Serverless Middleware
Serverless plugin to allow middleware handlers configured directly in serverless.yaml
Requirements:
- Serverless v3
- AWS provider
- Node.js 14+
Supported runtimes
- nodejs12.x (both Javascript and Typescript)
- nodejs14.x (both Javascript and Typescript)
- nodejs16.x (both Javascript and Typescript)
- nodejs18.x (both Javascript and Typescript)
- nodejs20.x (both Javascript and Typescript)
- dotnetcore2.1
- java8
- java11
- go1.x
- python2.7
- python3.7
- ruby2.5
- provided
Installation
Install via npm in the root of your Serverless service:
npm install serverless-middleware --save-dev
Add the plugin to the plugins
array in your Serverless serverless.yaml
:
plugins: - serverless-middleware
How it works
Middleware allows you to set up multiple handlers to be executed sequentially including error handlers that will capture any exception in the chain.
Middlewares are just standard AWS lambda handlers that return a promise (or are async).
Handlers using callback
will NOT work.
const myMiddleware = async (event, context) => { ... };
Once serverless-middleware
is installed you can set the function.middleware
property to an array and skip the function.handler
property.
Each middleware handler can be a string (like a standard handler would be) or an object containing the properties then
and/or catch
.
For example:
provider: name: aws runtime: nodejs20.x functions: myFunction: middleware: - auth.authenticate - auth.authorize - then: myFunction.handler # `then:` is unnecessary here. - catch: utils.handlerError - # or both can be combined then: logger.log catch: utils.handlerLoggerError
will result in an execution like:
Promise.resolve() .then(require('./auth').authenticate) .then(require('./auth').authorize) .then(require('./myFunction').handler) .catch(require('./utils').handlerError) .then(require('./logger').log) .catch(require('./utils').handlerLoggerError);
As with standard promises, catch handlers are only executed when there are exceptions. The resulting lambda will return the result returned by the last middleware handler executed.
The event
and context
objects are passed from handler to handler so you can attach new properties to be accessed by subsequent handlers.
context
always contains the result of the previous handler in the prev
property.
The user can also stop at any point in the chain by calling the end
method in the context
argument. After context.end()
is called, no more handlers will be executed.
For example:
const myMiddleware = async (event, context) => { if (context.prev === undefined) { // Previous middleware handler didn't return. End execution. context.end(); return { statusCode: 200, body: 'No results', }; } ...};
You can also add pre/pos- middleware handlers and maintain the function.handler
. These middleware are just prepended/appended to the main handler.
For example:
provider: name: aws runtime: nodejs20.x functions: myFunction: events: - http: path: my-function method: get handler: myFunction.handler middleware: pre: - auth.authenticate - auth.authorize pos: - catch: utils.handlerError
You can also add pre/pos- middleware handlers at the package level using the custom.middleware
section of serverless.yaml
. These middleware are just prepended/appended to all the function middleware handlers chain.
For example:
provider: name: aws runtime: nodejs20.xcustom: middleware: pre: - auth.authenticate pos: - catch: utils.handlerErrorfunctions: myAnonymousFunction: events: - http: path: my-anonymous-function method: get handler: myAnonymousFunction.handler myFunction: events: - http: path: my-function method: get handler: myFunction.handler middleware: pre: - auth.authorize
will result in a similar promise chain as above.
Packaging
In most cases, you shouldn't need to change the default packaging configuration. For edge cases, Middleware can be configured to use a specific intermediary folder and to not clear it after creating the serverless package.
These settings are also set in the custom.middleware
section of serverless.yaml
custom: middleware: folderName: my_custom_folder # defaults to '.middleware' cleanFolder: false # defaults to 'true'
This might be useful if you are using sls package
and building your own artifacts.
Migrations
v1.0.0 to 2.0.0
Use function.middleware instead fo function.custom.middleware
v0.0.14 to v0.0.15
Use function.custom.middleware instead fo function.handler
Passing an array to the handler property is not allowed anymore since Serverless is getting stricter with it's types and it also causes issues with Typescript.
So
functions: myFunction: handler: - auth.authenticate - auth.authorize - then: myFunction.handler # `then:` is unnecessary here. - catch: utils.handlerError - # or both can be combined then: logger.log catch: utils.handlerLoggerError
becomes
functions: myFunction: custom: middleware: - auth.authenticate - auth.authorize - then: myFunction.handler # `then:` is unnecessary here. - catch: utils.handlerError - # or both can be combined then: logger.log catch: utils.handlerLoggerError
Contribute
Help us to make this plugin better.
- Clone the code
- Install the dependencies with
npm install
- Create a feature branch
git checkout -b new_feature
- Add your code and add tests if you implement a new feature
- Validate your changes
npm run lint
andnpm test
(ornpm run test-with-coverage
)
License
This software is released under the MIT license. See the license file for more details.