Portable file opening and exclusive node file locks

1// Copyright (c) 2017-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#include <util/fs.h>
6
7#include <util/check.h>
8#include <util/syserror.h>
9
10#include <cerrno>
11#include <string>
12
13#ifndef WIN32
14#include <fcntl.h>
15#include <unistd.h>
16#else
17#include <limits>
18#include <windows.h>
19#endif
20
21namespace fsbridge {
22
23FILE *fopen(const fs::path& p, const char *mode)
24{
25#ifndef WIN32
26    return ::fopen(p.c_str(), mode);
27#else
28    return ::fopen(p.utf8string().c_str(), mode);
29#endif
30}
31
32fs::path AbsPathJoin(const fs::path& base, const fs::path& path)
33{
34    assert(base.is_absolute());
35    return path.empty() ? base : fs::path(base / path);
36}
37
38#ifndef WIN32
39
40static std::string GetErrorReason()
41{
42    return SysErrorString(errno);
43}
44
45FileLock::FileLock(const fs::path& file)
46{
47    fd = open(file.c_str(), O_RDWR);
48    if (fd == -1) {
49        reason = GetErrorReason();
50    }
51}
52
53FileLock::~FileLock()
54{
55    if (fd != -1) {
56        close(fd);
57    }
58}
59
60bool FileLock::TryLock()
61{
62    if (fd == -1) {
63        return false;
64    }
65
66    struct flock lock;
67    lock.l_type = F_WRLCK;
68    lock.l_whence = SEEK_SET;
69    lock.l_start = 0;
70    lock.l_len = 0;
71    if (fcntl(fd, F_SETLK, &lock) == -1) {
72        reason = GetErrorReason();
73        return false;
74    }
75
76    return true;
77}
78#else
79
80static std::string GetErrorReason() {
81    return Win32ErrorString(GetLastError());
82}
83
84FileLock::FileLock(const fs::path& file)
85{
86    hFile = CreateFileW(file.wstring().c_str(),  GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
87        nullptr, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
88    if (hFile == INVALID_HANDLE_VALUE) {
89        reason = GetErrorReason();
90    }
91}
92
93FileLock::~FileLock()
94{
95    if (hFile != INVALID_HANDLE_VALUE) {
96        CloseHandle(hFile);
97    }
98}
99
100bool FileLock::TryLock()
101{
102    if (hFile == INVALID_HANDLE_VALUE) {
103        return false;
104    }
105    _OVERLAPPED overlapped = {};
106    if (!LockFileEx(hFile, LOCKFILE_EXCLUSIVE_LOCK | LOCKFILE_FAIL_IMMEDIATELY, 0, std::numeric_limits<DWORD>::max(), std::numeric_limits<DWORD>::max(), &overlapped)) {
107        reason = GetErrorReason();
108        return false;
109    }
110    return true;
111}
112#endif
113
114} // namespace fsbridge
115