is transferred to the channel handler.

module.exports = {
    name: "payments",

    actions: {
        submitOrder: {
            async handler(ctx) {
                await broker.sendToChannel(
                    "order.created",
                    {
                        id: 1234,
                        items: [
                            /*...*/
                        ]
                    },
                    {
                        // Pass the `ctx` in options of `sendToChannel`
                        ctx
                    }
                );
            }
        }
    }
};

Tracing

To enable tracing for context-based handlers, you should register Tracing middleware in broker options.

The middleware works only with context: true.

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) {
                // ...
            }
        }
    }
});

To disable tracing, set `tracing: false in channel definition.

Adapters

Adapter options

Name	Type	Default value	Supported adapters	Description
`consumerName`	`String`	ServiceBroker nodeID	*	Consumer name used by adapters. By default it's the nodeID of ServiceBroker.
`prefix`	`String`	ServiceBroker namespace	*	Prefix is used to separate topics between environments. By default, the prefix value is the namespace of the ServiceBroker.
`serializer`	`String`, `Object`, `Serializer`	`JSON`	*	Message serializer. You can use any built-in serializer of Moleculer or create a custom one.
`maxRetries`	`Number`	`3`	*	Maximum number of retries before sending the message to dead-letter-queue or drop.
`maxInFlight`	`Number`	`1`	*	Max number of messages under processing at the same time.
`deadLettering.enabled`	`Boolean`	`false`	*	Enable "Dead-lettering" feature.
`deadLettering.queueName`	`String`	`FAILED_MESSAGES`	*	Name of dead-letter queue.
`redis`	`Object`, `String`, `Number`	`null`	Redis	Redis connection options. More info here
`redis.consumerOptions` `.readTimeoutInterval`	`Number`	`0`	Redis	Maximum time (in milliseconds) while waiting for new messages. By default equals to 0, i.e., never timeout. More info here
`redis.consumerOptions` `.minIdleTime`	`Number`	`60 * 60 * 1000`	Redis	Time (in milliseconds) after which pending messages are considered NACKed and should be claimed. Defaults to 1 hour.
`redis.consumerOptions` `.claimInterval`	`Number`	`100`	Redis	Interval (in milliseconds) between message claims.
`redis.consumerOptions` `.startID`	`String`	`$`	Redis	Starting point when consumers fetch data from the consumer group. By default equals to `$`, i.e., consumers will only see new elements arriving in the stream. More info here.
`redis.consumerOptions` `.processingAttemptsInterval`	`Number`	`0`	Redis	Interval (in milliseconds) between message transfer into `FAILED_MESSAGES` channel.
`redis.cluster`	`Object`	`null`	Redis	Redis cluster connection options. More info here
`redis.cluster.nodes`	`Array`	`null`	Redis	Redis Cluster nodes list.
`redis.cluster.clusterOptions`	`Object`	`null`	Redis	Redis Cluster options.
`amqp.url`	`String`	`null`	AMQP	Connection URI.
`amqp.socketOptions`	`Object`	`null`	AMQP	AMQP lib socket configuration. More info here.
`amqp.queueOptions`	`Object`	`null`	AMQP	AMQP lib queue configuration. More info here.
`amqp.exchangeOptions`	`Object`	`null`	AMQP	AMQP lib exchange configuration. More info here.
`amqp.messageOptions`	`Object`	`null`	AMQP	AMQP lib message configuration. More info here.
`amqp.consumerOptions`	`Object`	`null`	AMQP	AMQP lib consume configuration. More info here.
`amqp.publishAssertExchange.enabled`	`Boolean`	`false`	AMQP	Enable/disable calling once `channel.assertExchange()` before first publishing in new exchange by `sendToChannel()`. More info here.
`amqp.publishAssertExchange.exchangeOptions`	`Object`	`null`	AMQP	AMQP lib exchange configuration. More info here.
`nats.streamConfig`	`Object`	`null`	NATS	NATS JetStream storage configuration. More info here.
`nats.consumerOptions`	`Object`	`null`	NATS	NATS JetStream consumer configuration. More info here.
`kafka.brokers`	`String[]`	`null`	Kafka	Kafka bootstrap brokers.
`kafka.logCreator`	`Function`	`null`	Kafka	Kafka logCreator. More info here.
`kafka.producerOptions`	`Object`	`null`	Kafka	Kafka producer constructor configuration. More info here.
`kafka.consumerOptions`	`Object`	`null`	Kafka	Kafka consumer constructor configuration. More info here.

