StatusOr ParseConfigLine()

in src/config/config_util.cc [25:149]
121 lines of code
35 McCabe index (conditional complexity)

StatusOr<ConfigKV> ParseConfigLine(const std::string& line) {
  enum {
    KEY,              // in (unquoted) key string
    NORMAL,           // in unquoted value string
    QUOTED,           // in quoted value string
    PRE_KEY_SPACE,    // in whitespace characters before key
    AFTER_KEY_SPACE,  // in whitespace characters after key and before value
    AFTER_VAL_SPACE,  // in whitespace characters after value
    ESCAPE,           // in escape character of quoted string
    ERROR             // error state, e.g. encounter more than one value
  } state = PRE_KEY_SPACE;

  char quote = 0;  // single or double quote
  std::string current_str;
  ConfigKV res;

  for (auto i = line.begin(); i != line.end();) {
    switch (state) {
      case PRE_KEY_SPACE:
        if (!std::isspace(*i)) {
          if (*i == '#') {
            i = line.end();
          } else {
            state = KEY;
          }
        } else {
          i++;
        }
        break;
      case KEY:
        if (std::isspace(*i)) {
          res.first = current_str;
          current_str = "";
          state = AFTER_KEY_SPACE;
        } else if (*i == '#') {
          res.first = current_str;
          i = line.end();
        } else {
          current_str.push_back(*i);
          i++;
        }
        break;
      case AFTER_KEY_SPACE:
        if (!std::isspace(*i)) {
          if (*i == '"' || *i == '\'') {
            state = QUOTED;
            quote = *i;
            i++;
          } else if (*i == '#') {
            i = line.end();
          } else {
            state = NORMAL;
          }
        } else {
          i++;
        }
        break;
      case NORMAL:
        if (*i == '#') {
          res.second = current_str;
          i = line.end();
        } else {
          current_str.push_back(*i);
          i++;
        }
        break;
      case QUOTED:
        if (*i == '\\') {
          state = ESCAPE;
        } else if (*i == quote) {
          res.second = current_str;
          state = AFTER_VAL_SPACE;
        } else {
          current_str.push_back(*i);
        }
        i++;
        break;
      case ESCAPE:
        if (*i == '\'' || *i == '"' || *i == '\\') {
          current_str.push_back(*i);
        } else if (*i == 't') {
          current_str.push_back('\t');
        } else if (*i == 'r') {
          current_str.push_back('\r');
        } else if (*i == 'n') {
          current_str.push_back('\n');
        } else if (*i == 'v') {
          current_str.push_back('\v');
        } else if (*i == 'f') {
          current_str.push_back('\f');
        } else if (*i == 'b') {
          current_str.push_back('\b');
        }
        state = QUOTED;
        i++;
        break;
      case AFTER_VAL_SPACE:
        if (!std::isspace(*i)) {
          if (*i == '#') {
            i = line.end();
          } else {
            state = ERROR;
          }
        } else {
          i++;
        }
        break;
      case ERROR:
        i = line.end();
        break;
    }
  }

  if (state == KEY) {
    res.first = current_str;
  } else if (state == NORMAL) {
    res.second = util::Trim(current_str, " \t\r\n\v\f\b");
  } else if (state == QUOTED || state == ESCAPE) {
    return {Status::NotOK, "config line ends unexpectedly in quoted string"};
  } else if (state == ERROR) {
    return {Status::NotOK, "more than 2 item in config line"};
  }

  return res;
}