I am trying to download an image onto the user's desktop from a URL using Win32. I have taken care of all the HTTP request stuff and know for a fact that it is all working well. When I go to call CreateFile() the Visual Studios debugger just says "Exception: Application.exe has triggered a breakpoint" and that it will resume on the CreateFile() line. Also there is an error code "Critical error detected c0000374"
Here is my code:
VARIANT varResponse;
VariantInit(&varResponse);
...
hr = pIWinHttpRequest->get_ResponseBody(&varResponse);
...
if (SUCCEEDED(hr)) {
long upperBounds;
long lowerBounds;
unsigned char* buff;
//Make sure that varResponse is an array of unsigned bytes
if (varResponse.vt == (VT_ARRAY | VT_UI1)) {
long Dims = SafeArrayGetDim(varResponse.parray);
//It should only have one dimension
if (Dims == 1) {
//Get Array lower and upper bounds
SafeArrayGetLBound(varResponse.parray, 1, &lowerBounds);
SafeArrayGetUBound(varResponse.parray, 1, &upperBounds);
upperBounds++;
SafeArrayAccessData(varResponse.parray, (void**)&buff);
HANDLE hFile;
DWORD dwBytesWritten;
PWSTR filepath[MAX_PATH];
HRESULT hr = SHGetKnownFolderPath(FOLDERID_Desktop, 0, NULL, &*filepath);
if (SUCCEEDED(hr)) {
//PathCombine(filepathForImage, filepathToDesktop, L"\\todaysDailyImage.jpg");
PathAppend(*filepath, L"todaysDailyImage.jpg");
MessageBox(NULL, *filepath, L"Check if filepath works", MB_OK);
}
hFile = CreateFile(*filepath, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile == INVALID_HANDLE_VALUE) {
//File failed
}
else {
WriteFile(hFile, buff, upperBounds - lowerBounds, &dwBytesWritten, NULL);
//File was written
}
CloseHandle(hFile);
CoTaskMemFree(filepath);
SafeArrayUnaccessData(varResponse.parray);
MessageBox(NULL, L"Everything was cleaned up", L"Update:", MB_OK);
}
}
}
Am I doing anything wrong?
The way you are using filepath is all wrong.
You are declaring it as an array of MAX_PATH (260) number of PWSTR pointers.
When you refer to an array by its name alone, you end up with a pointer to the 1st element of the array. So, &*filepath is the same as &*(&filepath[0]), which is effectively &filepath[0]. And *filepath is the same as *(&filepath[0]), which is effectively filepath[0]. So, as far as SHGetKnownFolderPath() and MessageBox() are concerned, they are only operating on the 1st PWSTR pointer in the array, and the other 259 array elements are ignored. That part is ok, but wasteful.
However, PathAppend() requires a destination buffer that is an array of MAX_PATH number of WCHAR elements. You are appending to the WCHAR[] array that SHGetKnownFolderPath() allocates as its output, which is not large enough to hold the filename you are trying to append to it. So, you are triggering errors because you are trying to modify memory that hasn’t been allocated to hold that modification.
You don’t need the PWSTR array at all. Try something more like this instead:
PWSTR folderpath;
HRESULT hr = SHGetKnownFolderPath(FOLDERID_Desktop, 0, NULL, &folderpath);
if (FAILED(hr)) {
// ...
}
else {
PWSTR filepath;
hr = PathAllocCombine(folderpath, L"todaysDailyImage.jpg", 0, &filepath);
if (FAIlED(hr)) {
// ...
