问题
In my application, I am testing the behaviour of WriteFile when another Write operation is pending over the named pipe.
Pipe is in message mode (not in byte mode).
To make write operation pending, I kept the buffer of named pipe quite small and client sends the more data than buffer size. By this way, I am getting write operation pending at the client end.
I am facing the following problem at the server end:
ReadFile is failed with ERROR_MORE_DATA. It changes the content of the buffer, but not the number of bytes received.
Server code
//file server.cpp
#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <strsafe.h>
#define CONNECTING_STATE 0
#define READING_STATE 1
#define WRITING_STATE 2
#define INSTANCES 4
#define PIPE_TIMEOUT 5000
#define BUFSIZE 3
#define BUFSIZE2 1000
typedef struct
{
OVERLAPPED oOverlap;
HANDLE hPipeInst;
TCHAR chRequest[BUFSIZE2];
DWORD cbRead;
DWORD cbReadSoFar;
TCHAR chReply[BUFSIZE2];
DWORD cbToWrite;
DWORD dwState;
BOOL fPendingIO;
} PIPEINST, *LPPIPEINST;
VOID DisconnectAndReconnect(DWORD);
BOOL ConnectToNewClient(HANDLE, LPOVERLAPPED);
VOID GetAnswerToRequest(LPPIPEINST);
PIPEINST Pipe[INSTANCES];
HANDLE hEvents[INSTANCES];
int _tmain(VOID)
{
DWORD i, dwWait, cbRet, dwErr;
BOOL fSuccess;
LPTSTR lpszPipename = TEXT("\\\\.\\pipe\\mynamedpipe");
for (i = 0; i < INSTANCES; i++)
{
hEvents[i] = CreateEvent(NULL, TRUE, TRUE, NULL);
Pipe[i].oOverlap.hEvent = hEvents[i];
Pipe[i].hPipeInst = CreateNamedPipe(lpszPipename, PIPE_ACCESS_DUPLEX|FILE_FLAG_OVERLAPPED,
PIPE_TYPE_MESSAGE|PIPE_READMODE_MESSAGE|PIPE_WAIT, INSTANCES,
BUFSIZE*sizeof(TCHAR), BUFSIZE*sizeof(TCHAR), PIPE_TIMEOUT, NULL);
if (Pipe[i].hPipeInst == INVALID_HANDLE_VALUE)
{
printf("CreateNamedPipe failed with %d.\n", GetLastError());
return 0;
}
Pipe[i].fPendingIO = ConnectToNewClient(Pipe[i].hPipeInst, &Pipe[i].oOverlap);
Pipe[i].dwState = Pipe[i].fPendingIO ? CONNECTING_STATE : READING_STATE;
}
while (1)
{
dwWait = WaitForMultipleObjects(INSTANCES, hEvents, FALSE, INFINITE);
i = dwWait - WAIT_OBJECT_0; // determines which pipe
if (i < 0 || i > (INSTANCES - 1))
{
printf("Index out of range.\n");
return 0;
}
if (Pipe[i].fPendingIO)
{
fSuccess = GetOverlappedResult(Pipe[i].hPipeInst, &Pipe[i].oOverlap, &cbRet, FALSE);
DWORD lasterror = GetLastError();
switch (Pipe[i].dwState)
{
case CONNECTING_STATE:
if (! fSuccess)
{
printf("Error %d.\n", GetLastError());
return 0;
}
Pipe[i].dwState = READING_STATE;
Pipe[i].cbReadSoFar = 0;
break;
case READING_STATE:
if(ERROR_MORE_DATA == lasterror)
{
Pipe[i].cbReadSoFar += cbRet;
break;
}
if(ERROR_IO_PENDING == lasterror)
{
continue;
}
if (! fSuccess || cbRet == 0)
{
DisconnectAndReconnect(i);
continue;
}
Pipe[i].cbRead = cbRet;
Pipe[i].cbReadSoFar = 0;
printf("Message received: %s\n", Pipe[i].chRequest);
break;
default:
{
printf("Invalid pipe state.\n");
return 0;
}
}
}
switch (Pipe[i].dwState)
{
case READING_STATE:
fSuccess = ReadFile(
Pipe[i].hPipeInst,
Pipe[i].chRequest + Pipe[i].cbReadSoFar,
BUFSIZE*sizeof(TCHAR),
&Pipe[i].cbRead,
&Pipe[i].oOverlap);
dwErr = GetLastError();
if (! fSuccess && (dwErr == ERROR_IO_PENDING))
{
Pipe[i].fPendingIO = TRUE;
continue;
}
if(!fSuccess && dwErr == ERROR_MORE_DATA)
{
Pipe[i].cbReadSoFar += Pipe[i].cbRead;
continue;
}
if (fSuccess && Pipe[i].cbRead != 0)
{
Pipe[i].fPendingIO = FALSE;
Pipe[i].cbReadSoFar = 0;
//Log the message.
printf("Message received: %s\n", Pipe[i].chRequest);
continue;
}
// An error occurred; disconnect from the client.
