LSP Custom Requests — URI Wire Format

Why it breaks

• Connection.sendRequest(method, params) runs JSON.stringify(params).
• vscode-uri Uri.toJSON() returns UriComponents (plain data). See microsoft/vscode-uri src/uri.ts.
• Receiver gets a plain object — no prototype, no toString/fsPath.
• uri.toString() → "[object Object]" → fs.stat/readFile fails with EntryNotFound.

Rules

• Never call .toString() / .fsPath on a URI received over the wire without rehydrating first.
• Type URI params as UriComponents (derived); revive on receive.

Pattern — UriComponents + revive

Params type derived from URI.toJSON:

import type { URI } from 'vscode-uri';
type UriComponents = ReturnType<URI['toJSON']>;
type MyParams = { uri: UriComponents };

const params: MyParams = { uri: URI.parse(fileUri) };
connection.sendRequest('my/request', params);

const handler = (params: MyParams) => {
  const uri = URI.revive(params.uri);
};

Notes:

• vscode-uri's package entry does not re-export UriComponents; derive via ReturnType<URI['toJSON']>.
• URI.revive is the exact inverse of toJSON — restores _formatted / _fsPath caches too.

Don't

• uri: URI on a wire type and use .toString() / .fsPath on receive — this is the failure mode.
• Pass deserialized params straight to vscode.workspace.fs.* — those APIs expect a real URI instance.

When uri: URI in params looks fine but isn't

Compiles cleanly (URI on both sides). Runtime receiver sees a plain UriComponents. Check the handler log — uri=[object Object] confirms.