}
else {
MessageBoxW(NULL, filepath, L"Check if filepath works", MB_OK);
hFile = CreateFileW(filepath, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile == INVALID_HANDLE_VALUE) {
//File failed
}
else {
WriteFile(hFile, buff, upperBounds - lowerBounds, &dwBytesWritten, NULL);
//File was written
CloseHandle(hFile);
}
LocalFree(filepath);
}
CoTaskMemFree(folderpath);
}
I want to implement digital signature app using CryptVerifySignature. I've written this code(with help of MSDN example):
#define Check(condition, message) if (!(condition)) { fprintf(stderr, "%s\n", message); goto Exit; };
void DigSign(const char* inputFileName, const char* signFileName)
{
HCRYPTPROV hProv;
BYTE *pbBuffer= NULL;
DWORD dwBufferLen = 0;
HCRYPTHASH hHash;
HCRYPTKEY hKey;
HCRYPTKEY hPubKey;
BYTE *pbKeyBlob;
BYTE *pbSignature;
DWORD dwSigLen;
DWORD dwBlobLen;
FILE* inputFile = NULL;
Check((inputFile = fopen(inputFileName, "r")) != NULL, "File does not exists");
dwBufferLen = GetFileSize(inputFile);
Check(pbBuffer = (BYTE*)malloc(dwBufferLen + 1), "cannot allocate memory");
fread(pbBuffer, 1, dwBufferLen, inputFile);
pbBuffer[dwBufferLen] = '\0';
fclose(inputFile);
//-------------------------------------------------------------------
// Acquire a cryptographic provider context handle.
Check(CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0), "Error during CryptAcquireContext.");
if(!CryptGetUserKey(hProv, AT_SIGNATURE, &hKey))
{
if(NTE_NO_KEY == GetLastError())
{
Check(CryptGenKey(hProv, AT_SIGNATURE, CRYPT_EXPORTABLE, &hKey), "Could not create a user public key.\n");
}
else
{
goto Exit;
}
}
Check(CryptExportKey(hKey, NULL, PUBLICKEYBLOB, 0, NULL, &dwBlobLen), "Error computing BLOB length.");
Check(pbKeyBlob = (BYTE*)malloc(dwBlobLen), "Out of memory. \n");
Check(CryptExportKey(hKey, NULL, PUBLICKEYBLOB, 0, pbKeyBlob, &dwBlobLen), "Error during CryptExportKey.");
//-------------------------------------------------------------------
// Create the hash object.
Check(CryptCreateHash(hProv, CALG_SHA, 0, 0, &hHash), "Error during CryptCreateHash.");
//-------------------------------------------------------------------
// Compute the cryptographic hash of the buffer.
Check(CryptHashData(hHash, pbBuffer, dwBufferLen, 0), "Error during CryptHashData.");
//-------------------------------------------------------------------
// Determine the size of the signature and allocate memory.
dwSigLen= 0;
Check(CryptSignHash(hHash, AT_SIGNATURE, NULL, 0, NULL, &dwSigLen), "Error during CryptSignHash.");
//-------------------------------------------------------------------
// Allocate memory for the signature buffer.
Check(pbSignature = (BYTE *)malloc(dwSigLen), "Out of memory.");
//-------------------------------------------------------------------
// Sign the hash object.
Check(CryptSignHash(hHash, AT_SIGNATURE, NULL, 0, pbSignature, &dwSigLen), "Error during CryptSignHash.");
FILE* f = fopen(signFileName, "w");
fwrite(pbSignature, dwSigLen, 1, f);
printf("W: %.128s\n", pbSignature);
fwrite(pbKeyBlob, dwBlobLen, 1, f);
printf("W: %.148s\n", pbKeyBlob);
fclose(f);
//-------------------------------------------------------------------
// Destroy the hash object.
