text: //
  // Copyright 2020 Staysail Systems, Inc. <info@staysail.tech>
  // Copyright 2018 Capitar IT Group BV <info@capitar.com>
  //
  // This software is supplied under the terms of the MIT License, a
  // copy of which should be located in the distribution where this
  // file was obtained (LICENSE.txt).  A copy of the license may also be
  // found online at https://opensource.org/licenses/MIT.
  //
  #include <stdio.h>
  
  #include "core/nng_impl.h"
  #include "nng/protocol/reqrep0/req.h"
  
  // Request protocol.  The REQ protocol is the "request" side of a
  // request-reply pair.  This is useful for building RPC clients, for example.
  
  typedef struct req0_pipe req0_pipe;
  typedef struct req0_sock req0_sock;
  typedef struct req0_ctx  req0_ctx;
  
  static void req0_run_send_queue(req0_sock *, nni_list *);
  static void req0_ctx_reset(req0_ctx *);
  static void req0_ctx_timeout(void *);
  static void req0_pipe_fini(void *);
  static void req0_ctx_fini(void *);
  static int  req0_ctx_init(void *, void *);
  
  // A req0_ctx is a "context" for the request.  It uses most of the
  // socket, but keeps track of its own outstanding replays, the request ID,
  // and so forth.
  struct req0_ctx {
  	req0_sock *    sock;
  	nni_list_node  sock_node;  // node on the socket context list
  	nni_list_node  send_node;  // node on the send_queue
  	nni_list_node  pipe_node;  // node on the pipe list
  	uint32_t       request_id; // request ID, without high bit set
  	nni_aio *      recv_aio;   // user aio waiting to recv - only one!
  	nni_aio *      send_aio;   // user aio waiting to send
  	nng_msg *      req_msg;    // request message (owned by protocol)
  	size_t         req_len;    // length of request message (for stats)
  	nng_msg *      rep_msg;    // reply message
  	nni_timer_node timer;
  	nni_duration   retry;
  	bool           conn_reset; // sent message w/o retry, peer disconnect
  };
  
  // A req0_sock is our per-socket protocol private structure.
  struct req0_sock {
  	nni_duration   retry;
  	bool           closed;
  	nni_atomic_int ttl;
  	req0_ctx       master; // base socket master
  	nni_list       ready_pipes;
  	nni_list       busy_pipes;
  	nni_list       stop_pipes;
  	nni_list       contexts;
  	nni_list       send_queue; // contexts waiting to send.
  	nni_id_map     requests;   // contexts by request ID
  	nni_pollable   readable;
  	nni_pollable   writable;
  	nni_mtx        mtx;
  };
  
  // A req0_pipe is our per-pipe protocol private structure.
  struct req0_pipe {
  	nni_pipe *    pipe;
  	req0_sock *   req;
  	nni_list_node node;
  	nni_list      contexts; // contexts with pending traffic
  	bool          closed;
  	nni_aio       aio_send;
  	nni_aio       aio_recv;
  };
  
  static void req0_sock_fini(void *);
  static void req0_send_cb(void *);
  static void req0_recv_cb(void *);
  
  static int
  req0_sock_init(void *arg, nni_sock *sock)
  {
  	req0_sock *s = arg;
  
  	NNI_ARG_UNUSED(sock);
  
  	// Request IDs are 32 bits, with the high order bit set.
  	// We start at a random point, to minimize likelihood of
  	// accidental collision across restarts.
  	nni_id_map_init(&s->requests, 0x80000000u, 0xffffffffu, true);
  
  	nni_mtx_init(&s->mtx);
  
  	NNI_LIST_INIT(&s->ready_pipes, req0_pipe, node);
  	NNI_LIST_INIT(&s->busy_pipes, req0_pipe, node);
  	NNI_LIST_INIT(&s->stop_pipes, req0_pipe, node);
  	NNI_LIST_INIT(&s->send_queue, req0_ctx, send_node);
  	NNI_LIST_INIT(&s->contexts, req0_ctx, sock_node);
  
