tcp_client.h

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// Copyright(c) 2015-present, Gabi Melman & spdlog contributors.
// Distributed under the MIT License (http://opensource.org/licenses/MIT)
 
#pragma once
 
#ifdef _WIN32
#    error include tcp_client-windows.h instead
#endif
 
// tcp client helper
#include <spdlog/common.h>
#include <spdlog/details/os.h>
 
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/tcp.h>
 
#include <string>
 
namespace spdlog {
namespace details {
class tcp_client
{
    int socket_ = -1;
 
public:
    bool is_connected() const
    {
        return socket_ != -1;
    }
 
    void close()
    {
        if (is_connected())
        {
            ::close(socket_);
            socket_ = -1;
        }
    }
 
    int fd() const
    {
        return socket_;
    }
 
    ~tcp_client()
    {
        close();
    }
 
    // try to connect or throw on failure
    void connect(const std::string &host, int port)
    {
        close();
        struct addrinfo hints
        {};
        memset(&hints, 0, sizeof(struct addrinfo));
        hints.ai_family = AF_INET;       // IPv4
        hints.ai_socktype = SOCK_STREAM; // TCP
        hints.ai_flags = AI_NUMERICSERV; // port passed as as numeric value
        hints.ai_protocol = 0;
 
        auto port_str = std::to_string(port);
        struct addrinfo *addrinfo_result;
        auto rv = ::getaddrinfo(host.c_str(), port_str.c_str(), &hints, &addrinfo_result);
        if (rv != 0)
        {
            auto msg = fmt::format("::getaddrinfo failed: {}", gai_strerror(rv));
            throw_spdlog_ex(msg);
        }
 
        // Try each address until we successfully connect(2).
        int last_errno = 0;
        for (auto *rp = addrinfo_result; rp != nullptr; rp = rp->ai_next)
        {
#if defined(SOCK_CLOEXEC)
            const int flags = SOCK_CLOEXEC;
#else
            const int flags = 0;
#endif
            socket_ = ::socket(rp->ai_family, rp->ai_socktype | flags, rp->ai_protocol);
            if (socket_ == -1)
            {
                last_errno = errno;
                continue;
            }
            rv = ::connect(socket_, rp->ai_addr, rp->ai_addrlen);
            if (rv == 0)
            {
                break;
            }
            last_errno = errno;
            ::close(socket_);
            socket_ = -1;
        }
        ::freeaddrinfo(addrinfo_result);
        if (socket_ == -1)
        {
            throw_spdlog_ex("::connect failed", last_errno);
        }
 
        // set TCP_NODELAY
        int enable_flag = 1;
        ::setsockopt(socket_, IPPROTO_TCP, TCP_NODELAY, reinterpret_cast<char *>(&enable_flag), sizeof(enable_flag));
 
        // prevent sigpipe on systems where MSG_NOSIGNAL is not available
#if defined(SO_NOSIGPIPE) && !defined(MSG_NOSIGNAL)
        ::setsockopt(socket_, SOL_SOCKET, SO_NOSIGPIPE, reinterpret_cast<char *>(&enable_flag), sizeof(enable_flag));
#endif
 
#if !defined(SO_NOSIGPIPE) && !defined(MSG_NOSIGNAL)
#    error "tcp_sink would raise SIGPIPE since niether SO_NOSIGPIPE nor MSG_NOSIGNAL are available"
#endif
    }
 
    // Send exactly n_bytes of the given data.
    // On error close the connection and throw.
    void send(const char *data, size_t n_bytes)
    {
        size_t bytes_sent = 0;
        while (bytes_sent < n_bytes)
        {
#if defined(MSG_NOSIGNAL)
            const int send_flags = MSG_NOSIGNAL;
#else
            const int send_flags = 0;
#endif
            auto write_result = ::send(socket_, data + bytes_sent, n_bytes - bytes_sent, send_flags);
            if (write_result < 0)
            {
                close();
                throw_spdlog_ex("write(2) failed", errno);
            }
 
            if (write_result == 0) // (probably should not happen but in any case..)
            {
                break;
            }
            bytes_sent += static_cast<size_t>(write_result);
        }
    }
};
} // namespace details
} // namespace spdlog