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// Copyright (c) 2006-2009 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "build/build_config.h"
#include "base/safe_strerror_posix.h"
#include <errno.h>
#include <stdio.h>
#include <string.h>
#define USE_HISTORICAL_STRERRO_R (defined(__GLIBC__) || defined(OS_NACL))
#if USE_HISTORICAL_STRERRO_R && defined(__GNUC__)
// GCC will complain about the unused second wrap function unless we tell it
// that we meant for them to be potentially unused, which is exactly what this
// attribute is for.
#define POSSIBLY_UNUSED __attribute__((unused))
#else
#define POSSIBLY_UNUSED
#endif
#if USE_HISTORICAL_STRERRO_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.
static void POSSIBLY_UNUSED 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';
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_STRERRO_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).
static void POSSIBLY_UNUSED 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.
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.
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 == NULL || 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);
}
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