if(hHash)
CryptDestroyHash(hHash);
free(pbSignature);
free(pbKeyBlob);
if(hProv)
CryptReleaseContext(hProv, 0);
Exit:;
}
bool CheckDigSign(const char* inputFileName, const char* signFileName, const char* userName)
{
bool result = false;
HCRYPTPROV hProv;
BYTE *pbBuffer= (BYTE *)"The data that is to be hashed and signed.";
DWORD dwBufferLen = strlen((char *)pbBuffer)+1;
HCRYPTHASH hHash;
HCRYPTKEY hKey;
HCRYPTKEY hPubKey;
BYTE *pbKeyBlob;
BYTE *pbSignature;
DWORD dwSigLen;
DWORD dwBlobLen;
FILE* inputFile = NULL;
Check((inputFile = fopen(inputFileName, "r")) != NULL, "File does not exists");
dwBufferLen = GetFileSize(inputFile);
Check(pbBuffer = (BYTE*)malloc(dwBufferLen + 1), "cannot allocate memory");
fread(pbBuffer, 1, dwBufferLen, inputFile);
pbBuffer[dwBufferLen] = '\0';
fclose(inputFile);
FILE* signFile = NULL;
Check((signFile = fopen(signFileName, "r")) != NULL, "File does not exists");
DWORD dwSignFileLen = GetFileSize(signFile);
dwSigLen = 128;
pbSignature = (BYTE*)malloc(dwSigLen);
dwBlobLen = dwSignFileLen - dwSigLen;
pbKeyBlob = (BYTE*)malloc(dwBlobLen);
fread(pbSignature, 1, dwSigLen, signFile);
fread(pbKeyBlob, 1, dwBlobLen, signFile);
fclose(signFile);
printf("R: %.128s\n", pbSignature);
printf("R: %.148s\n", pbKeyBlob);
Check(CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0), "Error during CryptAcquireContext.");
Check(CryptImportKey(hProv, pbKeyBlob, dwBlobLen, 0, 0, &hPubKey), "Public key import failed.");
//-------------------------------------------------------------------
// Create a new hash object.
Check(CryptCreateHash(hProv, CALG_SHA, 0, 0, &hHash), "Error during CryptCreateHash.");
//-------------------------------------------------------------------
// Compute the cryptographic hash of the buffer.
Check(CryptHashData(hHash, pbBuffer, dwBufferLen, 0), "Error during CryptHashData.");
//-------------------------------------------------------------------
// Validate the digital signature.
result = CryptVerifySignature(hHash, pbSignature, dwSigLen, hPubKey, NULL, 0);
printf("%u %x", GetLastError(), GetLastError());
//-------------------------------------------------------------------
// Free memory to be used to store signature.
if(pbSignature)
free(pbSignature);
//-------------------------------------------------------------------
// Destroy the hash object.
if(hHash)
CryptDestroyHash(hHash);
//-------------------------------------------------------------------
// Release the provider handle.
if(hProv)
CryptReleaseContext(hProv, 0);
Exit:
return result;
}
int _tmain(int argc, _TCHAR* argv[])
{
DigSign("test3.txt", "test.sig");
printf("TEST: %u\n", CheckDigSign("test3.txt", "test.sig", ""));
}
DigSign function must sign content of file and write signature and public key to another file. CheckSign must return true if sign is right. But I don't understand why my code doesn't work. CheckDigSign in _tmain must return true, but it returns false. Can anybody help me pls?
I took your entire code sample, hacked it up a little, and used CreateFile, ReadFile, and WriteFile for all the file I/O. It works. The signature file with the appended public key checked against the source file just fine.
I therefore suspect it is the method of reading/writing your files, and specifically, the "w" and "r" vs. "wb" and "rb" that is horking over your bytes. Try changing those and see what you come up with.
For reference, the modified code is below, and there is NO error checking in the changes I made, so DON'T use this for anything special as it is literally worth less than the paper its printed on (i.e. nothing).