  	// this is "semi random" start for request IDs.
  	s->retry = NNI_SECOND * 60;
  
  	(void) req0_ctx_init(&s->master, s);
  
  	nni_pollable_init(&s->writable);
  	nni_pollable_init(&s->readable);
  
  	nni_atomic_init(&s->ttl);
  	nni_atomic_set(&s->ttl, 8);
  	return (0);
  }
  
  static void
  req0_sock_open(void *arg)
  {
  	NNI_ARG_UNUSED(arg);
  }
  
  static void
  req0_sock_close(void *arg)
  {
  	req0_sock *s = arg;
  
  	nni_mtx_lock(&s->mtx);
  	s->closed = true;
  	nni_mtx_unlock(&s->mtx);
  }
  
  static void
  req0_sock_fini(void *arg)
  {
  	req0_sock *s = arg;
  
  	nni_mtx_lock(&s->mtx);
  	NNI_ASSERT(nni_list_empty(&s->busy_pipes));
  	NNI_ASSERT(nni_list_empty(&s->stop_pipes));
  	NNI_ASSERT(nni_list_empty(&s->ready_pipes));
  	nni_mtx_unlock(&s->mtx);
  
  	req0_ctx_fini(&s->master);
  	nni_pollable_fini(&s->readable);
  	nni_pollable_fini(&s->writable);
  	nni_id_map_fini(&s->requests);
  	nni_mtx_fini(&s->mtx);
  }
  
  static void
  req0_pipe_stop(void *arg)
  {
  	req0_pipe *p = arg;
  	req0_sock *s = p->req;
  
  	nni_aio_stop(&p->aio_recv);
  	nni_aio_stop(&p->aio_send);
  	nni_mtx_lock(&s->mtx);
  	nni_list_node_remove(&p->node);
  	nni_mtx_unlock(&s->mtx);
  }
  
  static void
  req0_pipe_fini(void *arg)
  {
  	req0_pipe *p = arg;
  
  	nni_aio_fini(&p->aio_recv);
  	nni_aio_fini(&p->aio_send);
  }
  
  static int
  req0_pipe_init(void *arg, nni_pipe *pipe, void *s)
  {
  	req0_pipe *p = arg;
  
  	nni_aio_init(&p->aio_recv, req0_recv_cb, p);
  	nni_aio_init(&p->aio_send, req0_send_cb, p);
  	NNI_LIST_NODE_INIT(&p->node);
  	NNI_LIST_INIT(&p->contexts, req0_ctx, pipe_node);
  	p->pipe = pipe;
  	p->req  = s;
  	return (0);
  }
  
  static int
  req0_pipe_start(void *arg)
  {
  	req0_pipe *p = arg;
  	req0_sock *s = p->req;
  
  	if (nni_pipe_peer(p->pipe) != NNG_REQ0_PEER) {
  		return (NNG_EPROTO);
  	}
  
  	nni_mtx_lock(&s->mtx);
  	nni_list_append(&s->ready_pipes, p);
  	nni_pollable_raise(&s->writable);
  	req0_run_send_queue(s, NULL);
  	nni_mtx_unlock(&s->mtx);
  
  	nni_pipe_recv(p->pipe, &p->aio_recv);
  	return (0);
  }
  
  static void
  req0_pipe_close(void *arg)
  {
  	req0_pipe *p = arg;
  	req0_sock *s = p->req;
  	req0_ctx * ctx;
  
  	nni_aio_close(&p->aio_recv);
  	nni_aio_close(&p->aio_send);
  
  	nni_mtx_lock(&s->mtx);
  	// This removes the node from either busy_pipes or ready_pipes.
  	// It doesn't much matter which.  We stick the pipe on the stop
  	// list, so that we can wait for that to close down safely.
  	p->closed = true;
  	nni_list_node_remove(&p->node);
  	nni_list_append(&s->stop_pipes, p);
  	if (nni_list_empty(&s->ready_pipes)) {
  		nni_pollable_clear(&s->writable);
  	}
  
