path: root/extensions/json-language-features/server/README.md

# VSCode JSON Language Server

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The JSON Language server provides language-specific smarts for editing, validating and understanding JSON documents. It runs as a separate executable and implements the [language server protocol](https://microsoft.github.io/language-server-protocol/overview) to be connected by any code editor or IDE.

## Capabilities

### Server capabilities

The JSON language server supports requests on documents of language id `json` and `jsonc`.
- `json` documents are parsed and validated following the [JSON specification](https://tools.ietf.org/html/rfc7159).
- `jsonc` documents additionally accept single line (`//`) and multi-line comments (`/* ... */`). JSONC is a VSCode specific file format, intended for VSCode configuration files, without any aspirations to define a new common file format.

The server implements the following capabilities of the language server protocol:

- [Code completion](https://microsoft.github.io/language-server-protocol/specification#textDocument_completion) for JSON properties and values based on the document's [JSON schema](http://json-schema.org/) or based on existing properties and values used at other places in the document. JSON schemas are configured through the server configuration options.
- [Hover](https://microsoft.github.io/language-server-protocol/specification#textDocument_hover) for values based on descriptions in the document's [JSON schema](http://json-schema.org/).
- [Document Symbols](https://microsoft.github.io/language-server-protocol/specification#textDocument_documentSymbol) for quick navigation to properties in the document.
- [Document Colors](https://microsoft.github.io/language-server-protocol/specification#textDocument_documentColor) for showing color decorators on values representing colors and [Color Presentation](https://microsoft.github.io/language-server-protocol/specification#textDocument_colorPresentation) for color presentation information to support color pickers. The location of colors is defined by the document's [JSON schema](http://json-schema.org/). All values marked with `"format": "color-hex"` (VSCode specific, non-standard JSON Schema extension) are considered color values. The supported color formats are `#rgb[a]` and `#rrggbb[aa]`.
- [Code Formatting](https://microsoft.github.io/language-server-protocol/specification#textDocument_rangeFormatting) supporting ranges and formatting the whole document.
- [Folding Ranges](https://microsoft.github.io/language-server-protocol/specification#textDocument_foldingRange) for all folding ranges in the document.
- Semantic Selection for semantic selection for one or multiple cursor positions.
- [Goto Definition](https://microsoft.github.io/language-server-protocol/specification#textDocument_definition) for $ref references in JSON schemas
- [Diagnostics (Validation)](https://microsoft.github.io/language-server-protocol/specification#textDocument_publishDiagnostics) are pushed for all open documents
   - syntax errors
   - structural validation based on the document's [JSON schema](http://json-schema.org/).

In order to load JSON schemas, the JSON server uses NodeJS `http` and `fs` modules. For all other features, the JSON server only relies on the documents and settings provided by the client through the LSP.

### Client requirements:

The JSON language server expects the client to only send requests and notifications for documents of language id `json` and `jsonc`.

The JSON language server has the following dependencies on the client's capabilities:

- Code completion requires that the client capability has *snippetSupport*. If not supported by the client, the server will not offer the completion capability.
- Formatting support requires the client to support *dynamicRegistration* for *rangeFormatting*. If not supported by the client, the server will not offer the format capability.

## Configuration

### Initialization options

The client can send the following initialization options to the server:

- `provideFormatter: boolean | undefined`. If defined, the value defines whether the server provides the `documentRangeFormattingProvider` capability on initialization. If undefined, the setting `json.format.enable` is used to determine whether formatting is provided. The formatter will then be registered through dynamic registration. If the client does not support dynamic registration, no formatter will be available.
- `handledSchemaProtocols`: The URI schemas handles by the server. See section `Schema configuration` below.
- `customCapabilities`: Additional non-LSP client capabilities:
  - `rangeFormatting: { editLimit: x } }`: For performance reasons, limit the number of edits returned by the range formatter to `x`.

### Settings

Clients may send a `workspace/didChangeConfiguration` notification to notify the server of settings changes.
The server supports the following settings:

- http
   - `proxy`: The URL of the proxy server to use when fetching schema. When undefined or empty, no proxy is used.
   - `proxyStrictSSL`: Whether the proxy server certificate should be verified against the list of supplied CAs.

- json
  - `format`
    - `enable`: Whether the server should register the formatting support. This option is only applicable if the client supports *dynamicRegistration* for *rangeFormatting* and `initializationOptions.provideFormatter` is not defined.
  - `validate`
    - `enable`: Whether the server should validate. Defaults to `true` if not set.
  - `schemas`: Configures association of file names to schema URL or schemas and/or associations of schema URL to schema content.
    - `fileMatch`: an array of file names or paths (separated by `/`). `*` can be used as a wildcard. Exclusion patterns can also be defined and start with '!'. A file matches when there is at least one matching pattern and the last matching pattern is not an exclusion pattern.
    - `url`: The URL of the schema, optional when also a schema is provided.
    - `schema`: The schema content.
  - `resultLimit`: The max number folding ranges and outline symbols to be computed (for performance reasons)

```json
    {
        "http": {
            "proxy": "",
            "proxyStrictSSL": true
        },
        "json": {
            "format": {
                "enable": true
            },
            "schemas": [
                {
                    "fileMatch": [
                        "foo.json",
                        "*.superfoo.json"
                    ],
                    "url": "http://json.schemastore.org/foo",
                    "schema": {
                        "type": "array"
                    }
                }
            ]
        }
    }
```

### Schema configuration and custom schema content delivery

[JSON schemas](http://json-schema.org/) are essential for code assist, hovers, color decorators to work and are required for structural validation.

