zircon/system/ulib/cmdline/args_parser.cpp

// Copyright 2018 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <cmdline/args_parser.h>

#include <algorithm>

namespace cmdline {

namespace {

// Returns true if the argument is the special string that indicates the end
// of options.
bool IsOptionEndFlag(const char* arg) {
    return strcmp(arg, "--") == 0;
}

// Checks if the given argument is a short option and if it is, returns the
// letter. If not, returns 0.
char GetShortOption(const char* arg, const char** value_begin) {
    if (arg[0] == '-' && arg[1] != 0 && arg[1] != '-') {
        *value_begin = &arg[2]; // Arg (if any) follows immediately.
        return arg[1];
    }
    *value_begin = nullptr;
    return 0;
}

// Checks if the given argument is a long option and returns it, not including
// the preceding "--". If it's not an option, returns the empty string. To
// differentiate args consisting of only "--" and non-options, callers should
// call IsOptionEndFlag() before this.
std::string GetLongOption(const char* arg, const char** value_begin) {
    *value_begin = nullptr;
    if (arg[0] != '-' || arg[1] != '-')
        return std::string();

    // See if there's and "=<arg>" in this flag.
    const char* equals = strchr(arg, '=');
    if (!equals)
        return &arg[2]; // No "=<arg>".

    // value_begin gets everything after the equals.
    *value_begin = &equals[1];

    // Return everything between the '--' (2 bytes) and the equals.
    return std::string(&arg[2], equals - arg - 2);
}

} // namespace

GeneralArgsParser::GeneralArgsParser() = default;
GeneralArgsParser::~GeneralArgsParser() = default;

void GeneralArgsParser::AddGeneralSwitch(
    const char* long_name, const char short_name, const char* help,
    OnOffSwitchCallback on_switch, OnOffSwitchCallback off_switch) {
    Record& record = records_.emplace_back();
    record.long_name = long_name;
    record.short_name = short_name;
    record.help_text = help;
    record.on_switch_callback = std::move(on_switch);
    if (off_switch != nullptr) {
        record.off_switch_callback = std::move(off_switch);
    }
}

void GeneralArgsParser::AddGeneralSwitch(const char* long_name,
                                         const char short_name,
                                         const char* help,
                                         StringCallback cb) {
    Record& record = records_.emplace_back();
    record.long_name = long_name;
    record.short_name = short_name;
    record.help_text = help;
    record.string_callback = std::move(cb);
}

std::string GeneralArgsParser::GetHelp() const {
    std::vector<std::string> switches;
    for (const auto& record : records_)
        switches.push_back(record.help_text);

    std::sort(switches.begin(), switches.end());

    std::string result;
    for (const std::string& str : switches) {
        result.append(str);
        result.append("\n\n");
    }
    return result;
}

Status GeneralArgsParser::ParseGeneral(
    int argc, const char* argv[], std::vector<std::string>* params) const {
    // Expect argv[0] to be the program itself.
    if (argc <= 1)
        return Status::Ok();

    int last_option_index = argc - 1;
    for (int i = 1; i < argc; i++) {
        // Non-null when we find the argument.
        const char* arg_begin = nullptr;
        bool off_switch = false;

        const Record* record = nullptr;
        if (IsOptionEndFlag(argv[i])) {
            // End of option indicator.
            last_option_index = i;
            break;
        } else if (char c = GetShortOption(argv[i], &arg_begin)) {
            // Single-letter option.
            for (const Record& cur_record : records_) {
                if (cur_record.short_name == c) {
                    record = &cur_record;
                    break;
                }
            }
        } else if (auto long_opt = GetLongOption(argv[i], &arg_begin);
                   !long_opt.empty()) {
            // Long option.
            for (const Record& cur_record : records_) {
                if (cur_record.long_name == long_opt) {
                    record = &cur_record;
                    break;
                } else if (std::string("no") + cur_record.long_name == long_opt) {
                    off_switch = true;
                    record = &cur_record;
                    break;
                }
            }
        } else {
            // Non-option.
            last_option_index = i - 1;
            break;
        }

        // If we get here we should have found a record for the option.
        if (!record)
            return Status::Error(
                std::string(argv[i]) +
                " is not a valid option. " + invalid_option_suggestion_);

        if (NeedsArg(record)) {
            // Arguments can be already found ("-cfoo" or "--foo=bar") or they could
            // be the following parameter.
            if (!arg_begin || !*arg_begin) {
                // Argument is in the next token of the command line.
                if (i == argc - 1)
                    return Status::Error(
                        std::string(argv[i]) +
                        " expects an argument but none was given.\n\n" +
                        record->help_text);
                i++;
                arg_begin = argv[i];
            }
        } else {
            // Don't expect an arg for this switch.
            if (arg_begin && *arg_begin) {
                // Arg points somewhere other than the end of the string when we
                // weren't expecting an arg.
                return Status::Error(
                    std::string("Unexpected value for argument that doesn't take one:\n  ") +
                    argv[i] + "\n\n" +
                    record->help_text);
            }
        }

        // Execute the right callback.
        Status status = Status::Ok();
        if (off_switch) {
            if (record->off_switch_callback) {
                record->off_switch_callback();
            } else {
                status = Status::Error(
                    std::string("--") + record->long_name +
                    " can only be turned on, not off.\n\n" +
                    record->help_text);
            }
        } else if (record->on_switch_callback) {
            record->on_switch_callback();
        } else if (record->string_callback) {
            status = record->string_callback(arg_begin);
        }

        if (status.has_error())
            return status;
    }

    // Everything else following the parameters are the positional arguments.
    for (int i = last_option_index + 1; i < argc; i++)
        params->push_back(argv[i]);
    return Status::Ok();
}

// static
bool GeneralArgsParser::NeedsArg(const Record* record) {
    return !!record->string_callback;
}

} // namespace cmdline