How do I send data to a process? - process

Question

I'm trying to write a dart server application that will communicate to an application which accepts input and gives output, like the unix tool bc.
I can read the output of bc, but I cannot send a command to bc. Here is my code:
#import('dart:io');
void main() {
var p = Process.start('bc', ["-i"]);
var stdoutStream = new StringInputStream(p.stdout);
stdoutStream.onLine = () => print(stdoutStream.readLine());
p.stdin.writeString("quit\n");
p.onExit = (exitCode) {
print('exit code: $exitCode');
p.close();
};
}
When I run it, I get the following error:
Unhandled exception:
SocketIOException: writeList failed - invalid socket handle
0. Function: '_Socket#14117cc4.writeList' url: 'dart:io' line:4808 col:48
1. Function: '_SocketOutputStream#14117cc4._write#14117cc4' url: 'dart:io' line:4993 col:70
2. Function: '_SocketOutputStream#14117cc4.write' url: 'dart:io' line:4969 col:29
3. Function: '_BaseOutputStream#14117cc4.writeString' url: 'dart:io' line:5197 col:3
4. Function: '::main' url: 'file:///var/www/html/example.dart' line:8 col:22
If I comment out the line where I try to write "quit\n", then it runs and I can see the output of bc.
So how do I get my program to send commands to an application on my server like bc?

Answer 1

The problem is that you're writing to stdin before the process has properly started. Try:
#import('dart:io');
void main() {
var p = Process.start('bc', ["-i"]);
var stdoutStream = new StringInputStream(p.stdout);
stdoutStream.onLine = () => print(stdoutStream.readLine());
p.onStart = () => p.stdin.writeString("1+1\nquit\n");
p.onExit = (exitCode) {
print('exit code: $exitCode');
p.close();
};
}