boost实现FTP文件下载

Boost库提供了一个简单的FTP客户端库，可以用于FTP文件下载和上传。下面是一个使用Boost库实现FTP文件下载的示例代码：

#include <iostream>
#include <fstream>
#include <boost/asio.hpp>
#include <boost/asio/ssl.hpp>

using namespace boost::asio;
using namespace boost::asio::ip;

int main(int argc, char* argv[])
{
    if (argc != 4) {
        std::cerr << "Usage: " << argv[0] << " ftp://[<user>:<password>@]<host>/<url-path> <local-file> <ssl>\n";
        return 1;
    }

    std::string url = argv[1];
    std::string local_file = argv[2];
    bool ssl = std::stoi(argv[3]);

    // 解析URL
    std::string protocol, user, password, host, path;
    uint16_t port;
    try {
        std::regex url_regex(R"(^ftp://([^:@]+)(?::([^@]+))?@([^/]+)(?::(\d+))?(/.*)?$)");
        std::smatch url_match;
        if (!std::regex_match(url, url_match, url_regex)) throw std::runtime_error("invalid url");
        user = url_match[1].str();
        password = url_match[2].str();
        host = url_match[3].str();
        port = url_match[4].str().empty() ? (ssl ? 990 : 21) : std::stoi(url_match[4].str());
        path = url_match[5].str().empty() ? "/" : url_match[5].str();
        protocol = ssl ? "ftps" : "ftp";
    } catch (const std::exception& e) {
        std::cerr << "Error: " << e.what() << std::endl;
        return 1;
    }

    io_context io_ctx;
    if (ssl) {
        // SSL连接
        ssl::context ssl_ctx(ssl::context::tlsv12_client);
        ssl_ctx.set_default_verify_paths();
        ssl::stream<ip::tcp::socket> ssl_socket(io_ctx, ssl_ctx);
        tcp::resolver resolver(io_ctx);
        auto endpoints = resolver.resolve(protocol, host, std::to_string(port));
        connect(ssl_socket.lowest_layer(), endpoints);
        ssl_socket.handshake(ssl::stream_base::client);
        std::ostream request_stream(&ssl_socket);
        std::istream response_stream(&ssl_socket);
        std::string reply;
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "USER " << user << "\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '3') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "PASS " << password << "\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "TYPE I\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "PASV\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        std::regex pasv_regex(R"(^227 Entering Passive Mode \((\d+),(\d+),(\d+),(\d+),(\d+),(\d+)\)\.$)");
        std::smatch pasv_match;
        if (!std::regex_match(reply, pasv_match, pasv_regex)) {
            std::cerr << "Error: invalid PASV response" << std::endl;
            return 1;
        }
        uint16_t pasv_port = std::stoi(pasv_match[5].str()) * 256 + std::stoi(pasv_match[6].str());
        tcp::socket data_socket(io_ctx);
        tcp::endpoint data_endpoint(ip::address::from_string(host), pasv_port);
        data_socket.connect(data_endpoint);
        request_stream << "RETR " << path << "\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '1' && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        std::ofstream file(local_file, std::ios::binary);
        std::vector<char> buffer(1024);
        while (data_socket.available() > 0) {
            std::size_t bytes_transferred = data_socket.read_some(buffer.data(), buffer.size());
            file.write(buffer.data(), bytes_transferred);
        }
        data_socket.close();
        request_stream << "QUIT\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
    } else {
        // 非SSL连接
        tcp::socket control_socket(io_ctx);
        tcp::resolver resolver(io_ctx);
        auto endpoints = resolver.resolve(protocol, host, std::to_string(port));
        connect(control_socket, endpoints);
        std::ostream request_stream(&control_socket);
        std::istream response_stream(&control_socket);
        std::string reply;
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "USER " << user << "\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '3') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "PASS " << password << "\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "TYPE I\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        request_stream << "PASV\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        std::regex pasv_regex(R"(^227 Entering Passive Mode \((\d+),(\d+),(\d+),(\d+),(\d+),(\d+)\)\.$)");
        std::smatch pasv_match;
        if (!std::regex_match(reply, pasv_match, pasv_regex)) {
            std::cerr << "Error: invalid PASV response" << std::endl;
            return 1;
        }
        uint16_t pasv_port = std::stoi(pasv_match[5].str()) * 256 + std::stoi(pasv_match[6].str());
        tcp::socket data_socket(io_ctx);
        tcp::endpoint data_endpoint(ip::address::from_string(host), pasv_port);
        data_socket.connect(data_endpoint);
        request_stream << "RETR " << path << "\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '1' && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
        std::ofstream file(local_file, std::ios::binary);
        std::vector<char> buffer(1024);
        while (data_socket.available() > 0) {
            std::size_t bytes_transferred = data_socket.read_some(buffer.data(), buffer.size());
            file.write(buffer.data(), bytes_transferred);
        }
        data_socket.close();
        request_stream << "QUIT\r\n";
        std::getline(response_stream, reply);
        if (!reply.empty() && reply[0] != '2') {
            std::cerr << "Error: " << reply << std::endl;
            return 1;
        }
    }

    std::cout << "Downloaded " << url << " to " << local_file << std::endl;
    return 0;
}

该示例代码使用正则表达式解析FTP URL，并使用Boost库的io_context、tcp、ssl等模块实现FTP文件下载。其中，如果需要下载的是FTP over SSL（即FTPS），需要使用Boost库的ssl模块创建SSL连接，并在下载文件前进行身份验证。