To find the schema for a given JSON document, the server uses the following mechanisms:
- JSON documents can define the schema URL using a `$schema` property
- The settings define a schema association based on the documents URL. Settings can either associate a schema URL to a file or path pattern, and they can directly provide a schema.
- Additionally, schema associations can also be provided by a custom 'schemaAssociations' configuration call.

Schemas are identified by URLs. To load the content of a schema, the JSON language server either tries to load from that URI or path itself or delegates to the client.

The `initializationOptions.handledSchemaProtocols` initialization option defines which URLs are handled by the server. Requests for all other URIs are sent to the client.

`handledSchemaProtocols` is part of the initialization options and can't be changed while the server is running.

```ts
let clientOptions: LanguageClientOptions = {
		initializationOptions: {
			handledSchemaProtocols: ['file'] // language server should only try to load file URLs
		}
        ...
}
```

If `handledSchemaProtocols` is not set, the JSON language server will load the following URLs itself:

- `http`, `https`: Loaded using NodeJS's HTTP support. Proxies can be configured through the settings.
- `file`: Loaded using NodeJS's `fs` support.

#### Schema content request

Requests for schemas with URLs not handled by the server are forwarded to the client through an LSP request. This request is a JSON language server-specific, non-standardized, extension to the LSP.

Request:
- method: 'vscode/content'
- params: `string` - The schema URL to request.
- response: `string` - The content of the schema with the given URL

#### Schema content change notification

When the client is aware that a schema content has changed, it will notify the server through a notification. This notification is a JSON language server-specific, non-standardized, extension to the LSP.
The server will, as a response, clear the schema content from the cache and reload the schema content when required again.

#### Schema associations notification

In addition to the settings, schemas associations can also be provided through a notification from the client to the server. This notification is a JSON language server-specific, non-standardized, extension to the LSP.

Notification:
- method: 'json/schemaAssociations'
- params: `ISchemaAssociations` or `ISchemaAssociation[]` defined as follows

```ts
interface ISchemaAssociations {
  /**
   * An object where:
   *  - keys are file names or file paths (using `/` as path separator). `*` can be used as a wildcard.
   *  - values are an arrays of schema URIs
   */
  [pattern: string]: string[];
}

interface ISchemaAssociation {
  /**
   * The URI of the schema, which is also the identifier of the schema.
   */
  uri: string;

  /**
   * A list of file path patterns that are associated to the schema. The '*' wildcard can be used. Exclusion patterns starting with '!'.
   * For example '*.schema.json', 'package.json', '!foo*.schema.json'.
   * A match succeeds when there is at least one pattern matching and last matching pattern does not start with '!'.
   */
  fileMatch: string[];
  /*
   * The schema for the given URI.
   * If no schema is provided, the schema will be fetched with the schema request service (if available).
   */
  schema?: JSONSchema;
}

```
`ISchemaAssociations`
  - keys: a file names or file path (separated by `/`). `*` can be used as a wildcard.
  - values: An array of schema URLs

Notification:
- method: 'json/schemaContent'
- params: `string` the URL of the schema that has changed.

### Item Limit

If the setting `resultLimit` is set, the JSON language server will limit the number of folding ranges and document symbols computed.
When the limit is reached, a notification `json/resultLimitReached` is sent that can be shown that can be shown to the user.

Notification:
- method: 'json/resultLimitReached'
- params: a human readable string to show to the user.


## Try

The JSON language server is shipped with [Visual Studio Code](https://code.visualstudio.com/) as part of the built-in VSCode extension `json-language-features`. The server is started when the first JSON file is opened. The [VSCode JSON documentation](https://code.visualstudio.com/docs/languages/json) for detailed information on the user experience and has more information on how to configure the language support.

## Integrate

If you plan to integrate the JSON language server into an editor and IDE, check out [this page](https://microsoft.github.io/language-server-protocol/implementors/tools/) if there's already an LSP client integration available.

You can also launch the language server as a command and connect to it.
For that, install the `vscode-json-languageserver` npm module:

`npm install -g vscode-json-languageserver`

Start the language server with the `vscode-json-languageserver` command. Use a command line argument to specify the preferred communication channel:

```
vscode-json-languageserver --node-ipc
vscode-json-languageserver --stdio
vscode-json-languageserver --socket=<port>
```

To connect to the server from NodeJS, see Remy Suen's great write-up on [how to communicate with the server](https://github.com/rcjsuen/dockerfile-language-server-nodejs#communicating-with-the-server) through the available communication channels.

## Participate

The source code of the JSON language server can be found in the [VSCode repository](https://github.com/microsoft/vscode) at [extensions/json-language-features/server](https://github.com/microsoft/vscode/tree/master/extensions/json-language-features/server).

File issues and pull requests in the [VSCode GitHub Issues](https://github.com/microsoft/vscode/issues). See the document [How to Contribute](https://github.com/microsoft/vscode/wiki/How-to-Contribute) on how to build and run from source.

Most of the functionality of the server is located in libraries:
- [jsonc-parser](https://github.com/microsoft/node-jsonc-parser) contains the JSON parser and scanner.
- [vscode-json-languageservice](https://github.com/microsoft/vscode-json-languageservice) contains the implementation of all features as a re-usable library.
- [vscode-languageserver-node](https://github.com/microsoft/vscode-languageserver-node) contains the implementation of language server for NodeJS.

Help on any of these projects is very welcome.

## Code of Conduct

This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.

## License

Copyright (c) Microsoft Corporation. All rights reserved.

Licensed under the [MIT](https://github.com/microsoft/vscode/blob/master/LICENSE.txt) License.