Boost::Process Pipe 流和单元测试

Question

I have source which two stream like this:

bp::ipstream StdOut;
bp::opstream StdIn;
bp::child MyProcess = bp::child(processPath, bp::std_out > StdOut, bp::std_in < StdIn);
// Doing some stuff with StdOut and StdIn

I wanted to know if there is a way to write manually into this StdOut and read from StdIn in order to do unit tests? Thank you very much!

Answer 1

You can write to them as a normal stream:

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#include <boost/process.hpp>
#include <iostream>

namespace bp = boost::process;

int main() {
    bp::ipstream StdOut;
    bp::opstream StdIn;
    bp::child MyProcess = bp::child("/usr/bin/rev", bp::std_out > StdOut, bp::std_in < StdIn);

    for (int i = 0; i<100; ++i) {
        StdIn << "Sure no problem, " << i << std::endl;
    }
    StdIn.flush();
    StdIn.pipe().close();

    std::string il;
    while (getline(StdOut, il)) {
        std::cout << il << std::endl;
    }

    std::cout << "Bye\n";
}

Prints

0 ,melborp on eruS
1 ,melborp on eruS
2 ,melborp on eruS
...
99 ,melborp on eruS
Bye

Async Version

Note, like the documentation warns, if your process requires async IO you could end up deadlocking (eg waiting for output while the child process is waiting for input).

To achieve this, use Asio's asynchronous operations:

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#include <boost/process.hpp>
#include <boost/asio.hpp>
#include <boost/process/async.hpp>
#include <iostream>

namespace ba = boost::asio;
namespace bp = boost::process;

int main() {
    ba::io_context io;
    bp::async_pipe ip(io), op(io);
    //bp::async_pipe StdIn(io);

    bp::child MyProcess = bp::child("/usr/bin/tac", bp::std_out > op, bp::std_in < ip, io);

    std::function<void()> send_loop, recv_loop;

    ba::streambuf sb;
    send_loop = [&, i=0]() mutable {
        if (++i<100) {
            std::ostream(&sb) << "Sure no problem, " << i << std::endl;
            ba::async_write(ip, sb, [&send_loop](auto ec, auto /*tx*/) {
                //std::cout << "Sent " << tx << " bytes (" << ec.message() << ")\n";
                if (!ec) send_loop();
            });
        } else ip.close();
    };

    ba::streambuf rb;
    recv_loop = [&]() {
        ba::async_read_until(op, rb, "\n", [&](auto ec, auto /*tx*/) {
            //std::cout << "Received " << tx << " bytes (" << ec.message() << ")\n";
            std::cout << &rb << std::flush;
            if (!ec) recv_loop();
        });
    };

    io.post(send_loop);
    io.post(recv_loop);
    io.run();

    std::cout << "Bye\n";
}

Prints the expected:

Sure no problem, 99
Sure no problem, 98
Sure no problem, 97
Sure no problem, 96
Sure no problem, 95
Sure no problem, 94
Sure no problem, 93
Sure no problem, 92
Sure no problem, 91
Sure no problem, 90
Sure no problem, 89
Sure no problem, 88
Sure no problem, 87
Sure no problem, 86
Sure no problem, 85
Sure no problem, 84
Sure no problem, 83
Sure no problem, 82
Sure no problem, 81
Sure no problem, 80
Sure no problem, 79
Sure no problem, 78
Sure no problem, 77
Sure no problem, 76
Sure no problem, 75
Sure no problem, 74
Sure no problem, 73
Sure no problem, 72
Sure no problem, 71
Sure no problem, 70
Sure no problem, 69
Sure no problem, 68
Sure no problem, 67
Sure no problem, 66
Sure no problem, 65
Sure no problem, 64
Sure no problem, 63
Sure no problem, 62
Sure no problem, 61
Sure no problem, 60
Sure no problem, 59
Sure no problem, 58
Sure no problem, 57
Sure no problem, 56
Sure no problem, 55
Sure no problem, 54
Sure no problem, 53
Sure no problem, 52
Sure no problem, 51
Sure no problem, 50
Sure no problem, 49
Sure no problem, 48
Sure no problem, 47
Sure no problem, 46
Sure no problem, 45
Sure no problem, 44
Sure no problem, 43
Sure no problem, 42
Sure no problem, 41
Sure no problem, 40
Sure no problem, 39
Sure no problem, 38
Sure no problem, 37
Sure no problem, 36
Sure no problem, 35
Sure no problem, 34
Sure no problem, 33
Sure no problem, 32
Sure no problem, 31
Sure no problem, 30
Sure no problem, 29
Sure no problem, 28
Sure no problem, 27
Sure no problem, 26
Sure no problem, 25
Sure no problem, 24
Sure no problem, 23
Sure no problem, 22
Sure no problem, 21
Sure no problem, 20
Sure no problem, 19
Sure no problem, 18
Sure no problem, 17
Sure no problem, 16
Sure no problem, 15
Sure no problem, 14
Sure no problem, 13
Sure no problem, 12
Sure no problem, 11
Sure no problem, 10
Sure no problem, 9
Sure no problem, 8
Sure no problem, 7
Sure no problem, 6
Sure no problem, 5
Sure no problem, 4
Sure no problem, 3
Sure no problem, 2
Sure no problem, 1
Sure no problem, 1