platform_system_core/base/file.cpp

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/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "android-base/file.h"
#include <errno.h>
#include <fcntl.h>
#include <libgen.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <memory>
#include <mutex>
#include <string>
#include <vector>
#include "android-base/logging.h"
#include "android-base/macros.h" // For TEMP_FAILURE_RETRY on Darwin.
#include "android-base/unique_fd.h"
#include "android-base/utf8.h"
#if defined(__APPLE__)
#include <mach-o/dyld.h>
#endif
#if defined(_WIN32)
#include <windows.h>
#define O_CLOEXEC O_NOINHERIT
#define O_NOFOLLOW 0
#endif
namespace android {
namespace base {
// Versions of standard library APIs that support UTF-8 strings.
using namespace android::base::utf8;
bool ReadFdToString(int fd, std::string* content) {
content->clear();
// Although original we had small files in mind, this code gets used for
// very large files too, where the std::string growth heuristics might not
// be suitable. https://code.google.com/p/android/issues/detail?id=258500.
struct stat sb;
if (fstat(fd, &sb) != -1 && sb.st_size > 0) {
content->reserve(sb.st_size);
}
char buf[BUFSIZ];
ssize_t n;
while ((n = TEMP_FAILURE_RETRY(read(fd, &buf[0], sizeof(buf)))) > 0) {
content->append(buf, n);
}
return (n == 0) ? true : false;
}
bool ReadFileToString(const std::string& path, std::string* content, bool follow_symlinks) {
content->clear();
int flags = O_RDONLY | O_CLOEXEC | O_BINARY | (follow_symlinks ? 0 : O_NOFOLLOW);
android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(path.c_str(), flags)));
if (fd == -1) {
return false;
}
return ReadFdToString(fd, content);
}
bool WriteStringToFd(const std::string& content, int fd) {
const char* p = content.data();
size_t left = content.size();
while (left > 0) {
ssize_t n = TEMP_FAILURE_RETRY(write(fd, p, left));
if (n == -1) {
return false;
}
p += n;
left -= n;
}
return true;
}
static bool CleanUpAfterFailedWrite(const std::string& path) {
// Something went wrong. Let's not leave a corrupt file lying around.
int saved_errno = errno;
unlink(path.c_str());
errno = saved_errno;
return false;
}
#if !defined(_WIN32)
bool WriteStringToFile(const std::string& content, const std::string& path,
mode_t mode, uid_t owner, gid_t group,
bool follow_symlinks) {
int flags = O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_BINARY |
(follow_symlinks ? 0 : O_NOFOLLOW);
android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(path.c_str(), flags, mode)));
if (fd == -1) {
PLOG(ERROR) << "android::WriteStringToFile open failed";
return false;
}
// We do an explicit fchmod here because we assume that the caller really
// meant what they said and doesn't want the umask-influenced mode.
if (fchmod(fd, mode) == -1) {
PLOG(ERROR) << "android::WriteStringToFile fchmod failed";
return CleanUpAfterFailedWrite(path);
}
if (fchown(fd, owner, group) == -1) {
PLOG(ERROR) << "android::WriteStringToFile fchown failed";
return CleanUpAfterFailedWrite(path);
}
if (!WriteStringToFd(content, fd)) {
PLOG(ERROR) << "android::WriteStringToFile write failed";
return CleanUpAfterFailedWrite(path);
}
return true;
}
#endif
bool WriteStringToFile(const std::string& content, const std::string& path,
bool follow_symlinks) {
int flags = O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC | O_BINARY |
(follow_symlinks ? 0 : O_NOFOLLOW);
android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(path.c_str(), flags, 0666)));
if (fd == -1) {
return false;
}
return WriteStringToFd(content, fd) || CleanUpAfterFailedWrite(path);
}
bool ReadFully(int fd, void* data, size_t byte_count) {
uint8_t* p = reinterpret_cast<uint8_t*>(data);
size_t remaining = byte_count;
while (remaining > 0) {
ssize_t n = TEMP_FAILURE_RETRY(read(fd, p, remaining));
if (n <= 0) return false;
p += n;
remaining -= n;
}
return true;
}
bool WriteFully(int fd, const void* data, size_t byte_count) {
const uint8_t* p = reinterpret_cast<const uint8_t*>(data);
size_t remaining = byte_count;
while (remaining > 0) {
ssize_t n = TEMP_FAILURE_RETRY(write(fd, p, remaining));
if (n == -1) return false;
p += n;
remaining -= n;
}
return true;
}
bool RemoveFileIfExists(const std::string& path, std::string* err) {
struct stat st;
#if defined(_WIN32)
//TODO: Windows version can't handle symbol link correctly.