#define Check(condition, message) if (!(condition)) { fprintf(stderr, "%s\n", message); goto Exit; };
void DigSign(const char* inputFileName, const char* signFileName)
{
HCRYPTPROV hProv;
BYTE *pbBuffer= NULL;
DWORD dwBufferLen = 0;
HCRYPTHASH hHash;
HCRYPTKEY hKey;
BYTE *pbKeyBlob;
BYTE *pbSignature;
DWORD dwSigLen;
DWORD dwBlobLen;
FILE* inputFile = NULL;
HANDLE hFileInput = CreateFile(inputFileName, // file to open
GENERIC_READ, // open for reading
FILE_SHARE_READ, // share for reading
NULL, // default security
OPEN_EXISTING, // existing file only
FILE_ATTRIBUTE_NORMAL, // normal file
NULL);
dwBufferLen = GetFileSize(hFileInput, NULL);
Check(pbBuffer = (BYTE*)malloc(dwBufferLen + 1), "cannot allocate memory");
DWORD dwBytesRead = 0L;
ReadFile(hFileInput, pbBuffer, dwBufferLen, &dwBytesRead, NULL);
pbBuffer[dwBufferLen] = 0;
CloseHandle(hFileInput);
//-------------------------------------------------------------------
// Acquire a cryptographic provider context handle.
Check(CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0), "Error during CryptAcquireContext.");
if(!CryptGetUserKey(hProv, AT_SIGNATURE, &hKey))
{
if(NTE_NO_KEY == GetLastError())
{
Check(CryptGenKey(hProv, AT_SIGNATURE, CRYPT_EXPORTABLE, &hKey), "Could not create a user public key.\n");
}
else
{
goto Exit;
}
}
Check(CryptExportKey(hKey, NULL, PUBLICKEYBLOB, 0, NULL, &dwBlobLen), "Error computing BLOB length.");
Check(pbKeyBlob = (BYTE*)malloc(dwBlobLen), "Out of memory. \n");
Check(CryptExportKey(hKey, NULL, PUBLICKEYBLOB, 0, pbKeyBlob, &dwBlobLen), "Error during CryptExportKey.");
//-------------------------------------------------------------------
// Create the hash object.
Check(CryptCreateHash(hProv, CALG_SHA, 0, 0, &hHash), "Error during CryptCreateHash.");
//-------------------------------------------------------------------
// Compute the cryptographic hash of the buffer.
Check(CryptHashData(hHash, pbBuffer, dwBufferLen, 0), "Error during CryptHashData.");
//-------------------------------------------------------------------
// Determine the size of the signature and allocate memory.
dwSigLen= 0;
Check(CryptSignHash(hHash, AT_SIGNATURE, NULL, 0, NULL, &dwSigLen), "Error during CryptSignHash.");
//-------------------------------------------------------------------
// Allocate memory for the signature buffer.
Check(pbSignature = (BYTE *)malloc(dwSigLen), "Out of memory.");
//-------------------------------------------------------------------
// Sign the hash object.
Check(CryptSignHash(hHash, AT_SIGNATURE, NULL, 0, pbSignature, &dwSigLen), "Error during CryptSignHash.");
HANDLE hFileSign = CreateFile(signFileName, // name of the write
GENERIC_WRITE, // open for writing
0, // do not share
NULL, // default security
CREATE_NEW, // create new file only
FILE_ATTRIBUTE_NORMAL, // normal file
NULL); // no attr. template
DWORD dwBytesWritten = 0;
WriteFile(hFileSign, pbSignature, dwSigLen, &dwBytesWritten, NULL);
WriteFile(hFileSign, pbKeyBlob, dwBlobLen, &dwBytesWritten, NULL);
CloseHandle(hFileSign);
printf("W: %.128s\n", pbSignature);
printf("W: %.148s\n", pbKeyBlob);
//-------------------------------------------------------------------
// Destroy the hash object.
