Actions

The actions are the callable/public methods of the service. The action calling represents a remote-procedure-call (RPC). It has request parameters & returns response, like a HTTP request.

If you have multiple instances of services, the broker will load balancing the request among instances. Read more about balancing.


Action balancing diagram

Call services

To call a service, use the broker.call method. The broker looks for the service (and a node) which has the given action and call it. The function returns a Promise.

Syntax

const res = await broker.call(actionName, params, opts);

The actionName is a dot-separated string. The first part of it is the service name, while the second part of it represents the action name. So if you have a posts service with a create action, you can call it as posts.create.

The params is an object which is passed to the action as a part of the Context. The service can access it via ctx.params. It is optional.

The opts is an object to set/override some request parameters, e.g.: timeout, retryCount. It is optional.

Available calling options:

Name Type Default Description
timeout Number null Timeout of request in milliseconds. If the request is timed out and you don’t define fallbackResponse, broker will throw a RequestTimeout error. To disable set 0. If it’s not defined, broker uses the requestTimeout value of broker options. Read more
retries Number null Count of retry of request. If the request is timed out, broker will try to call again. To disable set 0. If it’s not defined, broker uses the retryPolicy.retries value of broker options. Read more
fallbackResponse Any null Returns it, if the request has failed. Read more
nodeID String null Target nodeID. If set, it will make a direct call to the given node.
meta Object null Metadata of request. Access it via ctx.meta in actions handlers. It will be transferred & merged at nested calls, as well.
parentCtx Context null Parent Context instance.
requestID String null Request ID or correlation ID. It appears in the metrics events.

Usages

Call without params

broker.call("user.list")
.then(res => console.log("User list: ", res));

Call with params

broker.call("user.get", { id: 3 })
.then(res => console.log("User: ", res));

Call with async/await

const res = await broker.call("user.get", { id: 3 });
console.log("User: ", res);

Call with options

broker.call("user.recommendation", { limit: 5 }, {
timeout: 500,
retries: 3,
fallbackResponse: defaultRecommendation
}).then(res => console.log("Result: ", res));

Call with error handling

broker.call("posts.update", { id: 2, title: "Modified post title" })
.then(res => console.log("Post updated!"))
.catch(err => console.error("Unable to update Post!", err));

Direct call: get health info from the “node-21” node

broker.call("$node.health", {}, { nodeID: "node-21" })
.then(res => console.log("Result: ", res));

Metadata

Send meta informations to services with meta property. Access it via ctx.meta in action handlers. Please note at nested calls the meta is merged.

broker.createService({
name: "test",
actions: {
first(ctx) {
return ctx.call("test.second", null, { meta: {
b: 5
}});
},
second(ctx) {
console.log(ctx.meta);
// Prints: { a: "John", b: 5 }
}
}
});

broker.call("test.first", null, { meta: {
a: "John"
}});

The meta is sent back to the caller service. Use it to send extra meta information back to the caller. E.g.: send response headers back to API gateway or set resolved logged in user to metadata.

broker.createService({
name: "test",
actions: {
async first(ctx) {
await ctx.call("test.second", null, { meta: {
a: "John"
}});

console.log(ctx.meta);
// Prints: { a: "John", b: 5 }
},
second(ctx) {
// Modify meta
ctx.meta.b = 5;
}
}
});

Streaming

Moleculer supports Node.js streams as request params and as response. Use it to transfer uploaded file from a gateway or encode/decode or compress/decompress streams.

Examples

Send a file to a service as a stream

const stream = fs.createReadStream(fileName);

broker.call("storage.save", stream, { meta: { filename: "avatar-123.jpg" }});

Please note, the params should be a stream, you cannot add any more variables to the params. Use the meta property to transfer additional data.

Receiving a stream in a service

module.exports = {
name: "storage",
actions: {
save(ctx) {
const s = fs.createWriteStream(`/tmp/${ctx.meta.filename}`);
ctx.params.pipe(s);
}
}
};

Return a stream as response in a service

module.exports = {
name: "storage",
actions: {
get: {
params: {
filename: "string"
},
handler(ctx) {
return fs.createReadStream(`/tmp/${ctx.params.filename}`);
}
}
}
};

Process received stream on the caller side

const filename = "avatar-123.jpg";
broker.call("storage.get", { filename })
.then(stream => {
const s = fs.createWriteStream(`./${filename}`);
stream.pipe(s);
s.on("close", () => broker.logger.info("File has been received"));
})

AES encode/decode example service

const crypto = require("crypto");
const password = "moleculer";

module.exports = {
name: "aes",
actions: {
encrypt(ctx) {
const encrypt = crypto.createCipher("aes-256-ctr", password);
return ctx.params.pipe(encrypt);
},

decrypt(ctx) {
const decrypt = crypto.createDecipher("aes-256-ctr", password);
return ctx.params.pipe(decrypt);
}
}
};

Action visibility

The action has a visibility property to control the visibility & callability of service actions.

