teems/App/net.cpp

#include <iostream>

#include "Enclave_u.h"
#include "Untrusted.hpp"
#include "net.hpp"

// The command type byte values

#define COMMAND_EPOCH 0x00
#define COMMAND_MESSAGE 0x01
#define COMMAND_CHUNK 0x02

#define VERBOSE_NET
// #define DEBUG_NET_CLIENTS

#define CEILDIV(x,y) (((x)+(y)-1)/(y))

NetIO *g_netio = NULL;
size_t client_count = 0;

NodeIO::NodeIO(tcp::socket &&socket, nodenum_t nodenum) :
    sock(std::move(socket)), node_num(nodenum), msgsize_inflight(0),
    chunksize_inflight(0), recv_msgsize_inflight(0),
    recv_chunksize_inflight(0), bytes_sent(0)
{
}

uint8_t *NodeIO::request_frame()
{
    if (frames_available.empty()) {
        // Allocate a new frame.  Note that this memory will (at this
        // time) never get deallocated.  In theory, we could deallocate
        // it in return_frame, but if a certain number of frames were
        // allocated here, it means we had that much data in flight
        // (queued but not accepted for sending by the OS), and we're
        // likely to need that much again.  Subsequent messages will
        // _reuse_ the allocated data, though, so the used memory won't
        // grow forever, and will be limited to the amount of in-flight
        // data needed.
        return new uint8_t[FRAME_SIZE];
    }
    // Copy the pointer to the frame out of the deque and remove it from
    // the deque.  Note this is _not_ taking the address of the element
    // *in* the deque (and then popping it, which would invalidate that
    // pointer).
    frame_deque_lock.lock();
    uint8_t *frame = frames_available.back();
    frames_available.pop_back();
    frame_deque_lock.unlock();
    return frame;
}

void NodeIO::return_frame(uint8_t *frame)
{
    if (!frame) return;

    // We push the frame back on to the end of the deque so that it will
    // be the next one used.  This may lead to better cache behaviour?
    frame_deque_lock.lock();
    frames_available.push_back(frame);
    frame_deque_lock.unlock();
}

void NodeIO::send_header_data(uint64_t header, uint8_t *data, size_t len)
{
    commands_deque_lock.lock();
    commands_inflight.push_back({header, data, len});
    if (commands_inflight.size() == 1) {
        async_send_commands();
    }
    commands_deque_lock.unlock();
}

void NodeIO::async_send_commands()
{
    std::vector<boost::asio::const_buffer> tosend;

    CommandTuple *commandp = &(commands_inflight.front());
    tosend.push_back(boost::asio::buffer(&(std::get<0>(*commandp)), 5));
    if (std::get<1>(*commandp) != NULL && std::get<2>(*commandp) > 0) {
        tosend.push_back(boost::asio::buffer(std::get<1>(*commandp),
            std::get<2>(*commandp)));
    }
    boost::asio::async_write(sock, tosend,
        [this, commandp](boost::system::error_code, std::size_t){
            // When the write completes, pop the command from the deque
            // (which should now be in the front)
            commands_deque_lock.lock();
            assert(!commands_inflight.empty() &&
                &(commands_inflight.front()) == commandp);
            bytes_sent = bytes_sent + 5 + std::get<2>(*commandp);
            uint8_t *data = std::get<1>(*commandp);
            commands_inflight.pop_front();
            if (commands_inflight.size() > 0) {
                async_send_commands();
            }
            // And return the frame
            return_frame(data);
            commands_deque_lock.unlock();
        });
}

void NodeIO::send_epoch(uint32_t epoch_num)
{
    uint64_t header = (uint64_t(epoch_num) << 8) + COMMAND_EPOCH;
    send_header_data(header, NULL, 0);
}

void NodeIO::send_message_header(uint32_t tot_message_len)
{
    uint64_t header = (uint64_t(tot_message_len) << 8) + COMMAND_MESSAGE;
    send_header_data(header, NULL, 0);
    // If we're sending a new message header, we have to have finished
    // sending the previous message.
    assert(chunksize_inflight == msgsize_inflight);
    msgsize_inflight = tot_message_len;
    chunksize_inflight = 0;
#ifdef TRACE_SOCKIO
    struct timeval now;
    gettimeofday(&now, NULL);
    printf("%lu.%06lu: RTE queueing %u bytes to %s\n", now.tv_sec,
        now.tv_usec, msgsize_inflight,
        g_netio->config().nodes[node_num].name.c_str());
    if (msgsize_inflight == 0) {
        printf("%lu.%06lu: RTE queued %u bytes to %s\n", now.tv_sec,
            now.tv_usec, msgsize_inflight,
            g_netio->config().nodes[node_num].name.c_str());
    }
#endif
}

