RtlUnicodeStringCchCatNEx - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers 
#ifndef _NTSTRSAFE_H_INCLUDED_
#ifndef NTSTRSAFE_LIB_IMPL
#ifndef NTSTRSAFE_NO_UNICODE_STRING_FUNCTIONS
#ifndef NTSTRSAFE_NO_CCH_FUNCTIONS

NTSTRSAFEDDI
RtlUnicodeStringCchCatNEx(
        _Inout_   PUNICODE_STRING  DestinationString,
        _In_      PCUNICODE_STRING SourceString,
        _In_      size_t           cchToAppend,
        _Out_opt_ PUNICODE_STRING  RemainingString,
        _In_      DWORD            dwFlags)
{
    NTSTATUS status;
    wchar_t* pszDest;
    size_t cchDest;
    size_t cchDestLength;

    status = RtlUnicodeStringValidateDestWorker(DestinationString,
            &pszDest,
            &cchDest,
            &cchDestLength,
            NTSTRSAFE_UNICODE_STRING_MAX_CCH,
            dwFlags);

    if (NT_SUCCESS(status))
    {
        wchar_t* pszSrc;
        size_t cchSrcLength;
        wchar_t* pszDestEnd = pszDest + cchDestLength;
        size_t cchRemaining = cchDest - cchDestLength;
        size_t cchNewDestLength = cchDestLength;

        status = RtlUnicodeStringValidateSrcWorker(SourceString,
                &pszSrc,
                &cchSrcLength,
                NTSTRSAFE_UNICODE_STRING_MAX_CCH,
                dwFlags);

        if (NT_SUCCESS(status))
        {
            if (cchToAppend > NTSTRSAFE_UNICODE_STRING_MAX_CCH)
            {
                status = STATUS_INVALID_PARAMETER;
            }
            else
            {
                if (cchSrcLength < cchToAppend)
                {
                    cchToAppend = cchSrcLength;
                }

                if (dwFlags & (~STRSAFE_UNICODE_STRING_VALID_FLAGS))
                {
                    status = STATUS_INVALID_PARAMETER;
                }
                else if (cchRemaining == 0)
                {
                    // only fail if there was actually src data to append
                    if (cchToAppend != 0)
                    {
                        if (pszDest == NULL)
                        {
                            status = STATUS_INVALID_PARAMETER;
                        }
                        else
                        {
                            status = STATUS_BUFFER_OVERFLOW;
                        }
                    }
                }
                else
                {
                    size_t cchCopied = 0;

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

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

                    cchNewDestLength = cchDestLength + cchCopied;

                    if (NT_SUCCESS(status)              &&
                            (dwFlags & STRSAFE_FILL_BEHIND) &&
                            (cchRemaining != 0))
                    {
                        // handle the STRSAFE_FILL_BEHIND flag
                        RtlUnicodeStringExHandleFill(pszDestEnd, cchRemaining, dwFlags);
                    }
                }
            }
        }

        if (!NT_SUCCESS(status)                                                                                      &&
                (dwFlags & (STRSAFE_NO_TRUNCATION | STRSAFE_FILL_ON_FAILURE | STRSAFE_ZERO_LENGTH_ON_FAILURE))  &&
                (cchDest != 0))
        {
            // handle the STRSAFE_NO_TRUNCATION, STRSAFE_FILL_ON_FAILURE, and STRSAFE_ZERO_LENGTH_ON_FAILURE flags
            RtlUnicodeStringExHandleOtherFlags(pszDest,
                    cchDest,
                    cchDestLength,
                    &cchNewDestLength,
                    &pszDestEnd,
                    &cchRemaining,
                    dwFlags);
        }

        if (DestinationString)
        {
            // safe to multiply cchNewDestLength * sizeof(wchar_t) since cchDest < NTSTRSAFE_UNICODE_STRING_MAX_CCH and sizeof(wchar_t) is 2
            DestinationString->Length = (USHORT)(cchNewDestLength * sizeof(wchar_t));
        }

        if (NT_SUCCESS(status) || (status == STATUS_BUFFER_OVERFLOW))
        {
            if (RemainingString)
            {
                RemainingString->Length = 0;
                // safe to multiply cchRemaining * sizeof(wchar_t) since cchRemaining < NTSTRSAFE_UNICODE_STRING_MAX_CCH and sizeof(wchar_t) is 2
                RemainingString->MaximumLength = (USHORT)(cchRemaining * sizeof(wchar_t));
                RemainingString->Buffer = pszDestEnd;
            }
        }
    }

    return status;
}

#endif
#endif
#endif
#endif

View code on GitHub
// ntstrsafe.h

NTSTRSAFEDDI RtlUnicodeStringCchCatNEx(
  [in, out]       PUNICODE_STRING  DestinationString,
  [in]            PCUNICODE_STRING SourceString,
  [in]            size_t           cchToAppend,
  [out, optional] PUNICODE_STRING  RemainingString,
  [in]            DWORD            dwFlags
);
View the official Windows Driver Kit DDI reference

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Windows Driver Kit DDI reference (nf-ntstrsafe-rtlunicodestringcchcatnex)

RtlUnicodeStringCchCatNEx function

Description

The RtlUnicodeStringCchCatNEx function concatenates two strings that are contained in UNICODE_STRING structures while limiting the size of the copied string.