if(hHash)
CryptDestroyHash(hHash);
free(pbSignature);
free(pbKeyBlob);
if(hProv)
CryptReleaseContext(hProv, 0);
Exit:;
}
bool CheckDigSign(const char* inputFileName, const char* signFileName, const char* userName)
{
BOOL result = false;
HCRYPTPROV hProv;
BYTE *pbBuffer= (BYTE *)"The data that is to be hashed and signed.";
DWORD dwBufferLen = strlen((char *)pbBuffer)+1;
HCRYPTHASH hHash;
HCRYPTKEY hPubKey;
BYTE *pbKeyBlob;
BYTE *pbSignature;
DWORD dwSigLen;
DWORD dwBlobLen;
HANDLE hFileInput = CreateFile(inputFileName, // file to open
GENERIC_READ, // open for reading
FILE_SHARE_READ, // share for reading
NULL, // default security
OPEN_EXISTING, // existing file only
FILE_ATTRIBUTE_NORMAL, // normal file
NULL);
dwBufferLen = GetFileSize(hFileInput, NULL);
Check(pbBuffer = (BYTE*)malloc(dwBufferLen + 1), "cannot allocate memory");
DWORD dwBytesRead = 0;
ReadFile(hFileInput, pbBuffer, dwBufferLen, &dwBytesRead, NULL);
pbBuffer[dwBufferLen] = 0;
CloseHandle(hFileInput);
HANDLE hFileSig = CreateFile(signFileName, // file to open
GENERIC_READ, // open for reading
FILE_SHARE_READ, // share for reading
NULL, // default security
OPEN_EXISTING, // existing file only
FILE_ATTRIBUTE_NORMAL, // normal file
NULL);
DWORD dwSignFileLen = GetFileSize(hFileSig, NULL);
dwSigLen = 128;
pbSignature = (BYTE*)malloc(dwSigLen);
dwBlobLen = dwSignFileLen - dwSigLen;
pbKeyBlob = (BYTE*)malloc(dwBlobLen);
ReadFile(hFileSig, pbSignature, dwSigLen, &dwBytesRead, NULL);
ReadFile(hFileSig, pbKeyBlob, dwBlobLen, &dwBytesRead, NULL);
CloseHandle(hFileSig);
printf("R: %.128s\n", pbSignature);
printf("R: %.148s\n", pbKeyBlob);
Check(CryptAcquireContext(&hProv, NULL, NULL, PROV_RSA_FULL, 0), "Error during CryptAcquireContext.");
Check(CryptImportKey(hProv, pbKeyBlob, dwBlobLen, 0, 0, &hPubKey), "Public key import failed.");
//-------------------------------------------------------------------
// Create a new hash object.
Check(CryptCreateHash(hProv, CALG_SHA, 0, 0, &hHash), "Error during CryptCreateHash.");
//-------------------------------------------------------------------
// Compute the cryptographic hash of the buffer.
Check(CryptHashData(hHash, pbBuffer, dwBufferLen, 0), "Error during CryptHashData.");
//-------------------------------------------------------------------
// Validate the digital signature.
result = CryptVerifySignature(hHash, pbSignature, dwSigLen, hPubKey, NULL, 0);
printf("%u %x", GetLastError(), GetLastError());
//-------------------------------------------------------------------
// Free memory to be used to store signature.
if(pbSignature)
free(pbSignature);
//-------------------------------------------------------------------
// Destroy the hash object.
if(hHash)
CryptDestroyHash(hHash);
//-------------------------------------------------------------------
// Release the provider handle.
if(hProv)
CryptReleaseContext(hProv, 0);
Exit:
return !!result;
}
int _tmain(int argc, _TCHAR* argv[])
{
if (argc == 3)
{
DigSign(argv[1], argv[2]);
printf("TEST: %u\n", CheckDigSign(argv[1], argv[2],""));
return 0;
}
return 1;
}
I try to create Named Shared Memory on win CE 6.0 but probably the process does not save the data.
I wrote two processes. The 1st writes the text to the shared memory and the 2nd reads. The 2nd show empty message window.
1st process:
#include "stdafx.h"
#include <stdlib.h>
#define BUFFSIZE 256
TCHAR szName[]=TEXT("MyFileMappingObject");
TCHAR szText[]=TEXT("Process write");
int _tmain(int argc, TCHAR *argv[], TCHAR *envp[])
{
HANDLE hMutex;
HANDLE hMapFile;
LPCTSTR pBuff;
BOOL fFirstApp = TRUE;
int rc;
// Create mutex used to share memory-mapped structure.
hMutex = CreateMutex (NULL, TRUE, TEXT ("MyFileMOWRT"));
rc = GetLastError();
if (rc == ERROR_ALREADY_EXISTS)
fFirstApp = FALSE;
else if (rc)
{
_tprintf(TEXT("rc1 (%d).\n"), GetLastError());
return 0;
}
// Wait here for ownership to ensure that the initialization is done.