  	while ((ctx = nni_list_first(&p->contexts)) != NULL) {
  		nni_list_remove(&p->contexts, ctx);
  		nng_aio *aio;
  		if (ctx->retry <= 0) {
  			// If we can't retry, then just cancel the operation
  			// altogether.  We should only be waiting for recv,
  			// because we will already have sent if we are here.
  			if ((aio = ctx->recv_aio) != NULL) {
  				ctx->recv_aio = NULL;
  				nni_aio_finish_error(aio, NNG_ECONNRESET);
                                  req0_ctx_reset(ctx);
  			} else {
  				req0_ctx_reset(ctx);
  				ctx->conn_reset = true;
  			}
  		} else {
  			// Reset the timer on this so it expires immediately.
  			// This is actually easier than canceling the timer and
  			// running the send_queue separately.  (In particular,
  			// it avoids a potential deadlock on cancelling the
  			// timer.)
  			nni_timer_schedule(&ctx->timer, NNI_TIME_ZERO);
  		}
  	}
  	nni_mtx_unlock(&s->mtx);
  }
  
  // For cooked mode, we use a context, and send out that way.  This
  // completely bypasses the upper write queue.  Each context keeps one
  // message pending; these are "scheduled" via the send_queue.  The send_queue
  // is ordered, so FIFO ordering between contexts is provided for.
  
  static void
  req0_send_cb(void *arg)
  {
  	req0_pipe *p = arg;
  	req0_sock *s = p->req;
  	nni_aio *  aio;
  	nni_list   sent_list;
  
  	nni_aio_list_init(&sent_list);
  	if (nni_aio_result(&p->aio_send) != 0) {
  		// We failed to send... clean up and deal with it.
  		nni_msg_free(nni_aio_get_msg(&p->aio_send));
  		nni_aio_set_msg(&p->aio_send, NULL);
  		nni_pipe_close(p->pipe);
  		return;
  	}
  
  	// We completed a cooked send, so we need to reinsert ourselves
  	// in the ready list, and re-run the send_queue.
  
  	nni_mtx_lock(&s->mtx);
  	if (p->closed || s->closed) {
  		// This occurs if the req0_pipe_close has been called.
  		// In that case we don't want any more processing.
  		nni_mtx_unlock(&s->mtx);
  		return;
  	}
  	nni_list_remove(&s->busy_pipes, p);
  	nni_list_append(&s->ready_pipes, p);
  	if (nni_list_empty(&s->send_queue)) {
  		nni_pollable_raise(&s->writable);
  	}
  	req0_run_send_queue(s, &sent_list);
  	nni_mtx_unlock(&s->mtx);
  
  	while ((aio = nni_list_first(&sent_list)) != NULL) {
  		nni_list_remove(&sent_list, aio);
  		nni_aio_finish_synch(aio, 0, 0);
  	}
  }
  
  static void
  req0_recv_cb(void *arg)
  {
  	req0_pipe *p = arg;
  	req0_sock *s = p->req;
  	req0_ctx * ctx;
  	nni_msg *  msg;
  	nni_aio *  aio;
  	uint32_t   id;
  
  	if (nni_aio_result(&p->aio_recv) != 0) {
  		nni_pipe_close(p->pipe);
  		return;
  	}
  
  	msg = nni_aio_get_msg(&p->aio_recv);
  	nni_aio_set_msg(&p->aio_recv, NULL);
  	nni_msg_set_pipe(msg, nni_pipe_id(p->pipe));
  
  	// We yank 4 bytes from front of body, and move them to the header.
  	if (nni_msg_len(msg) < 4) {
  		// Malformed message.
  		goto malformed;
  	}
  	id = nni_msg_trim_u32(msg);
  
  	// Schedule another receive while we are processing this.
  	nni_mtx_lock(&s->mtx);
  
  	// NB: If close was called, then this will just abort.
  	nni_pipe_recv(p->pipe, &p->aio_recv);
  