Redis Streams

Redis Streams was introduced in Redis 5.0. Hoverer, since this module relies on the XAUTOCLAIM command, Redis >= 6.2.0 is required.

To use this adapter, install the ioredis module with npm install ioredis command.

Redis Adapter Overview

Example

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: "redis://localhost:6379"
        })
    ]
};

Example with options

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: {
                type: "Redis",
                options: {
                    redis: {
                        // ioredis constructor options: https://github.com/luin/ioredis#connect-to-redis
                        host: "127.0.0.1",
                        port: 6379,
                        db: 3,
                        password: "pass1234",
                        consumerOptions: {
                            // Timeout interval (in milliseconds) while waiting for new messages. By default never timeout
                            readTimeoutInterval: 0,
                            // Time (in milliseconds) after which pending messages are considered NACKed and should be claimed. Defaults to 1 hour.
                            minIdleTime: 5000,
                            // Interval (in milliseconds) between two claims
                            claimInterval: 100,
                            // "$" is a special ID. Consumers fetching data from the consumer group will only see new elements arriving in the stream.
                            // More info: https://redis.io/commands/XGROUP
                            startID: "$",
                            // Interval (in milliseconds) between message transfer into FAILED_MESSAGES channel
                            processingAttemptsInterval: 1000
                        }
                    }
                }
            }
        })
    ]
};

You can overwrite the default values in the handler definition.

Overwrite default options in service

module.exports = {
    name: "payments",

    actions: {
        /*...*/
    },

    channels: {
        "order.created": {
            maxInFlight: 6,
            async handler(payload) {
                /*...*/
            }
        },
        "payment.processed": {
            redis: {
                minIdleTime: 10,
                claimInterval: 10
            }
            deadLettering: {
                enabled: true,
                queueName: "DEAD_LETTER"
            },
            async handler(payload) {
                /*...*/
            }
        }
    }
};

Redis Cluster

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: {
                type: "Redis",
                options: {
                    redis: {
                        cluster: {
                            nodes: [
                                { port: 6380, host: "127.0.0.1" },
                                { port: 6381, host: "127.0.0.1" },
                                { port: 6382, host: "127.0.0.1" }
                            ],
                            options: {
                                /* More information: https://github.com/luin/ioredis#cluster */
                                redisOptions: {
                                    password: "fallback-password"
                                }
                            }
                        },
                        consumerOptions: {
                            // Timeout interval (in milliseconds) while waiting for new messages. By default never timeout
                            readTimeoutInterval: 0,
                            // Time (in milliseconds) after which pending messages are considered NACKed and should be claimed. Defaults to 1 hour.
                            minIdleTime: 5000,
                            // Interval (in milliseconds) between two claims
                            claimInterval: 100,
                            // "$" is a special ID. Consumers fetching data from the consumer group will only see new elements arriving in the stream.
                            // More info: https://redis.io/commands/XGROUP
                            startID: "$",
                            // Interval (in milliseconds) between message transfer into FAILED_MESSAGES channel
                            processingAttemptsInterval: 1000
                        }
                    },
                    deadLettering: {
                        transformErrorToHeaders: err => {
                            if (!err) return null;

                            let errorHeaders = {
                                // primitive properties
                                ...(err.message
                                    ? { [HEADER_ERROR_MESSAGE]: err.message.toString() }
                                    : {}),
                                ...(err.code ? { [HEADER_ERROR_CODE]: err.code.toString() } : {}),
                                ...(err.type ? { [HEADER_ERROR_TYPE]: err.type.toString() } : {}),
                                ...(err.name ? { [HEADER_ERROR_NAME]: err.name.toString() } : {}),
                                ...(typeof err.retryable === "boolean"
                                    ? { [HEADER_ERROR_RETRYABLE]: err.retryable.toString() }
                                    : {}),

                                // complex properties
                                // Encode to base64 because of special characters For example, NATS JetStream does not support \n or \r in headers
                                ...(err.stack ? { [HEADER_ERROR_STACK]: toBase64(err.stack) } : {}),
                                ...(err.data ? { [HEADER_ERROR_DATA]: toBase64(err.data) } : {})
                            };