// This is necessary since CreateMutex doesn’t wait.
rc = WaitForSingleObject(hMutex, 2000);
if (rc != WAIT_OBJECT_0)
{
_tprintf(TEXT("rc2 wait (%d).\n"), GetLastError());
return 0;
}
// Create a file-mapping object.
hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0,
BUFFSIZE, szName);
if (hMapFile == NULL)
{
_tprintf(TEXT("Could not create file mapping object (%d).\n"), GetLastError());
return 1;
}
else
printf("File mapping object was created\n");
// Map into memory the file-mapping object.
pBuff = (LPTSTR)MapViewOfFile(hMapFile, FILE_MAP_WRITE, 0, 0, BUFFSIZE);
if (pBuff == NULL)
{
_tprintf(TEXT("Could not map view of file (%d).\n"), GetLastError());
CloseHandle(hMapFile);
return 1;
}
else
printf("Map view of file\n");
CopyMemory((PVOID)pBuff, szText, (_tcslen(szText) * sizeof(TCHAR)));
UnmapViewOfFile(pBuff);
// Release the mutex. We need to release the mutex twice
// if we owned it when we entered the wait above. ReleaseMutex(hMutex);
ReleaseMutex(hMutex);
if (fFirstApp)
ReleaseMutex(hMutex);
CloseHandle(hMapFile);
CloseHandle(hMutex);
return 0;
}
2nd process:
#include "stdafx.h"
#include <stdlib.h>
#define BUFFSIZE 256
TCHAR szName[]=TEXT("MyFileMappingObject");
int _tmain(int argc, TCHAR *argv[], TCHAR *envp[])
{
HANDLE hMutex;
HANDLE hMapFile;
LPCTSTR pBuf;
BOOL fFirstApp = TRUE;
int rc;
// Create mutex used to share memory-mapped structure.
hMutex = CreateMutex (NULL, TRUE, TEXT ("MyFileMOWRT"));
rc = GetLastError();
if (rc == ERROR_ALREADY_EXISTS)
fFirstApp = FALSE;
else if (rc)
{
_tprintf(TEXT("rc1 (%d).\n"), GetLastError());
return 0;
}
// Wait here for ownership to ensure that the initialization is done.
// This is necessary since CreateMutex doesn’t wait.
rc = WaitForSingleObject(hMutex, 2000);
if (rc != WAIT_OBJECT_0)
{
_tprintf(TEXT("rc2 wait (%d).\n"), GetLastError());
return 0;
}
// Create a file-mapping object.
hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0,
BUFFSIZE, szName);
if (hMapFile == NULL)
{
_tprintf(TEXT("Could not create file mapping object (%d).\n"), GetLastError());
return 1;
}
else
printf("File mapping object was created\n");
pBuf = (LPTSTR) MapViewOfFile(hMapFile, FILE_MAP_READ, 0, 0, 0);
if (pBuf)
{
MessageBox(NULL, pBuf, TEXT("Process2"), MB_OK);
}
else
{
_tprintf(TEXT("Could not map view of file (%d).\n"), GetLastError());
CloseHandle(hMapFile);
return 1;
}
UnmapViewOfFile(pBuf);
// Release the mutex. We need to release the mutex twice
// if we owned it when we entered the wait above. ReleaseMutex(hMutex);
ReleaseMutex(hMutex);
if (fFirstApp)
ReleaseMutex(hMutex);
CloseHandle(hMapFile);
CloseHandle(hMutex);
return 0;
}
Program which runs processes:
#include "stdafx.h"
#include <stdlib.h>
int _tmain(int argc, TCHAR *argv[], TCHAR *envp[])
{
CreateProcess(TEXT("\\Windows\\Mutex_proces.exe"), NULL, 0,0,0,0,0,0,0,0);
CreateProcess(TEXT("\\Windows\\Mutex_proces_rd.exe"), NULL, 0,0,0,0,0,0,0,0);
return 0;
}
After you get pointer to shared memory from MapViewOfFile, your code in both processes should setup synchronized pattern for reading/writing from/to this memory so:
Process 1 - P1
creates named file mapping
gets pointer to memory
writes to memory
create named mutex,
signalize to P2 (using mutex) that it has written memory, and P2 can read it. .