  	// Look for a context to receive it.
  	if (((ctx = nni_id_get(&s->requests, id)) == NULL) ||
  	    (ctx->send_aio != NULL) || (ctx->rep_msg != NULL)) {
  		nni_mtx_unlock(&s->mtx);
  		// No waiting context, we have not sent the request out to
  		// the wire yet, or context already has a reply ready.
  		// Discard the message.
  		nni_msg_free(msg);
  		return;
  	}
  
  	// We have our match, so we can remove this.
  	nni_list_node_remove(&ctx->send_node);
  	nni_id_remove(&s->requests, id);
  	ctx->request_id = 0;
  	if (ctx->req_msg != NULL) {
  		nni_msg_free(ctx->req_msg);
  		ctx->req_msg = NULL;
  	}
  
  	// Is there an aio waiting for us?
  	if ((aio = ctx->recv_aio) != NULL) {
  		ctx->recv_aio = NULL;
  		nni_mtx_unlock(&s->mtx);
  		nni_aio_set_msg(aio, msg);
  		nni_aio_finish_synch(aio, 0, nni_msg_len(msg));
  	} else {
  		// No AIO, so stash msg.  Receive will pick it up later.
  		ctx->rep_msg = msg;
  		if (ctx == &s->master) {
  			nni_pollable_raise(&s->readable);
  		}
  		nni_mtx_unlock(&s->mtx);
  	}
  	return;
  
  malformed:
  	nni_msg_free(msg);
  	nni_pipe_close(p->pipe);
  }
  
  static void
  req0_ctx_timeout(void *arg)
  {
  	req0_ctx * ctx = arg;
  	req0_sock *s   = ctx->sock;
  
  	nni_mtx_lock(&s->mtx);
  	if ((ctx->req_msg != NULL) && (!s->closed)) {
  		if (!nni_list_node_active(&ctx->send_node)) {
  			nni_list_append(&s->send_queue, ctx);
  		}
  		req0_run_send_queue(s, NULL);
  	}
  	nni_mtx_unlock(&s->mtx);
  }
  
  static int
  req0_ctx_init(void *arg, void *sock)
  {
  	req0_sock *s   = sock;
  	req0_ctx * ctx = arg;
  
  	nni_timer_init(&ctx->timer, req0_ctx_timeout, ctx);
  
  	nni_mtx_lock(&s->mtx);
  	ctx->sock     = s;
  	ctx->recv_aio = NULL;
  	ctx->retry    = s->retry;
  	nni_list_append(&s->contexts, ctx);
  	nni_mtx_unlock(&s->mtx);
  
  	return (0);
  }
  
  static void
  req0_ctx_fini(void *arg)
  {
  	req0_ctx * ctx = arg;
  	req0_sock *s   = ctx->sock;
  	nni_aio *  aio;
  
  	nni_mtx_lock(&s->mtx);
  	if ((aio = ctx->recv_aio) != NULL) {
  		ctx->recv_aio = NULL;
  		nni_aio_finish_error(aio, NNG_ECLOSED);
  	}
  	if ((aio = ctx->send_aio) != NULL) {
  		ctx->send_aio = NULL;
  		nni_aio_set_msg(aio, ctx->req_msg);
  		ctx->req_msg = NULL;
  		nni_aio_finish_error(aio, NNG_ECLOSED);
  	}
  	req0_ctx_reset(ctx);
  	nni_list_remove(&s->contexts, ctx);
  	nni_mtx_unlock(&s->mtx);
  
  	nni_timer_cancel(&ctx->timer);
  	nni_timer_fini(&ctx->timer);
  }
  
  static int
  req0_ctx_set_resend_time(void *arg, const void *buf, size_t sz, nni_opt_type t)
  {
  	req0_ctx *ctx = arg;
  	return (nni_copyin_ms(&ctx->retry, buf, sz, t));
  }
  
  static int
  req0_ctx_get_resend_time(void *arg, void *buf, size_t *szp, nni_opt_type t)
  {
  	req0_ctx *ctx = arg;
  	return (nni_copyout_ms(ctx->retry, buf, szp, t));
  }
  
  static void
  req0_run_send_queue(req0_sock *s, nni_list *sent_list)
  {
  	req0_ctx *ctx;
  	nni_aio * aio;
  
