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      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 #if defined(__ANDROID__)
      6 // Post-L versions of bionic define the GNU-specific strerror_r if _GNU_SOURCE
      7 // is defined, but the symbol is renamed to __gnu_strerror_r which only exists
      8 // on those later versions. To preserve ABI compatibility with older versions,
      9 // undefine _GNU_SOURCE and use the POSIX version.
     10 #undef _GNU_SOURCE
     11 #endif
     12 
     13 #include "base/posix/safe_strerror.h"
     14 
     15 #include <errno.h>
     16 #include <stdio.h>
     17 #include <string.h>
     18 
     19 #include "build/build_config.h"
     20 
     21 namespace base {
     22 
     23 #define USE_HISTORICAL_STRERRO_R (defined(__GLIBC__) || defined(OS_NACL))
     24 
     25 #if USE_HISTORICAL_STRERRO_R && defined(__GNUC__)
     26 // GCC will complain about the unused second wrap function unless we tell it
     27 // that we meant for them to be potentially unused, which is exactly what this
     28 // attribute is for.
     29 #define POSSIBLY_UNUSED __attribute__((unused))
     30 #else
     31 #define POSSIBLY_UNUSED
     32 #endif
     33 
     34 #if USE_HISTORICAL_STRERRO_R
     35 // glibc has two strerror_r functions: a historical GNU-specific one that
     36 // returns type char *, and a POSIX.1-2001 compliant one available since 2.3.4
     37 // that returns int. This wraps the GNU-specific one.
     38 static void POSSIBLY_UNUSED wrap_posix_strerror_r(
     39     char *(*strerror_r_ptr)(int, char *, size_t),
     40     int err,
     41     char *buf,
     42     size_t len) {
     43   // GNU version.
     44   char *rc = (*strerror_r_ptr)(err, buf, len);
     45   if (rc != buf) {
     46     // glibc did not use buf and returned a static string instead. Copy it
     47     // into buf.
     48     buf[0] = '\0';
     49     strncat(buf, rc, len - 1);
     50   }
     51   // The GNU version never fails. Unknown errors get an "unknown error" message.
     52   // The result is always null terminated.
     53 }
     54 #endif  // USE_HISTORICAL_STRERRO_R
     55 
     56 // Wrapper for strerror_r functions that implement the POSIX interface. POSIX
     57 // does not define the behaviour for some of the edge cases, so we wrap it to
     58 // guarantee that they are handled. This is compiled on all POSIX platforms, but
     59 // it will only be used on Linux if the POSIX strerror_r implementation is
     60 // being used (see below).
     61 static void POSSIBLY_UNUSED wrap_posix_strerror_r(
     62     int (*strerror_r_ptr)(int, char *, size_t),
     63     int err,
     64     char *buf,
     65     size_t len) {
     66   int old_errno = errno;
     67   // Have to cast since otherwise we get an error if this is the GNU version
     68   // (but in such a scenario this function is never called). Sadly we can't use
     69   // C++-style casts because the appropriate one is reinterpret_cast but it's
     70   // considered illegal to reinterpret_cast a type to itself, so we get an
     71   // error in the opposite case.
     72   int result = (*strerror_r_ptr)(err, buf, len);
     73   if (result == 0) {
     74     // POSIX is vague about whether the string will be terminated, although
     75     // it indirectly implies that typically ERANGE will be returned, instead
     76     // of truncating the string. We play it safe by always terminating the
     77     // string explicitly.
     78     buf[len - 1] = '\0';
     79   } else {
     80     // Error. POSIX is vague about whether the return value is itself a system
     81     // error code or something else. On Linux currently it is -1 and errno is
     82     // set. On BSD-derived systems it is a system error and errno is unchanged.
     83     // We try and detect which case it is so as to put as much useful info as
     84     // we can into our message.
     85     int strerror_error;  // The error encountered in strerror
     86     int new_errno = errno;
     87     if (new_errno != old_errno) {
     88       // errno was changed, so probably the return value is just -1 or something
     89       // else that doesn't provide any info, and errno is the error.
     90       strerror_error = new_errno;
     91     } else {
     92       // Either the error from strerror_r was the same as the previous value, or
     93       // errno wasn't used. Assume the latter.
     94       strerror_error = result;
     95     }
     96     // snprintf truncates and always null-terminates.
     97     snprintf(buf,
     98              len,
     99              "Error %d while retrieving error %d",
    100              strerror_error,
    101              err);
    102   }
    103   errno = old_errno;
    104 }
    105 
    106 void safe_strerror_r(int err, char *buf, size_t len) {
    107   if (buf == NULL || len <= 0) {
    108     return;
    109   }
    110   // If using glibc (i.e., Linux), the compiler will automatically select the
    111   // appropriate overloaded function based on the function type of strerror_r.
    112   // The other one will be elided from the translation unit since both are
    113   // static.
    114   wrap_posix_strerror_r(&strerror_r, err, buf, len);
    115 }
    116 
    117 std::string safe_strerror(int err) {
    118   const int buffer_size = 256;
    119   char buf[buffer_size];
    120   safe_strerror_r(err, buf, sizeof(buf));
    121   return std::string(buf);
    122 }
    123 
    124 }  // namespace base
    125