libc/src/__support/StringUtil/error_to_string.cpp

   1 //===-- Implementation of a class for mapping errors to strings -----------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "src/__support/StringUtil/error_to_string.h"
  10
  11 #include "src/errno/libc_errno.h" // For error macros
  12
  13 #include "src/__support/CPP/array.h"
  14 #include "src/__support/CPP/span.h"
  15 #include "src/__support/CPP/string_view.h"
  16 #include "src/__support/CPP/stringstream.h"
  17 #include "src/__support/StringUtil/message_mapper.h"
  18 #include "src/__support/integer_to_string.h"
  19
  20 #include "src/__support/StringUtil/tables/error_table.h"
  21
  22 #include <stddef.h>
  23
  24 namespace __llvm_libc {
  25 namespace internal {
  26
  27 constexpr size_t max_buff_size() {
  28   constexpr size_t unknown_str_len = sizeof("Unknown error");
  29   constexpr size_t max_num_len =
  30       __llvm_libc::IntegerToString::dec_bufsize<int>();
  31   // the buffer should be able to hold "Unknown error" + ' ' + num_str
  32   return (unknown_str_len + 1 + max_num_len) * sizeof(char);
  33 }
  34
  35 // This is to hold error strings that have to be custom built. It may be
  36 // rewritten on every call to strerror (or other error to string function).
  37 constexpr size_t ERR_BUFFER_SIZE = max_buff_size();
  38 thread_local char error_buffer[ERR_BUFFER_SIZE];
  39
  40 constexpr size_t TOTAL_STR_LEN = total_str_len(PLATFORM_ERRORS);
  41
  42 // Since the StringMappings array is a map from error numbers to their
  43 // corresponding strings, we have to have an array large enough we can use the
  44 // error numbers as indexes. The current linux configuration has 132 values with
  45 // the maximum value being 133 (41 and 58 are skipped). If other platforms use
  46 // negative numbers or discontiguous ranges, then the array should be turned
  47 // into a proper hashmap.
  48 constexpr size_t ERR_ARRAY_SIZE = max_key_val(PLATFORM_ERRORS) + 1;
  49
  50 constexpr MessageMapper<ERR_ARRAY_SIZE, TOTAL_STR_LEN>
  51     error_mapper(PLATFORM_ERRORS);
  52
  53 cpp::string_view build_error_string(int err_num, cpp::span<char> buffer) {
  54   // if the buffer can't hold "Unknown error" + ' ' + num_str, then just
  55   // return "Unknown error".
  56   if (buffer.size() <
  57       (sizeof("Unknown error") + 1 + IntegerToString::dec_bufsize<int>()))
  58     return const_cast<char *>("Unknown error");
  59
  60   cpp::StringStream buffer_stream(
  61       {const_cast<char *>(buffer.data()), buffer.size()});
  62   buffer_stream << "Unknown error" << ' ' << err_num << '\0';
  63   return buffer_stream.str();
  64 }
  65
  66 } // namespace internal
  67
  68 cpp::string_view get_error_string(int err_num) {
  69   return get_error_string(err_num,
  70                           {internal::error_buffer, internal::ERR_BUFFER_SIZE});
  71 }
  72
  73 cpp::string_view get_error_string(int err_num, cpp::span<char> buffer) {
  74   auto opt_str = internal::error_mapper.get_str(err_num);
  75   if (opt_str)
  76     return *opt_str;
  77   else
  78     return internal::build_error_string(err_num, buffer);
  79 }
  80
  81 } // namespace __llvm_libc