I need to send file from my directory to user. The problem file was not send.
Can any one help me?
My code is like:
CHttpServerContext* pCtxt;
// ... there i set headers for open
DWORD dwRead;
CString fileName = "c:\txt.doc";
HANDLE hFile = CreateFile (fileName, GENERIC_READ, FILE_SHARE_READ,
(LPSECURITY_ATTRIBUTES) NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_READONLY, (HANDLE) NULL);
if (hFile == INVALID_HANDLE_VALUE)
{
return;
}
int c = 0;
CHAR szBuffer [2048];
do
{
if (c++ > 20) {
break;
return;
}
// read chunk of the file
if (!ReadFile (hFile, szBuffer, 2048, &dwRead, NULL))
{
return;
}
if (!dwRead)
// EOF reached, bail out
break;
// Send binary chunk to the browser
if (!pCtxt->WriteClient( szBuffer, &dwRead, 0))
{
return;
}
}
while (1);
CloseHandle (hFile);
}
Doctor, I'm sick. What's wrong with me?
I mean, you give almost no information about what happened.
Do you know if some function returned you an error in your code?
Why do you abort the loop after 20 iterations? This limits you to 40KB.
How exactly do you initialize CHttpServerContext?
You might use high-performance TransmitFile function if you just send the file as-is.
What is your client? How do you know it didn't get the file?
No point in re-inventing the wheel - just use the TransmitFile API instead - it is built into CHttpServerContent::TransmitFile().
Related
Can someone tell me what is wrong with my code?
I am trying to download a file from the internet using WinInet. The function connects to the target site just fine, I don't understand why this code isn't working. Can anyone help me out?
Here is my code:
HANDLE hFile = CreateFileW(FilePath, GENERIC_WRITE, NULL, NULL, CREATE_ALWAYS, NULL, NULL);
if (hFile != INVALID_HANDLE_VALUE || GetLastError() == ERROR_ALREADY_EXISTS)
{
CHAR Buffer[2048];
DWORD BytesRead=0, BytesToRead=0;
DWORD BytesWritten=0, BytesToWrite=0;
SetFilePointer(hFile, 0, 0, FILE_BEGIN);
do
{
if (BytesRead)
{
WriteFile(hFile, Buffer, BytesWritten, &BytesToWrite, FALSE);
}
}
while
(InternetReadFile(hRequest, (LPVOID)Buffer, BytesToRead, &BytesRead) != FALSE);
}
CloseHandle(hFile);
}
hRequest is passed to the function, it is the HINTERNET handle from HttpOpenRequestA.
Your code has some logic problems.
you are misusing GetLastError() when calling CreateFileW(). Regardless of whether the file already exists or not, CreateFileW() will not return INVALID_HANDLE if it successfully creates/opens the file. That is all you need to check for (call GetLastError() only if CreateFileW() fails and you want to find out why). also, there is no need to call SetFilePointer() at all, as CREATE_ALWAYS ensures the opened file is empty, truncating the file if it already exists and has data in it.
your do..while loop should be a while loop instead, so that InternetReadFile() is called first. There is no point in skipping WriteFile() on the first loop iteration. If you use a do..while loop, InternetReadFile() should not be used as the loop condition.
more importantly, you are breaking the loop only if InternetReadFile() fails with an error. You are expecting it to fail when it reaches the end of the response, but it actually returns TRUE and sets BytesRead to 0. This is documented behavior, which you are not handling at all:
InternetReadFile function
InternetReadFile operates much like the base ReadFile function, with a few exceptions. Typically, InternetReadFile retrieves data from an HINTERNET handle as a sequential stream of bytes. The amount of data to be read for each call to InternetReadFile is specified by the dwNumberOfBytesToRead parameter and the data is returned in the lpBuffer parameter. A normal read retrieves the specified dwNumberOfBytesToRead for each call to InternetReadFile until the end of the file is reached. To ensure all data is retrieved, an application must continue to call the InternetReadFile function until the function returns TRUE and the lpdwNumberOfBytesRead parameter equals zero. This is especially important if the requested data is written to the cache, because otherwise the cache will not be properly updated and the file downloaded will not be committed to the cache. Note that caching happens automatically unless the original request to open the data stream set the INTERNET_FLAG_NO_CACHE_WRITE flag.