bool NodeIO::send_chunk(uint8_t *data, uint32_t chunk_len)
{
    assert(chunk_len <= FRAME_SIZE);
    uint64_t header = (uint64_t(chunk_len) << 8) + COMMAND_CHUNK;
    send_header_data(header, data, chunk_len);
    chunksize_inflight += chunk_len;
    assert(chunksize_inflight <= msgsize_inflight);
#ifdef TRACE_SOCKIO
    if (msgsize_inflight == chunksize_inflight) {
        struct timeval now;
        gettimeofday(&now, NULL);
        printf("%lu.%06lu: RTE queued %u bytes to %s\n", now.tv_sec,
            now.tv_usec, msgsize_inflight,
            g_netio->config().nodes[node_num].name.c_str());
    }
#endif
    return (chunksize_inflight < msgsize_inflight);
}

void NodeIO::recv_commands(
    std::function<void(boost::system::error_code)> error_cb,
    std::function<void(uint32_t)> epoch_cb)
{
    // Asynchronously read the header
    receive_header = 0;
    boost::asio::async_read(sock, boost::asio::buffer(&receive_header, 5),
        [this, error_cb, epoch_cb]
        (boost::system::error_code ec, std::size_t) {
            if (ec) {
                error_cb(ec);
                return;
            }
            if ((receive_header & 0xff) == COMMAND_EPOCH) {
                epoch_cb(uint32_t(receive_header >> 8));
                recv_commands(error_cb, epoch_cb);
            } else if ((receive_header & 0xff) == COMMAND_MESSAGE) {
                assert(recv_msgsize_inflight == recv_chunksize_inflight);
                recv_msgsize_inflight = uint32_t(receive_header >> 8);
                recv_chunksize_inflight = 0;
#ifdef TRACE_SOCKIO
                struct timeval now;
                gettimeofday(&now, NULL);
                printf("%lu.%06lu: RTE receiving %u bytes from %s\n", now.tv_sec,
                    now.tv_usec, recv_msgsize_inflight,
                    g_netio->config().nodes[node_num].name.c_str());
                if (recv_msgsize_inflight == 0) {
                    printf("%lu.%06lu: RTE received %u bytes from %s\n", now.tv_sec,
                        now.tv_usec, recv_msgsize_inflight,
                        g_netio->config().nodes[node_num].name.c_str());
                }
#endif
                if (ecall_message(node_num, recv_msgsize_inflight)) {
                    recv_commands(error_cb, epoch_cb);
                } else {
                    printf("ecall_message failed\n");
                }
            } else if ((receive_header & 0xff) == COMMAND_CHUNK) {
                uint32_t this_chunk_size = uint32_t(receive_header >> 8);
                assert(recv_chunksize_inflight + this_chunk_size <=
                    recv_msgsize_inflight);
                recv_chunksize_inflight += this_chunk_size;
                boost::asio::async_read(sock, boost::asio::buffer(
                    receive_frame, this_chunk_size),
                    [this, error_cb, epoch_cb, this_chunk_size]
                    (boost::system::error_code ecc, std::size_t) {
                        if (ecc) {
                            error_cb(ecc);
                            return;
                        }
#ifdef TRACE_SOCKIO
                    if (recv_msgsize_inflight == recv_chunksize_inflight) {
                        struct timeval now;
                        gettimeofday(&now, NULL);
                        printf("%lu.%06lu: RTE received %u bytes from %s\n", now.tv_sec,
                            now.tv_usec, recv_msgsize_inflight,
                            g_netio->config().nodes[node_num].name.c_str());
                    }
#endif
                        if (ecall_chunk(node_num, receive_frame,
                                this_chunk_size)) {
                            recv_commands(error_cb, epoch_cb);
                        } else {
                            printf("ecall_chunk failed\n");
                        }
                    });
            } else {
                error_cb(boost::system::errc::make_error_code(
                    boost::system::errc::errc_t::invalid_argument));
            }
        });
}


uint64_t NodeIO::reset_bytes_sent()
{
    uint64_t b_sent = bytes_sent;
    bytes_sent = 0;
    return b_sent;
}

