1/*
2 * Copyright 2013-present Facebook, Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#pragma once
18
19#include <sys/stat.h>
20#include <sys/types.h>
21
22#include <cassert>
23#include <limits>
24
25#include <folly/Portability.h>
26#include <folly/Range.h>
27#include <folly/ScopeGuard.h>
28#include <folly/net/NetworkSocket.h>
29#include <folly/portability/Fcntl.h>
30#include <folly/portability/SysUio.h>
31#include <folly/portability/Unistd.h>
32
33namespace folly {
34
35/**
36 * Convenience wrappers around some commonly used system calls. The *NoInt
37 * wrappers retry on EINTR. The *Full wrappers retry on EINTR and also loop
38 * until all data is written. Note that *Full wrappers weaken the thread
39 * semantics of underlying system calls.
40 */
41int openNoInt(const char* name, int flags, mode_t mode = 0666);
42// Two overloads, as we may be closing either a file or a socket.
43int closeNoInt(int fd);
44int closeNoInt(NetworkSocket fd);
45int dupNoInt(int fd);
46int dup2NoInt(int oldfd, int newfd);
47int fsyncNoInt(int fd);
48int fdatasyncNoInt(int fd);
49int ftruncateNoInt(int fd, off_t len);
50int truncateNoInt(const char* path, off_t len);
51int flockNoInt(int fd, int operation);
52int shutdownNoInt(NetworkSocket fd, int how);
53
54ssize_t readNoInt(int fd, void* buf, size_t n);
55ssize_t preadNoInt(int fd, void* buf, size_t n, off_t offset);
56ssize_t readvNoInt(int fd, const iovec* iov, int count);
57
58ssize_t writeNoInt(int fd, const void* buf, size_t n);
59ssize_t pwriteNoInt(int fd, const void* buf, size_t n, off_t offset);
60ssize_t writevNoInt(int fd, const iovec* iov, int count);
61
62/**
63 * Wrapper around read() (and pread()) that, in addition to retrying on
64 * EINTR, will loop until all data is read.
65 *
66 * This wrapper is only useful for blocking file descriptors (for non-blocking
67 * file descriptors, you have to be prepared to deal with incomplete reads
68 * anyway), and only exists because POSIX allows read() to return an incomplete
69 * read if interrupted by a signal (instead of returning -1 and setting errno
70 * to EINTR).
71 *
72 * Note that this wrapper weakens the thread safety of read(): the file pointer
73 * is shared between threads, but the system call is atomic. If multiple
74 * threads are reading from a file at the same time, you don't know where your
75 * data came from in the file, but you do know that the returned bytes were
76 * contiguous. You can no longer make this assumption if using readFull().
77 * You should probably use pread() when reading from the same file descriptor
78 * from multiple threads simultaneously, anyway.
79 *
80 * Note that readvFull and preadvFull require iov to be non-const, unlike
81 * readv and preadv. The contents of iov after these functions return
82 * is unspecified.
83 */
84FOLLY_NODISCARD ssize_t readFull(int fd, void* buf, size_t n);
85FOLLY_NODISCARD ssize_t preadFull(int fd, void* buf, size_t n, off_t offset);
86FOLLY_NODISCARD ssize_t readvFull(int fd, iovec* iov, int count);
87FOLLY_NODISCARD ssize_t preadvFull(int fd, iovec* iov, int count, off_t offset);
88
89/**
90 * Similar to readFull and preadFull above, wrappers around write() and
91 * pwrite() that loop until all data is written.
92 *
93 * Generally, the write() / pwrite() system call may always write fewer bytes
94 * than requested, just like read(). In certain cases (such as when writing to
95 * a pipe), POSIX provides stronger guarantees, but not in the general case.
96 * For example, Linux (even on a 64-bit platform) won't write more than 2GB in
97 * one write() system call.
98 *
99 * Note that writevFull and pwritevFull require iov to be non-const, unlike
100 * writev and pwritev. The contents of iov after these functions return
101 * is unspecified.
102 *
103 * These functions return -1 on error, or the total number of bytes written
104 * (which is always the same as the number of requested bytes) on success.
105 */
106ssize_t writeFull(int fd, const void* buf, size_t n);
107ssize_t pwriteFull(int fd, const void* buf, size_t n, off_t offset);
108ssize_t writevFull(int fd, iovec* iov, int count);
109ssize_t pwritevFull(int fd, iovec* iov, int count, off_t offset);
110
111/**
112 * Read entire file (if num_bytes is defaulted) or no more than
113 * num_bytes (otherwise) into container *out. The container is assumed
114 * to be contiguous, with element size equal to 1, and offer size(),
115 * reserve(), and random access (e.g. std::vector<char>, std::string,
116 * fbstring).
