RtlUnicodeStringCatString - 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

/*++

  NTSTATUS
  RtlUnicodeStringCatString(
  _Inout_  PUNICODE_STRING DestinationString,
  _In_     LPCTSTR         pszSrc
  );

  Routine Description:

  This routine is a safer version of the C built-in function 'strcat' for
  UNICODE_STRINGs.

  This function returns an NTSTATUS value, and not a pointer.  It returns
  STATUS_SUCCESS if the string was concatenated without truncation, otherwise
  it will return a failure code. In failure cases as much of pszSrc will be
  appended to DestinationString as possible.

Arguments:

DestinationString   -   pointer to the counted unicode destination string

pszSrc              -   source string which must be null terminated

Notes:
Behavior is undefined if source and destination strings overlap.

DestinationString and pszSrc should not be NULL.  See RtlUnicodeStringCatStringEx
if you require the handling of NULL values.

Return Value:

STATUS_SUCCESS -   if there was source data and it was all concatenated

failure        -   the operation did not succeed

STATUS_BUFFER_OVERFLOW
Note: This status has the severity class Warning - IRPs completed with this
status do have their data copied back to user mode
-   this return value is an indication that the
operation failed due to insufficient space. When this
error occurs, the destination buffer is modified to
contain a truncated version of the ideal result.
This is useful for situations where truncation is ok.

It is strongly recommended to use the NT_SUCCESS() macro to test the
return value of this function.

--*/

NTSTRSAFEDDI
RtlUnicodeStringCatString(
        _Inout_ PUNICODE_STRING DestinationString,
        _In_ NTSTRSAFE_PCWSTR pszSrc)
{
    NTSTATUS status;
    wchar_t* pszDest;
    size_t cchDest;
    size_t cchDestLength;

    status = RtlUnicodeStringValidateDestWorker(DestinationString,
            &pszDest,
            &cchDest,
            &cchDestLength,
            NTSTRSAFE_UNICODE_STRING_MAX_CCH,
            0);

    if (NT_SUCCESS(status))
    {
        size_t cchCopied = 0;

        status = RtlWideCharArrayCopyStringWorker(pszDest + cchDestLength,
                cchDest - cchDestLength,
                &cchCopied,
                pszSrc,
                NTSTRSAFE_UNICODE_STRING_MAX_CCH);

        // safe to multiply (cchDestLength + cchCopied) * sizeof(wchar_t) since (cchDestLength + cchCopied) < NTSTRSAFE_UNICODE_STRING_MAX_CCH and sizeof(wchar_t) is 2
        DestinationString->Length = (USHORT)((cchDestLength + cchCopied) * sizeof(wchar_t));
    }

    return status;
}

#endif
#endif
#endif

View code on GitHub
// ntstrsafe.h

NTSTRSAFEDDI RtlUnicodeStringCatString(
  [in, out] PUNICODE_STRING  DestinationString,
  [in]      NTSTRSAFE_PCWSTR pszSrc
);
View the official Windows Driver Kit DDI reference

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

RtlUnicodeStringCatString function

Description

The RtlUnicodeStringCatString function concatenates two strings when the destination string is contained in a UNICODE_STRING structure.

Parameters

DestinationString [in, out]

A pointer to a UNICODE_STRING structure. This structure includes a buffer that, on input, contains a destination 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 (excluding the terminating null) is added to the end of the destination string. The maximum number of bytes in the structure's string buffer is NTSTRSAFE_UNICODE_STRING_MAX_CCH * sizeof(WCHAR).

pszSrc [in]

A pointer to a null-terminated string. This string will be concatenated to the end of the string that is contained in the buffer that the UNICODE_STRING structure points to.

Return value

RtlUnicodeStringCatString returns one of the following NTSTATUS values.

Return code Description
STATUS_SUCCESS This success status means that source data was present, the strings were concatenated without truncation, and the resultant destination buffer is null-terminated.
STATUS_BUFFER_OVERFLOW This warning status means that the concatenation operation did not complete because of insufficient buffer space. The destination buffer contains a truncated, null-terminated version of the intended result.
STATUS_INVALID_PARAMETER This error status means that the function received an invalid input parameter. For more information, see the following list.

RtlUnicodeStringCatString returns the STATUS_INVALID_PARAMETER value when one of the following occurs:

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

Remarks

The RtlUnicodeStringCatString function uses the destination buffer's size to ensure that the concatenation operation does not write past the end of the buffer. The function does not terminate the resultant string with a null character value (that is, with zero).

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

The pszSrc and DestinationString pointers cannot be NULL. If you need to handle NULL pointer values, use the RtlUnicodeStringCatStringEx function.

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

See also

RtlUnicodeStringCatStringEx

UNICODE_STRING

View the official Windows Driver Kit DDI reference

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