ReadFile function
When a synchronous read operation reaches the end of a file, ReadFile returns TRUE and sets *lpNumberOfBytesRead to zero.
when calling WriteFile(), you are passing BytesWritten to the nNumberOfBytesToWrite parameter, but BytesWritten is never set to anything other than 0, so nothing gets written to the file. You need to pass BytesRead instead.
With that said, use something more like this:
HANDLE hFile = CreateFileW(FilePath, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_FLAG_SEQUENTIAL_SCAN, NULL);
if (hFile == INVALID_HANDLE_VALUE)
{
// handle error as needed...
}
else
{
BYTE Buffer[2048];
DWORD BytesRead, BytesWritten;
do
{
if (!InternetReadFile(hRequest, Buffer, sizeof(Buffer), &BytesRead))
{
// handle error as needed...
break;
}
if (!BytesRead)
break;
if (!WriteFile(hFile, Buffer, BytesRead, &BytesWritten, FALSE))
{
// handle error as needed...
break;
}
}
while (true);
CloseHandle(hFile);
}
MSDN even has a full example of how to use InternetReadFile():
HOWTO: Using InternetReadFile To Get File
BOOL GetFile (HINTERNET IN hOpen, // Handle from InternetOpen()
CHAR *szUrl, // Full URL
CHAR *szFileName) // Local file name
{
DWORD dwSize;
CHAR szHead[] = "Accept: */*\r\n\r\n";
VOID * szTemp[25];
HINTERNET hConnect;
FILE * pFile;
if ( !(hConnect = InternetOpenUrl ( hOpen, szUrl, szHead,
lstrlen (szHead), INTERNET_FLAG_DONT_CACHE, 0)))
{
cerr << "Error !" << endl;
return 0;
}
if ( !(pFile = fopen (szFileName, "wb" ) ) )
{
cerr << "Error !" << endl;
return FALSE;
}
do
{
// Keep coping in 25 bytes chunks, while file has any data left.
// Note: bigger buffer will greatly improve performance.
if (!InternetReadFile (hConnect, szTemp, 50, &dwSize) )
{
fclose (pFile);
cerr << "Error !" << endl;
return FALSE;
}
if (!dwSize)
break; // Condition of dwSize=0 indicate EOF. Stop.
else
fwrite(szTemp, sizeof (char), dwSize , pFile);
} // do
while (TRUE);
fflush (pFile);
fclose (pFile);
return TRUE;
}
I have the following code as part of another module that sends messages to the client. This was for IPC. Two dll's are loaded by the exe and these two need to communicate
In DLL-1 I have the following line of code as the server named pipe.
pipe = CreateNamedPipe("\\\\.\\pipe\\S2D8",PIPE_ACCESS_OUTBOUND | FILE_FLAG_OVERLAPPED /**1-way, send only with overlapped IO*/,
PIPE_TYPE_MESSAGE,1,0,0, 0, NULL);
if( INVALID_HANDLE_VALUE != pipe )
{
log("Created Named Pipe as Serverl\n");
}
else
{
log("Cannot create Named Pipe as Server\n");
}
And somewhere else in the DLL-1 I have the following for the server
bool result = ConnectNamedPipe(pipe, NULL);
if (!result)
{
CloseHandle(pipe); // close the pipe
}
else
{
DWORD numWritten;
WriteFile(pipe,KeyBoardBuffer,strlen(KeyBoardBuffer) * sizeof(char),&numWritten,0);
log("Bytes writtern to pipe:%d\n",numWritten);
}
When I look at the logs, I can see the that named pipe. Good so far.
