C++ on Windows: Pipe to stdin not properly transferring data + ReadFile stucks when reading from pipe

Question

I tried to create a pwntools-like program for windows. I implemented a send and recv to send data to stdin of a and to receive data from stdout. I did that using pipes.

#include <iostream>
#include <cstdio>
#include <windows.h>

void spawn();
void pwn_send(CONST CHAR chBuf[]);
CHAR* pwn_recv(SIZE_T sz);
CHAR* pwn_recv();

HANDLE stdout_write = NULL;
HANDLE stdout_read = NULL;
HANDLE stdin_write = NULL;
HANDLE stdin_read = NULL;

int main() {
    SECURITY_ATTRIBUTES saAttr;

    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
    saAttr.bInheritHandle = TRUE;
    saAttr.lpSecurityDescriptor = NULL;

    if(!CreatePipe(&stdout_read, &stdout_write, &saAttr, 0)) return -1;
    if(!SetHandleInformation(stdout_read, HANDLE_FLAG_INHERIT, 0)) return -1;
    if(!CreatePipe(&stdin_read, &stdin_write, &saAttr, 0)) return -1;
    if(!SetHandleInformation(stdin_write, HANDLE_FLAG_INHERIT, 0)) return -1;

    spawn();

    CHAR chBuf[] = "mkdir C:\\Users\\comma\\Desktop\\x\r\n";
    pwn_send(chBuf);

    std::cout << pwn_recv(20) << std::endl;

    return 0;
}

void spawn() {
    TCHAR cmd[] = TEXT("cmd.exe");
    STARTUPINFO si;
    PROCESS_INFORMATION pi;
    ZeroMemory(&si, sizeof(si));
    si.cb = sizeof(si);
    si.hStdError = stdout_write;
    si.hStdOutput = stdout_write;
    si.hStdInput = stdin_read;
    si.dwFlags |= STARTF_USESTDHANDLES;
    ZeroMemory(&pi, sizeof(pi));

    if(!CreateProcess(NULL, cmd, NULL, NULL, FALSE, 0, NULL, NULL, &si, &pi)) exit(-1);
    return;
}

void pwn_send(CONST CHAR chBuf[]) {
    DWORD dwRead = 0, dwWritten = 0;
    BOOL bSuccess = FALSE;

    while(1) {
        bSuccess = WriteFile(stdin_write, chBuf, strlen(chBuf), &dwWritten, NULL);
        if (bSuccess) break;
    }

    CloseHandle(stdin_write);
    return;
}

CHAR* pwn_recv(SIZE_T sz) {
    HANDLE hHeap = GetProcessHeap();
    DWORD dwRead = 0, dwWritten = 0;
    BOOL bSuccess = FALSE;

    CHAR* chBuf = (CHAR*)HeapAlloc(hHeap, 0, sz+1);

    while (1) {
        std::cout << "XXX" << std::endl;
        bSuccess = ReadFile(stdout_read, chBuf, sz, &dwRead, NULL);
        std::cout << "YYY" << std::endl;
        if (bSuccess) break;
    }

    return chBuf;
}

CHAR* pwn_recv() {
    HANDLE hHeap = GetProcessHeap();
    DWORD dwRead = 0, dwWritten = 0;
    BOOL bSuccess = FALSE;

    CHAR* chBuf = (CHAR*)HeapAlloc(hHeap, 0, 0x1000);

    while (1) {
        bSuccess = ReadFile(stdout_read, chBuf, 0x1000, &dwWritten, NULL);
        if (bSuccess) break;
    }

    return chBuf;
}

So the first issue here is that the program I started with spawn(cmd.exe) doesn't properly receive the command I send to stdin. No folder is created anywhere. CreateProcess succeeds. Receiving output doesn't work either, because ReadFile seems to stuck. XXX is displayed in the console, butYYY never. Any ideas?