JavaScript Parser

Use this package to parse and validate AsyncAPI documents —either YAML or JSON— in your Node.js or browser application. Updated bundle for the browser is always attached to the GitHub Release.

⚠️ This package doesn't support AsyncAPI 1.x anymore. We recommend to upgrade to the latest AsyncAPI version using the AsyncAPI converter. If you need to convert documents on the fly, you may use the Node.js or Go converters.

• Install
• Examples
  • Example passing inline AsyncAPI
  • Example passing a URL
  • Example using Avro schemas
  • Example using OpenAPI schemas
  • Example using RAML data types
• API documentation
• Using in the browser
• Custom message parsers
• Error types
• Custom extensions
• Circular references
• Stringify
• Develop
• Contributing
• Contributors

Install

npm install @asyncapi/parser

The parser by default supports AsyncAPI Schema Format and JSON Schema Format. For additional formats, you need to install additional plugins. For example:

• Avro schema

  npm install @asyncapi/avro-schema-parser
  

• OpenAPI Schema Object

  npm install @asyncapi/openapi-schema-parser
  

• RAML data type

  npm install @asyncapi/raml-dt-schema-parser
  

Examples

Example passing inline AsyncAPI

const parser = require('@asyncapi/parser');

const doc = await parser.parse(`
  asyncapi: '2.1.0'
  info:
    title: Example
    version: '0.1.0'
  channels:
    example-channel:
      subscribe:
        message:
          payload:
            type: object
            properties:
              exampleField:
                type: string
              exampleNumber:
                type: number
              exampleDate:
                type: string
                format: date-time
`);

console.log(doc.info().title());
// => Example

Example passing a URL

const parser = require('@asyncapi/parser');

const doc = await parser.parseFromUrl('https://my.server.com/example-asyncapi.yaml');

console.log(doc.info().title());
// => Example

Example using Avro schemas

Head over to asyncapi/avro-schema-parser for more information.

Example using OpenAPI schemas

Head over to asyncapi/openapi-schema-parser for more information.

Example using RAML data types

Head over to asyncapi/raml-dt-schema-parser for more information.

API documentation

The parser API is generally structured the same way as the AsyncAPI specification, with additional support functions such as has<Something>(). The parser uses wrapped functions to get the properties stored in JSON. This means in order to get the info object you would use the function doc.info() and to get the title inside the info object you call doc.info().title().

See API documentation for more example and full API reference information.

Using in the browser

The package contains a built-in version of the parser, which is created via browserify. To use it, you need to import the parser into the HTML file as below:

<script src="https://unpkg.com/@asyncapi/parser@latest/dist/bundle.js"></script>

<script>
  const parser = window['AsyncAPIParser'];
  ...
</script>

Or, if you want to use a parser in a JS application of the SPA kind, import the parser as shown below:

import '@asyncapi/parser/dist/bundle';

const parser = window['AsyncAPIParser'];
...

Otherwise, if your application is bundled via bundlers like webpack, you can import the parser like a regular package:

import parser from '@asyncapi/parser';

Custom message parsers

AsyncAPI doesn't enforce one schema format for messages. You can have payload of your messages described with OpenAPI, Avro, etc. This parser by default parses only AsyncAPI schema format. You can extend it by creating a custom parser and registering it within the parser:

1. Create custom parser module that exports two functions:

   module.exports = {
     /*
      * message {Object} is the object containing AsyncAPI Message property
      * defaultSchemaFormat {String} information about the default schema format mime type
      * schemaFormat {String} information about custom schemaFormat mime type provided in AsyncAPI Document
      * fileFormat {String} information if provided AsyncAPI Document was JSON or YAML
      * parsedAsyncAPIDocument {Object} Full AsyncAPI Document parsed into Object
      * pathToPayload {String} path of the message passed to the parser, relative to the root of AsyncAPI Document
     */
     parse: ({ message, defaultSchemaFormat, originalAsyncAPIDocument, schemaFormat, fileFormat, parsedAsyncAPIDocument, pathToPayload }) => { /* custom parsing logic */ },
     getMimeTypes: () => [
       '//mime types that will be used as the `schemaFormat` property of the message to specify its mime type',
       'application/vnd.custom.type;version=1.0.0',
       'application/vnd.custom.type+json;version=1.0.0',
     ]
   }

2. Before parsing an AsyncAPI document with a parser, register the additional custom schema parser:

   const myCustomParser = require('mycustomParser');
   
   parser.registerSchemaParser(myCustomParser);

Error types

This package throws a bunch of different error types. All errors contain a type (prefixed by this repo URL) and a title field. The following table describes all the errors and the extra fields they include:

Type	Extra Fields	Description
null-or-falsey-document	None	The AsyncAPI document is null or a JS "falsey" value.
invalid-document-type	None	The AsyncAPI document is not a string nor a JS object.
invalid-json	detail, location	The AsyncAPI document is not valid JSON.
invalid-yaml	detail, location	The AsyncAPI document is not valid YAML.
impossible-to-convert-to-json	detail	Internally, this parser only handles JSON so it tries to immediately convert the YAML to JSON. This error means this process failed.
missing-asyncapi-field	parsedJSON	The AsyncAPI document doesn't have the mandatory asyncapi field.
unsupported-version	detail, parsedJSON, validationErrors	The version of the asyncapi field is not supported. Typically, this means that you're using a version below 2.0.0.
dereference-error	parsedJSON, refs	This means the parser tried to resolve and dereference $ref's and the process failed. Typically, this means the $ref it's pointing to doesn't exist.
unexpected-error	parsedJSON	We have our code covered with try/catch blocks and you should never see this error. If you see it, please open an issue to let us know.
validation-errors	parsedJSON, validationErrors	The AsyncAPI document contains errors. See validationErrors for more information.
impossible-to-register-parser	None	Registration of custom message parser failed.
schema-validation-errors	parsedJSON, validationErrors	Schema of the payload provided in the AsyncAPI document is not valid with AsyncAPI schema format.
fetch-url-error	None	The URL provided for fetching AsynAPI document is invalid.

For more information about the ParserError class, check out the documentation.

Custom extensions

The parser uses custom extensions to define additional information about the spec. Each has a different purpose but all of them are there to make it much easier to work with the AsyncAPI document. These extensions are prefixed with x-parser-. The following extensions are used :

• x-parser-spec-parsed is used to specify if the AsyncAPI document is already parsed by the parser. Property x-parser-spec-parsed is added to the root of the document with the true value.
• x-parser-message-parsed is used to specify if the message is already parsed by the message parser. Property x-parser-message-parsed is added to the root of the document with the true value.
• x-parser-message-name is used to specify the name of the message if it is not provided. For messages without names, the parser generates anonymous names. Property x-parser-message-name is added to a message object with a value that follows this pattern: <anonymous-message-${number}>. This value is returned by message.uid() when regular name property is not present.
• x-parser-schema-id is used to specify the ID of the schema if it is not provided. For schemas without IDs, the parser generates anonymous names. Property x-parser-schema-id is added to every object of a schema with a value that follows this pattern: <anonymous-schema-${number}>. This value is returned by schema.uid() when regular $id property is not present.
• x-parser-original-traits is where traits are stored after they are applied on the AsyncAPI document. The reason is because the original traits property is removed.
• x-parser-original-schema-format holds information about the original schema format of the payload. You can use different schema formats with the AsyncAPI documents and the parser converts them to AsyncAPI schema. This is why different schema format is set, and the original one is preserved in the extension.
• x-parser-original-payload holds the original payload of the message. You can use different formats for payloads with the AsyncAPI documents and the parser converts them to. For example, it converts payload described with Avro schema to AsyncAPI schema. The original payload is preserved in the extension.
• x-parser-circular

NOTE: All extensions added by the parser (including all properties) should be retrieved using special functions. Names of extensions and their location may change, and their eventual changes will not be announced.

Circular references

Parser dereferences all circular references by default. In addition, to simplify interactions with the parser, the following is added:

• x-parser-circular property is added to the root of the AsyncAPI document to indicate that the document contains circular references. Tooling developer that doesn't want to support circular references can use the hasCircular() function to check the document and provide a proper message to the user.
• isCircular() function is added to the Schema Model to determine if a given schema is circular with respect to previously occurring schemas in the tree.

Stringify

Converting a parsed document to a string may be necessary when saving the parsed document to a database, or similar situations where you need to parse the document just once and then reuse it.

For that, the Parser supports the ability to stringify a parsed AsyncAPI document through the static AsyncAPIDocument.stringify(...parsedDoc) method. This method differs from the native JSON.stringify(...json) implementation, in that every reference that occurs (at least twice throughout the document) is converted into a JSON Pointer path with a $ref: prefix:

{
  "foo": "$ref:$.some.path.to.the.bar"
}

To parse a stringified document into an AsyncAPIDocument instance, you must use the static AsyncAPIDocument.parse(...stringifiedDoc) method. It isn't compatible with the native JSON.parse() method. It replaces the given references pointed by the JSON Pointer path, with an $ref: prefix to the original objects.

A few advantages of this solution:

• The string remains as small as possible due to the use of JSON Pointers.
• All circular references are preserved.

Develop

1. Write code and tests.
2. Make sure all tests pass npm test
3. Make sure code is well formatted and secure npm run lint

Release regenerates API documentation and browser bundle, so you do not have to regenerate it manually with npm run docs and npm run prepublishOnly.

Contributing

Read CONTRIBUTING guide.

Contributors

Thanks goes to these wonderful people (emoji key):

Fran Méndez 💬 🐛 💻 📖 🤔 🚧 🔌 👀 ⚠️	Lukasz Gornicki 💬 🐛 💻 📖 🤔 🚧 👀 ⚠️	Jonas Lagoni 💬 🐛 💻 🤔 👀	Maciej Urbańczyk 🐛 💻 👀
Juan Mellado 💻	James Crowley 💻	raisel melian 💻	danielchu 🚇 💻
Jürgen B. 💻	Viacheslav Turovskyi ⚠️	Khuda Dad Nomani 💻 🐛 ⚠️	Aayush Kumar Sahu ⚠️
Jordan Tucker ⚠️ 💻	vishesh13byte ⚠️	Elakya 💻

This project follows the all-contributors specification. Contributions of any kind welcome!