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 "error_to_string.h"
  10 #include "platform_errors.h"
  11
  12 #include "src/__support/CPP/span.h"
  13 #include "src/__support/CPP/string_view.h"
  14 #include "src/__support/CPP/stringstream.h"
  15 #include "src/__support/StringUtil/message_mapper.h"
  16 #include "src/__support/integer_to_string.h"
  17 #include "src/__support/macros/attributes.h"
  18
  19 #include <stddef.h>
  20
  21 namespace LIBC_NAMESPACE {
  22 namespace internal {
  23
  24 constexpr size_t max_buff_size() {
  25   constexpr size_t unknown_str_len = sizeof("Unknown error");
  26   // the buffer should be able to hold "Unknown error" + ' ' + num_str
  27   return (unknown_str_len + 1 + IntegerToString<int>::buffer_size()) *
  28          sizeof(char);
  29 }
  30
  31 // This is to hold error strings that have to be custom built. It may be
  32 // rewritten on every call to strerror (or other error to string function).
  33 constexpr size_t ERR_BUFFER_SIZE = max_buff_size();
  34 LIBC_THREAD_LOCAL char error_buffer[ERR_BUFFER_SIZE];
  35
  36 constexpr size_t TOTAL_STR_LEN = total_str_len(PLATFORM_ERRORS);
  37
  38 // Since the StringMappings array is a map from error numbers to their
  39 // corresponding strings, we have to have an array large enough we can use the
  40 // error numbers as indexes. The current linux configuration has 132 values with
  41 // the maximum value being 133 (41 and 58 are skipped). If other platforms use
  42 // negative numbers or discontiguous ranges, then the array should be turned
  43 // into a proper hashmap.
  44 constexpr size_t ERR_ARRAY_SIZE = max_key_val(PLATFORM_ERRORS) + 1;
  45
  46 constexpr MessageMapper<ERR_ARRAY_SIZE, TOTAL_STR_LEN>
  47     error_mapper(PLATFORM_ERRORS);
  48
  49 cpp::string_view build_error_string(int err_num, cpp::span<char> buffer) {
  50   // if the buffer can't hold "Unknown error" + ' ' + num_str, then just
  51   // return "Unknown error".
  52   if (buffer.size() <
  53       (sizeof("Unknown error") + 1 + IntegerToString<int>::buffer_size()))
  54     return const_cast<char *>("Unknown error");
  55
  56   cpp::StringStream buffer_stream(
  57       {const_cast<char *>(buffer.data()), buffer.size()});
  58   buffer_stream << "Unknown error" << ' ' << err_num << '\0';
  59   return buffer_stream.str();
  60 }
  61
  62 } // namespace internal
  63
  64 cpp::string_view get_error_string(int err_num) {
  65   return get_error_string(err_num,
  66                           {internal::error_buffer, internal::ERR_BUFFER_SIZE});
  67 }
  68
  69 cpp::string_view get_error_string(int err_num, cpp::span<char> buffer) {
  70   auto opt_str = internal::error_mapper.get_str(err_num);
  71   if (opt_str)
  72     return *opt_str;
  73   else
  74     return internal::build_error_string(err_num, buffer);
  75 }
  76
  77 } // namespace LIBC_NAMESPACE