DisconnectAndReconnect(i);
break;
default:
{
printf("Invalid pipe state.\n");
return 0;
}
}
}
return 0;
}
VOID DisconnectAndReconnect(DWORD i)
{
if (! DisconnectNamedPipe(Pipe[i].hPipeInst) )
{
printf("DisconnectNamedPipe failed with %d.\n", GetLastError());
}
Pipe[i].fPendingIO = ConnectToNewClient(
Pipe[i].hPipeInst,
&Pipe[i].oOverlap);
Pipe[i].dwState = Pipe[i].fPendingIO ?
CONNECTING_STATE : // still connecting
READING_STATE; // ready to read
}
BOOL ConnectToNewClient(HANDLE hPipe, LPOVERLAPPED lpo)
{
BOOL fConnected, fPendingIO = FALSE;
fConnected = ConnectNamedPipe(hPipe, lpo);
if (fConnected)
{
printf("ConnectNamedPipe failed with %d.\n", GetLastError());
return 0;
}
switch (GetLastError())
{
case ERROR_IO_PENDING:
fPendingIO = TRUE;
break;
case ERROR_PIPE_CONNECTED:
if (SetEvent(lpo->hEvent))
break;
default:
{
printf("ConnectNamedPipe failed with %d.\n", GetLastError());
return 0;
}
}
return fPendingIO;
}
VOID GetAnswerToRequest(LPPIPEINST pipe)
{
_tprintf( TEXT("[%d] %s\n"), pipe->hPipeInst, pipe->chRequest);
StringCchCopy( pipe->chReply, BUFSIZE, TEXT("Default answer from server") );
pipe->cbToWrite = (lstrlen(pipe->chReply)+1)*sizeof(TCHAR);
}
And client code is
//file: client.cpp
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#define BUFSIZE 512
#define NUM_MESSAGE 4
int _tmain(int argc, TCHAR *argv[])
{
HANDLE hPipe;
LPTSTR lpvMessage=TEXT("Default message from the client.");
TCHAR chBuf[NUM_MESSAGE+1][BUFSIZE];
BOOL fSuccess = FALSE;
DWORD cbRead, cbToWrite, cbWritten, dwMode;
LPTSTR lpszPipename = TEXT("\\\\.\\pipe\\mynamedpipe");
while (1)
{
hPipe = CreateFile(lpszPipename, GENERIC_READ|GENERIC_WRITE,
0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);
if (hPipe != INVALID_HANDLE_VALUE)
break;
if (GetLastError() != ERROR_PIPE_BUSY)
{
_tprintf( TEXT("Could not open pipe. GLE=%d\n"), GetLastError() );
return -1;
}
if ( ! WaitNamedPipe(lpszPipename, 20000))
{
printf("Could not open pipe: 20 second wait timed out.");
return -1;
}
}
dwMode = PIPE_READMODE_MESSAGE;
fSuccess = SetNamedPipeHandleState(hPipe, &dwMode, NULL, NULL);
if (!fSuccess)
{
_tprintf(TEXT("SetNamedPipeHandleState failed. GLE=%d\n"), GetLastError());
return -1;
}
cbToWrite = (lstrlen(lpvMessage)+1)*sizeof(TCHAR);
_tprintf( TEXT("Sending %d byte message: \"%s\"\n"), cbToWrite, lpvMessage);
OVERLAPPED woverlapped[NUM_MESSAGE];
HANDLE wevent[NUM_MESSAGE];
memset(woverlapped, 0, sizeof(woverlapped));
for(int i=0; i<NUM_MESSAGE; ++i)
{
wevent[i] = CreateEvent(NULL, 0, 0, NULL);
woverlapped[i].hEvent = wevent[i];
}
const int retrycount = NUM_MESSAGE;
int numberofsend = retrycount;
wretry:
cbToWrite = _stprintf(chBuf[retrycount-numberofsend], TEXT("Message %d from Client"), retrycount - numberofsend + 1);
cbToWrite *= sizeof(TCHAR);
fSuccess = WriteFile(hPipe, chBuf[retrycount-numberofsend], cbToWrite,
&cbWritten, &woverlapped[retrycount-numberofsend]);
--numberofsend;
if(!fSuccess)
{
_tprintf( TEXT("WriteFile to pipe failed. GLE=%d\n"), GetLastError() );
//return -1;
if(GetLastError() != ERROR_IO_PENDING)
return -1;
}
if(numberofsend)
goto wretry;
bool wait = true;
while(wait)
{
DWORD retval = WaitForMultipleObjects(NUM_MESSAGE, wevent, FALSE, INFINITE);
retval -= WAIT_OBJECT_0;
DWORD cbret;
DWORD success = ::GetOverlappedResult(hPipe, &woverlapped[retval], &cbret, FALSE);
DWORD laserr = ::GetLastError();
++numberofsend;
if(numberofsend == retrycount)
wait = false;
}
CloseHandle(hPipe);
return 0;
}
Am I doing anything wrong at server end in such case? Or is it expected?
回答1:
To quote MSDN:
If a named pipe is being read in message mode and the next message is longer than the nNumberOfBytesToRead parameter specifies, ReadFile returns FALSE and GetLastError returns ERROR_MORE_DATA. The remainder of the message can be read by a subsequent call to the ReadFile or PeekNamedPipefunction.
来源：https://stackoverflow.com/questions/23101729/multiple-writefile-after-error-io-pending