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83ff08f9db
This fixes a load-time failure on versions of Windows too old to have that function in kernel32.dll. We use it to determine whether a file was safe to overwrite in the context of PuTTY session logging: if it's safe, we skip the 'do you want to overwrite or append?' dialog box. On earlier Windows you can use FindFirstFile to get a similar effect, so that's what we fall back to. It's not quite the same, though - if you pass a wildcard then it will succeed when you'd rather it had failed. But it's good enough to at least work in normal cases.
77 lines
2.7 KiB
C
77 lines
2.7 KiB
C
/*
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* Implementation of open_for_write_would_lose_data for Windows.
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*/
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#include "putty.h"
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/*
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* This is slightly fiddly because we want to be backwards-compatible
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* with systems too old to have GetFileAttributesEx. The next best
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* thing is FindFirstFile, which will return a different data
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* structure, but one that also contains the fields we want. (But it
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* will behave more unhelpfully - for this application - in the
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* presence of wildcards, so we'd prefer to use GFAE if we can.)
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*/
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static inline bool open_for_write_would_lose_data_impl(
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DWORD dwFileAttributes, DWORD nFileSizeHigh, DWORD nFileSizeLow)
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{
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if (dwFileAttributes & (FILE_ATTRIBUTE_DEVICE|FILE_ATTRIBUTE_DIRECTORY)) {
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/*
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* File is something other than an ordinary disk file, so
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* opening it for writing will not cause truncation. (It may
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* not _succeed_ either, but that's not our problem here!)
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*/
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return false;
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}
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if (nFileSizeHigh == 0 && nFileSizeLow == 0) {
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/*
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* File is zero-length (or may be a named pipe, which
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* dwFileAttributes can't tell apart from a regular file), so
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* opening it for writing won't truncate any data away because
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* there's nothing to truncate anyway.
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*/
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return false;
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}
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return true;
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}
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bool open_for_write_would_lose_data(const Filename *fn)
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{
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static HMODULE kernel32_module;
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DECL_WINDOWS_FUNCTION(static, BOOL, GetFileAttributesExA,
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(LPCSTR, GET_FILEEX_INFO_LEVELS, LPVOID));
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if (!kernel32_module) {
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kernel32_module = load_system32_dll("kernel32.dll");
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GET_WINDOWS_FUNCTION(kernel32_module, GetFileAttributesExA);
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}
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if (p_GetFileAttributesExA) {
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WIN32_FILE_ATTRIBUTE_DATA attrs;
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if (!p_GetFileAttributesExA(fn->path, GetFileExInfoStandard, &attrs)) {
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/*
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* Generally, if we don't identify a specific reason why we
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* should return true from this function, we return false, and
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* let the subsequent attempt to open the file for real give a
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* more useful error message.
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*/
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return false;
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}
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return open_for_write_would_lose_data_impl(
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attrs.dwFileAttributes, attrs.nFileSizeHigh, attrs.nFileSizeLow);
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} else {
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WIN32_FIND_DATA fd;
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HANDLE h = FindFirstFile(fn->path, &fd);
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if (h == INVALID_HANDLE_VALUE) {
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/*
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* As above, if we can't find the file at all, return false.
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*/
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return false;
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}
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CloseHandle(h);
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return open_for_write_would_lose_data_impl(
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fd.dwFileAttributes, fd.nFileSizeHigh, fd.nFileSizeLow);
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}
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}
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