  	// Note: This routine should be called with the socket lock held.
  	while ((ctx = nni_list_first(&s->send_queue)) != NULL) {
  		req0_pipe *p;
  
  		if ((p = nni_list_first(&s->ready_pipes)) == NULL) {
  			return;
  		}
  
  		// We have a place to send it, so do the send.
  		// If a sending error occurs that causes the message to
  		// be dropped, we rely on the resend timer to pick it up.
  		// We also notify the completion callback if this is the
  		// first send attempt.
  		nni_list_remove(&s->send_queue, ctx);
  
  		// Schedule a resubmit timer.  We only do this if we got
  		// a pipe to send to.  Otherwise, we should get handled
  		// the next time that the send_queue is run.  We don't do this
  		// if the retry is "disabled" with NNG_DURATION_INFINITE.
  		if (ctx->retry > 0) {
  			nni_timer_schedule(
  			    &ctx->timer, nni_clock() + ctx->retry);
  		}
  
  		// Put us on the pipe list of active contexts.
  		// This gives the pipe a chance to kick a resubmit
  		// if the pipe is removed.
  		nni_list_node_remove(&ctx->pipe_node);
  		nni_list_append(&p->contexts, ctx);
  
  		nni_list_remove(&s->ready_pipes, p);
  		nni_list_append(&s->busy_pipes, p);
  		if (nni_list_empty(&s->ready_pipes)) {
  			nni_pollable_clear(&s->writable);
  		}
  
  		if ((aio = ctx->send_aio) != NULL) {
  			ctx->send_aio = NULL;
  			nni_aio_bump_count(aio, ctx->req_len);
  			// If the list was passed in, we want to do a
  			// synchronous completion later.
  			if (sent_list != NULL) {
  				nni_list_append(sent_list, aio);
  			} else {
  				nni_aio_finish(aio, 0, 0);
  			}
  		}
  
  		// At this point, we will never give this message back to
  		// to the user, so we don't have to worry about making it
  		// unique.  We can freely clone it.
  		nni_msg_clone(ctx->req_msg);
  		nni_aio_set_msg(&p->aio_send, ctx->req_msg);
  		nni_pipe_send(p->pipe, &p->aio_send);
  	}
  }
  
  void
  req0_ctx_reset(req0_ctx *ctx)
  {
  	req0_sock *s = ctx->sock;
  	// Call with sock lock held!
  
  	// We cannot safely "wait" using nni_timer_cancel, but this removes
  	// any scheduled timer activation.  If the timeout is already running
  	// concurrently, it will still run.  It should do nothing, because
  	// we toss the request.  There is still a very narrow race if the
  	// timeout fires, but doesn't actually start running before we
  	// both finish this function, *and* manage to reschedule another
  	// request.  The consequence of that occurring is that the request
  	// will be emitted on the wire twice.  This is not actually tragic.
  	nni_timer_schedule(&ctx->timer, NNI_TIME_NEVER);
  
  	nni_list_node_remove(&ctx->pipe_node);
  	nni_list_node_remove(&ctx->send_node);
  	if (ctx->request_id != 0) {
  		nni_id_remove(&s->requests, ctx->request_id);
  		ctx->request_id = 0;
  	}
  	if (ctx->req_msg != NULL) {
  		nni_msg_free(ctx->req_msg);
  		ctx->req_msg = NULL;
  	}
  	if (ctx->rep_msg != NULL) {
  		nni_msg_free(ctx->rep_msg);
  		ctx->rep_msg = NULL;
  	}
  	ctx->conn_reset = false;
  }
  
  static void
  req0_ctx_cancel_recv(nni_aio *aio, void *arg, int rv)
  {
  	req0_ctx * ctx = arg;
  	req0_sock *s   = ctx->sock;
  
  	nni_mtx_lock(&s->mtx);
  	if (ctx->recv_aio == aio) {
  		ctx->recv_aio = NULL;
  