Available values:

  • published or null: public action. It can be called locally, remotely and can be published via API Gateway
  • public: public action, can be called locally & remotely but not published via API GW
  • protected: can be called only locally (from local services)
  • private: can be called only internally (via this.actions.xy() inside service)

Change visibility

module.exports = {
name: "posts",
actions: {
// It's published by default
find(ctx) {},
clean: {
// Callable only via `this.actions.clean`
visibility: "private",
handler(ctx) {}
}
},
methods: {
cleanEntities() {
// Call the action directly
return this.actions.clean();
}
}
}

The default values is null (means published) due to backward compatibility.

Action hooks

Define action hooks to wrap certain actions coming from mixins.
There are before, after and error hooks. Assign it to a specified action or all actions (*) in service.
The hook can be a Function or a String. The latter must be a local service method name.

Before hooks

const DbService = require("moleculer-db");

module.exports = {
name: "posts",
mixins: [DbService]
hooks: {
before: {
// Define a global hook for all actions
// The hook will call the `resolveLoggedUser` method.
"*": "resolveLoggedUser",

// Define multiple hooks
remove: [
function isAuthenticated(ctx) {
if (!ctx.user)
throw new Error("Forbidden");
},
function isOwner(ctx) {
if (!this.checkOwner(ctx.params.id, ctx.user.id))
throw new Error("Only owner can remove it.");
}
]
}
},

methods: {
async resolveLoggedUser(ctx) {
if (ctx.meta.user)
ctx.user = await ctx.call("users.get", { id: ctx.meta.user.id });
}
}
}

After & Error hooks

const DbService = require("moleculer-db");

module.exports = {
name: "users",
mixins: [DbService]
hooks: {
after: {
// Define a global hook for all actions to remove sensitive data
"*": function(ctx, res) {
// Remove password
delete res.password;

// Please note, must return result (either the original or a new)
return res;
},
get: [
// Add a new virtual field to the entity
async function (ctx, res) {
res.friends = await ctx.call("friends.count", { query: { follower: res._id }});

return res;
},
// Populate the `referrer` field
async function (ctx, res) {
if (res.referrer)
res.referrer = await ctx.call("users.get", { id: res._id });

return res;
}
]
},
error: {
// Global error handler
"*": function(ctx, err) {
this.logger.error(`Error occurred when '${ctx.action.name}' action was called`, err);

// Throw further the error
throw err;
}
}
}
};

The recommended use case is to create mixins filling up the service with methods and in hooks set method names.

Mixin

module.exports = {
methods: {
checkIsAuthenticated(ctx) {
if (!ctx.meta.user)
throw new Error("Unauthenticated");
},
checkUserRole(ctx) {
if (ctx.action.role && ctx.meta.user.role != ctx.action.role)
throw new Error("Forbidden");
},
checkOwner(ctx) {
// Check the owner of entity
}
}
}

Use mixin methods in hooks

const MyAuthMixin = require("./my.mixin");

module.exports = {
name: "posts",
mixins: [MyAuthMixin]
hooks: {
before: {
"*": ["checkIsAuthenticated"],
create: ["checkUserRole"],
update: ["checkUserRole", "checkOwner"],
remove: ["checkUserRole", "checkOwner"]
}
},

actions: {
find: {
// No required role
handler(ctx) {}
},
create: {
role: "admin",
handler(ctx) {}
},
update: {
role: "user",
handler(ctx) {}
}
}
};

Contexts

When you call an action, the broker creates a Context instance which contains all request information and passes it to the action handler as a single argument.

Available properties & methods of Context:

Name Type Description
ctx.id String Context ID
ctx.broker ServiceBroker Instance of the broker.
ctx.action Object Instance of action definition.
ctx.nodeID String The caller or target Node ID.
ctx.requestID String Request ID. If you make nested-calls, it will be the same ID.
ctx.parentID String Parent context ID (in nested-calls).
ctx.params Any Request params. Second argument from broker.call.
ctx.meta Any Request metadata. It will be also transferred to nested-calls.
ctx.level Number Request level (in nested-calls). The first level is 1.
ctx.call() Function Make nested-calls. Same arguments like in broker.call
ctx.emit() Function Emit an event, same as broker.emit
ctx.broadcast() Function Broadcast an event, same as broker.broadcast

Context tracking

If you want graceful service shutdowns, enable the Context tracking feature in broker options. If you enable it, all services will wait for all running contexts before shutdown.
A timeout value can be defined with shutdownTimeout broker option. The default values is 5 seconds.

**Enable context tracking & change the timeout value.

const broker = new ServiceBroker({
nodeID: "node-1",
tracking: {
enabled: true,
shutdownTimeout: 10 * 1000
}
});

The shutdown timeout can be overwritten by $shutdownTimeout property in service settings.

Disable tracking in calling option

broker.call("posts.find", {}, { tracking: false });