1 // Copyright 2006-2009 The Chromium Authors
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 "base/posix/safe_strerror.h"
6
7 #include <errno.h>
8 #include <stdio.h>
9 #include <string.h>
10
11 #include "build/build_config.h"
12
13 namespace base {
14
15 #if defined(__GLIBC__) || BUILDFLAG(IS_NACL)
16 #define USE_HISTORICAL_STRERROR_R 1
17 // Post-L versions of bionic define the GNU-specific strerror_r if _GNU_SOURCE
18 // is defined, but the symbol is renamed to __gnu_strerror_r which only exists
19 // on those later versions. For parity, add the same condition as bionic.
20 #elif defined(__BIONIC__) && defined(_GNU_SOURCE) && __ANDROID_API__ >= 23
21 #define USE_HISTORICAL_STRERROR_R 1
22 #else
23 #define USE_HISTORICAL_STRERROR_R 0
24 #endif
25
26 #if USE_HISTORICAL_STRERROR_R
27 // glibc has two strerror_r functions: a historical GNU-specific one that
28 // returns type char *, and a POSIX.1-2001 compliant one available since 2.3.4
29 // that returns int. This wraps the GNU-specific one.
wrap_posix_strerror_r(char * (* strerror_r_ptr)(int,char *,size_t),int err,char * buf,size_t len)30 [[maybe_unused]] static void wrap_posix_strerror_r(
31 char* (*strerror_r_ptr)(int, char*, size_t),
32 int err,
33 char* buf,
34 size_t len) {
35 // GNU version.
36 char *rc = (*strerror_r_ptr)(err, buf, len);
37 if (rc != buf) {
38 // glibc did not use buf and returned a static string instead. Copy it
39 // into buf.
40 buf[0] = '\0';
41 strncat(buf, rc, len - 1);
42 }
43 // The GNU version never fails. Unknown errors get an "unknown error" message.
44 // The result is always null terminated.
45 }
46 #endif // USE_HISTORICAL_STRERROR_R
47
48 // Wrapper for strerror_r functions that implement the POSIX interface. POSIX
49 // does not define the behaviour for some of the edge cases, so we wrap it to
50 // guarantee that they are handled. This is compiled on all POSIX platforms, but
51 // it will only be used on Linux if the POSIX strerror_r implementation is
52 // being used (see below).
wrap_posix_strerror_r(int (* strerror_r_ptr)(int,char *,size_t),int err,char * buf,size_t len)53 [[maybe_unused]] static void wrap_posix_strerror_r(
54 int (*strerror_r_ptr)(int, char*, size_t),
55 int err,
56 char* buf,
57 size_t len) {
58 int old_errno = errno;
59 // Have to cast since otherwise we get an error if this is the GNU version
60 // (but in such a scenario this function is never called). Sadly we can't use
61 // C++-style casts because the appropriate one is reinterpret_cast but it's
62 // considered illegal to reinterpret_cast a type to itself, so we get an
63 // error in the opposite case.
64 int result = (*strerror_r_ptr)(err, buf, len);
65 if (result == 0) {
66 // POSIX is vague about whether the string will be terminated, although
67 // it indirectly implies that typically ERANGE will be returned, instead
68 // of truncating the string. We play it safe by always terminating the
69 // string explicitly.
70 buf[len - 1] = '\0';
71 } else {
72 // Error. POSIX is vague about whether the return value is itself a system
73 // error code or something else. On Linux currently it is -1 and errno is
74 // set. On BSD-derived systems it is a system error and errno is unchanged.
75 // We try and detect which case it is so as to put as much useful info as
76 // we can into our message.
77 int strerror_error; // The error encountered in strerror
78 int new_errno = errno;
79 if (new_errno != old_errno) {
80 // errno was changed, so probably the return value is just -1 or something
81 // else that doesn't provide any info, and errno is the error.
82 strerror_error = new_errno;
83 } else {
84 // Either the error from strerror_r was the same as the previous value, or
85 // errno wasn't used. Assume the latter.
86 strerror_error = result;
87 }
88 // snprintf truncates and always null-terminates.
89 snprintf(buf,
90 len,
91 "Error %d while retrieving error %d",
92 strerror_error,
93 err);
94 }
95 errno = old_errno;
96 }
97
safe_strerror_r(int err,char * buf,size_t len)98 void safe_strerror_r(int err, char *buf, size_t len) {
99 if (buf == nullptr || len <= 0) {
100 return;
101 }
102 // If using glibc (i.e., Linux), the compiler will automatically select the
103 // appropriate overloaded function based on the function type of strerror_r.
104 // The other one will be elided from the translation unit since both are
105 // static.
106 wrap_posix_strerror_r(&strerror_r, err, buf, len);
107 }
108
safe_strerror(int err)109 std::string safe_strerror(int err) {
110 const int buffer_size = 256;
111 char buf[buffer_size];
112 safe_strerror_r(err, buf, sizeof(buf));
113 return std::string(buf);
114 }
115
116 } // namespace base
117