Read child process’s stdout and stderr using Named Pipe and IO Completion port(IOCP) asynchronously

spawn.cpp

#include <windows.h>
#include <assert.h>
#include <stdio.h>

struct Stdio;

typedef void (*Callback)(struct Stdio* self, DWORD len);

struct Stdio {
    OVERLAPPED ol;
    HANDLE pipe;
    BYTE buf[100];
    Callback callback;
};

typedef struct CTX {
    struct Stdio Stdout, Stderr, Stdin;
} CTX, *LCTX, *LPCTX;

HANDLE Hstdout=INVALID_HANDLE_VALUE;
HANDLE Hstderr=INVALID_HANDLE_VALUE;

DWORD WINAPI Worker(LPVOID iocp){
    struct Stdio *stdio;
    OVERLAPPED *ol;
    DWORD dwIoSize;
    for(;;){
        if (!GetQueuedCompletionStatus(iocp, &dwIoSize, (PDWORD_PTR)&stdio, &ol, INFINITE) || dwIoSize==0 || ol==NULL || stdio==NULL){
            switch (GetLastError()){
                case ERROR_BROKEN_PIPE:
                    puts("the process has been exited, exit thread...");
                    break;
                default:
                    printf("error = %d, exit thread\n", GetLastError());
            }
            break;
        }
        stdio->callback(stdio, dwIoSize);
    }
    return 0;
}
void OnStdoutRead(struct Stdio *self, DWORD len){
    WriteConsoleA(Hstdout, self->buf, len, NULL, NULL);
    ReadFile(self->pipe, self->buf, sizeof(self->buf), NULL, &self->ol);
}
void OnStderrRead(struct Stdio *self, DWORD len){
    WriteConsoleA(Hstderr, self->buf, len, NULL, NULL);
    ReadFile(self->pipe, self->buf, sizeof(self->buf), NULL, &self->ol);
}

int wmain(){
    assert(Hstdout = GetStdHandle(STD_OUTPUT_HANDLE));
    assert(Hstderr = GetStdHandle(STD_ERROR_HANDLE));
    HANDLE Pstdout, Pstderr; // child process's
    CTX ctx{.Stdout=Stdio{.callback=OnStdoutRead}, .Stderr=Stdio{.callback=OnStderrRead}};

    HANDLE iocp = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 0);
    HANDLE hThread =  CreateThread(NULL, 0, Worker, iocp, 0, NULL); // Worker thread

    SECURITY_ATTRIBUTES sa{.nLength=sizeof(SECURITY_ATTRIBUTES), .bInheritHandle=TRUE};

    const WCHAR* pipe_name1 = L"\\\\.\\Pipe\\child-1";

    assert((ctx.Stdout.pipe = CreateNamedPipeW(
        pipe_name1,
        PIPE_ACCESS_INBOUND | FILE_FLAG_OVERLAPPED,
        PIPE_TYPE_BYTE,
        1,
        4096,
        4096,
        5000,
        NULL))!=INVALID_HANDLE_VALUE);

    assert(INVALID_HANDLE_VALUE != (Pstdout = CreateFileW(
        pipe_name1,
        GENERIC_WRITE,
        0,
        &sa,
        OPEN_EXISTING,
        FILE_FLAG_OVERLAPPED,
        NULL)));

    const WCHAR *pipe_name2 = L"\\\\.\\Pipe\\child-2";

    assert((ctx.Stderr.pipe = CreateNamedPipeW(
        pipe_name2,
        PIPE_ACCESS_INBOUND | FILE_FLAG_OVERLAPPED,
        PIPE_TYPE_BYTE,
        1,
        4096,
        4096,
        5000,
        NULL))!=INVALID_HANDLE_VALUE);

    assert((Pstderr = CreateFileW(
        pipe_name2,
        GENERIC_WRITE,
        0,
        &sa,
        OPEN_EXISTING,
        FILE_FLAG_OVERLAPPED,
        NULL))!=INVALID_HANDLE_VALUE);

    STARTUPINFOW si{.cb = sizeof(si), 
        .dwFlags = STARTF_USESTDHANDLES | STARTF_USESHOWWINDOW, 
        .wShowWindow = SW_HIDE, 
        .hStdInput = GetStdHandle(STD_INPUT_HANDLE), // use current stdin
        .hStdOutput = Pstdout, 
        .hStdError = Pstderr};

    WCHAR cmd[] = L"powershell"; // or cmd, py, bash...
    PROCESS_INFORMATION pInfo{};

    assert(CreateProcessW(
        NULL, cmd, NULL, NULL,
        TRUE, 0, NULL, NULL,
        &si, &pInfo));

    assert(CloseHandle(Pstdout)); // we don't need this
    assert(CloseHandle(Pstderr)); // we don't need this

    assert(CreateIoCompletionPort(ctx.Stdout.pipe, iocp, (ULONG_PTR)&ctx.Stdout, 0));
    assert(CreateIoCompletionPort(ctx.Stderr.pipe, iocp, (ULONG_PTR)&ctx.Stderr, 0));

    ReadFile(ctx.Stdout.pipe, ctx.Stdout.buf, sizeof(ctx.Stdout.buf), NULL, &ctx.Stdout.ol);
    ReadFile(ctx.Stderr.pipe, ctx.Stdout.buf, sizeof(ctx.Stderr.buf), NULL, &ctx.Stderr.ol);

    WaitForSingleObject(pInfo.hProcess, INFINITE); // wait for process exit
    PostQueuedCompletionStatus(iocp, 0, 0, NULL); // tell IOCP Worker exit
    WaitForSingleObject(hThread, INFINITE); // wait for thread exit

    assert(CloseHandle(hThread));
    assert(CloseHandle(ctx.Stderr.pipe));
    assert(CloseHandle(ctx.Stdout.pipe));
    assert(CloseHandle(pInfo.hProcess));
    assert(CloseHandle(iocp));
    assert(CloseHandle(Hstderr));
    puts("exit main function..."); // !!important: before close stdout
    assert(CloseHandle(Hstdout));
}