int result = stat(path.c_str(), &st);
bool file_type_removable = (result == 0 && S_ISREG(st.st_mode));
#else
int result = lstat(path.c_str(), &st);
bool file_type_removable = (result == 0 && (S_ISREG(st.st_mode) || S_ISLNK(st.st_mode)));
#endif
if (result == 0) {
if (!file_type_removable) {
if (err != nullptr) {
*err = "is not a regular or symbol link file";
}
return false;
}
if (unlink(path.c_str()) == -1) {
if (err != nullptr) {
*err = strerror(errno);
}
return false;
}
}
return true;
}
#if !defined(_WIN32)
bool Readlink(const std::string& path, std::string* result) {
result->clear();
// Most Linux file systems (ext2 and ext4, say) limit symbolic links to
// 4095 bytes. Since we'll copy out into the string anyway, it doesn't
// waste memory to just start there. We add 1 so that we can recognize
// whether it actually fit (rather than being truncated to 4095).
std::vector<char> buf(4095 + 1);
while (true) {
ssize_t size = readlink(path.c_str(), &buf[0], buf.size());
// Unrecoverable error?
if (size == -1) return false;
// It fit! (If size == buf.size(), it may have been truncated.)
if (static_cast<size_t>(size) < buf.size()) {
result->assign(&buf[0], size);
return true;
}
// Double our buffer and try again.
buf.resize(buf.size() * 2);
}
}
#endif
#if !defined(_WIN32)
bool Realpath(const std::string& path, std::string* result) {
result->clear();
char* realpath_buf = realpath(path.c_str(), nullptr);
if (realpath_buf == nullptr) {
return false;
}
result->assign(realpath_buf);
free(realpath_buf);
return true;
}
#endif
std::string GetExecutablePath() {
#if defined(__linux__)
std::string path;
android::base::Readlink("/proc/self/exe", &path);
return path;
#elif defined(__APPLE__)
char path[PATH_MAX + 1];
uint32_t path_len = sizeof(path);
int rc = _NSGetExecutablePath(path, &path_len);
if (rc < 0) {
std::unique_ptr<char> path_buf(new char[path_len]);
_NSGetExecutablePath(path_buf.get(), &path_len);
return path_buf.get();
}
return path;
#elif defined(_WIN32)
char path[PATH_MAX + 1];
DWORD result = GetModuleFileName(NULL, path, sizeof(path) - 1);
if (result == 0 || result == sizeof(path) - 1) return "";
path[PATH_MAX - 1] = 0;
return path;
#else
#error unknown OS
#endif
}
std::string GetExecutableDirectory() {
return Dirname(GetExecutablePath());
}
std::string Basename(const std::string& path) {
// Copy path because basename may modify the string passed in.
std::string result(path);
#if !defined(__BIONIC__)
// Use lock because basename() may write to a process global and return a
// pointer to that. Note that this locking strategy only works if all other
// callers to basename in the process also grab this same lock, but its
// better than nothing. Bionic's basename returns a thread-local buffer.
static std::mutex& basename_lock = *new std::mutex();
std::lock_guard<std::mutex> lock(basename_lock);
#endif
// Note that if std::string uses copy-on-write strings, &str[0] will cause
// the copy to be made, so there is no chance of us accidentally writing to
// the storage for 'path'.
char* name = basename(&result[0]);
// In case basename returned a pointer to a process global, copy that string
// before leaving the lock.
result.assign(name);
return result;
}
std::string Dirname(const std::string& path) {
// Copy path because dirname may modify the string passed in.
std::string result(path);
#if !defined(__BIONIC__)
// Use lock because dirname() may write to a process global and return a
// pointer to that. Note that this locking strategy only works if all other
// callers to dirname in the process also grab this same lock, but its
// better than nothing. Bionic's dirname returns a thread-local buffer.
static std::mutex& dirname_lock = *new std::mutex();
std::lock_guard<std::mutex> lock(dirname_lock);
#endif
// Note that if std::string uses copy-on-write strings, &str[0] will cause
// the copy to be made, so there is no chance of us accidentally writing to
// the storage for 'path'.
char* parent = dirname(&result[0]);
// In case dirname returned a pointer to a process global, copy that string
// before leaving the lock.
result.assign(parent);
return result;
}
} // namespace base
} // namespace android