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// Copyright 2006-2009 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/posix/safe_strerror.h"
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include "base/compiler_specific.h"
#include "build/build_config.h"
namespace base {
#if defined(__GLIBC__) || BUILDFLAG(IS_NACL)
#define USE_HISTORICAL_STRERROR_R 1
// Post-L versions of bionic define the GNU-specific strerror_r if _GNU_SOURCE
// is defined, but the symbol is renamed to __gnu_strerror_r which only exists
// on those later versions. For parity, add the same condition as bionic.
#elif defined(__BIONIC__) && defined(_GNU_SOURCE) && __ANDROID_API__ >= 23
#define USE_HISTORICAL_STRERROR_R 1
#else
#define USE_HISTORICAL_STRERROR_R 0
#endif
#if USE_HISTORICAL_STRERROR_R
// glibc has two strerror_r functions: a historical GNU-specific one that
// returns type char *, and a POSIX.1-2001 compliant one available since 2.3.4
// that returns int. This wraps the GNU-specific one.
[[maybe_unused]] static void wrap_posix_strerror_r(
char* (*strerror_r_ptr)(int, char*, size_t),
int err,
char* buf,
size_t len) {
// GNU version.
char* rc = (*strerror_r_ptr)(err, buf, len);
if (rc != buf) {
// glibc did not use buf and returned a static string instead. Copy it
// into buf.
buf[0] = '\0';
UNSAFE_TODO(strncat(buf, rc, len - 1));
}
// The GNU version never fails. Unknown errors get an "unknown error" message.
// The result is always null terminated.
}
#endif // USE_HISTORICAL_STRERROR_R
// Wrapper for strerror_r functions that implement the POSIX interface. POSIX
// does not define the behaviour for some of the edge cases, so we wrap it to
// guarantee that they are handled. This is compiled on all POSIX platforms, but
// it will only be used on Linux if the POSIX strerror_r implementation is
// being used (see below).
[[maybe_unused]] static void wrap_posix_strerror_r(
int (*strerror_r_ptr)(int, char*, size_t),
int err,
char* buf,
size_t len) {
int old_errno = errno;
// Have to cast since otherwise we get an error if this is the GNU version
// (but in such a scenario this function is never called). Sadly we can't use
// C++-style casts because the appropriate one is reinterpret_cast but it's
// considered illegal to reinterpret_cast a type to itself, so we get an
// error in the opposite case.
int result = (*strerror_r_ptr)(err, buf, len);
if (result == 0) {
// POSIX is vague about whether the string will be terminated, although
// it indirectly implies that typically ERANGE will be returned, instead
// of truncating the string. We play it safe by always terminating the
// string explicitly.
UNSAFE_TODO(buf[len - 1]) = '\0';
} else {
// Error. POSIX is vague about whether the return value is itself a system
// error code or something else. On Linux currently it is -1 and errno is
// set. On BSD-derived systems it is a system error and errno is unchanged.
// We try and detect which case it is so as to put as much useful info as
// we can into our message.
int strerror_error; // The error encountered in strerror
int new_errno = errno;
if (new_errno != old_errno) {
// errno was changed, so probably the return value is just -1 or something
// else that doesn't provide any info, and errno is the error.
strerror_error = new_errno;
} else {
// Either the error from strerror_r was the same as the previous value, or
// errno wasn't used. Assume the latter.
strerror_error = result;
}
// snprintf truncates and always null-terminates.
UNSAFE_TODO(snprintf(buf, len, "Error %d while retrieving error %d",
strerror_error, err));
}
errno = old_errno;
}
void safe_strerror_r(int err, char* buf, size_t len) {
if (buf == nullptr || len <= 0) {
return;
}
// If using glibc (i.e., Linux), the compiler will automatically select the
// appropriate overloaded function based on the function type of strerror_r.
// The other one will be elided from the translation unit since both are
// static.
wrap_posix_strerror_r(&strerror_r, err, buf, len);
}
std::string safe_strerror(int err) {
const int buffer_size = 256;
char buf[buffer_size];
safe_strerror_r(err, buf, sizeof(buf));
return std::string(buf);
}
} // namespace base
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