P1 should wait till P2 reads shared memory, it can simply wait on mutex from point 4.
Process 2 - P2
Creates named mutex, but if it does not exists then either returns with error, or waits till P1 creates this mutex.
Create named filemapping and get pointer to its memory
Handle to mutex (from 1.) is aquired, P2 now waits until P1 signals (use WaitForSingleObject)
When signal arrives then you can read memory, after reading release mutex so that P1 can proceed with processing from point 6.
I want to make a share memory pool for all the other process to share the data, but after I read about the CreateFileMapping API document, I was confused about that it will need to specify the size of the share memory. I actually want it to be dynamic allocate and free which looks more like a service. Is there some way to do the share memory dynamic using createFileMapping or not?
Creating Named Shared Memory.
First Process
The first process creates the file mapping object by calling the CreateFileMapping function with INVALID_HANDLE_VALUE and a name for the object. By using the PAGE_READWRITE flag, the process has read/write permission to the memory through any file views that are created.
Then the process uses the file mapping object handle that CreateFileMapping returns in a call to MapViewOfFile to create a view of the file in the process address space. The MapViewOfFile function returns a pointer to the file view, pBuf. The process then uses the CopyMemory function to write a string to the view that can be accessed by other processes.
Process 1 code:
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#define BUF_SIZE 256
TCHAR szName[]=TEXT("Global\\MyFileMappingObject");
TCHAR szMsg[]=TEXT("Message from first process.");
int _tmain()
{
HANDLE hMapFile;
LPCTSTR pBuf;
hMapFile = CreateFileMapping(
INVALID_HANDLE_VALUE, // use paging file
NULL, // default security
PAGE_READWRITE, // read/write access
0, // maximum object size (high-order DWORD)
BUF_SIZE, // maximum object size (low-order DWORD)
szName); // name of mapping object
if (hMapFile == NULL)
{
_tprintf(TEXT("Could not create file mapping object (%d).\n"),
GetLastError());
return 1;
}
pBuf = (LPTSTR) MapViewOfFile(hMapFile, // handle to map object
FILE_MAP_ALL_ACCESS, // read/write permission
0,
0,
BUF_SIZE);
if (pBuf == NULL)
{
_tprintf(TEXT("Could not map view of file (%d).\n"),
GetLastError());
CloseHandle(hMapFile);
return 1;
}
CopyMemory((PVOID)pBuf, szMsg, (_tcslen(szMsg) * sizeof(TCHAR)));
_getch();
UnmapViewOfFile(pBuf);
CloseHandle(hMapFile);
return 0;
}
Second Process
A second process can access the string written to the shared memory by the first process by calling the OpenFileMapping function specifying the same name for the mapping object as the first process. Then it can use the MapViewOfFile function to obtain a pointer to the file view, pBuf. The process can display this string as it would any other string. In this example, the message box displayed contains the message "Message from first process" that was written by the first process.
