worker.cpp (from https://github.com/nikhilm/uvbook/blob/master/code/multi-echo-server/worker.c)

worker.cpp

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <uv.h>

#include <uvw.hpp>

uv_loop_t *loop;
uv_pipe_t queue;

typedef struct {
    uv_write_t req;
    uv_buf_t buf;
} write_req_t;

void free_write_req(uv_write_t *req) {
    write_req_t *wr = (write_req_t*) req;
    free(wr->buf.base);
    free(wr);
}

void alloc_buffer(uv_handle_t *handle, size_t suggested_size, uv_buf_t *buf) {
    buf->base = static_cast<char*>(malloc(suggested_size));
    buf->len = suggested_size;
}

void echo_write(uv_write_t *req, int status) {
    if (status) {
        fprintf(stderr, "Write error %s\n", uv_err_name(status));
    }
    free_write_req(req);
}

void echo_read(uv_stream_t *client, ssize_t nread, const uv_buf_t *buf) {
    if (nread > 0) {
        write_req_t *req = (write_req_t*) malloc(sizeof(write_req_t));
        req->buf = uv_buf_init(buf->base, nread);
        uv_write((uv_write_t*) req, client, &req->buf, 1, echo_write);
        return;
    }
    
    if (nread < 0) {
        if (nread != UV_EOF)
            fprintf(stderr, "Read error %s\n", uv_err_name(nread));
        uv_close((uv_handle_t*) client, NULL);
    }
    
    free(buf->base);
}

void on_new_connection(uv_stream_t *q, ssize_t nread, const uv_buf_t *buf) {
    if (nread < 0) {
        if (nread != UV_EOF)
            fprintf(stderr, "Read error %s\n", uv_err_name(nread));
        uv_close((uv_handle_t*) q, NULL);
        return;
    }
    
    uv_pipe_t *pipe = (uv_pipe_t*) q;
    if (!uv_pipe_pending_count(pipe)) {
        fprintf(stderr, "No pending count\n");
        return;
    }
    
    uv_handle_type pending = uv_pipe_pending_type(pipe);
    assert(pending == UV_TCP);
    
    uv_tcp_t *client = (uv_tcp_t*) malloc(sizeof(uv_tcp_t));
    uv_tcp_init(loop, client);
    if (uv_accept(q, (uv_stream_t*) client) == 0) {
        uv_os_fd_t fd;
        uv_fileno((const uv_handle_t*) client, &fd);
        fprintf(stderr, "Worker %d: Accepted fd %d\n", getpid(), fd);
        uv_read_start((uv_stream_t*) client, alloc_buffer, echo_read);
    }
    else {
        uv_close((uv_handle_t*) client, NULL);
    }
}

// *************
//
// This is the new UVW based socket listener that should get the handle from IPC
//
// *************
void listen(uvw::Loop &loop) {
    auto server = loop.resource<uvw::PipeHandle>(true);
    
    server->on<uvw::ErrorEvent>([](const uvw::ErrorEvent &errorEvent, uvw::PipeHandle &) { std::cerr << errorEvent.what(); });
    server->on<uvw::CloseEvent>([](const uvw::CloseEvent &, uvw::PipeHandle &socket) { std::cerr << "close"; });
    server->on<uvw::EndEvent>([](const uvw::EndEvent &, uvw::PipeHandle &socket) { std::cerr << "end"; socket.close(); });
    server->on<uvw::DataEvent>([](const uvw::DataEvent &, uvw::PipeHandle &socket) {
        
        std::cerr << "\n\nPENDING" << socket.pending() << "\n";

        // TCP Client
        std::shared_ptr<uvw::TCPHandle> tcpClient = socket.loop().resource<uvw::TCPHandle>();
        tcpClient->once<uvw::EndEvent>([](const uvw::EndEvent &, uvw::TCPHandle &client) { client.close(); });
        tcpClient->on<uvw::DataEvent>([](const uvw::DataEvent &, uvw::TCPHandle &) {
            std::cerr << "Data received!!!";
        });
        
        // THIS FAILS!
        socket.accept(*tcpClient);

        tcpClient->read();
    });
    
    server->open(0);
    server->read();
}

int main() {
    
    // Original C -based system

    //    loop = uv_default_loop();
    
    //    uv_pipe_init(loop, &queue, 1 /* ipc */);
    //    uv_pipe_open(&queue, 0);
    //    uv_read_start((uv_stream_t*)&queue, alloc_buffer, on_new_connection);
    //    return uv_run(loop, UV_RUN_DEFAULT);

    
    // Let's try to do the same with UVW
    
    auto loop = uvw::Loop::getDefault();
    listen(*loop);
    loop->run();

}