Function cbm_popen_isolated

src/foundation/compat_fs.c:234–368

On failure returns NULL with *stage naming the failing step and *gle the * GetLastError value captured at that step (0 when errno is the signal). */

/* On failure returns NULL with *stage naming the failing step and *gle the
 * GetLastError value captured at that step (0 when errno is the signal). */
static FILE *cbm_popen_isolated(const char *cmd, const char **stage, DWORD *gle) {
    *stage = "";
    *gle = 0;
    InitOnceExecuteOnce(&g_popen_once, cbm_popen_init, NULL, NULL);

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

    HANDLE rd = NULL, wr = NULL;
    if (!CreatePipe(&rd, &wr, &sa, 0)) {
        *stage = "pipe";
        *gle = GetLastError();
        return NULL;
    }
    /* The parent read-end must never cross into the child. */
    SetHandleInformation(rd, HANDLE_FLAG_INHERIT, 0);

    /* NUL for the child's stdin/stderr so it never touches our real stdin
     * pipe. If NUL cannot be opened, fail: STARTF_USESTDHANDLES slots must
     * never carry INVALID_HANDLE_VALUE. */
    HANDLE nul = CreateFileW(L"NUL", GENERIC_READ | GENERIC_WRITE,
                             FILE_SHARE_READ | FILE_SHARE_WRITE, &sa, OPEN_EXISTING, 0, NULL);
    if (nul == INVALID_HANDLE_VALUE) {
        *stage = "nul";
        *gle = GetLastError();
        CloseHandle(rd);
        CloseHandle(wr);
        return NULL;
    }

    HANDLE inherit[2];
    inherit[0] = wr;
    inherit[1] = nul;

    SIZE_T attr_sz = 0;
    InitializeProcThreadAttributeList(NULL, 1, 0, &attr_sz);
    LPPROC_THREAD_ATTRIBUTE_LIST attr = (LPPROC_THREAD_ATTRIBUTE_LIST)malloc(attr_sz);
    BOOL attr_init = attr && InitializeProcThreadAttributeList(attr, 1, 0, &attr_sz);
    BOOL prepared =
        attr_init && UpdateProcThreadAttribute(attr, 0, PROC_THREAD_ATTRIBUTE_HANDLE_LIST, inherit,
                                               sizeof(inherit), NULL, NULL);
    DWORD attr_gle = prepared ? 0 : GetLastError();

    STARTUPINFOEXW si;
    ZeroMemory(&si, sizeof(si));
    si.StartupInfo.cb = sizeof(si);
    si.StartupInfo.dwFlags = STARTF_USESTDHANDLES;
    si.StartupInfo.hStdInput = nul;
    si.StartupInfo.hStdOutput = wr;
    si.StartupInfo.hStdError = nul;
    si.lpAttributeList = attr;

    /* Run through cmd.exe /c so command quoting and `2>NUL` behave as under
     * _popen. The command line is heap-composed (no fixed-size truncation)
     * and widened via UTF-8 so non-ASCII repo paths survive intact. */
    wchar_t *app = cbm_resolve_comspec();