uint64_t NetIO::reset_bytes_sent()
{
    uint64_t total=0;
    for(size_t i = 0; i<nodeios.size(); i++) {
        if(nodeios[i].has_value()) {
            total+=((nodeios[i].value()).reset_bytes_sent());
        }
    }

    return total;
}

/*
    Receive clients dropped off messages, i.e. a CLIENT_MESSAGE_BUNDLE
*/

void NetIO::ing_receive_msgbundle(tcp::socket* csocket, clientid_t c_simid)
{

    unsigned char *msgbundle = (unsigned char*) malloc(msgbundle_size);

    boost::asio::async_read(*csocket, boost::asio::buffer(msgbundle, msgbundle_size),
        [this, csocket, msgbundle, c_simid]
        (boost::system::error_code ec, std::size_t) {
        if (ec) {
            if(ec == boost::asio::error::eof) {
                // Client connection terminated so we delete this socket
                delete(csocket);
            }
            else {
                printf("Error ing_receive_msgbundle : %s\n", ec.message().c_str());
            }
            return;
        }

#ifdef TRACE_SOCKIO
        struct timeval now;
        gettimeofday(&now, NULL);
        long elapsedus = (now.tv_sec - last_ing.tv_sec) * 1000000
            + (now.tv_usec - last_ing.tv_usec);
        if (num_ing > 0 && elapsedus > 500000) {
            printf("%lu.%06lu: End ingestion of %lu messages\n",
                last_ing.tv_sec, last_ing.tv_usec, num_ing);
            num_ing = 0;
        }
        if (num_ing == 0) {
            printf("%lu.%06lu: Begin ingestion\n", now.tv_sec,
                now.tv_usec);
        }
#endif

        bool ret;
        //Ingest the message_bundle
        if(conf.private_routing) {
            ret = ecall_ingest_msgbundle(c_simid, msgbundle, conf.m_priv_out);
        } else {
            ret = ecall_ingest_msgbundle(c_simid, msgbundle, conf.m_pub_out);
        }
        free(msgbundle);

#ifdef TRACE_SOCKIO
        gettimeofday(&last_ing, NULL);
        ++num_ing;
#endif

        // Continue to async receive client message bundles
        if(ret) {
            ing_receive_msgbundle(csocket, c_simid);
        }
    });
}

/*
    Handle new client connections.
    New clients always send an authentication message.
    For ingestion this is then followed by their msg_bundles every epoch.
*/
void NetIO::ing_authenticate_new_client(tcp::socket* csocket,
    const boost::system::error_code& error)
{
    if(error) {
        printf("Accept handler failed\n");
        return;
    }

#ifdef DEBUG_NET_CLIENTS
        printf("Accept handler success\n");
#endif
    unsigned char* auth_message = (unsigned char*) malloc(auth_size);
    boost::asio::async_read(*csocket, boost::asio::buffer(auth_message, auth_size),
        [this, csocket, auth_message]
        (boost::system::error_code ec, std::size_t) {
        if (ec) {
            if(ec == boost::asio::error::eof) {
                // Client connection terminated so we delete this socket
                delete(csocket);
            } else {
                printf("Error ing_auth_new_client : %s\n", ec.message().c_str());
            }
            return;
        }
        else {
            clientid_t c_simid = *((clientid_t *)(auth_message));
            // Read the authentication token
            unsigned char *auth_ptr = auth_message + sizeof(clientid_t);
            bool ret = ecall_authenticate(c_simid, auth_ptr);
            free(auth_message);

            // Receive client message bundles on this socket
            // for client sim_id c_simid
            if(ret) {
                client_count++;
                ing_receive_msgbundle(csocket, c_simid);
            } else{
                printf("Client <-> Ingestion authentication failed\n");
                delete(csocket);
            }
        }
    });
    ing_start_accept();
}

#ifdef TRACE_SOCKIO
static size_t stg_clients_connected = 0;
static size_t stg_clients_authenticated = 0;
#endif

/*
    Handle new client connections.
    New clients always send an authentication message.
    For storage this is then followed by the storage servers sending them
    their mailbox every epoch.
*/

void NetIO::stg_authenticate_new_client(tcp::socket* csocket,
    const boost::system::error_code& error)
{
    if(error) {
        printf("Accept handler failed\n");
        return;
    }