  		// Cancellation of a pending receive is treated as aborting the
  		// entire state machine.  This allows us to preserve the
  		// semantic of exactly one receive operation per send
  		// operation, and should be the least surprising for users. The
  		// main consequence is that if a receive operation is completed
  		// (in error or otherwise), the user must submit a new send
  		// operation to restart the state machine.
  		req0_ctx_reset(ctx);
  
  		nni_aio_finish_error(aio, rv);
  	}
  	nni_mtx_unlock(&s->mtx);
  }
  
  static void
  req0_ctx_recv(void *arg, nni_aio *aio)
  {
  	req0_ctx * ctx = arg;
  	req0_sock *s   = ctx->sock;
  	nni_msg *  msg;
  
  	if (nni_aio_begin(aio) != 0) {
  		return;
  	}
  	nni_mtx_lock(&s->mtx);
  	if ((ctx->recv_aio != NULL) ||
  	    ((ctx->req_msg == NULL) && (ctx->rep_msg == NULL))) {
  		// We have already got a pending receive or have not
  		// tried to send a request yet.
  		// Either of these violate our basic state assumptions.
  		int rv;
  		if (ctx->conn_reset) {
  			ctx->conn_reset = false;
  			rv              = NNG_ECONNRESET;
  		} else {
  			rv = NNG_ESTATE;
  		}
  		nni_mtx_unlock(&s->mtx);
  		nni_aio_finish_error(aio, rv);
  		return;
  	}
  
  	if ((msg = ctx->rep_msg) == NULL) {
  		int rv;
  		rv = nni_aio_schedule(aio, req0_ctx_cancel_recv, ctx);
  		if (rv != 0) {
  			nni_mtx_unlock(&s->mtx);
  			nni_aio_finish_error(aio, rv);
  			return;
  		}
  		ctx->recv_aio = aio;
  		nni_mtx_unlock(&s->mtx);
  		return;
  	}
  
  	ctx->rep_msg = NULL;
  
  	// We have got a message to pass up, yay!
  	nni_aio_set_msg(aio, msg);
  	if (ctx == &s->master) {
  		nni_pollable_clear(&s->readable);
  	}
  	nni_mtx_unlock(&s->mtx);
  	nni_aio_finish(aio, 0, nni_msg_len(msg));
  }
  
  static void
  req0_ctx_cancel_send(nni_aio *aio, void *arg, int rv)
  {
  	req0_ctx * ctx = arg;
  	req0_sock *s   = ctx->sock;
  
  	nni_mtx_lock(&s->mtx);
  	if (ctx->send_aio == aio) {
  		// There should not be a pending reply, because we canceled
  		// it while we were waiting.
  		NNI_ASSERT(ctx->recv_aio == NULL);
  		ctx->send_aio = NULL;
  		// Restore the message back to the aio.
  		nni_aio_set_msg(aio, ctx->req_msg);
  		nni_msg_header_clear(ctx->req_msg);
  		ctx->req_msg = NULL;
  
  		// Cancellation of a pending receive is treated as aborting the
  		// entire state machine.  This allows us to preserve the
  		// semantic of exactly one receive operation per send
  		// operation, and should be the least surprising for users. The
  		// main consequence is that if a receive operation is completed
  		// (in error or otherwise), the user must submit a new send
  		// operation to restart the state machine.
  		req0_ctx_reset(ctx);
  
  		nni_aio_finish_error(aio, rv);
  	}
  	nni_mtx_unlock(&s->mtx);
  }
  
  static void
  req0_ctx_send(void *arg, nni_aio *aio)
  {
  	req0_ctx * ctx = arg;
  	req0_sock *s   = ctx->sock;
  	nng_msg *  msg = nni_aio_get_msg(aio);
  	int        rv;
  
