How to make async data observable?

Question

New to observables. I'm using ssh2 to get a list of files/folders on my server. I can't figure out how to get my data back as an observable since all of the examples of online use http rather than a 3rd party module.

How can I set this service up so that I can get the list back as an observable?

import {Injectable, NgZone} from '@angular/core';
import {Observable} from 'rxjs';
var Client = require('ssh2').Client;
var user = require('credentials.json')
@Injectable()
export class ConnectionService {
    public connSettings:any;

    constructor(private zone: NgZone){
        this.connSettings = {
            host: user.url,
            username: user.username,
            password: user.password
        };
        this.openConnection();

    }
    openConnection() {
        let remotePathToList = '/home/user';
        var conn = new Client();

        conn.on('ready', ()=>{
            conn.sftp((err:any, sftp:any)=>{
                if (err) throw err;
                sftp.readdir(remotePathToList, (err:any, list:any)=>{
                    conn.end();

                    //return observable data here

                    return list;

                })
            })
        }).connect(this.connSettings);

    }


}

Answer 1

If you want a generic attribute to access the list at any time (unrelated to the openConnection()-method, you could use a ReplaySubject:

@Injectable()
export class ConnectionService {
    public yourList$: ReplaySubject<any> = new ReplaySubject<any>(1);
    public connSettings:any;

    constructor(private zone: NgZone){
        this.connSettings = {
            host: user.url,
            username: user.username,
            password: user.password
        };
        this.openConnection();

    }
    openConnection() {
        let remotePathToList = '/home/user';
        var conn = new Client();

        conn.on('ready', ()=>{
            conn.sftp((err:any, sftp:any)=>{
                if (err) throw err;
                sftp.readdir(remotePathToList, (err:any, list:any)=>{
                    conn.end();

                    //return observable data here
                    yourList$.next(list);
                    return list;

                })
            })
        }).connect(this.connSettings);
    }
}

---

If you want to only have it as a returned Observable of the openConnection you could create a custom Observable:

@Injectable()
export class ConnectionService {
    public yourList$: ReplaySubject<any> = new ReplaySubject<any>(1);
    public connSettings:any;

    constructor(private zone: NgZone){
        this.connSettings = {
            host: user.url,
            username: user.username,
            password: user.password
        };
        this.openConnection();

    }
    openConnection(): Observable<any> {
        return Observable.create(obs => {
            let remotePathToList = '/home/user';
            var conn = new Client();

            conn.on('ready', ()=>{
                conn.sftp((err:any, sftp:any)=>{
                    if (err) throw err;
                    sftp.readdir(remotePathToList, (err:any, list:any)=>{
                        conn.end();

                        //return observable data here
                        obs.next(list);
                        obs.complete(); // required, otherwise your subscription would never close
                    })
                })
            }).connect(this.connSettings);
        });
    }
}

Please note, that with the 2nd solution, you will have to call subscribe on openConnection otherwise nothing will happen, since it is now wrapped inside an observable:

connectionService
    .openConnection()
    .subscribe(list => console.log(list));