#ifdef DEBUG_NET_CLIENTS
        printf("Accept handler success\n");
#endif

    unsigned char* auth_message = (unsigned char*) malloc(auth_size);
    boost::asio::async_read(*csocket, boost::asio::buffer(auth_message, auth_size),
        [this, csocket, auth_message]
        (boost::system::error_code ec, std::size_t) {
        if (ec) {
            if(ec == boost::asio::error::eof) {
                // Client connection terminated so we delete this socket
                delete(csocket);
            } else {
                printf("Error stg_auth_new_client: %s\n", ec.message().c_str());
            }
            return;
        }
        else {
#ifdef TRACE_SOCKIO
                ++stg_clients_connected;
                if (stg_clients_connected % 1000 == 0) {
                    struct timeval now;
                    gettimeofday(&now, NULL);
                    printf("%lu.%06lu: STG %lu clients connected\n",
                        now.tv_sec, now.tv_usec, stg_clients_connected);
                }
#endif
            clientid_t c_simid = *((clientid_t *)(auth_message));
            // Read the authentication token
            unsigned char *auth_ptr = auth_message + sizeof(clientid_t);

            bool ret = ecall_storage_authenticate(c_simid, auth_ptr);
            free(auth_message);

            // If the auth is successful, store this socket into
            // a client socket array at the local_c_simid index
            // for storage servers to send clients their mailbox periodically.
            if(ret) {
                uint32_t lcid = c_simid / num_stg_nodes;
                client_sockets[lcid] = csocket;
#ifdef TRACE_SOCKIO
                ++stg_clients_authenticated;
                if (stg_clients_authenticated % 1000 == 0) {
                    struct timeval now;
                    gettimeofday(&now, NULL);
                    printf("%lu.%06lu: STG %lu clients authenticated\n",
                        now.tv_sec, now.tv_usec, stg_clients_authenticated);
                }
#endif
            }
            else{
                printf("Client <-> Storage authentication failed\n");
                delete (csocket);
            }
        }
    });
    stg_start_accept();
}

/*
  Asynchronously accept new client connections
*/
void NetIO::ing_start_accept()
{
    tcp::socket *csocket = new tcp::socket(io_context());
#ifdef DEBUG_NET_CLIENTS
    std::cout << "Accepting on " << myconf.clistenhost << ":" << myconf.clistenport << "\n";
#endif
    ingestion_acceptor->async_accept(*csocket,
        boost::bind(&NetIO::ing_authenticate_new_client, this, csocket,
        boost::asio::placeholders::error));
}

void NetIO::stg_start_accept()
{
    tcp::socket *csocket = new tcp::socket(io_context());
#ifdef DEBUG_NET_CLIENTS
    std::cout << "Accepting on " << myconf.slistenhost << ":" << myconf.slistenport << "\n";
#endif
    storage_acceptor->async_accept(*csocket,
        boost::bind(&NetIO::stg_authenticate_new_client, this, csocket,
        boost::asio::placeholders::error));
}


void NetIO::send_client_mailbox()
{

#ifdef PROFILE_NET_CLIENTS
    struct timespec tp;
    clock_gettime(CLOCK_REALTIME_COARSE, &tp);
    unsigned long start = tp.tv_sec * 1000000 + tp.tv_nsec/1000;
#endif

#ifdef TRACE_SOCKIO
    size_t clients_without_sockets = 0;
    size_t mailboxes_queued = 0;
#endif

    // Send each client their tokens for the next epoch
    for(uint32_t lcid = 0; lcid < num_clients_per_stg; lcid++)
    {
        unsigned char *tkn_ptr = epoch_tokens + lcid * token_bundle_size;
        unsigned char *buf_ptr = epoch_mailboxes + lcid * mailbox_size;

        if(client_sockets[lcid]!=nullptr) {
            boost::asio::async_write(*(client_sockets[lcid]),
                boost::asio::buffer(tkn_ptr, token_bundle_size),
                [this, lcid, buf_ptr](boost::system::error_code ec, std::size_t){

                if (ec) {
                    if(ec == boost::asio::error::eof) {
                        // Client connection terminated so we delete this socket
                        delete(client_sockets[lcid]);
                        printf("Client socket terminated!\n");
                    } else {
                        printf("Error send_client_mailbox tokens: %s\n", ec.message().c_str());
                    }
                    return;
                }

                boost::asio::async_write(*(client_sockets[lcid]),
                    boost::asio::buffer(buf_ptr, mailbox_size),
                    [this, lcid](boost::system::error_code ecc, std::size_t){

