Node child_process await result

Question

I have a async function which makes a face_detection command line call. It's working fine otherwise, but I can't make it to wait for the response. Here is my function:

async uploadedFile(@UploadedFile() file) {
    let isThereFace: boolean;
    const foo: child.ChildProcess = child.exec(
      `face_detection ${file.path}`,
      (error: child.ExecException, stdout: string, stderr: string) => {
        console.log(stdout.length);

        if (stdout.length > 0) {
          isThereFace = true;
        } else {
          isThereFace = false;
        }
        console.log(isThereFace);

        return isThereFace;
      },
    );

    console.log(file);

    const response = {
      filepath: file.path,
      filename: file.filename,
      isFaces: isThereFace,
    };
    console.log(response);

    return response;
  }

isThereFace in my response I return is always undefined because the response is sent to client before the response from face_detection is ready. How could I make this work?

Answer 1

You can either use the child_process.execSync call, which will wait for the exec to finish. But executing sync calls is discouraged ...

Or you can wrap child_process.exec with a promise

const result = await new Promise((resolve, reject) => {
   child.exec(
      `face_detection ${file.path}`,
      (error: child.ExecException, stdout: string, stderr: string) => {
        if (error) {
          reject(error);
        } else {
          resolve(stdout); 
        }
      });
});