minimal lsp

Author: andrewgryan

package.json

@@ -4,7 +4,11 @@
   "main": "index.js",
   "author": "andrewgryan <[email protected]>",
   "license": "MIT",
+  "scripts": {
+    "test": "vitest"
+  },
   "devDependencies": {
-    "@types/node": "^20.14.2"
+    "@types/node": "^20.14.2",
+    "vitest": "^1.6.0"
   }
 }

src/main.test.ts

@@ -0,0 +1,14 @@
+import { expect, test } from 'vitest'
+import { encode, decode } from "./main" 
+
+test('encode', () => {
+  const expected = "Content-Length: 2\r\n\r\n{}"
+  expect(encode({})).toEqual(expected)
+})
+
+test('decode request', () => {
+  const payload = {id: 1, jsonrpc: "2.0", method: "textDocument/completion", params: {}}
+  const request = encode(payload)
+  const actual = decode(request)
+  expect(actual).toEqual(payload)
+})

src/main.ts

@@ -9,9 +9,68 @@ const log = (msg: string) => {
   })
 }
 
+// Encode message
+export const encode = (payload: Object) => {
+  const content = JSON.stringify(payload)
+  return `Content-Length: ${content.length}\r\n\r\n${content}`
+}
+
+interface Message {
+  jsonrpc: string;
+}
+
+interface RequestMessage extends Message {
+  id: number;
+  method: string;
+}
+
+// Decode message
+export const decode = (content: string): RequestMessage | null => {
+  const [header, body] = content.split("\r\n\r\n")
+  if (header.startsWith("Content-Length")) {
+    const length = parseInt(header.split(": ")[1])
+    return JSON.parse(body.substring(0, length))
+  } else {
+    log(`Could not parse: ${content}\n`)
+    return null
+  }
+}
+
+const respond = (id: number, result: Object | null) => {
+  const response = encode({ jsonrpc: "2.0", id, result })
+  process.stdout.write(response)
+  log(response + "\n")
+}
+
+const initializeResult = () => {
+  return {
+    capabilities: {
+      textDocumentSync: 1
+    },
+    serverInfo: {
+      name: "leaflet-html",
+      version: "0.0.0"
+    }
+  }
+}
+
+const shutdownResult = () => null
+
 // Listen on stdin/stdout
 process.stdin.on("data", (buf) => {
   const message = buf.toString()
-  log(message)
-  process.stdout.write(message)
+  log(message + "\n")
+  const payload = decode(message)
+  if (payload !== null) {
+    switch (payload.method) {
+      case("initialize"):
+        respond(payload.id, initializeResult());
+        break;
+      case("shutdown"):
+        respond(payload.id, shutdownResult());
+        break;
+      case("exit"):
+        process.exit(0)
+    }
+  }
 })

tsconfig.json

@@ -6,5 +6,6 @@
     "lib": ["es2022"],
     "target": "es5"
   },
-  "include": ["./src/**/*.ts"]
+  "include": ["./src/**/*.ts"],
+  "exclude": ["./src/**/*.test.ts"]
 }