                    //printf("NetIO::send_client_mailbox, Client %d messages was sent\n", lcid);
                    if (ecc) {
                        if(ecc == boost::asio::error::eof) {
                            // Client connection terminated so we delete this socket
                            delete(client_sockets[lcid]);
                            printf("Client socket terminated!\n");
                        } else {
                            printf("Error send_client_mailbox mailbox (lcid = %d): %s\n",
                                lcid, ecc.message().c_str());
                        }
                        return;
                    }
                });
            });
#ifdef TRACE_SOCKIO
            ++mailboxes_queued;
        } else {
            ++clients_without_sockets;
#endif
        }
    }

#ifdef TRACE_SOCKIO
    struct timeval now;
    gettimeofday(&now, NULL);
    printf("%lu.%06lu: STG queued %lu mailboxes; %lu clients without sockets\n",
        now.tv_sec, now.tv_usec, mailboxes_queued,
        clients_without_sockets);
#endif

#ifdef PROFILE_NET_CLIENTS
    clock_gettime(CLOCK_REALTIME_COARSE, &tp);
    unsigned long end = tp.tv_sec * 1000000 + tp.tv_nsec/1000;
    unsigned long diff = end - start;
    printf("send_client_mailbox time: %lu.%06lu s\n", diff/1000000, diff%1000000);
#endif

}

NetIO::NetIO(boost::asio::io_context &io_context, const Config &config)
    : context(io_context), conf(config),
      myconf(config.nodes[config.my_node_num])
{
    num_nodes = nodenum_t(conf.nodes.size());
    nodeios.resize(num_nodes);
    me = conf.my_node_num;

#ifdef TRACE_SOCKIO
    last_ing = {0, 0};
    num_ing = 0;
#endif

    // Node number n will accept connections from nodes 0, ..., n-1 and
    // make connections to nodes n+1, ..., num_nodes-1.  This is all
    // single threaded, but it doesn't deadlock because node 0 isn't
    // waiting for any incoming connections, so it immediately makes
    // outgoing connections.  When it connects to node 1, that node
    // accepts its (only) incoming connection, and then starts making
    // its outgoing connections, etc.

    tcp::resolver resolver(io_context);
    tcp::acceptor acceptor(io_context,
        resolver.resolve(myconf.listenhost, myconf.listenport)->endpoint());

    for(size_t i=0; i<me; ++i) {
#ifdef VERBOSE_NET
        std::cerr << "Accepting number " << i << "\n";
#endif
        tcp::socket nodesock = acceptor.accept();
#ifdef VERBOSE_NET
        std::cerr << "Accepted number " << i << "\n";
#endif
        // Read 2 bytes from the socket, which will be the
        // connecting node's node number
        unsigned short node_num;
        boost::asio::read(nodesock,
            boost::asio::buffer(&node_num, sizeof(node_num)));
        if (node_num >= num_nodes) {
            std::cerr << "Received bad node number\n";
        } else {
            nodeios[node_num].emplace(std::move(nodesock), node_num);
#ifdef VERBOSE_NET
            std::cerr << "Received connection from " <<
                config.nodes[node_num].name << "\n";
#endif
        }
    }

    for(size_t i=me+1; i<num_nodes; ++i) {
        boost::system::error_code err;
        tcp::socket nodesock(io_context);
        while(1) {
#ifdef VERBOSE_NET
            std::cerr << "Connecting to " << config.nodes[i].name << "...\n";
#endif
            boost::asio::connect(nodesock,
                resolver.resolve(config.nodes[i].listenhost,
                    config.nodes[i].listenport), err);
            if (!err) break;
            std::cerr << "Connection to " << config.nodes[i].name <<
                " refused, will retry.\n";
            sleep(1);
        }
        // Write 2 bytes to the socket to tell the peer node our node
        // number
        nodenum_t node_num = (nodenum_t)me;
        boost::asio::write(nodesock,
            boost::asio::buffer(&node_num, sizeof(node_num)));
        nodeios[i].emplace(std::move(nodesock), i);
#ifdef VERBOSE_NET
        std::cerr << "Connected to " << config.nodes[i].name << "\n";
#endif
    }


