Client only saves one callback at a time

Description

When using a Service Client, and sending two request in a row, because the Client saves one callback at a time, only the latest is used when processing the response message from the service. (look at line 63) https://github.com/RobotWebTools/rclnodejs/blob/2e05913fb0e818f0c3a58904764ef752902a9a5e/lib/client.js#L51-L64

• Library Version: latest develop
• ROS Version: galactic
• Platform / OS: Linux Ubuntu 20.04

Steps To Reproduce

Here is a minimal example that reproduces the bug (based on the example/client-example.js):

'use strict';

const rclnodejs = require('../index.js');

rclnodejs
  .init()
  .then(() => {
    const node = rclnodejs.createNode('client_example_node');

    const client = node.createClient(
      'example_interfaces/srv/AddTwoInts',
      'add_two_ints'
    );

    // First call
    client.waitForService(1000).then((result) => {
      const request = {
        a: Math.floor(1),
        b: Math.floor(2),
      };
      if (!result) {
        console.log('Error: service not available');
        // rclnodejs.shutdown();
        return;
      }
      console.log(`Sending: ${typeof request}`, request);
      client.sendRequest(request, (response) => {
        console.log(`Result1: ${typeof response}`, response);
        // rclnodejs.shutdown();
      });
    });

    // Second call
    client.waitForService(1000).then((result) => {

      const request = {
        a: Math.floor(10),
        b: Math.floor(20),
      };
      if (!result) {
        console.log('Error: service not available');
        // rclnodejs.shutdown();
        return;
      }
      console.log(`Sending: ${typeof request}`, request);
      client.sendRequest(request, (response) => {
        console.log(`Result2: ${typeof response}`, response);
        // rclnodejs.shutdown();
      });
    });

    rclnodejs.spin(node);
    setTimeout(() => {
      rclnodejs.shutdown();
    }, 1000);
  })
  .catch((e) => {
    console.log(`Error: ${e}`);
  });

Expected Behavior

The console log output should be:

Sending: object { a: 1, b: 2 }
Sending: object { a: 10, b: 20 }
Result1: object { sum: 3 }
Result2: object { sum: 30 }

Actual Behavior

Result2 is printed twice:

Sending: object { a: 1, b: 2 }
Sending: object { a: 10, b: 20 }
Result2: object { sum: 3 }
Result2: object { sum: 30 }

[minggangw]

@ejalaa12 Yes, we should handle the response exactly as the rclcpp does, thanks for investigating the C++ implementation. For nodejs, as you said we can keep a sequence <-> callback map in my mind, and what you need is to change the following

https://github.com/RobotWebTools/rclnodejs/blob/b9ac65211cc19bd6c53a7bca6f1a59ab9591d64c/lib/node.js#L207-L214

• L.209: passing the sequence number stored in the map.
• L.213: passing the sequence number back to the processResponse() and letting the client find the proper callback if success is true.

I haven’t touched the code for a looong time, maybe make some mistake, just for your reference.

[minggangw]

Just submit a PR to add your names and contributions into https://github.com/RobotWebTools/rclnodejs/blob/develop/CONTRIBUTORS.md, then I will merge it