The editor is used every day. What is the working principle of language service protocol?

language-service-protocol What is it?

As a development engineer , The most common tool we use every day is the editor . In use , There are some specific functions , such as ： Add autocomplete for programming languages 、 Go to definition 、 Hover document, etc . Traditionally , This must be repeated for each individual development tool , Because each tool provides different API To achieve the same function .

language-service To provide language specific intelligence and communication protocols , Enable interprocess communication development tools to communicate .

language-service-protocol（ Hereinafter referred to as “LSP”） The purpose of is to standardize the protocol of how such servers and development tools communicate . adopt LSP, A single voice server can be reused in multiple development tools , Thus, it can support multiple languages .

language-service-protocol How it works

language-service Run as a separate process , Development tools use JSON-RPC The language protocol on communicates with the server .

JSON-RPC, Is a stateless and lightweight remote procedure call （RPC） Transmission protocol , Its content is transmitted through JSON Mainly .

JSON-RPC The format is like this ：

Content-Length: ...\r\n
\r\n
{
    
  "jsonrpc": "2.0",
  "id": 1,
  "method": "textDocument/didOpen",
  "params": {
    
    ...
  }
} 

method It is an event triggered by the user , such as ：

• textDocument/completion Complete the code from the user cursor
• textDocument/signatureHelp Get the function signature information from the user cursor
• textDocument/definition Go from the user click location to definition
• …

The following figure shows a tool and language-service An example of how to communicate during an editing session ：

1. The user opens the file in the tool ： Tool notification language-service The document is open . from now on , The authenticity of the document content no longer exists in the file system , Instead, it is stored in memory by the tool . Now you have to be in tools and language-service Sync content between .
2. Users edit ： The tool notifies you of document changes language-service, And the language of the document is represented by language-service to update .language-service Will analyze this information , And return the detected errors and warnings to the tool .
3. The user executes on the symbol of the open document “ Go to definition ”： The tool sends a request with two parameters （ file URL、 Go to the defined text location ） Send to the server . The server responds according to these two parameters in the request .
4. The user closes the document ： The tool sends a shutdown notification , notice language-service The document is no longer in memory . The current content is now up to date on the file system .

“ Go to definition ” An example of （c++）

request ：

{
    
    "jsonrpc": "2.0",
    "id" : 1,
    "method": "textDocument/definition",
    "params": {
    
        "textDocument": {
    
            "uri": "file:///p%3A/mseng/VSCode/Playgrounds/cpp/use.cpp"
        },
        "position": {
    
            "line": 3,
            "character": 12
        }
    }
}

Respond ：

{
    
    "jsonrpc": "2.0",
    "id": 1,
    "result": {
    
        "uri": "file:///p%3A/mseng/VSCode/Playgrounds/cpp/provide.cpp",
        "range": {
    
            "start": {
    
                "line": 0,
                "character": 4
            },
            "end": {
    
                "line": 0,
                "character": 11
            }
        }
    }
}

When users use different languages , Development tools typically launch one for each programming language language-service.

️ Be careful ：language-service The actual integration with the tool is not by LSP Defined , But decided by the tool implementer .

LSP Provider and consumer Libraries SDK

1. Each development tool usually provides one for integration language-service The library of , For example, for JavaScript/Typescript, There are language clients npm modular .
2. For different implementation languages language-service SDK, There is one SDK To implement a specific language language-service. For example, to use Node.js Realization language-service, There is a language server npm modular .

LSP What problems have been solved

Previously, for editors , A interlinked language should implement its own set of code , So there are N Chinese language ,M Of IDE, It means writing N*M Set of codes , There is now a LSP As a middle layer of abstraction , You just need to write N+M The condom code is enough .

Another advantage is language-service Run in a separate process ：

• language-service Belong to CPU Intensive program , In order to verify a file correctly , Need to parse a large number of files （ structure AST-> Static program analysis ）, stay VSCode Plug in , All plug-ins in each window share one Extension Host, If the language service gets stuck , All plug-ins will be affected . Run in a unique process language-service This performance problem can be avoided .