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 balance 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. If you don’t define, it will be {}.

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, the requestTimeout value from broker options will be used. 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, the retryPolicy.retries value from broker options will be used. 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 specified node.
meta Object {} 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. Use it to chain the calls.
requestID String null Request ID or Correlation ID. Use it for tracing.

Usages

Call without params

const res = await broker.call("user.list");

Call with params

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

Call with calling options

const res = await broker.call("user.recommendation", { limit: 5 }, {
timeout: 500,
retries: 3,
fallbackResponse: defaultRecommendation
});

Call with promise 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

const res = await broker.call("$node.health", null, { nodeID: "node-21" })

Metadata

Send meta information to services with meta property. Access it via ctx.meta in action handlers. Please note that in 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;
}
}
});

When making internal calls to actions (this.actions.xy()) you should set parentCtx to pass meta data.

Internal calls

broker.createService({
name: "mod",
actions: {
hello(ctx) {
console.log(ctx.meta);
// Prints: { user: 'John' }
ctx.meta.age = 123
return this.actions.subHello(ctx.params, { parentCtx: ctx });
},

subHello(ctx) {
console.log("meta from subHello:", ctx.meta);
// Prints: { user: 'John', age: 123 }
return "hi!";
}
}
});

broker.call("mod.hello", { param: 1 }, { meta: { user: "John" } });

Timeout

Timeout can be set in action definition, as well. It overwrites the global broker requestTimeout option, but not the timeout in calling options.

Example

// moleculer.config.js
module.exports = {
nodeID: "node-1",
requestTimeout: 3000
};

// greeter.service.js
module.exports = {
name: "greeter",
actions: {
normal: {
handler(ctx) {
return "Normal";
}
},
slow: {
timeout: 5000, // 5 secs
handler(ctx) {
return "Slow";
}
}
},

Calling examples

// It uses the global 3000 timeout
await broker.call("greeter.normal");
// It uses the 5000 timeout from action definition
await broker.call("greeter.slow");
// It uses 1000 timeout from calling option
await broker.call("greeter.slow", null, { timeout: 1000 });

Multiple calls

Calling multiple actions at the same time is also possible. To do it use broker.mcall or ctx.mcall.

mcall with Array< Object >

await broker.mcall(
[
{ action: 'posts.find', params: { author: 1 }, options: { /* Calling options for this call. */} },
{ action: 'users.find', params: { name: 'John' } }
],
{
// Common calling options for all calls.
meta: { token: '63f20c2d-8902-4d86-ad87-b58c9e2333c2' }
}
);

mcall with Object

await broker.mcall(
{
posts: { action: 'posts.find', params: { author: 1 }, options: { /* Calling options for this call. */} },
users: { action: 'users.find', params: { name: 'John' } }
},
{
// Common calling options for all calls.
meta: { token: '63f20c2d-8902-4d86-ad87-b58c9e2333c2' }
}
);

Streaming

Moleculer supports Node.js streams as request params and as response. Use it to transfer an incoming file from a gateway, 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" }});
Object Mode Streaming

Object Mode Streaming is also supported. In order to enable it set $streamObjectMode: true in meta.

Please note, the params should be a stream, you cannot add any additional 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) {
// Save the received stream to a file
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

Action hooks are pluggable and reusable middleware functions that can be registered before, after or on errors of service actions. A hook is either a Function or a String. In case of a String it must be equal to service’s method name.

Before hooks

In before hooks, it receives the ctx, it can manipulate the ctx.params, ctx.meta, or add custom variables into ctx.locals what you can use in the action handlers.
If there are any problem, it can throw an Error. Please note, you can’t break/skip the further executions of hooks or action handler.

Main usages:

  • parameter sanitization
  • parameter validation
  • entity finding
  • authorization

After hooks

In after hooks, it receives the ctx and the response. It can manipulate or completely change the response.
In the hook, it has to return the response.

Main usages:

  • property populating
  • remove sensitive data.
  • wrapping the response into an Object
  • convert the structure of the response

Error hooks

The error hooks are called when an Error is thrown during action calling. It receives the ctx and the err. It can handle the error and return another response (fallback) or throws further the error.

Main usages:

  • error handling
  • wrap the error into another one
  • fallback response

Service level declaration

Hooks can be assigned to a specific action (by indicating action name) or all actions (*) in service.

Please notice that hook registration order matter as it defines sequence by which hooks are executed. For more information take a look at hook execution order.

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 for action `remove`
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;
}
}
}
};

Action level declaration

Hooks can be also registered inside action declaration.

Please note that hook registration order matter as it defines sequence by which hooks are executed. For more information take a look at hook execution order.

Before & After hooks

broker.createService({
name: "greeter",
actions: {
hello: {
hooks: {
before(ctx) {
broker.logger.info("Before action hook");
},
after(ctx, res) {
broker.logger.info("After action hook"));
return res;
}
},

handler(ctx) {
broker.logger.info("Action handler");
return `Hello ${ctx.params.name}`;
}
}
}
});

Execution order

It is important to keep in mind that hooks have a specific execution order. This is especially important to remember when multiple hooks are registered at different (service and/or action) levels. Overall, the hooks have the following execution logic:

  • before hooks: global (*) -> service level -> action level.

  • after hooks: action level -> service level -> global (*).

Example of a global, service & action level hook execution chain

broker.createService({
name: "greeter",
hooks: {
before: {
"*"(ctx) {
broker.logger.info(chalk.cyan("Before all hook"));
},
hello(ctx) {
broker.logger.info(chalk.magenta(" Before hook"));
}
},
after: {
"*"(ctx, res) {
broker.logger.info(chalk.cyan("After all hook"));
return res;
},
hello(ctx, res) {
broker.logger.info(chalk.magenta(" After hook"));
return res;
}
},
},

actions: {
hello: {
hooks: {
before(ctx) {
broker.logger.info(chalk.yellow.bold(" Before action hook"));
},
after(ctx, res) {
broker.logger.info(chalk.yellow.bold(" After action hook"));
return res;
}
},

handler(ctx) {
broker.logger.info(chalk.green.bold(" Action handler"));
return `Hello ${ctx.params.name}`;
}
}
}
});

Output produced by global, service & action level hooks

INFO  - Before all hook
INFO - Before hook
INFO - Before action hook
INFO - Action handler
INFO - After action hook
INFO - After hook
INFO - After all hook

Reusability

The most efficient way of reusing hooks is by declaring them as service methods in a separate file and import them with the mixin mechanism. This way a single hook can be easily shared across multiple actions.

// authorize.mixin.js
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
}
}
}
// posts.service.js
const MyAuthMixin = require("./authorize.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) {}
}
}
};

Local Storage

The locals property of Context object is a simple storage that can be used to store some additional data and pass it to the action handler. locals property and hooks are a powerful combo:

Setting ctx.locals in before hook

module.exports = {
name: "user",

hooks: {
before: {
async get(ctx) {
const entity = await this.findEntity(ctx.params.id);
ctx.locals.entity = entity;
}
}
},

actions: {
get: {
params: {
id: "number"
},
handler(ctx) {
this.logger.info("Entity", ctx.locals.entity);
}
}
}
}