Socket EventEmitter memory leak

[rwilmar]

Behavior:
After several iterations using the same connection node shows the warning:
MaxListenersExceededWarning: Possible EventEmitter memory leak detected. XX data listeners added to [Socket]

Identified cause: socket.onData functions are not unsubscribed after returning promise in connect() and write() methods()
Proposed patch:

use a helper function to resolve the promise, using it to unsubscribe from event:
Original code:
`
public write(queries: string[]): Promise<{ [prop: string]: string }[] | []> {
return new Promise((resolve, reject) => {
this.writeWords(queries);

  const result: {
    type: string;
    messages: string[];
    data: any[];
  } = {
    type: "",
    messages: [],
    data: [],
  };

  let isDone = false;

  this.socket.on("data", (bufferData) => {
    useSentenceParser(bufferData, (line) => {
      if (line === "!re") {
        result.data.push({});
        result.type = "success";
      } else if (line === "!trap") {
        result.type = "error";
      } else if (isDone && line.startsWith("=ret=")) {
        const [, key, value] = line.split("=");
        resolve([{ [key]: value }]);
      } else if (line.startsWith("=") && result.type !== "error") {
        const [, key, value] = line.split("=");
        result.data[result.data.length - 1][key] = value;
      } else if (line.startsWith("=") && result.type === "error") {
        const [, key, value] = line.split("=");
        result.messages.push(value);
      } else if (line === "!done") {
        isDone = true;
      } else if (line === "" && isDone) {
        if (result.type === "success") {
          resolve(result.data);
        } else if (result.type === "") {
          resolve(result.data);
        } else {
          reject(new RouterosException(result.messages.join(". ")));
        }
      }
    });
  });
});

}
proposed change
public write(queries: string[]): Promise<{ [prop: string]: string }[] | []> {
return new Promise((resolve, reject) => {
this.writeWords(queries);

  const result: {
    type: string;
    messages: string[];
    data: any[];
  } = {
    type: "",
    messages: [],
    data: [],
  };

  let isDone = false;
  const promiseResolve = (data: any) => {
      this.socket.off("data", dataRecvFn);
      resolve(data);
  };
  const promiseReject = (error: any) => {
      this.socket.off("data", dataRecvFn);
      reject(error);
  };
  const dataRecvFn = (bufferData: Buffer) => {
    useSentenceParser(bufferData, (line) => {
      if (line === "!re") {
        result.data.push({});
        result.type = "success";
      } else if (line === "!trap") {
        result.type = "error";
      } else if (isDone && line.startsWith("=ret=")) {
        const [, key, value] = line.split("=");
        promiseResolve([{ [key]: value }]);
      } else if (line.startsWith("=") && result.type !== "error") {
        const [, key, value] = line.split("=");
        result.data[result.data.length - 1][key] = value;
      } else if (line.startsWith("=") && result.type === "error") {
        const [, key, value] = line.split("=");
        result.messages.push(value);
      } else if (line === "!done") {
        isDone = true;
      } else if (line === "" && isDone) {
        if (result.type === "success") {
          promiseResolve(result.data);
        } else if (result.type === "") {
          promiseResolve(result.data);
        } else {
          promiseReject(new RouterosException(result.messages.join(". ")));
        }
      }
    });
  }
  this.socket.on("data", dataRecvFn);
});

}
`