parentchild_pipe on Windows naively ported to Zig

child.zig

const std = @import("std");
const os = std.os;

pub fn main() !void {
    const buf_size = 25;
    var rd_h = os.windows.HANDLE;
    var buf: [buf_size]u8 = undefined;
    var read: os.windows.DWORD = undefined;
    rd_h = try os.windows.GetStdHandle(os.windows.STD_INPUT_HANDLE);
    if (try os.windows.ReadFile(rd_h, buf, buf_size, &read, null)) {
        std.debug.print("child read {d}", .{buf});
    } else {
        std.debug.print("error reading from pipe", .{});
    }
}

parent.zig

const std = @import("std");
const os = std.os;
pub fn main() !void {
    var rd_h: os.windows.HANDLE = undefined;
    var wr_h: os.windows.HANDLE = undefined;
    // docs show zeroing out of startup and process information
    // https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src/ProcThread/creating-processes.md
    var si = os.windows.STARTUPINFOW{
        .cb = @sizeOf(os.windows.STARTUPINFOW),
        .hStdError = null,
        .hStdOutput = null,
        .hStdInput = null,
        .dwFlags = os.windows.STARTF_USESTDHANDLES,
        .lpReserved = null,
        .lpDesktop = null,
        .lpTitle = null,
        .dwX = 0,
        .dwY = 0,
        .dwXSize = 0,
        .dwYSize = 0,
        .dwXCountChars = 0,
        .dwYCountChars = 0,
        .dwFillAttribute = 0,
        .wShowWindow = 0,
        .cbReserved2 = 0,
        .lpReserved2 = null,
    };
    var pi = os.windows.PROCESS_INFORMATION{
        .hProcess = undefined,
        .hThread = undefined,
        .dwProcessId = 0,
        .dwThreadId = 0,
    };
    const msg: []const u8 = "hello";
    // security attributes to allow pipes to be inherited
    const sa = os.windows.SECURITY_ATTRIBUTES{
        .nLength = @sizeOf(os.windows.SECURITY_ATTRIBUTES),
        .lpSecurityDescriptor = null,
        .bInheritHandle = os.windows.TRUE,
    };


    try os.windows.CreatePipe(&rd_h, &wr_h, &sa);
    si.hStdOutput = try os.windows.GetStdHandle(os.windows.STD_OUTPUT_HANDLE);
    si.hStdInput = rd_h; // redirect stdin to read end of pipe

    // replace all handles all of the handles instead of connecting to them
    try os.windows.SetHandleInformation(wr_h, os.windows.HANDLE_FLAG_INHERIT, 0);
    // create child process (+ erase const)
    const child_name: [*:0]const u16 = std.unicode.utf8ToUtf16LeStringLiteral("child.exe");
    const ch_n = @intToPtr([*:0]u16, @ptrToInt(child_name));
    //const ch_n: [*:0]u16 = @ptrCast([*:0]u16, child_name); @ptrCast can not erase const
    //0 for inherit handle
    os.windows.CreateProcessW(null, ch_n, null, null, os.windows.TRUE, 0, null, null, &si, &pi) catch |err| {
        // TODO(DEBUG): this panics before reaching the panic message due a segfault
        std.debug.print("err: {s}", .{@errorName(err)});
        @panic("could not create Process");
    };
    os.windows.CloseHandle(rd_h); // close unused end of pipe

    const written: u64 = try os.windows.WriteFile(wr_h, msg, null, std.io.default_mode);
    std.debug.assert(written > 0);
    //wait for the child process to exit
    try os.windows.WaitForSingleObject(pi.hProcess, os.windows.INFINITE);
    os.windows.CloseHandle(pi.hProcess);
    os.windows.CloseHandle(pi.hThread);
}