Salticidae: minimal C++ asynchronous network library.

Features

• Simplicity. The library is self-contained, small in code base, and only relies on libuv and libssl/libcrypto (OpenSSL, for SHA256 purpose). Despite the multi-threaded nature of the library, a user only needs to understand the callbacks are invoked in a sequential order driven by a single user-initiated event loop.
• Clarity. With moderate use of C++ template and new features, the vast majority of the code is self-documenting.
• Layered design. You can use network abstraction from the lowest socket connection level to the highest P2P network level.
• Performance. Based on a hybrid solution that combines both thread-based and event-driven concurrency paradigms, it gets the best of both worlds. The implementation strives to incur very little overhead in processing network I/O, and avoid unnecessary memory copies thanks to the move semantics.
• Utilities. The library also provides with some useful gadgets, such as command-line parser, libuv abstraction, etc.
• Security. It supports SSL/TLS, with customized certificate verification (as part of the connection callback).
• Bindings for other languages. The library itself supports C APIs and the other project salticidae-go supports invoking the library in Go through cgo.

Functionalities

• ConnPool: byte level connection pool implementation, ConnPool::Conn (or ConnPool::conn_t) objects represent connections to which one can send/receive a stream of binary data asynchronously.
• MsgNetwork<OpcodeType>: message level network pool implementation, MsgNetwork::Conn (or MsgNetwork::cont_t) objects represent channels to which one can send/receive predefined messages asynchronously. Message handler functions are registered by reg_handler() and invoked upon receiving a new message. OpcodeType is the type used for identifying message types. A valid message class must have:
  • a static member opcode typed OpcodeType as the message type identifier
  • a member serialized typed DataStream which contains the serialized data of the message.
  • a constructor MsgType(DataStream &&) that parse the message from stream.

Based on MsgNetwork, salticidae provides the following higher level abstractions:

• PeerNetwork<OpcodeType>: simple P2P network pool implementation. It will ensure exactly one underlying bi-directional connection is established per added peer, and retry the connection when it is broken. Ping-pong messages are utilized to test the connectivity periodically.
• ClientNetwork<OpcodeType>: simple client-server network pool implementation. A server who initially calls listen() will accept the incoming client messages, while a client simply calls connect() to connect to a known server.

Dependencies

• CMake >= 3.9
• C++14
• libuv >= 1.10.0
• openssl >= 1.1.0

Minimal working P2P network

#include <memory>
#include "salticidae/event.h"
#include "salticidae/network.h"

using Net = salticidae::PeerNetwork<uint8_t>;

int main() {
    std::vector<std::pair<salticidae::NetAddr, std::unique_ptr<Net>>> nodes;
    Net::Config config;
    salticidae::EventContext ec;
    config.ping_period(2);
    nodes.resize(4);
    for (size_t i = 0; i < nodes.size(); i++)
    {
        salticidae::NetAddr addr("127.0.0.1:" + std::to_string(10000 + i));
        auto &net = (nodes[i] = std::make_pair(addr, std::make_unique<Net>(ec, config))).second;
        net->start();
        net->listen(addr);
    }
    for (size_t i = 0; i < nodes.size(); i++)
        for (size_t j = 0; j < nodes.size(); j++)
            if (i != j)
            {
                auto &node = nodes[i].second;
                auto &peer_addr = nodes[j].first;
                salticidae::PeerId pid{peer_addr};
                node->add_peer(pid);
                node->set_peer_addr(pid, peer_addr);
                node->conn_peer(pid);
            }
    ec.dispatch();
    return 0;
}

Using MsgNetwork class

#include <cstdio>
#include <string>
#include <functional>

#include "salticidae/msg.h"
#include "salticidae/event.h"
#include "salticidae/network.h"
#include "salticidae/stream.h"

using salticidae::NetAddr;
using salticidae::DataStream;
using salticidae::MsgNetwork;
using salticidae::htole;
using salticidae::letoh;
using std::placeholders::_1;
using std::placeholders::_2;

