xapian-core/common/errno_to_string.cc

   1 /** @file
   2  * @brief Convert errno value to std::string, thread-safely if possible
   3  */
   4 /* Copyright (C) 2014,2015,2016,2021 Olly Betts
   5  *
   6  * Permission is hereby granted, free of charge, to any person obtaining a copy
   7  * of this software and associated documentation files (the "Software"), to
   8  * deal in the Software without restriction, including without limitation the
   9  * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
  10  * sell copies of the Software, and to permit persons to whom the Software is
  11  * furnished to do so, subject to the following conditions:
  12  *
  13  * The above copyright notice and this permission notice shall be included in
  14  * all copies or substantial portions of the Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  22  * IN THE SOFTWARE.
  23  */
  24
  25 #include <config.h>
  26
  27 #include "errno_to_string.h"
  28
  29 // On Linux, sys_errlist and sys_nerr need <stdio.h>, though the man page
  30 // says <errno.h>.  The man page seems to match other platforms such as
  31 // NetBSD, so include both headers to ensure we get them.
  32 #include <errno.h>
  33 // <cstring> doesn't give us strerror_r() with Sun C++ 5.9.
  34 #include <string.h>
  35 #if defined HAVE__SYS_ERRLIST_AND__SYS_NERR || \
  36     defined HAVE_SYS_ERRLIST_AND_SYS_NERR
  37 # include <stdio.h>
  38 // With mingw and MSVC they're provided by <stdlib.h>.
  39 # include <stdlib.h>
  40 #endif
  41
  42 #include "str.h"
  43
  44 using namespace std;
  45
  46 void
  47 errno_to_string(int e, string& s)
  48 {
  49     // Use a thread-safe way to convert an errno value to a string if possible.
  50 #ifdef HAVE_STRERRORDESC_NP
  51     // GNU-specific replacement for sys_errlist and sys_nerr, added in glibc
  52     // 2.32.
  53     const char* desc = strerrordesc_np(e);
  54     if (desc) {
  55         s += desc;
  56     } else {
  57         s += "Unknown error ";
  58         s += str(e);
  59     }
  60 #elif defined HAVE__SYS_ERRLIST_AND__SYS_NERR
  61     // Old-style Unix fixed array of strings.
  62     if (e >= 0 && e < _sys_nerr && _sys_errlist[e]) {
  63         s += _sys_errlist[e];
  64     } else {
  65         s += "Unknown error ";
  66         s += str(e);
  67     }
  68 #elif defined HAVE_SYS_ERRLIST_AND_SYS_NERR
  69     // Old-style Unix fixed array of strings.
  70     if (e >= 0 && e < sys_nerr && sys_errlist[e]) {
  71         s += sys_errlist[e];
  72     } else {
  73         s += "Unknown error ";
  74         s += str(e);
  75     }
  76 #elif HAVE_DECL_STRERROR_R
  77     // POSIX specifies strerror_r() to provide a thread-safe way to translate
  78     // an errno value to a string.
  79     //
  80     // Unhelpfully this requires us to pass in a buffer, but we don't know how
  81     // big to make it to reliably be able to convert all possible errno values,
  82     // and the implementation is permitted to return localised strings so the
  83     // maximum possible length may vary depending on the current locale
  84     // settings.
  85     //
  86     // If the buffer passed is too small, then with older glibc errno gets
  87     // stomped on, so growing the buffer on error and retrying isn't a great
  88     // answer.  Hence we only use strerror_r() if we don't have a better
  89     // alternative.
  90     //
  91     // Another reason to have support for alternative approaches is that
  92     // strerror_r() is marked as "optional" by POSIX.
  93     //
  94     // A further complication is there's a GNU-specific strerror_r() with a
  95     // different return value type.
  96     //
  97     // The strerror_r(3) man page on Linux suggests a buffer size of 1024
  98     // characters, noting that glibc uses this size for strerror().  The
  99     // actual longest on Linux in English is EILSEQ which needs 50 bytes.
 100     char buf[1024];
 101 # ifdef STRERROR_R_CHAR_P
 102     // Returns char* pointing to string describing error.
 103     s += strerror_r(e, buf, sizeof(buf));
 104 # else
 105     // XSI-compliant strerror_r returns int:  0 means success; a positive error
 106     // number should be returned on error, but glibc < 2.13 returns -1 and sets
 107     // errno.
 108     int r = strerror_r(e, buf, sizeof(buf));
 109     if (r == 0) {
 110         s += buf;
 111     } else {
 112         s += "Unknown error ";
 113         s += str(e);
 114     }
 115 # endif
 116 #else
 117     // Not thread safe.
 118     //
 119     // We can assume the return value is non-NULL because "C99 and POSIX.1-2008
 120     // require the return value to be non-NULL" and we require C++11 which
 121     // incorporates C99.
 122     s += strerror(e);
 123 #endif
 124 }