How make long-term pipe connection between go and c# console application

Question

I have pretty straightforward C# console app. It will be a process that add double variables that were passed from go part.

double sum = 0;
bool flag = true;

while(flag) {  // exit on convert error
    var str = Console.ReadLine(); // ask string 

    double addend;
    flag = double.TryParse(str, out addend); // convert to double

    sum += flag ? addend : 0;  //add on success
    Console.WriteLine(sum);
}

return 0;

And my go part is simple too. It create process with previous console app, send strings to it and read back results.

package main

import (
    "fmt"
    "io"
    "log"
    "os/exec"
)

func main() {

    cmd := exec.Command("%path to app%\\ConsoleApp.exe") // process that will be started
    
stdout, err := cmd.StdoutPipe() // use std out pipe
    if err != nil {
        log.Fatal(err)
    }

    stdin, err := cmd.StdinPipe() // use std in pipe
    if err != nil {
        log.Fatal(err)
    }

    if err := cmd.Start(); err != nil { // start
        log.Fatal(err)
    }

    for true {
        var w1 string
        _, err := fmt.Scanln(&w1) // read line

        if err != nil {
            log.Fatal()
        }

        go func() {
            io.WriteString(stdin, w1) // pass it to console app
        }()

        read, err := io.ReadAll(stdout) // read result

        fmt.Println(read)

        if err != nil {
            log.Fatal()
        }
    }
}

I start debug for process of console app (it appears in task manager, RMC - Debug) but there is symbol errors, so I can't even understand did my app get the string or didn't.

That's only half of my trouble. I think once or twice my console app got string (I mean in previous times), but only there first one, cause pipe closes after transmition/copying from it. So how can I control this? I want to do several transactions, write and read, and close pipes only when I need it.

EDIT: I've changed ConsoleApp a bit. Now it looks like this:

double sum = 0;
bool flag = true;
while(flag) {
    var str = Console.ReadLine();
    double addend;
    flag = double.TryParse(str, out addend);

    // File creation will indicate that message was recieved. 
    using(StreamWriter writer = new StreamWriter("t.txt")) { 
        writer.WriteLine($"{flag}");
    }

    sum += flag ? addend : 0;
    Console.WriteLine(sum);
}

return 0;

Answer 1

So, @maxm was realy close (or even has got the solution, but it didn't work with me, fsr).

The go part:

package main

import (
    "bufio"
    "fmt"
    "log"

    "os/exec"
)

func main() {
    cmd := exec.Command("%path to the exe%")

    stdout, err := cmd.StdoutPipe() 
    if err != nil {
        log.Fatal(err)
    }

    stderr, err := cmd.StderrPipe()
    if err != nil {
        log.Fatal(err)
    }

    scanner := bufio.NewScanner(stdout)

    stdin, err := cmd.StdinPipe()
    if err != nil {
        log.Fatal(err)
    }

    if err := cmd.Start(); err != nil {
        log.Fatal(err)
    }

    for {
        var w1 string
        _, err := fmt.Scanln(&w1)
        w2 := []byte(w1) // important! You need convert string to byte array

        if err != nil {
            log.Fatal()
        }

        if _, err := stdin.Write(w2); err != nil { // pass byte array
            log.Fatal(stderr)
            panic(err)
        } 

        if scanner.Scan() {
            read := scanner.Text()
            fmt.Println(read)
        } else {
            if err := scanner.Err(); err != nil {
                panic(err)
            }
        }
    }
}

C# part is pretty easy. First of all you need restore string from byte array:

public static string ByteArrayToString(this byte[] byteArray, int size) {
    // get decoder to decode input encoding
    var decoder = Console.InputEncoding.GetDecoder(); 

    // count char that will be restored
    int charCount = decoder.GetCharCount(byteArray, 0, size);

    // initialize char array
    char[] charArray = new char[charCount];
    // restore to char array
    decoder.GetChars(byteArray, 0, size, charArray, 0);

    // get and return string from our char array
    return new string(charArray);
}

Main part is next:

double sum = 0;
bool flag = true;
while(flag) {
    string str;

    using Stream stdin = Console.OpenStandardInput(); // for reading 

    byte[] buffer = new byte[2048];
    int bytes = 0; // bytes count

    while((bytes = stdin.Read(buffer, 0, buffer.Length)) > 0) { // read
        str = buffer.ByteArrayToString(bytes); // restore string
        flag = double.TryParse(str, out double addend);
        sum += flag ? addend : 0;
        Console.WriteLine(sum); //write

        if(!flag)
            break;
    }
}

return 0;