  	if (nni_aio_begin(aio) != 0) {
  		return;
  	}
  	nni_mtx_lock(&s->mtx);
  	if (s->closed) {
  		nni_mtx_unlock(&s->mtx);
  		nni_aio_finish_error(aio, NNG_ECLOSED);
  		return;
  	}
  	// Sending a new request cancels the old one, including any
  	// outstanding reply.
  	if (ctx->recv_aio != NULL) {
  		nni_aio_finish_error(ctx->recv_aio, NNG_ECANCELED);
  		ctx->recv_aio = NULL;
  	}
  	if (ctx->send_aio != NULL) {
  		nni_aio_set_msg(ctx->send_aio, ctx->req_msg);
  		nni_msg_header_clear(ctx->req_msg);
  		ctx->req_msg = NULL;
  		nni_aio_finish_error(ctx->send_aio, NNG_ECANCELED);
  		ctx->send_aio = NULL;
  		nni_list_remove(&s->send_queue, ctx);
  	}
  
  	// This resets the entire state machine.
  	req0_ctx_reset(ctx);
  
  	// Insert us on the per ID hash list, so that receives can find us.
  	if ((rv = nni_id_alloc(&s->requests, &ctx->request_id, ctx)) != 0) {
  		nni_mtx_unlock(&s->mtx);
  		nni_aio_finish_error(aio, rv);
  		return;
  	}
  	nni_msg_header_clear(msg);
  	nni_msg_header_append_u32(msg, ctx->request_id);
  
  	// If no pipes are ready, and the request was a poll (no background
  	// schedule), then fail it.  Should be NNG_ETIMEDOUT.
  	rv = nni_aio_schedule(aio, req0_ctx_cancel_send, ctx);
  	if ((rv != 0) && (nni_list_empty(&s->ready_pipes))) {
  		nni_id_remove(&s->requests, ctx->request_id);
  		nni_mtx_unlock(&s->mtx);
  		nni_aio_finish_error(aio, rv);
  		return;
  	}
  	ctx->req_len  = nni_msg_len(msg);
  	ctx->req_msg  = msg;
  	ctx->send_aio = aio;
  	nni_aio_set_msg(aio, NULL);
  
  	// Stick us on the send_queue list.
  	nni_list_append(&s->send_queue, ctx);
  
  	req0_run_send_queue(s, NULL);
  	nni_mtx_unlock(&s->mtx);
  }
  
  static void
  req0_sock_send(void *arg, nni_aio *aio)
  {
  	req0_sock *s = arg;
  	req0_ctx_send(&s->master, aio);
  }
  
  static void
  req0_sock_recv(void *arg, nni_aio *aio)
  {
  	req0_sock *s = arg;
  	req0_ctx_recv(&s->master, aio);
  }
  
  static int
  req0_sock_set_max_ttl(void *arg, const void *buf, size_t sz, nni_opt_type t)
  {
  	req0_sock *s = arg;
  	int        ttl;
  	int        rv;
  	if ((rv = nni_copyin_int(&ttl, buf, sz, 1, NNI_MAX_MAX_TTL, t)) == 0) {
  		nni_atomic_set(&s->ttl, ttl);
  	}
  	return (rv);
  }
  
  static int
  req0_sock_get_max_ttl(void *arg, void *buf, size_t *szp, nni_opt_type t)
  {
  	req0_sock *s = arg;
  	return (nni_copyout_int(nni_atomic_get(&s->ttl), buf, szp, t));
  }
  
  static int
  req0_sock_set_resend_time(
      void *arg, const void *buf, size_t sz, nni_opt_type t)
  {
  	req0_sock *s = arg;
  	int        rv;
  	rv       = req0_ctx_set_resend_time(&s->master, buf, sz, t);
  	s->retry = s->master.retry;
  	return (rv);
  }
  
  static int
  req0_sock_get_resend_time(void *arg, void *buf, size_t *szp, nni_opt_type t)
  {
  	req0_sock *s = arg;
  	return (req0_ctx_get_resend_time(&s->master, buf, szp, t));
  }
  
