From 98d0eb964413f6cc655640f207dde4bf5f1ce89d Mon Sep 17 00:00:00 2001
From: Guus Sliepen <guus@meshlink.io>
Date: Thu, 4 Jul 2019 20:40:09 +0200
Subject: [PATCH] Prevent meshlink_join() when the joining node is already part
 of a mesh.

---
 src/meshlink.c     | 10 +++++++++-
 test/invite-join.c | 36 ++++++++++++++++++++++++++++++++++--
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/src/meshlink.c b/src/meshlink.c
index 9b13dca1..302624fc 100644
--- a/src/meshlink.c
+++ b/src/meshlink.c
@@ -2310,7 +2310,15 @@ bool meshlink_join(meshlink_handle_t *mesh, const char *invitation) {
 
 	//Before doing meshlink_join make sure we are not connected to another mesh
 	if(mesh->threadstarted) {
-		logger(mesh, MESHLINK_DEBUG, "Already connected to a mesh\n");
+		logger(mesh, MESHLINK_ERROR, "Cannot join while started\n");
+		meshlink_errno = MESHLINK_EINVAL;
+		pthread_mutex_unlock(&(mesh->mesh_mutex));
+		return false;
+	}
+
+	// Refuse to join a mesh if we are already part of one. We are part of one if we know at least one other node.
+	if(mesh->nodes->count > 1) {
+		logger(mesh, MESHLINK_ERROR, "Already part of an existing mesh\n");
 		meshlink_errno = MESHLINK_EINVAL;
 		pthread_mutex_unlock(&(mesh->mesh_mutex));
 		return false;
diff --git a/test/invite-join.c b/test/invite-join.c
index b69eb3d8..52a922a8 100644
--- a/test/invite-join.c
+++ b/test/invite-join.c
@@ -106,8 +106,6 @@ int main() {
 		return 1;
 	}
 
-	free(baz_url);
-
 	if(!meshlink_start(mesh2)) {
 		fprintf(stderr, "Baz could not start\n");
 		return 1;
@@ -140,6 +138,15 @@ int main() {
 		return 1;
 	}
 
+	// Check that an invitation cannot be used twice
+
+	if(meshlink_join(mesh3, baz_url)) {
+		fprintf(stderr, "Quux could join foo's mesh using an already used invitation\n");
+		return 1;
+	}
+
+	free(baz_url);
+
 	// Check that nodes cannot join with expired invitations
 
 	meshlink_set_invitation_timeout(mesh1, 0);
@@ -151,6 +158,31 @@ int main() {
 
 	free(quux_url);
 
+	// Check that existing nodes cannot join another mesh
+
+	char *corge_url = meshlink_invite(mesh3, NULL, "corge");
+
+	if(!corge_url) {
+		fprintf(stderr, "Quux could not generate an invitation for corge\n");
+		return 1;
+	}
+
+	fprintf(stderr, "Invitation URL for corge: %s\n", corge_url);
+
+	if(!meshlink_start(mesh3)) {
+		fprintf(stderr, "Quux could not start\n");
+		return 1;
+	}
+
+	meshlink_stop(mesh2);
+
+	if(meshlink_join(mesh2, corge_url)) {
+		fprintf(stderr, "Bar could join twice\n");
+		return 1;
+	}
+
+	free(corge_url);
+
 	// Clean up.
 
 	meshlink_close(mesh3);
-- 
2.39.5