fixes #523 dialers could support multiple outstanding dial requests

fixes #179 DNS resolution should be done at connect time
fixes #586 Windows IO completion port work could be better
fixes #339 Windows iocp could use synchronous completions
fixes #280 TCP abstraction improvements

This is a rather monstrous set of changes, which refactors TCP, and
the underlying Windows I/O completion path logic, in order to obtain
a cleaner, simpler API, with support for asynchronous DNS lookups performed
on connect rather than initialization time, the ability to have multiple
connects or accepts pending, as well as fewer extraneous function calls.

The Windows code also benefits from greatly reduced context switching,
fewer lock operations performed, and a reduced number of system calls
on the hot code path.  (We use automatic event resetting instead of manual.)

Some dead code was removed as well, and a few potential edge case leaks
on failure paths (in the websocket code) were plugged.

Note that all TCP based transports benefit from this work. The IPC code
on Windows still uses the legacy IOCP for now, as does the UDP code (used
for ZeroTier.)  We will be converting those soon too.

1 files changed, 67 insertions, 62 deletions

diff --git a/src/supplemental/http/http_client.c b/src/supplemental/http/http_client.c
index 4034bbff..6842b271 100644
--- a/src/supplemental/http/http_client.c
+++ b/src/supplemental/http/http_client.c
@@ -20,72 +20,97 @@
 #include "http_api.h"
 
 struct nng_http_client {
-	nni_list               aios;
-	nni_mtx                mtx;
-	bool                   closed;
-	struct nng_tls_config *tls;
-	nni_aio *              connaio;
-	nni_plat_tcp_ep *      tep;
+	nni_list        aios;
+	nni_mtx         mtx;
+	bool            closed;
+	bool            resolving;
+	nng_tls_config *tls;
+	nni_aio *       aio;
+	nng_sockaddr    sa;
+	nni_tcp_dialer *dialer;
+	char *          host;
+	char *          port;
+	nni_url *       url;
 };
 
 static void
-http_conn_start(nni_http_client *c)
+http_dial_start(nni_http_client *c)
 {
-	nni_plat_tcp_ep_connect(c->tep, c->connaio);
+	nni_aio *aio;
+
+	if ((aio = nni_list_first(&c->aios)) == NULL) {
+		return;
+	}
+	c->resolving = true;
+	nni_aio_set_input(c->aio, 0, &c->sa);
+	nni_tcp_resolv(c->host, c->port, NNG_AF_UNSPEC, 0, c->aio);
 }
 
 static void
-http_conn_done(void *arg)
+http_dial_cb(void *arg)
 {
-	nni_http_client *  c = arg;
-	nni_aio *          aio;
-	int                rv;
-	nni_plat_tcp_pipe *p;
-	nni_http_conn *    conn;
+	nni_http_client *c = arg;
+	nni_aio *        aio;
+	int              rv;
+	nni_tcp_conn *   tcp;
+	nni_http_conn *  conn;
 
 	nni_mtx_lock(&c->mtx);
-	rv = nni_aio_result(c->connaio);
-	p  = rv == 0 ? nni_aio_get_output(c->connaio, 0) : NULL;
+	rv = nni_aio_result(c->aio);
+
 	if ((aio = nni_list_first(&c->aios)) == NULL) {
-		if (p != NULL) {
-			nni_plat_tcp_pipe_fini(p);
-		}
+		// User abandoned request, and no residuals left.
 		nni_mtx_unlock(&c->mtx);
+		if ((rv == 0) && !c->resolving) {
+			tcp = nni_aio_get_output(c->aio, 0);
+			nni_tcp_conn_fini(tcp);
+		}
 		return;
 	}
-	nni_aio_list_remove(aio);
 
 	if (rv != 0) {
+		nni_aio_list_remove(aio);
+		http_dial_start(c);
+		nni_mtx_unlock(&c->mtx);
 		nni_aio_finish_error(aio, rv);
+		return;
+	}
+
+	if (c->resolving) {
+		// This was a DNS lookup -- advance to normal TCP connect.
+		c->resolving = false;
+		nni_tcp_dialer_dial(c->dialer, &c->sa, c->aio);
 		nni_mtx_unlock(&c->mtx);
 		return;
 	}
 
+	nni_aio_list_remove(aio);
+	tcp = nni_aio_get_output(c->aio, 0);
+	NNI_ASSERT(tcp != NULL);
+
 	if (c->tls != NULL) {
-		rv = nni_http_conn_init_tls(&conn, c->tls, p);
+		rv = nni_http_conn_init_tls(&conn, c->tls, tcp);
 	} else {
-		rv = nni_http_conn_init_tcp(&conn, p);
+		rv = nni_http_conn_init_tcp(&conn, tcp);
 	}
+	http_dial_start(c);
+	nni_mtx_unlock(&c->mtx);
+
 	if (rv != 0) {
+		// the conn_init function will have already discard tcp.
 		nni_aio_finish_error(aio, rv);
-		nni_mtx_unlock(&c->mtx);
 		return;
 	}
 
