MEDIUM: sink: Refactor sink forwarder appctx creation

A .init callback function is defined for the sink_forward_applet applet.
This function finishes the appctx startup by calling
appctx_finalize_startup() and its handles the stream customization.
diff --git a/src/sink.c b/src/sink.c
index 681f363..21b590e 100644
--- a/src/sink.c
+++ b/src/sink.c
@@ -594,6 +594,43 @@
 	task_wakeup(sink->forward_task, TASK_WOKEN_MSG);
 }
 
+static int sink_forward_session_init(struct appctx *appctx)
+{
+	struct sink_forward_target *sft = appctx->svcctx;
+	struct stream *s;
+	struct sockaddr_storage *addr = NULL;
+
+	if (!sockaddr_alloc(&addr, &sft->srv->addr, sizeof(sft->srv->addr)))
+		goto out_error;
+
+	if (appctx_finalize_startup(appctx, sft->sink->forward_px, &BUF_NULL) == -1)
+		goto out_free_addr;
+
+	s = appctx_strm(appctx);
+	s->csb->dst = addr;
+	s->csb->flags |= CS_FL_NOLINGER;
+
+	s->target = &sft->srv->obj_type;
+	s->flags = SF_ASSIGNED;
+
+	s->do_log = NULL;
+	s->uniq_id = 0;
+
+	s->res.flags |= CF_READ_DONTWAIT;
+	/* for rto and rex to eternity to not expire on idle recv:
+	 * We are using a syslog server.
+	 */
+	s->res.rto = TICK_ETERNITY;
+	s->res.rex = TICK_ETERNITY;
+	sft->appctx = appctx;
+
+	return 0;
+
+ out_free_addr:
+	sockaddr_free(&addr);
+ out_error:
+	return -1;
+}
 
 static void sink_forward_session_release(struct appctx *appctx)
 {
@@ -612,6 +649,7 @@
 	.obj_type = OBJ_TYPE_APPLET,
 	.name = "<SINKFWD>", /* used for logging */
 	.fct = sink_forward_io_handler,
+	.init = sink_forward_session_init,
 	.release = sink_forward_session_release,
 };
 
@@ -619,6 +657,7 @@
 	.obj_type = OBJ_TYPE_APPLET,
 	.name = "<SINKFWDOC>", /* used for logging */
 	.fct = sink_forward_oc_io_handler,
+	.init = sink_forward_session_init,
 	.release = sink_forward_session_release,
 };
 
@@ -628,13 +667,8 @@
  */
 static struct appctx *sink_forward_session_create(struct sink *sink, struct sink_forward_target *sft)
 {
-	struct proxy *p = sink->forward_px;
 	struct appctx *appctx;
-	struct session *sess;
-	struct conn_stream *cs;
-	struct stream *s;
 	struct applet *applet = &sink_forward_applet;
-	struct sockaddr_storage *addr = NULL;
 
 	if (sft->srv->log_proto == SRV_LOG_PROTO_OCTET_COUNTING)
 		applet = &sink_forward_oc_applet;
@@ -642,49 +676,16 @@
 	appctx = appctx_new(applet, NULL);
 	if (!appctx)
 		goto out_close;
-
 	appctx->svcctx = (void *)sft;
 
-	sess = session_new(p, NULL, &appctx->obj_type);
-	if (!sess) {
-		ha_alert("out of memory in sink_forward_session_create().\n");
-		goto out_free_appctx;
-	}
-	appctx->sess = sess;
-
-	if (!sockaddr_alloc(&addr, &sft->srv->addr, sizeof(sft->srv->addr)))
-		goto out_free_appctx;
-
-	cs = cs_new_from_endp(appctx->endp, sess, &BUF_NULL);
-	if (!cs) {
-		ha_alert("Failed to initialize stream in sink_forward_session_create().\n");
+	if (appctx_init(appctx) == -1)
 		goto out_free_appctx;
-	}
-	s = DISGUISE(cs_strm(cs));
 
-	s->csb->dst = addr;
-	s->csb->flags |= CS_FL_NOLINGER;
-
-	s->target = &sft->srv->obj_type;
-	s->flags = SF_ASSIGNED;
-
-	s->do_log = NULL;
-	s->uniq_id = 0;
-
-	s->res.flags |= CF_READ_DONTWAIT;
-	/* for rto and rex to eternity to not expire on idle recv:
-	 * We are using a syslog server.
-	 */
-	s->res.rto = TICK_ETERNITY;
-	s->res.rex = TICK_ETERNITY;
-	sft->appctx = appctx;
 	return appctx;
 
 	/* Error unrolling */
- out_free_addr:
-	sockaddr_free(&addr);
  out_free_appctx:
-	appctx_free(appctx);
+	appctx_free_on_early_error(appctx);
  out_close:
 	return NULL;
 }