RtlStringCbCatNExW - NtDoc

#ifndef _NTSTRSAFE_H_INCLUDED_
#ifndef NTSTRSAFE_LIB_IMPL
#ifndef NTSTRSAFE_NO_CB_FUNCTIONS

NTSTRSAFEDDI
    RtlStringCbCatNExW(
            _Inout_updates_bytes_(cbDest) _Always_(_Post_z_) NTSTRSAFE_PWSTR pszDest,
            _In_ size_t cbDest,
            _In_reads_bytes_(cbToAppend) STRSAFE_PCNZWCH pszSrc,
            _In_ size_t cbToAppend,
            _Outptr_opt_result_bytebuffer_(*pcbRemaining) NTSTRSAFE_PWSTR* ppszDestEnd,
            _Out_opt_ size_t* pcbRemaining,
            _In_ DWORD dwFlags)
{
    NTSTATUS status;
    size_t cchDest = cbDest / sizeof(wchar_t);
    size_t cchDestLength;

    status = RtlStringExValidateDestAndLengthW(pszDest,
            cchDest,
            &cchDestLength,
            NTSTRSAFE_MAX_CCH,
            dwFlags);

    if (NT_SUCCESS(status))
    {
        NTSTRSAFE_PWSTR pszDestEnd = pszDest + cchDestLength;
        size_t cchRemaining = cchDest - cchDestLength;
        size_t cchToAppend = cbToAppend / sizeof(wchar_t);

        status = RtlStringExValidateSrcW(&pszSrc, &cchToAppend, NTSTRSAFE_MAX_CCH, dwFlags);

        if (NT_SUCCESS(status))
        {
            if (dwFlags & (~STRSAFE_VALID_FLAGS))
            {
                status = STATUS_INVALID_PARAMETER;
            }
            else if (cchRemaining <= 1)
            {
                // only fail if there was actually src data to append
                if ((cchToAppend != 0) && (*pszSrc != L'\0'))
                {
                    if (pszDest == NULL)
                    {
                        status = STATUS_INVALID_PARAMETER;
                    }
                    else
                    {
                        status = STATUS_BUFFER_OVERFLOW;
                    }
                }
            }
            else
            {
                size_t cchCopied = 0;

                status = RtlStringCopyWorkerW(pszDestEnd,
                        cchRemaining,
                        &cchCopied,
                        pszSrc,
                        cchToAppend);

                pszDestEnd = pszDestEnd + cchCopied;
                cchRemaining = cchRemaining - cchCopied;

                if (NT_SUCCESS(status) && (dwFlags & STRSAFE_FILL_BEHIND_NULL))
                {
                    size_t cbRemaining;

                    // safe to multiply cchRemaining * sizeof(wchar_t) since cchRemaining < NTSTRSAFE_MAX_CCH and sizeof(wchar_t) is 2
                    cbRemaining = (cchRemaining * sizeof(wchar_t)) + (cbDest % sizeof(wchar_t));

                    // handle the STRSAFE_FILL_BEHIND_NULL flag
                    RtlStringExHandleFillBehindNullW(pszDestEnd, cbRemaining, dwFlags);
                }
            }
        }

        if (!NT_SUCCESS(status)                                                                              &&
                (dwFlags & (STRSAFE_NO_TRUNCATION | STRSAFE_FILL_ON_FAILURE | STRSAFE_NULL_ON_FAILURE)) &&
                (cbDest != 0))
        {
            // handle the STRSAFE_FILL_ON_FAILURE, STRSAFE_NULL_ON_FAILURE, and STRSAFE_NO_TRUNCATION flags
            RtlStringExHandleOtherFlagsW(pszDest,
                    cbDest,
                    cchDestLength,
                    &pszDestEnd,
                    &cchRemaining,
                    dwFlags);
        }

        if (NT_SUCCESS(status) || (status == STATUS_BUFFER_OVERFLOW))
        {
            if (ppszDestEnd)
            {
                *ppszDestEnd = pszDestEnd;
            }

            if (pcbRemaining)
            {
                // safe to multiply cchRemaining * sizeof(wchar_t) since cchRemaining < NTSTRSAFE_MAX_CCH and sizeof(wchar_t) is 2
                *pcbRemaining = (cchRemaining * sizeof(wchar_t)) + (cbDest % sizeof(wchar_t));
            }
        }
    }

    return status;
}

#endif
#endif
#endif
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