  static int
  req0_sock_get_send_fd(void *arg, void *buf, size_t *szp, nni_opt_type t)
  {
  	req0_sock *s = arg;
  	int        rv;
  	int        fd;
  
  	if ((rv = nni_pollable_getfd(&s->writable, &fd)) != 0) {
  		return (rv);
  	}
  	return (nni_copyout_int(fd, buf, szp, t));
  }
  
  static int
  req0_sock_get_recv_fd(void *arg, void *buf, size_t *szp, nni_opt_type t)
  {
  	req0_sock *s = arg;
  	int        rv;
  	int        fd;
  
  	if ((rv = nni_pollable_getfd(&s->readable, &fd)) != 0) {
  		return (rv);
  	}
  
  	return (nni_copyout_int(fd, buf, szp, t));
  }
  
  static nni_proto_pipe_ops req0_pipe_ops = {
  	.pipe_size  = sizeof(req0_pipe),
  	.pipe_init  = req0_pipe_init,
  	.pipe_fini  = req0_pipe_fini,
  	.pipe_start = req0_pipe_start,
  	.pipe_close = req0_pipe_close,
  	.pipe_stop  = req0_pipe_stop,
  };
  
  static nni_option req0_ctx_options[] = {
  	{
  	    .o_name = NNG_OPT_REQ_RESENDTIME,
  	    .o_get  = req0_ctx_get_resend_time,
  	    .o_set  = req0_ctx_set_resend_time,
  	},
  	{
  	    .o_name = NULL,
  	},
  };
  
  static nni_proto_ctx_ops req0_ctx_ops = {
  	.ctx_size    = sizeof(req0_ctx),
  	.ctx_init    = req0_ctx_init,
  	.ctx_fini    = req0_ctx_fini,
  	.ctx_recv    = req0_ctx_recv,
  	.ctx_send    = req0_ctx_send,
  	.ctx_options = req0_ctx_options,
  };
  
  static nni_option req0_sock_options[] = {
  	{
  	    .o_name = NNG_OPT_MAXTTL,
  	    .o_get  = req0_sock_get_max_ttl,
  	    .o_set  = req0_sock_set_max_ttl,
  	},
  	{
  	    .o_name = NNG_OPT_REQ_RESENDTIME,
  	    .o_get  = req0_sock_get_resend_time,
  	    .o_set  = req0_sock_set_resend_time,
  	},
  	{
  	    .o_name = NNG_OPT_RECVFD,
  	    .o_get  = req0_sock_get_recv_fd,
  	},
  	{
  	    .o_name = NNG_OPT_SENDFD,
  	    .o_get  = req0_sock_get_send_fd,
  	},
  	// terminate list
  	{
  	    .o_name = NULL,
  	},
  };
  
  static nni_proto_sock_ops req0_sock_ops = {
  	.sock_size    = sizeof(req0_sock),
  	.sock_init    = req0_sock_init,
  	.sock_fini    = req0_sock_fini,
  	.sock_open    = req0_sock_open,
  	.sock_close   = req0_sock_close,
  	.sock_options = req0_sock_options,
  	.sock_send    = req0_sock_send,
  	.sock_recv    = req0_sock_recv,
  };
  
  static nni_proto req0_proto = {
  	.proto_version  = NNI_PROTOCOL_VERSION,
  	.proto_self     = { NNG_REQ0_SELF, NNG_REQ0_SELF_NAME },
  	.proto_peer     = { NNG_REQ0_PEER, NNG_REQ0_PEER_NAME },
  	.proto_flags    = NNI_PROTO_FLAG_SNDRCV | NNI_PROTO_FLAG_NOMSGQ,
  	.proto_sock_ops = &req0_sock_ops,
  	.proto_pipe_ops = &req0_pipe_ops,
  	.proto_ctx_ops  = &req0_ctx_ops,
  };
  
  int
  nng_req0_open(nng_socket *sock)
  {
  	return (nni_proto_open(sock, &req0_proto));
  }
  