/** Hello Message. */
struct MsgHello {
    static const uint8_t opcode = 0x0;
    DataStream serialized;
    std::string name;
    std::string text;
    /** Defines how to serialize the msg. */
    MsgHello(const std::string &name,
            const std::string &text) {
        serialized << htole((uint32_t)name.length());
        serialized << name << text;
    }
    /** Defines how to parse the msg. */
    MsgHello(DataStream &&s) {
        uint32_t len;
        s >> len;
        len = letoh(len);
        name = std::string((const char *)s.get_data_inplace(len), len);
        len = s.size();
        text = std::string((const char *)s.get_data_inplace(len), len);
    }
};

/** Acknowledgement Message. */
struct MsgAck {
    static const uint8_t opcode = 0x1;
    DataStream serialized;
    MsgAck() {}
    MsgAck(DataStream &&s) {}
};

const uint8_t MsgHello::opcode;
const uint8_t MsgAck::opcode;

using MsgNetworkByteOp = MsgNetwork<uint8_t>;

struct MyNet: public MsgNetworkByteOp {
    const std::string name;
    const NetAddr peer;

    MyNet(const salticidae::EventContext &ec,
            const std::string name,
            const NetAddr &peer):
            MsgNetwork<uint8_t>(ec, MsgNetwork::Config()),
            name(name),
            peer(peer) {
        /* message handler could be a bound method */
        reg_handler(
            salticidae::generic_bind(&MyNet::on_receive_hello, this, _1, _2));

        reg_conn_handler([this](const ConnPool::conn_t &conn, bool connected) {
            if (connected)
            {
                if (conn->get_mode() == ConnPool::Conn::ACTIVE)
                {
                    printf("[%s] connected, sending hello.\n",
                            this->name.c_str());
                    /* send the first message through this connection */
                    send_msg(MsgHello(this->name, "Hello there!"),
                            salticidae::static_pointer_cast<Conn>(conn));
                }
                else
                    printf("[%s] accepted, waiting for greetings.\n",
                            this->name.c_str());
            }
            else
            {
                printf("[%s] disconnected, retrying.\n", this->name.c_str());
                /* try to reconnect to the same address */
                connect(conn->get_addr(), false);
            }
            return true;
        });
    }

    void on_receive_hello(MsgHello &&msg, const MyNet::conn_t &conn) {
        printf("[%s] %s says %s\n", name.c_str(), msg.name.c_str(), msg.text.c_str());
        /* send acknowledgement */
        send_msg(MsgAck(), conn);
    }
};

void on_receive_ack(MsgAck &&msg, const MyNet::conn_t &conn) {
    auto net = static_cast<MyNet *>(conn->get_net());
    printf("[%s] the peer knows\n", net->name.c_str());
}

int main() {
    salticidae::EventContext ec;
    NetAddr alice_addr("127.0.0.1:12345");
    NetAddr bob_addr("127.0.0.1:12346");

    /* test two nodes in the same main loop */
    MyNet alice(ec, "alice", bob_addr);
    MyNet bob(ec, "bob", alice_addr);

    /* message handler could be a normal function */
    alice.reg_handler(on_receive_ack);
    bob.reg_handler(on_receive_ack);

    /* start all threads */
    alice.start();
    bob.start();

    /* accept incoming connections */
    alice.listen(alice_addr);
    bob.listen(bob_addr);

    /* try to connect once */
    alice.connect(bob_addr, false);
    bob.connect(alice_addr, false);

    /* the main loop can be shutdown by ctrl-c or kill */
    auto shutdown = [&](int) {ec.stop();};
    salticidae::SigEvent ev_sigint(ec, shutdown);
    salticidae::SigEvent ev_sigterm(ec, shutdown);
    ev_sigint.add(SIGINT);
    ev_sigterm.add(SIGTERM);

    /* enter the main loop */
    ec.dispatch();
    return 0;
}