Process 2 code:
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <tchar.h>
#pragma comment(lib, "user32.lib")
#define BUF_SIZE 256
TCHAR szName[]=TEXT("Global\\MyFileMappingObject");
int _tmain()
{
HANDLE hMapFile;
LPCTSTR pBuf;
hMapFile = OpenFileMapping(
FILE_MAP_ALL_ACCESS, // read/write access
FALSE, // do not inherit the name
szName); // name of mapping object
if (hMapFile == NULL)
{
_tprintf(TEXT("Could not open file mapping object (%d).\n"),
GetLastError());
return 1;
}
pBuf = (LPTSTR) MapViewOfFile(hMapFile, // handle to map object
FILE_MAP_ALL_ACCESS, // read/write permission
0,
0,
BUF_SIZE);
if (pBuf == NULL)
{
_tprintf(TEXT("Could not map view of file (%d).\n"),
GetLastError());
CloseHandle(hMapFile);
return 1;
}
MessageBox(NULL, pBuf, TEXT("Process2"), MB_OK);
UnmapViewOfFile(pBuf);
CloseHandle(hMapFile);
return 0;
}
Source : http://msdn.microsoft.com/en-us/library/windows/desktop/aa366551(v=vs.85).aspx
I have this function which gives the full file name(path) from the file handle. The only problem is CreateFileMapping fails for directory handles. Is there a workaround for it?
I get the handle using NtCreateFile()
ULONG status = NtCreatefile(&f, GENERIC_ALL, &oa, iosb, NULL, FILE_ATTRIBUTE_NORMAL, FILE_SHARE_READ | FILE_SHARE_WRITE, FILE_OPEN, FILE_OPEN_BY_FILE_ID , NULL, 0);
printf("status: %X, handle: %x\n", status, f);
AND
BOOL CHouseKeeper::GetFileNameFromHandle(HANDLE hFile)
{
BOOL bSuccess = FALSE;
TCHAR pszFilename[MAX_PATH+1];
HANDLE hFileMap;
// Get the file size.
DWORD dwFileSizeHi = 0;
DWORD dwFileSizeLo = GetFileSize(hFile, &dwFileSizeHi);
if( dwFileSizeLo == 0 && dwFileSizeHi == 0 )
{
_tprintf(TEXT("Cannot map a file with a length of zero.\n"));
return FALSE;
}
// Create a file mapping object.
//It fails here if a directory handle is passed, it returns 0
hFileMap = CreateFileMapping(hFile,
NULL,
PAGE_READONLY,
0,
1,
NULL);
if (hFileMap)
{
// Create a file mapping to get the file name.
void* pMem = MapViewOfFile(hFileMap, FILE_MAP_READ, 0, 0, 1);
if (pMem)
{
if (GetMappedFileName (GetCurrentProcess(),
pMem,
pszFilename,
MAX_PATH))
{
// Translate path with device name to drive letters.
TCHAR szTemp[BUFSIZE];
szTemp[0] = '\0';
if (GetLogicalDriveStrings(BUFSIZE-1, szTemp))
{
TCHAR szName[MAX_PATH];
TCHAR szDrive[3] = TEXT(" :");
BOOL bFound = FALSE;
TCHAR* p = szTemp;
do
{
// Copy the drive letter to the template string
*szDrive = *p;
// Look up each device name
if (QueryDosDevice(szDrive, szName, MAX_PATH))
{
size_t uNameLen = _tcslen(szName);
if (uNameLen < MAX_PATH)
{
bFound = _tcsnicmp(pszFilename, szName, uNameLen) == 0
&& *(pszFilename + uNameLen) == _T('\\');
if (bFound)
{
// Reconstruct pszFilename using szTempFile
// Replace device path with DOS path
TCHAR szTempFile[MAX_PATH];
StringCchPrintf(szTempFile,
MAX_PATH,
TEXT("%s%s"),
szDrive,
pszFilename+uNameLen);
StringCchCopyN(pszFilename, MAX_PATH+1, szTempFile, _tcslen(szTempFile));
}
}
}
// Go to the next NULL character.
while (*p++);
} while (!bFound && *p); // end of string
}
}
bSuccess = TRUE;
UnmapViewOfFile(pMem);
}
CloseHandle(hFileMap);
}else {
wcout<<GetLastError()<<endl;
}
_tprintf(TEXT("File name is %s\n"), pszFilename);
return(bSuccess);
}
You can use NtQueryInformationFile with FileNameInformation to retrieve the name associated with a file handle.