This utility provides JSON Schema validation for events and responses, including JMESPath support to unwrap events before validation.
Powertools for AWS Lambda (TypeScript) is a developer toolkit to implement Serverless best practices and increase developer velocity. You can use the library in both TypeScript and JavaScript code bases.
To get started, install the package by running:
npm i @aws-lambda-powertools/validation
You can validate inbound and outbound payloads using the @validator class method decorator or validator Middy.js middleware.
You can also use the standalone validate function, if you want more control over the validation process such as handling a validation error.
The @validator decorator is a TypeScript class method decorator that you can use to validate both the incoming event and the response payload.
If the validation fails, we will throw a SchemaValidationError.
import { validator } from '@aws-lambda-powertools/validation/decorator';
import type { Context } from 'aws-lambda';
const inboundSchema = {
type: 'object',
properties: {
value: { type: 'number' },
},
required: ['value'],
additionalProperties: false,
};
const outboundSchema = {
type: 'object',
properties: {
result: { type: 'number' },
},
required: ['result'],
additionalProperties: false,
};
class Lambda {
@validator({
inboundSchema,
outboundSchema,
})
async handler(event: { value: number }, _context: Context) {
// Your handler logic here
return { result: event.value * 2 };
}
}
const lambda = new Lambda();
export const handler = lambda.handler.bind(lambda);
It's not mandatory to validate both the inbound and outbound payloads. You can either use one, the other, or both.
If you are using Middy.js, you can instead use the validator middleware to validate the incoming event and response payload.
import { validator } from '@aws-lambda-powertools/validation/middleware';
import middy from '@middy/core';
const inboundSchema = {
type: 'object',
properties: {
foo: { type: 'string' },
},
required: ['foo'],
additionalProperties: false,
};
const outboundSchema = {
type: 'object',
properties: {
bar: { type: 'number' },
},
required: ['bar'],
additionalProperties: false,
};
export const handler = middy()
.use(validation({ inboundSchema, outboundSchema }))
.handler(async (event) => {
// Your handler logic here
return { bar: 42 };
});
Like the @validator decorator, you can choose to validate only the inbound or outbound payload.
The validate function gives you more control over the validation process, and is typically used within the Lambda handler, or any other function that needs to validate data.
When using the standalone function, you can gracefully handle schema validation errors by catching SchemaValidationError errors.
import { validate } from '@aws-lambda-powertools/validation';
import { SchemaValidationError } from '@aws-lambda-powertools/validation/errors';
const schema = {
type: 'object',
properties: {
name: { type: 'string' },
age: { type: 'number' },
},
required: ['name', 'age'],
additionalProperties: false,
} as const;
const payload = { name: 'John', age: 30 };
export const handler = async (event: unknown) => {
try {
const validatedData = validate({
payload,
schema,
});
// Your handler logic here
} catch (error) {
if (error instanceof SchemaValidationError) {
// Handle the validation error
return {
statusCode: 400,
body: JSON.stringify({ message: error.message }),
};
}
// Handle other errors
throw error;
}
}
In some cases you might want to validate only a portion of the event payload - this is what the envelope option is for.
You can use JMESPath expressions to specify the path to the property you want to validate. The validator will unwrap the event before validating it.
import { validate } from '@aws-lambda-powertools/validation';
const schema = {
type: 'object',
properties: {
user: { type: 'string' },
},
required: ['user'],
additionalProperties: false,
} as const;
const payload = {
data: {
user: 'Alice',
},
};
const validatedData = validate({
payload,
schema,
envelope: 'data',
});
Since the validator is built on top of Ajv, you can extend it with custom formats and external schemas, as well as bringing your own ajv instance.
The example below shows how to pass additional options to the validate function, but you can also pass them to the @validator decorator and validator middleware.
import { validate } from '@aws-lambda-powertools/validation';
const formats = {
ageRange: (value: number) => return value >= 0 && value <= 120,
};
const definitionSchema = {
$id: 'https://example.com/schemas/definitions.json',
definitions: {
user: {
type: 'object',
properties: {
name: { type: 'string' },
age: { type: 'number', format: 'ageRange' },
},
required: ['name', 'age'],
additionalProperties: false,
}
}
} as const;
const schema = {
$id: 'https://example.com/schemas/user.json',
type: 'object',
properties: {
user: { $ref: 'definitions.json#/definitions/user' },
},
required: ['user'],
additionalProperties: false,
} as const;
const payload = {
user: {
name: 'Alice',
age: 25,
},
};
const validatedData = validate({
payload,
schema,
externalRefs: [definitionSchema],
formats,
});
For more information on how to use the validate function, please refer to the documentation.
If you are interested in contributing to this project, please refer to our Contributing Guidelines.
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This library is licensed under the MIT-0 License. See the LICENSE file.