    auth_size = sizeof(clientid_t) + sizeof(unsigned long) + SGX_AESGCM_KEY_SIZE;
    uint16_t priv_out, priv_in, pub_in;
    if(config.private_routing) {
        priv_out = conf.m_priv_out;
        priv_in = conf.m_priv_in;
        msgbundle_size = SGX_AESGCM_IV_SIZE
            + (conf.m_priv_out * (conf.msg_size + TOKEN_SIZE))
            + SGX_AESGCM_MAC_SIZE;
        token_bundle_size = ((priv_out * TOKEN_SIZE)
            + SGX_AESGCM_IV_SIZE + SGX_AESGCM_MAC_SIZE);
        mailbox_size = (priv_in * conf.msg_size) + SGX_AESGCM_IV_SIZE
            + SGX_AESGCM_MAC_SIZE;
    } else {
        pub_in = conf.m_pub_in;
        msgbundle_size = SGX_AESGCM_IV_SIZE
            + (conf.m_pub_out * conf.msg_size)
            + SGX_AESGCM_MAC_SIZE;
        mailbox_size = (pub_in * conf.msg_size) + SGX_AESGCM_IV_SIZE
            + SGX_AESGCM_MAC_SIZE;
    }


    if(myconf.roles & ROLE_STORAGE) {
        // Setup the client sockets
        // Compute no_of_clients per storage_server
        uint32_t num_users = config.user_count;
        NodeConfig nc;
        num_stg_nodes = 0;
        for (nodenum_t i=0; i<num_nodes; ++i) {
            nc = conf.nodes[i];
            if(nc.roles & ROLE_STORAGE) {
                num_stg_nodes++;
            }
        }
        num_clients_per_stg = CEILDIV(num_users, num_stg_nodes);

        for(uint32_t i = 0; i<num_clients_per_stg; i++) {
            client_sockets.emplace_back(nullptr);
        }

        uint32_t epoch_mailboxes_size = num_clients_per_stg * mailbox_size;
        uint32_t epoch_tokens_size = num_clients_per_stg * token_bundle_size;
        epoch_mailboxes = (unsigned char *) malloc(epoch_mailboxes_size);
        epoch_tokens = (unsigned char *) malloc (epoch_tokens_size);
        ecall_supply_storage_buffers(epoch_mailboxes, epoch_mailboxes_size,
            epoch_tokens, epoch_tokens_size);

        storage_acceptor = std::shared_ptr<tcp::acceptor>(
            new tcp::acceptor(io_context,
                resolver.resolve(this->myconf.slistenhost,
                this->myconf.slistenport)->endpoint()));

        stg_start_accept();
    }

    if(myconf.roles & ROLE_INGESTION) {
        ingestion_acceptor = std::shared_ptr<tcp::acceptor>(
            new tcp::acceptor(io_context,
                resolver.resolve(this->myconf.clistenhost,
                this->myconf.clistenport)->endpoint()));

        ing_start_accept();
    }
}


void NetIO::recv_commands(
    std::function<void(boost::system::error_code)> error_cb,
    std::function<void(uint32_t)> epoch_cb)
{
    for (nodenum_t node_num = 0; node_num < num_nodes; ++node_num) {
        if (node_num == me) continue;
        NodeIO &n = node(node_num);
        n.recv_commands(error_cb, epoch_cb);
    }
}

void NetIO::close()
{
    for (nodenum_t node_num = 0; node_num < num_nodes; ++node_num) {
        if (node_num == me) continue;
        NodeIO &n = node(node_num);
        n.close();
    }
}

/* The enclave calls this to inform the untrusted app that there's a new
 * messaage to send. The return value is the frame the enclave should
 * use to store the first (encrypted) chunk of this message. */
uint8_t *ocall_message(nodenum_t node_num, uint32_t message_len)
{
    assert(g_netio != NULL);
    NodeIO &node = g_netio->node(node_num);
    node.send_message_header(message_len);
    return node.request_frame();
}

/* The enclave calls this to inform the untrusted app that there's a new
 * chunk to send.  The return value is the frame the enclave should use
 * to store the next (encrypted) chunk of this message, or NULL if this
 * was the last chunk. */
uint8_t *ocall_chunk(nodenum_t node_num, uint8_t *chunkdata,
    uint32_t chunklen)
{
    assert(g_netio != NULL);
    NodeIO &node = g_netio->node(node_num);
    bool morechunks = node.send_chunk(chunkdata, chunklen);
    if (morechunks) {
        return node.request_frame();
    }
    return NULL;
}