While in DLL-2 I have the following as the client part
log("Connecting to named pipe at client\n");
if(pipe2 == NULL || pipe2 == INVALID_HANDLE_VALUE)
{
pipe2 = CreateFile("\\\\.\\pipe\\S2D8", GENERIC_READ ,
FILE_SHARE_READ | FILE_SHARE_WRITE,NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL,NULL);
if (pipe2 == INVALID_HANDLE_VALUE)
{
log("Cannot connect to named pipe at client%x\n", GetLastError());
CloseHandle(pipe2);
}
else
{
log("Connected to named pipe at client! Going to read!!!\n");
char buffer[256] = {'\0'};
DWORD numBytesRead = 0;
BOOL result = ReadFile(
pipe2,
buffer, // the data from the pipe will be put here
sizeof(buffer) * sizeof(char), // number of bytes allocated
&numBytesRead, // this will store number of bytes actually read
NULL // not using overlapped IO
);
if (result)
{
kbBuffer[numBytesRead / sizeof(char)] = '\0'; // null terminate the string
log( "Number of bytes read: %d\n",numBytesRead);
log(kbBuffer );
}
else
{
log("Failed to read data from the pipe.\n");
}
}
}
And in my logs, I can see the line "Connecting to named pipe at client" and then "Connected to named pipe at client! Going to read!!!", after that there is nothing in the log, everything seems stuck.
Is the naming convention of pipe correct? Or is there any security settings I have to define?
I am using VS2010, Win7 x64.
Any guidance is much appreciated.
You're calling the wrong method. The pipe is supposed to pre-exist, so you should be calling OpenFile(), not CreateFile().
Ah, I found the answer to the hang, I had to do a PeekNamedPipe(pipe2, NULL, 0, NULL, &bytesAvailable, NULL); and then check for the bytesAvailable to be greater than zero before I did a ReadFile()
Everytime this function is called the old text data is lost?? Tell me how to maintain previous data and appending new data.
This function is called 10 times:
void WriteEvent(LPWSTR pRenderedContent)
{
HANDLE hFile;
DWORD dwBytesToWrite = ((DWORD)wcslen(pRenderedContent)*2);
DWORD dwBytesWritten = 0;
BOOL bErrorFlag = FALSE;
printf("\n");
hFile = CreateFile(L"D:\\EventsLog.txt", FILE_ALL_ACCESS, 0, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile == INVALID_HANDLE_VALUE)
{
printf("Terminal failure: Unable to open file \"EventsLog.txt\" for write.\n");
return;
}
printf("Writing %d bytes to EventsLog.txt.\n", dwBytesToWrite);
bErrorFlag = WriteFile(
hFile, // open file handle
pRenderedContent, // start of data to write
dwBytesToWrite, // number of bytes to write
&dwBytesWritten, // number of bytes that were written
NULL); // no overlapped structure
if (FALSE == bErrorFlag)
{
printf("Terminal failure: Unable to write to file.\n");
}
else
{
if (dwBytesWritten != dwBytesToWrite)
{
printf("Error: dwBytesWritten != dwBytesToWrite\n");
}
else
{
printf("Wrote %d bytes to EventsLog.txt successfully.\n",dwBytesWritten);
}
}
CloseHandle(hFile);
}
You should pass FILE_APPEND_DATA as the dwDesiredAccess to CreateFile, as documented under File Access Rights Constants (see sample code at Appending One File to Another File). While this opens the file using the correct access rights, your code is still responsible for setting the file pointer. This is necessary, because:
Each time a file is opened, the system places the file pointer at the beginning of the file, which is offset zero.
The file pointer can be set using the SetFilePointer API after opening the file:
hFile = CreateFile( L"D:\\EventsLog.txt", FILE_APPEND_DATA, 0x0, nullptr,
OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, nullptr );
if ( hFile == INVALID_HANDLE_VALUE ) {
printf( "Terminal failure: Unable to open file \"EventsLog.txt\" for write.\n" );
return;
}
// Set the file pointer to the end-of-file:
DWORD dwMoved = ::SetFilePointer( hFile, 0l, nullptr, FILE_END );
if ( dwMoved == INVALID_SET_FILE_POINTER ) {
printf( "Terminal failure: Unable to set file pointer to end-of-file.\n" );
return;
}
printf("Writing %d bytes to EventsLog.txt.\n", dwBytesToWrite);
bErrorFlag = WriteFile( // ...
Unrelated to your question, the calculation of dwBytesToWrite should not use magic numbers. Instead of * 2 you should probably write * sizeof(*pRenderedContent). The parameter to WriteEvent should be constant as well:
WriteEvent(LPCWSTR pRenderedContent)
The parameter for appending data to a file is FILE_APPEND_DATA instead of FILE_ALL_ACCESS in the CreateFile function.