                            if (Object.keys(errorHeaders).length === 0) return null;

                            errorHeaders[HEADER_ERROR_TIMESTAMP] = Date.now().toString();

                            return errorHeaders;
                        },

                        transformHeadersToErrorData: headers => {
                            if (!headers || typeof headers !== "object") return null;

                            // parse back complex properties
                            const complexPropertiesList = [HEADER_ERROR_STACK, HEADER_ERROR_DATA];

                            let errorInfo = {};

                            for (let key in headers) {
                                if (!key.startsWith(HEADER_ERROR_PREFIX)) continue;

                                errorInfo[key] = complexPropertiesList.includes(key)
                                    ? parseBase64(headers[key])
                                    : (errorInfo[key] = parseStringData(headers[key]));
                            }

                            return errorInfo;
                        },

                        // Time to live for error info in dedicated hash (in seconds). Default: 24 hours
                        errorInfoTTL: 24 * 60 * 60 // 24 hours
                    }
                }
            }
        })
    ]
};

Capped Streams

To support Redis "capped streams", you can define the MAXLEN value in sendToChannel options as xaddMaxLen. It can be a number or a string with ~ prefix like ~1000. It will be transformed to ...MAXLEN ~ 1000 ...

Example

broker.sendToChannel(
    "order.created",
    {
        id: 1234,
        items: [
            /*...*/
        ]
    },
    {
        xaddMaxLen: "~1000"
    }
);

AMQP (RabbitMQ)

The AMQP adapter uses the exchange-queue logic of RabbitMQ for creating consumer groups. It means the sendToChannel method sends the message to the exchange and not for a queue.

To use this adapter, install the amqplib module with npm install amqplib command.

Example

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: "amqp://localhost:5672"
        })
    ]
};

Example with options

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: {
                type: "AMQP",
                options: {
                    amqp: {
                        url: "amqp://localhost:5672",
                        // Options for `Amqplib.connect`
                        socketOptions: {},
                        // Options for `assertQueue()`
                        queueOptions: {},
                        // Options for `assertExchange()`
                        exchangeOptions: {},
                        // Options for `channel.publish()`
                        messageOptions: {},
                        // Options for `channel.consume()`
                        consumerOptions: {},
                        // Note: options for `channel.assertExchange()` before first publishing in new exchange
                        publishAssertExchange: {
                            // Enable/disable calling once `channel.assertExchange()` before first publishing in new exchange by `sendToChannel`
                            enabled: false,
                            // Options for `channel.assertExchange()` before publishing by `sendToChannel`
                            exchangeOptions: {}
                        }
                    },
                    maxInFlight: 10,
                    maxRetries: 3,
                    deadLettering: {
                        enabled: false
                        //queueName: "DEAD_LETTER",
                        //exchangeName: "DEAD_LETTER"
                    }
                }
            }
        })
    ]
};

Example Producing messages with options

broker.sendToChannel(
    "order.created",
    {
        id: 1234,
        items: [
            /*...*/
        ]
    },
    {
        // Using specific `assertExchange()` options only for the current sending case
        publishAssertExchange: {
            // Enable/disable calling once `channel.assertExchange()` before first publishing in new exchange by `sendToChannel`
            enabled: true,
            // Options for `channel.assertExchange()` before publishing
            exchangeOptions: {
                /*...*/
            }
        }
    }
);

Note: If you know that the exchange will be created before sendToChannel is called by someone else, then it is better to skip publishAssertExchange option

Kafka

The Kafka adapter uses Apache Kafka topics.

In Kafka adapter, the maxInFlight function works differently than other adapters. Reading messages from a partition is processed sequentially in order. So if you want to process multiple messages, you should read messages from multiple partition. To enable it, use the kafka.partitionsConsumedConcurrently option in channel options. More info.

To use this adapter, install the kafkajs module with npm install kafkajs command.

Example

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: "kafka://localhost:9092"
        })
    ]
};

Example with options

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: {
                type: "Kafka",
                options: {
                    kafka: {
                        brokers: ["kafka-1:9092", "kafka-1:9092"],
                        // Options for `producer()`
                        producerOptions: {},
                        // Options for `consumer()`
                        consumerOptions: {}
                    },
                    maxRetries: 3,
                    deadLettering: {
                        enabled: false,
                        queueName: "DEAD_LETTER"
                    }
                }
            }
        })
    ]
};

NATS JetStream

To use this adapter, install the nats module with npm install nats command.

