vmm_sys_util/errno.rs
1// Copyright 2019 Intel Corporation. All Rights Reserved.
2//
3// Copyright 2018 Amazon.com, Inc. or its affiliates. All Rights Reserved.
4//
5// Portions Copyright 2017 The Chromium OS Authors. All rights reserved.
6//
7// SPDX-License-Identifier: BSD-3-Clause
8
9//! Structures, helpers, and type definitions for working with
10//! [`errno`](http://man7.org/linux/man-pages/man3/errno.3.html).
11
12use std::fmt::{Display, Formatter};
13use std::io;
14use std::result;
15
16/// Wrapper over [`errno`](http://man7.org/linux/man-pages/man3/errno.3.html).
17///
18/// The error number is an integer number set by system calls and some libc
19/// functions in case of error.
20#[derive(Clone, Copy, Debug, PartialEq, Eq)]
21pub struct Error(i32);
22
23/// A specialized [Result](https://doc.rust-lang.org/std/result/enum.Result.html) type
24/// for operations that can return `errno`.
25///
26/// This typedef is generally used to avoid writing out `errno::Error` directly and is
27/// otherwise a direct mapping to `Result`.
28pub type Result<T> = result::Result<T, Error>;
29
30impl Error {
31 /// Creates a new error from the given error number.
32 ///
33 /// # Arguments
34 ///
35 /// * `errno`: error number used for creating the `Error`.
36 ///
37 /// # Examples
38 ///
39 /// ```
40 /// # extern crate libc;
41 /// extern crate vmm_sys_util;
42 /// #
43 /// # use libc;
44 /// use vmm_sys_util::errno::Error;
45 ///
46 /// let err = Error::new(libc::EIO);
47 /// ```
48 pub fn new(errno: i32) -> Error {
49 Error(errno)
50 }
51
52 /// Returns the last occurred `errno` wrapped in an `Error`.
53 ///
54 /// Calling `Error::last()` is the equivalent of using
55 /// [`errno`](http://man7.org/linux/man-pages/man3/errno.3.html) in C/C++.
56 /// The result of this function only has meaning after a libc call or syscall
57 /// where `errno` was set.
58 ///
59 /// # Examples
60 ///
61 /// ```
62 /// # extern crate libc;
63 /// extern crate vmm_sys_util;
64 /// #
65 /// # use libc;
66 /// # use std::fs::File;
67 /// # use std::io::{self, Read};
68 /// # use std::env::temp_dir;
69 /// use vmm_sys_util::errno::Error;
70 /// #
71 /// // Reading from a file without permissions returns an error.
72 /// let mut path = temp_dir();
73 /// path.push("test");
74 /// let mut file = File::create(path).unwrap();
75 /// let mut buf: Vec<u8> = Vec::new();
76 /// assert!(file.read_to_end(&mut buf).is_err());
77 ///
78 /// // Retrieve the error number of the previous operation using `Error::last()`:
79 /// let read_err = Error::last();
80 /// #[cfg(unix)]
81 /// assert_eq!(read_err, Error::new(libc::EBADF));
82 /// #[cfg(not(unix))]
83 /// assert_eq!(read_err, Error::new(libc::EIO));
84 /// ```
85 pub fn last() -> Error {
86 // It's safe to unwrap because this `Error` was constructed via `last_os_error`.
87 Error(io::Error::last_os_error().raw_os_error().unwrap())
88 }
89
90 /// Returns the raw integer value (`errno`) corresponding to this Error.
91 ///
92 /// # Examples
93 /// ```
94 /// extern crate vmm_sys_util;
95 /// use vmm_sys_util::errno::Error;
96 ///
97 /// let err = Error::new(13);
98 /// assert_eq!(err.errno(), 13);
99 /// ```
100 pub fn errno(self) -> i32 {
101 self.0
102 }
103}
104
105impl Display for Error {
106 fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
107 io::Error::from_raw_os_error(self.0).fmt(f)
108 }
109}
110
111impl std::error::Error for Error {}
112
113impl From<io::Error> for Error {
114 fn from(e: io::Error) -> Self {
115 Error::new(e.raw_os_error().unwrap_or_default())
116 }
117}
118
119impl From<Error> for io::Error {
120 fn from(err: Error) -> io::Error {
121 io::Error::from_raw_os_error(err.0)
122 }
123}
124
125/// Returns the last `errno` as a [`Result`] that is always an error.
126///
127/// [`Result`]: type.Result.html
128pub fn errno_result<T>() -> Result<T> {
129 Err(Error::last())
130}
131
132#[cfg(test)]
133mod tests {
134 use super::*;
135 use std::env::temp_dir;
136 use std::error::Error as _;
137 use std::fs::OpenOptions;
138 use std::io::{self, Read};
139
140 #[test]
141 pub fn test_errno() {
142 #[cfg(unix)]
143 let expected_errno = libc::EBADF;
144 #[cfg(not(unix))]
145 let expected_errno = libc::EIO;
146
147 // try to read from a file without read permissions
148 let mut path = temp_dir();
149 path.push("test");
150 let mut file = OpenOptions::new()
151 .read(false)
152 .write(true)
153 .create(true)
154 .truncate(true)
155 .open(path)
156 .unwrap();
157 let mut buf: Vec<u8> = Vec::new();
158 assert!(file.read_to_end(&mut buf).is_err());
159
160 // Test that errno_result returns Err and the error is the expected one.
161 let last_err = errno_result::<i32>().unwrap_err();
162 assert_eq!(last_err, Error::new(expected_errno));
163
164 // Test that the inner value of `Error` corresponds to expected_errno.
165 assert_eq!(last_err.errno(), expected_errno);
166 assert!(last_err.source().is_none());
167
168 // Test creating an `Error` from a `std::io::Error`.
169 assert_eq!(last_err, Error::from(io::Error::last_os_error()));
170
171 // Test that calling `last()` returns the same error as `errno_result()`.
172 assert_eq!(last_err, Error::last());
173
174 let last_err: io::Error = last_err.into();
175 // Test creating a `std::io::Error` from an `Error`
176 assert_eq!(io::Error::last_os_error().kind(), last_err.kind());
177 }
178
179 #[test]
180 pub fn test_display() {
181 // Test the display implementation.
182 #[cfg(target_os = "linux")]
183 assert_eq!(
184 format!("{}", Error::new(libc::EBADF)),
185 "Bad file descriptor (os error 9)"
186 );
187 #[cfg(not(unix))]
188 assert_eq!(
189 format!("{}", Error::new(libc::EIO)),
190 "Access is denied. (os error 5)"
191 );
192 }
193}