Question: How to connect to the started language server via Java socket?

I am new to LSP. Previously I want to analyze programs with static analysis techniques (not developing a plugin or extension or editor), but I do not want to write one parser for each language, that leads me to the LSP.

Currently I have successfully started this language server with the following command under windows:

set CLIENT_PORT=8679
set CLIENT_HOST=localhost
$ java -agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=1044 -Declipse.application=org.eclipse.jdt.ls.core.id1 -Dosgi.bundles.defaultStartLevel=4 -Declipse.product=org.eclipse.jdt.ls.core.product -Dlog.level=ALL -noverify -Xmx1G -jar ./plugins/org.eclipse.equinox.launcher.win32.win32.x86_64_1.1.1100.v20190715-0945.jar -configuration ./config_win -data D:\java
Listening for transport dt_socket at address: 1044

Then I write some client code to connect and send request to the server:

public static void main(String[] args) {
        try (Socket socket = new Socket("localhost", 1044)) {
            PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            sendInitJava(out, in);
//            sendOpen(out, in);
//            sendDefinition(out, in);
            out.close();
            in.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
    private static void sendInitJava(PrintWriter out, BufferedReader in) throws IOException {
        JSONObject json = new JSONObject();
        JSONObject params = new JSONObject();
        json.put("jsonrpc", "2.0");
        json.put("id", 0);
        json.put("method", "initialize");

        params.put("rootPath", "D:/java");
        params.put("rootUri", "file:///D:/java");

        JSONObject capabilities = new JSONObject();
        JSONObject textCapabilities = new JSONObject();
        JSONObject ref = new JSONObject();
        ref.put("dynamicRegistration", true);
        textCapabilities.put("references", ref);
        JSONObject def = new JSONObject();
        def.put("dynamicRegistration", true);
        textCapabilities.put("definition", def);
        capabilities.put("textDocument", textCapabilities);
        JSONObject workspaceCapabilities = new JSONObject();
        workspaceCapabilities.put("workspaceFolders", true);

        capabilities.put("workspace", workspaceCapabilities);
        params.put("capabilities", capabilities);

        json.put("params", params);

        String content = json.toString() + "\n";
        String headers = "Content-Length: " + content.length() + "\r\n\r\n";
        String request = headers + content;
        out.write(request);
        out.flush();
        System.out.println("init request:");
        System.out.println(request);

        json = new JSONObject();
        params = new JSONObject();
        json.put("jsonrpc", "2.0");
        json.put("method", "textDocument/didOpen");
        JSONObject textDoc = new JSONObject();
        textDoc.put("uri", "file:///D:/java/jj.java");
        textDoc.put("languageId", "java");
        textDoc.put("version", 0);
        params.put("textDocument", textDoc);
        json.put("params", params);

        content = json.toString() + "\n";
        headers = "Content-Length: " + content.length() + "\r\n\r\n";
        request = headers + content;
        out.write(request);
        out.flush();
        System.out.println("open request:");
        System.out.println(request);

        json.put("jsonrpc", "2.0");
        json.put("id", 1);
        json.put("method", "textDocument/documentSymbol ");
        textDoc = new JSONObject();
        textDoc.put("uri", "file:///D:/java/jj.java");
        params.put("textDocument", textDoc);
        json.put("params", params);

        content = json.toString() + "\n";
        headers = "Content-Length: " + content.length() + "\r\n\r\n";
        request = headers + content;
        out.write(request);
        out.flush();
        System.out.println("symbol request:");
        System.out.println(request);

        json.put("jsonrpc", "2.0");
        json.put("id", 2);
        json.put("method", "textDocument/definition");
        textDoc = new JSONObject();
        textDoc.put("uri", "file:///D:/java/jj.java");
        textDoc.put("languageId", "java");
        params.put("textDocument", textDoc);
        JSONObject pos = new JSONObject();
        pos.put("line", 24);
        pos.put("character", 17);
        params.put("position", pos);
//            params.put(textDoc);
        json.put("params", params);

        content = json.toString() + "\n";
        headers = "Content-Length: " + content.length() + "\r\n\r\n";
        request = headers + content;
        out.write(request);
        out.flush();
        System.out.println("def request:");
        System.out.println(request);

        StringBuilder sb = new StringBuilder();
        String line = "";
        while ((line = in.readLine()) != null) {
            sb.append(line);
            System.out.println(line);
            if(!line.startsWith("Content")&&line.length()>0){
                line = line.substring(0, line.lastIndexOf("}")+1);
                JSONObject response = JSONObject
                        .parseObject(line);
                System.out.println(response.getString("jsonrpc"));
            }
        }
        JSONObject response = JSONObject
                .parseObject(sb.toString());
        String s = JSON.toJSONString(JSON.parseArray(response.getJSONArray("result").toJSONString()));
        System.out.println(s);
    }

Then error happens, the Java console gives the following error:

java.net.SocketException: Software caused connection abort: recv failed

While the server side gives the following error:

Debugger failed to attach: handshake failed - received >Content-Length< - expected >JDWP-Handshake<

I found a related issue #181, but failed to find solution. Do you have any idea? @rcjsuen

[rcjsuen]

@Symbolk In the README.md file in my language server, I have some bits of example code for connecting to a language server using stdio, network sockets, or JSON-RPC that may be helpful to you. They are written in TypeScript but I’m sure you’ll be able to transcribe them into Java or JavaScript.

[goldfita]

Is it possible to connect to the language server as a server. The docker example says a port has to be opened on the client and then the language server is started, which reverses their roles. I would like to connect to a remote LS using the method described in this post.