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: "nats://localhost:4222"
        })
    ]
};

Example with options

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: {
                type: "NATS",
                options: {
                    nats: {
                        url: "nats://localhost:4222",
                        /** @type {ConnectionOptions} */
                        connectionOptions: {},
                        /** @type {StreamConfig} More info: https://docs.nats.io/jetstream/concepts/streams */
                        streamConfig: {},
                        /** @type {ConsumerOpts} More info: https://docs.nats.io/jetstream/concepts/consumers */
                        consumerOptions: {
                            config: {
                                // More info: https://docs.nats.io/jetstream/concepts/consumers#deliverpolicy-optstartseq-optstarttime
                                deliver_policy: "new",
                                // More info: https://docs.nats.io/jetstream/concepts/consumers#ackpolicy
                                ack_policy: "explicit",
                                // More info: https://docs.nats.io/jetstream/concepts/consumers#maxackpending
                                max_ack_pending: 1
                            }
                        }
                    },
                    maxInFlight: 10,
                    maxRetries: 3,
                    deadLettering: {
                        enabled: false,
                        queueName: "DEAD_LETTER"
                    }
                }
            }
        })
    ]
};

Jetstream - Single stream with multiple topics

It is possible to configure single stream to handle multiple topics (e.g., streamOneTopic.abc and streamOneTopic.xyz). Moreover it possible for a single handler to receive any message that matches the filter streamOneTopic.*. Please check the example for all the details.

Fake adapter

This adapter is made for unit/integration tests. The adapter uses the built-in Moleculer event bus to send messages instead of an external module. It means that the message sending is not reliable but can be a good option to test the channel handlers in a test environment. The fake adapter is doesn't support retries and dead-letter topic features. For multiple brokers, you should define a transporter (at least the FakeTransporter)

Do NOT use this adapter in production!

Example

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

module.exports = {
    middlewares: [
        ChannelsMiddleware({
            adapter: "Fake"
        })
    ]
};

Benchmark

Tests are running on Intel i7 4770K, 32GB RAM on Windows 10 with WSL.

Tested adapters

Name	Adapter	Description
Redis	Redis	Simple Redis Stream adapter.
RedisCluster	Redis	Clustered Redis Stream adapter with 3 nodes.
NATS JetStream	NATS	NATS JetStream adapter.
Kafka	Kafka	Kafka adapter.

Latency test

In this test, we send one message at a time. After processing the current message, another one is sent. This test measures the latency of processing a message. The maxInFlight is 1.

Adapter	Time	msg/sec
Redis	2ms	452
RedisCluster	2ms	433
AMQP	51ms	20
NATS JetStream	1ms	584
Kafka	1ms	637

Throughput test (maxInFlight: 10)

In this test, we send 10k messages and wait for all be processed. This test measures the throughput. The maxInFlight is 10.

Adapter	msg/sec
Redis	1294
RedisCluster	4118
AMQP	11143
NATS JetStream	589
Kafka	1831

Throughput test (maxInFlight: 100)

In this test, we send 10k messages and wait for all be processed. This test measures the throughput. The maxInFlight is 100.

Adapter	msg/sec
Redis	4081
RedisCluster	4198
AMQP	21438
NATS JetStream	646
Kafka	1916

License

The project is available under the MIT license.

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CHANGELOG.md		CHANGELOG.md
LICENSE		LICENSE
README.md		README.md
index.js		index.js
package-lock.json		package-lock.json
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@moleculer/channels

Features

Install

Communication diagram

Usage

Register middleware in broker options

Consuming messages in Moleculer services

Producing messages

Multiple adapters

Middleware options

Channel options

Failed message

Graceful stopping

Publishing

Method options

Middleware hooks

Context-based messages

Tracing

Adapters

Adapter options

Redis Streams

Capped Streams

AMQP (RabbitMQ)

Kafka

NATS JetStream

Jetstream - Single stream with multiple topics

Fake adapter

Benchmark

Tested adapters

Latency test

Throughput test (maxInFlight: 10)

Throughput test (maxInFlight: 100)

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