1// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "build/build_config.h"
6#include "base/safe_strerror_posix.h"
7
8#include <errno.h>
9#include <stdio.h>
10#include <string.h>
11
12#define USE_HISTORICAL_STRERRO_R (defined(__GLIBC__) || defined(OS_NACL))
13
14#if USE_HISTORICAL_STRERRO_R && defined(__GNUC__)
15// GCC will complain about the unused second wrap function unless we tell it
16// that we meant for them to be potentially unused, which is exactly what this
17// attribute is for.
18#define POSSIBLY_UNUSED __attribute__((unused))
19#else
20#define POSSIBLY_UNUSED
21#endif
22
23#if USE_HISTORICAL_STRERRO_R
24// glibc has two strerror_r functions: a historical GNU-specific one that
25// returns type char *, and a POSIX.1-2001 compliant one available since 2.3.4
26// that returns int. This wraps the GNU-specific one.
27static void POSSIBLY_UNUSED wrap_posix_strerror_r(
28    char *(*strerror_r_ptr)(int, char *, size_t),
29    int err,
30    char *buf,
31    size_t len) {
32  // GNU version.
33  char *rc = (*strerror_r_ptr)(err, buf, len);
34  if (rc != buf) {
35    // glibc did not use buf and returned a static string instead. Copy it
36    // into buf.
37    buf[0] = '\0';
38    strncat(buf, rc, len - 1);
39  }
40  // The GNU version never fails. Unknown errors get an "unknown error" message.
41  // The result is always null terminated.
42}
43#endif  // USE_HISTORICAL_STRERRO_R
44
45// Wrapper for strerror_r functions that implement the POSIX interface. POSIX
46// does not define the behaviour for some of the edge cases, so we wrap it to
47// guarantee that they are handled. This is compiled on all POSIX platforms, but
48// it will only be used on Linux if the POSIX strerror_r implementation is
49// being used (see below).
50static void POSSIBLY_UNUSED wrap_posix_strerror_r(
51    int (*strerror_r_ptr)(int, char *, size_t),
52    int err,
53    char *buf,
54    size_t len) {
55  int old_errno = errno;
56  // Have to cast since otherwise we get an error if this is the GNU version
57  // (but in such a scenario this function is never called). Sadly we can't use
58  // C++-style casts because the appropriate one is reinterpret_cast but it's
59  // considered illegal to reinterpret_cast a type to itself, so we get an
60  // error in the opposite case.
61  int result = (*strerror_r_ptr)(err, buf, len);
62  if (result == 0) {
63    // POSIX is vague about whether the string will be terminated, although
64    // it indirectly implies that typically ERANGE will be returned, instead
65    // of truncating the string. We play it safe by always terminating the
66    // string explicitly.
67    buf[len - 1] = '\0';
68  } else {
69    // Error. POSIX is vague about whether the return value is itself a system
70    // error code or something else. On Linux currently it is -1 and errno is
71    // set. On BSD-derived systems it is a system error and errno is unchanged.
72    // We try and detect which case it is so as to put as much useful info as
73    // we can into our message.
74    int strerror_error;  // The error encountered in strerror
75    int new_errno = errno;
76    if (new_errno != old_errno) {
77      // errno was changed, so probably the return value is just -1 or something
78      // else that doesn't provide any info, and errno is the error.
79      strerror_error = new_errno;
80    } else {
81      // Either the error from strerror_r was the same as the previous value, or
82      // errno wasn't used. Assume the latter.
83      strerror_error = result;
84    }
85    // snprintf truncates and always null-terminates.
86    snprintf(buf,
87             len,
88             "Error %d while retrieving error %d",
89             strerror_error,
90             err);
91  }
92  errno = old_errno;
93}
94
95void safe_strerror_r(int err, char *buf, size_t len) {
96  if (buf == NULL || len <= 0) {
97    return;
98  }
99  // If using glibc (i.e., Linux), the compiler will automatically select the
100  // appropriate overloaded function based on the function type of strerror_r.
101  // The other one will be elided from the translation unit since both are
102  // static.
103  wrap_posix_strerror_r(&strerror_r, err, buf, len);
104}
105
106std::string safe_strerror(int err) {
107  const int buffer_size = 256;
108  char buf[buffer_size];
109  safe_strerror_r(err, buf, sizeof(buf));
110  return std::string(buf);
111}
112