Memformat Pesan Peristiwa

Peristiwa dapat berisi string pesan yang dilokalkan yang dapat Anda format untuk ditampilkan. Untuk mendapatkan string pesan dari peristiwa, panggil fungsi EvtFormatMessage . Peristiwa dapat berisi string pesan berikut:

• String pesan untuk peristiwa itu sendiri.
• String pesan yang menjelaskan nilai tingkat yang ditetapkan ke peristiwa.
• String pesan yang menjelaskan nilai tugas yang ditetapkan ke peristiwa.
• String pesan yang menjelaskan nilai opcode yang ditetapkan ke peristiwa.
• String pesan yang menjelaskan nilai kata kunci yang ditetapkan ke peristiwa.
• String pesan yang menjelaskan nilai saluran yang ditetapkan ke peristiwa.

Anda juga dapat menggunakan EvtFormatMessage untuk mendapatkan string pesan untuk penyedia atau string XML yang berisi peristiwa dan semua string pesan.

Selain mendapatkan string pesan dari peristiwa yang Anda kueri, Anda juga bisa mendapatkan string pesan dari metadata penyedia. Untuk detail tentang memformat pesan berdasarkan pengidentifikasi pesan yang Anda dapatkan dari metadata penyedia, lihat Mendapatkan Metadata Penyedia.

Contoh berikut menunjukkan cara mendapatkan string pesan dari suatu peristiwa.

#include <windows.h>
#include <stdio.h>
#include <sddl.h>
#include <winevt.h>

#pragma comment(lib, "wevtapi.lib")

LPWSTR GetMessageString(EVT_HANDLE hMetadata, EVT_HANDLE hEvent, EVT_FORMAT_MESSAGE_FLAGS FormatId);

void main(void)
{
    EVT_HANDLE hProviderMetadata = NULL;
    EVT_HANDLE hResults = NULL;
    EVT_HANDLE hEvent = NULL;
    DWORD status = ERROR_SUCCESS;
    DWORD dwReturned = 0;
    LPWSTR pwsMessage = NULL;
    LPWSTR pwsPath = L"<name of the channel goes here>";
    LPWSTR pwsQuery = L"<xpath query goes here>";
    LPWSTR pwszPublisherName = L"<name of the publisher goes here>";

    // Get the handle to the provider's metadata that contains the message strings.
    hProviderMetadata = EvtOpenPublisherMetadata(NULL, pwszPublisherName, NULL, 0, 0);
    if (NULL == hProviderMetadata)
    {
        wprintf(L"EvtOpenPublisherMetadata failed with %d\n", GetLastError());
        goto cleanup;
    }

    // Query for an event.
    hResults = EvtQuery(NULL, pwsPath, pwsQuery, EvtQueryChannelPath);
    if (NULL == hResults)
    {
        status = GetLastError();

        if (ERROR_EVT_CHANNEL_NOT_FOUND == status)
            wprintf(L"Channel %s was not found.\n", pwsPath);
        else
            wprintf(L"EvtQuery failed with %lu.\n", status);

        goto cleanup;
    }

    // Get a single event from the result set.
    if (!EvtNext(hResults, 1, &hEvent, INFINITE, 0, &dwReturned))
    {
        wprintf(L"EvtNext failed with %lu\n", status);
        goto cleanup;
    }

    // Get the various message strings from the event.
    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageEvent);
    if (pwsMessage)
    {
        wprintf(L"Event message string: %s\n\n", pwsMessage);
        free(pwsMessage);
        pwsMessage = NULL;
    }

    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageLevel);
    if (pwsMessage)
    {
        wprintf(L"Level message string: %s\n\n", pwsMessage);
        free(pwsMessage);
        pwsMessage = NULL;
    }

    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageTask);
    if (pwsMessage)
    {
        wprintf(L"Task message string: %s\n\n", pwsMessage);
        free(pwsMessage);
        pwsMessage = NULL;
    }

    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageOpcode);
    if (pwsMessage)
    {
        wprintf(L"Opcode message string: %s\n\n", pwsMessage);
        free(pwsMessage);
        pwsMessage = NULL;
    }

    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageKeyword);
    if (pwsMessage)
    {
        LPWSTR ptemp = pwsMessage;

        wprintf(L"Keyword message string: %s", ptemp);

        while (*(ptemp += wcslen(ptemp)+1))
            wprintf(L", %s", ptemp);

        wprintf(L"\n\n");
        free(pwsMessage);
        pwsMessage = NULL;
    }

    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageChannel);
    if (pwsMessage)
    {
        wprintf(L"Channel message string: %s\n\n", pwsMessage);
        free(pwsMessage);
        pwsMessage = NULL;
    }

    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageProvider);
    if (pwsMessage)
    {
        wprintf(L"Provider message string: %s\n\n", pwsMessage);
        free(pwsMessage);
        pwsMessage = NULL;
    }

    pwsMessage = GetMessageString(hProviderMetadata, hEvent, EvtFormatMessageXml);
    if (pwsMessage)
    {
        wprintf(L"XML message string: %s\n\n", pwsMessage);
        free(pwsMessage);
        pwsMessage = NULL;
    }

cleanup:

    if (hEvent)
        EvtClose(hEvent);

    if (hResults)
        EvtClose(hResults);
    
    if (hProviderMetadata)
        EvtClose(hProviderMetadata);
}


// Gets the specified message string from the event. If the event does not
// contain the specified message, the function returns NULL.
LPWSTR GetMessageString(EVT_HANDLE hMetadata, EVT_HANDLE hEvent, EVT_FORMAT_MESSAGE_FLAGS FormatId)
{
    LPWSTR pBuffer = NULL;
    DWORD dwBufferSize = 0;
    DWORD dwBufferUsed = 0;
    DWORD status = 0;

    if (!EvtFormatMessage(hMetadata, hEvent, 0, 0, NULL, FormatId, dwBufferSize, pBuffer, &dwBufferUsed))
    {
        status = GetLastError();
        if (ERROR_INSUFFICIENT_BUFFER == status)
        {
            // An event can contain one or more keywords. The function returns keywords
            // as a list of keyword strings. To process the list, you need to know the
            // size of the buffer, so you know when you have read the last string, or you
            // can terminate the list of strings with a second null terminator character 
            // as this example does.
            if ((EvtFormatMessageKeyword == FormatId))
                pBuffer[dwBufferSize-1] = L'\0';
            else
                dwBufferSize = dwBufferUsed;

            pBuffer = (LPWSTR)malloc(dwBufferSize * sizeof(WCHAR));

            if (pBuffer)
            {
                EvtFormatMessage(hMetadata, hEvent, 0, 0, NULL, FormatId, dwBufferSize, pBuffer, &dwBufferUsed);

                // Add the second null terminator character.
                if ((EvtFormatMessageKeyword == FormatId))
                    pBuffer[dwBufferUsed-1] = L'\0';
            }
            else
            {
                wprintf(L"malloc failed\n");
            }
        }
        else if (ERROR_EVT_MESSAGE_NOT_FOUND == status || ERROR_EVT_MESSAGE_ID_NOT_FOUND == status)
            ;
        else
        {
            wprintf(L"EvtFormatMessage failed with %u\n", status);
        }
    }

    return pBuffer;
}