117 *
118 * Returns: true on success or false on failure. In the latter case
119 * errno will be set appropriately by the failing system primitive.
120 */
121template <class Container>
122bool readFile(
123 int fd,
124 Container& out,
125 size_t num_bytes = std::numeric_limits<size_t>::max()) {
126 static_assert(
127 sizeof(out[0]) == 1,
128 "readFile: only containers with byte-sized elements accepted");
129
130 size_t soFar = 0; // amount of bytes successfully read
131 SCOPE_EXIT {
132 DCHECK(out.size() >= soFar); // resize better doesn't throw
133 out.resize(soFar);
134 };
135
136 // Obtain file size:
137 struct stat buf;
138 if (fstat(fd, &buf) == -1) {
139 return false;
140 }
141 // Some files (notably under /proc and /sys on Linux) lie about
142 // their size, so treat the size advertised by fstat under advise
143 // but don't rely on it. In particular, if the size is zero, we
144 // should attempt to read stuff. If not zero, we'll attempt to read
145 // one extra byte.
146 constexpr size_t initialAlloc = 1024 * 4;
147 out.resize(std::min(
148 buf.st_size > 0 ? (size_t(buf.st_size) + 1) : initialAlloc, num_bytes));
149
150 while (soFar < out.size()) {
151 const auto actual = readFull(fd, &out[soFar], out.size() - soFar);
152 if (actual == -1) {
153 return false;
154 }
155 soFar += actual;
156 if (soFar < out.size()) {
157 // File exhausted
158 break;
159 }
160 // Ew, allocate more memory. Use exponential growth to avoid
161 // quadratic behavior. Cap size to num_bytes.
162 out.resize(std::min(out.size() * 3 / 2, num_bytes));
163 }
164
165 return true;
166}
167
168/**
169 * Same as above, but takes in a file name instead of fd
170 */
171template <class Container>
172bool readFile(
173 const char* file_name,
174 Container& out,
175 size_t num_bytes = std::numeric_limits<size_t>::max()) {
176 DCHECK(file_name);
177
178 const auto fd = openNoInt(file_name, O_RDONLY | O_CLOEXEC);
179 if (fd == -1) {
180 return false;
181 }
182
183 SCOPE_EXIT {
184 // Ignore errors when closing the file
185 closeNoInt(fd);
186 };
187
188 return readFile(fd, out, num_bytes);
189}
190
191/**
192 * Writes container to file. The container is assumed to be
193 * contiguous, with element size equal to 1, and offering STL-like
194 * methods empty(), size(), and indexed access
195 * (e.g. std::vector<char>, std::string, fbstring, StringPiece).
196 *
197 * "flags" dictates the open flags to use. Default is to create file
198 * if it doesn't exist and truncate it.
199 *
200 * Returns: true on success or false on failure. In the latter case
201 * errno will be set appropriately by the failing system primitive.
202 *
203 * Note that this function may leave the file in a partially written state on
204 * failure. Use writeFileAtomic() if you want to ensure that the existing file
205 * state will be unchanged on error.
206 */
207template <class Container>
208bool writeFile(
209 const Container& data,
210 const char* filename,
211 int flags = O_WRONLY | O_CREAT | O_TRUNC,
212 mode_t mode = 0666) {
213 static_assert(
214 sizeof(data[0]) == 1, "writeFile works with element size equal to 1");
215 int fd = open(filename, flags, mode);
216 if (fd == -1) {
217 return false;
218 }
219 bool ok = data.empty() ||
220 writeFull(fd, &data[0], data.size()) == static_cast<ssize_t>(data.size());
221 return closeNoInt(fd) == 0 && ok;
222}
223
224/**
225 * Write file contents "atomically".
226 *
227 * This writes the data to a temporary file in the destination directory, and
228 * then renames it to the specified path. This guarantees that the specified
229 * file will be replaced the the specified contents on success, or will not be
230 * modified on failure.
231 *
232 * Note that on platforms that do not provide atomic filesystem rename
233 * functionality (e.g., Windows) this behavior may not be truly atomic.
234 */
235void writeFileAtomic(
236 StringPiece filename,
237 iovec* iov,
238 int count,
239 mode_t permissions = 0644);
240void writeFileAtomic(
241 StringPiece filename,
242 ByteRange data,
243 mode_t permissions = 0644);
244void writeFileAtomic(
245 StringPiece filename,
246 StringPiece data,
247 mode_t permissions = 0644);
248
249/**
250 * A version of writeFileAtomic() that returns an errno value instead of
251 * throwing on error.
252 *
253 * Returns 0 on success or an errno value on error.
254 */
255int writeFileAtomicNoThrow(
256 StringPiece filename,
257 iovec* iov,
258 int count,
259 mode_t permissions = 0644);
260
261} // namespace folly
262