 	nni_aio_set_output(aio, 0, conn);
 	nni_aio_finish(aio, 0, 0);
-
-	if (!nni_list_empty(&c->aios)) {
-		http_conn_start(c);
-	}
-	nni_mtx_unlock(&c->mtx);
 }
 
 void
 nni_http_client_fini(nni_http_client *c)
 {
-	nni_aio_fini(c->connaio);
-	nni_plat_tcp_ep_fini(c->tep);
+	nni_aio_fini(c->aio);
+	nni_tcp_dialer_fini(c->dialer);
 	nni_mtx_fini(&c->mtx);
 #ifdef NNG_SUPP_TLS
 	if (c->tls != NULL) {
@@ -100,10 +125,6 @@ nni_http_client_init(nni_http_client **cp, const nni_url *url)
 {
 	int              rv;
 	nni_http_client *c;
-	nni_aio *        aio;
-	nni_sockaddr     sa;
-	char *           host;
-	char *           port;
 
 	if (strlen(url->u_hostname) == 0) {
 		// We require a valid hostname.
@@ -118,29 +139,17 @@ nni_http_client_init(nni_http_client **cp, const nni_url *url)
 		return (NNG_EADDRINVAL);
 	}
 
-	// For now we are looking up the address.  We would really like
-	// to do this later, but we need TcP support for this.  One
-	// imagines the ability to create a tcp dialer that does the
-	// necessary DNS lookups, etc. all asynchronously.
-	if ((rv = nni_aio_init(&aio, NULL, NULL)) != 0) {
-		return (rv);
-	}
-	nni_aio_set_input(aio, 0, &sa);
-	host = (strlen(url->u_hostname) != 0) ? url->u_hostname : NULL;
-	port = (strlen(url->u_port) != 0) ? url->u_port : NULL;
-	nni_plat_tcp_resolv(host, port, NNG_AF_UNSPEC, false, aio);
-	nni_aio_wait(aio);
-	rv = nni_aio_result(aio);
-	nni_aio_fini(aio);
-	if (rv != 0) {
-		return (rv);
-	}
-
 	if ((c = NNI_ALLOC_STRUCT(c)) == NULL) {
 		return (NNG_ENOMEM);
 	}
 	nni_mtx_init(&c->mtx);
 	nni_aio_list_init(&c->aios);
+	if (((c->host = nni_strdup(url->u_hostname)) == NULL) ||
+	    ((strlen(url->u_port) != 0) &&
+	        ((c->port = nni_strdup(url->u_port)) == NULL))) {
+		nni_http_client_fini(c);
+		return (NNG_ENOMEM);
+	}
 
 #ifdef NNG_SUPP_TLS
 	if ((strcmp(url->u_scheme, "https") == 0) ||
@@ -167,16 +176,12 @@ nni_http_client_init(nni_http_client **cp, const nni_url *url)
 	}
 #endif
 
-	rv = nni_plat_tcp_ep_init(&c->tep, NULL, &sa, NNI_EP_MODE_DIAL);
-	if (rv != 0) {
+	if (((rv = nni_tcp_dialer_init(&c->dialer)) != 0) ||
+	    ((rv = nni_aio_init(&c->aio, http_dial_cb, c)) != 0)) {
 		nni_http_client_fini(c);
 		return (rv);
 	}
 
-	if ((rv = nni_aio_init(&c->connaio, http_conn_done, c)) != 0) {
-		nni_http_client_fini(c);
-		return (rv);
-	}
 	*cp = c;
 	return (0);
 }
@@ -224,7 +229,7 @@ nni_http_client_get_tls(nni_http_client *c, struct nng_tls_config **tlsp)
 }
 
 static void
-http_connect_cancel(nni_aio *aio, int rv)
+http_dial_cancel(nni_aio *aio, int rv)
 {
 	nni_http_client *c = nni_aio_get_prov_data(aio);
 	nni_mtx_lock(&c->mtx);
@@ -233,7 +238,7 @@ http_connect_cancel(nni_aio *aio, int rv)
 		nni_aio_finish_error(aio, rv);
 	}
 	if (nni_list_empty(&c->aios)) {
-		nni_aio_abort(c->connaio, rv);
+		nni_aio_abort(c->aio, rv);
 	}
 	nni_mtx_unlock(&c->mtx);
 }
@@ -246,14 +251,14 @@ nni_http_client_connect(nni_http_client *c, nni_aio *aio)
 		return;
 	}
 	nni_mtx_lock(&c->mtx);
-	if ((rv = nni_aio_schedule(aio, http_connect_cancel, c)) != 0) {
+	if ((rv = nni_aio_schedule(aio, http_dial_cancel, c)) != 0) {
 		nni_mtx_unlock(&c->mtx);
 		nni_aio_finish_error(aio, rv);
 		return;
 	}
 	nni_list_append(&c->aios, aio);
 	if (nni_list_first(&c->aios) == aio) {
-		http_conn_start(c);
+		http_dial_start(c);
 	}
 	nni_mtx_unlock(&c->mtx);
 }