Parameters

DestinationString [in, out]

Optional. A pointer to a UNICODE_STRING structure. This structure includes a buffer that, on input, contains a string to which the source string will be concatenated. On output, this buffer is the destination buffer that contains the entire resultant string. The source string is added to the end of the destination string. The maximum number of characters in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH. DestinationString can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

SourceString [in]

Optional. A pointer to a UNICODE_STRING structure. This structure includes a buffer that contains the source string. This string will be added to the end of the destination string. The maximum number of characters in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH. SourceString can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

cchToAppend [in]

The maximum number of characters to append to the string that the DestinationString parameter describes.

RemainingString [out, optional]

Optional. If the caller supplies a non-NULL pointer to a UNICODE_STRING structure, the function sets this structure's Buffer member to the end of the concatenated string, sets the structure's Length member to zero, and sets the structure's MaximumLength member to the number of bytes that are remaining in the destination buffer. RemainingString can be NULL, but only if STRSAFE_IGNORE_NULLS is set in dwFlags.

dwFlags [in]

One or more flags and, optionally, a fill byte. The flags are defined as follows:

Value Meaning
STRSAFE_FILL_BEHIND If this flag is set and the function succeeds, the low byte of dwFlags is used to fill the portion of the destination buffer that follows the last character in the string.
STRSAFE_IGNORE_NULLS If this flag is set, the source or destination pointer, or both, can be NULL. RtlUnicodeStringCchCatNEx treats NULL source buffer pointers like empty strings (TEXT("")), which can be copied. NULL destination buffer pointers cannot receive nonempty strings.
STRSAFE_FILL_ON_FAILURE If this flag is set and the function fails, the low byte of dwFlags is used to fill the entire destination buffer. This operation overwrites any preexisting buffer contents.
STRSAFE_NULL_ON_FAILURE If this flag is set and the function fails, the destination buffer is set to an empty string (TEXT("")). This operation overwrites any preexisting buffer contents.
STRSAFE_NO_TRUNCATION If this flag is set and the function returns STATUS_BUFFER_OVERFLOW:

* If STRSAFE_FILL_ON_FAILURE is also specified, STRSAFE_NO_TRUNCATION fills the destination buffer accordingly.
* Otherwise, the destination buffer will be unmodified.
STRSAFE_ZERO_LENGTH_ON_FAILURE If this flag is set and the function returns STATUS_BUFFER_OVERFLOW, the destination string length is set to zero bytes.

Return value

RtlUnicodeStringCchCatNEx returns one of the following NTSTATUS values.

Return code Description
STATUS_SUCCESS This success status means source data was present, and the strings were concatenated without truncation.
STATUS_BUFFER_OVERFLOW This warning status means that the concatenated operation did not complete because of insufficient space in the destination buffer. If STRSAFE_NO_TRUNCATION is set, see the dwFlags parameter for more information.
STATUS_INVALID_PARAMETER This error status means that the function received an invalid input parameter. For more information, see the following list.

RtlUnicodeStringCchCatNEx returns the STATUS_INVALID_PARAMETER value when:

For information about how to test NTSTATUS values, see Using NTSTATUS Values.

Remarks

The RtlUnicodeStringCchCatNEx function uses the destination buffer's size to ensure that the concatenation operation does not write past the end of the buffer. By default, the function does not terminate the resultant string with a null character value (that is, with zero). As an option, the caller can use the STRSAFE_FILL_BEHIND flag and a fill byte value of zero to null-terminate a resultant string that does not occupy the entire destination buffer.

RtlUnicodeStringCchCatNEx adds to the functionality of the RtlUnicodeStringCchCatN function by returning a UNICODE_STRING structure that identifies the end of the destination string and the number of bytes that are left unused in that string. You can pass flags to RtlUnicodeStringCchCatNEx for additional control.

If the source and destination strings overlap, the behavior of the function is undefined.

The SourceString and DestinationString pointers cannot be NULL unless the STRSAFE_IGNORE_NULLS flag is set in dwFlags. If STRSAFE_IGNORE_NULLS is set, one or both can be NULL. If the DestinationString pointer is NULL, the SourceString pointer must be NULL or the UNICODE_STRING structure must specify an empty string.

For more information about the safe string functions, see Using safe string functions.

See also

View the official Windows Driver Kit DDI reference

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