Here is an example: http://msdn.microsoft.com/en-us/library/windows/desktop/aa363778(v=vs.85).aspx
I wrote the c++ code below in order to read a file asynchronously:
#define BUF_SIZE 1024
HANDLE hFile;
DWORD NumberOfBytesRead = 0;
BYTE *buf = (BYTE*)malloc(BUF_SIZE*sizeof(BYTE));
OVERLAPPED overlapped;
overlapped.Offset = overlapped.OffsetHigh = 0;
hFile = CreateFile("C:\\Users\\Desktop\\FOO.cpp",
GENERIC_READ,
FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
FILE_FLAG_OVERLAPPED,
NULL);
if (hFile == INVALID_HANDLE_VALUE)
printf("invalid hfile\n");
int i;
i= ReadFile(hFile,
&buf,
BUF_SIZE,
&NumberOfBytesRead,
&overlapped);
if(!i && GetLastError() != ERROR_IO_PENDING)
printf ("ReadFile failed with error %d.\n", GetLastError());
else
{
WaitForSingleObject(&(overlapped.hEvent), 0);
printf("here it is %d",NumberOfBytesRead );
}
CloseHandle(hFile);
But the return value from ReadFile is 0, and the last error equals to 6.
Does anyone have any idea why? and what does 6 error code say?
Thanks!.
Maybe your problem is with OVERLAPPED structure, which you don't initialize properly.
See: "Any unused members of this structure should always be initialized to zero before the structure is used in a function call. Otherwise, the function may fail and return ERROR_INVALID_PARAMETER." in remarks here: here. You can use memset to clear all of it.
Error code 6 means invalid handle.
http://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx
Which seems odd since you check for invalid handle value. Not sure if this helped you but I might try opening the file synchronously first.
How can I make the code below to read correct text. In my text file has Hello welcome to C++, however at the end of the text, it has a new line. With the code below, my readBuffer always contains extra characters.
DWORD byteWritten;
int fileSize = 0;
//Use CreateFile to check if the file exists or not.
HANDLE hFile = CreateFile(myFile, GENERIC_READ, FILE_SHARE_READ, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if(hFile != INVALID_HANDLE_VALUE)
{
BOOL readSuccess;
DWORD byteReading;
char readBuffer[256];
readSuccess = ReadFile(hFile, readBuffer, byteReading, &byteReading, NULL);
if(readSuccess == TRUE)
{
TCHAR myBuffer[256];
mbstowcs(myBuffer, readBuffer, 256);
if(_tcscmp(myBuffer, TEXT("Hello welcome to C++")) == 0)
{
FindClose(hFile);
CloseHandle(hFile);
WriteResultFile(TRUE, TEXT("success!"));
}
}
}
Thanks,
There are a few problems:
You're passing uninitialized data (byteReading) as the "# of bytes to read" parameter to ReadFile().
Depending on how you created the file, the file's contents may not have a terminating 0 byte. The code assumes that the terminator is present.
FindClose(hFile) doesn't make sense. CloseHandle(hFile) is all you need.
You need to call CloseHandle if CreateFile() succeeds. Currently, you call it only if you find the string you're looking for.
This isn't a bug, but it's helpful to zero-initialize your buffers. That makes it easier to see in the debugger exactly how much data is being read.
HANDLE hFile = CreateFile(myfile, GENERIC_READ, FILE_SHARE_READ, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
if(hFile != INVALID_HANDLE_VALUE)
{
BOOL readSuccess;
DWORD byteReading = 255;
char readBuffer[256];
readSuccess = ReadFile(hFile, readBuffer, byteReading, &byteReading, NULL);
readBuffer[byteReading] = 0;
if(readSuccess == TRUE)
{
TCHAR myBuffer[256];
mbstowcs(myBuffer, readBuffer, 256);
if(_tcscmp(myBuffer, TEXT("Hello welcome to C++")) == 0)
{
rv = 0;
}
}
CloseHandle(hFile);
}
I see two things:
byteReading isn't initialized
you are reading bytes so you have to terminate the string by 0.
CloseHandle is sufficient
Either remove the new line character from the file or use _tcsstr for checking the existence of the string "Hello Welcome to C++".