import os


class Piper:

    def run(self, *args):
        readend, writeend = os.pipe()
        if not os.fork():
            try:
                # in the child
                os.close(readend)
                self.generate(writeend, *args)
            finally:
                os._exit(0)
        os.close(writeend)
        self.readend = readend

    def __del__(self):
        if hasattr(self, 'readend'):
            os.close(self.readend)

    def fileno(self):
        return self.readend

    def read(self):
        result = []
        while 1:
            t = os.read(self.readend, 4096)
            if not t: break
            result.append(t)
        return ''.join(result)

    def as_file(self):
        f = os.fdopen(self.readend)
        del self.readend
        return f


class StringWriter(Piper):
    
    def __init__(self, data):
        self.run(data)

    def generate(self, writeend, data):
        while data:
            data = data[os.write(writeend, data):]


class Process(Piper):
    
    def __init__(self, executable, *args):
        args = list(args)
        for i in range(len(args)):
            arg = args[i]
            if hasattr(arg, 'fileno'):
                fd = arg.fileno()
                args[i] = '/dev/fd/%d' % fd
        self.run(executable, args)

    def generate(self, writeend, executable, args):
        os.dup2(writeend, 1)
        os.close(writeend)
        os.close(0)
        os.execvp(executable, [executable] + args)