From: Guus Sliepen <guus@meshlink.io>
Date: Sun, 24 May 2020 19:23:13 +0000 (+0200)
Subject: The maximum unreliable packet size is 65535 bytes.
X-Git-Url: https://git.meshlink.io/?a=commitdiff_plain;h=f2ffa5a92d66b69767c9225616f19679465a55b0;p=meshlink

The maximum unreliable packet size is 65535 bytes.

This matches how real UDP works and avoids 16 bit integer overflow.
---

diff --git a/src/utcp.c b/src/utcp.c
index dc5a2fcf..c4305cd4 100644
--- a/src/utcp.c
+++ b/src/utcp.c
@@ -1147,7 +1147,7 @@ static void handle_unreliable(struct utcp_connection *c, const struct hdr *hdr,
 	}
 
 	// Ensure reassembled packet are not larger than 64 kiB
-	if(hdr->wnd >= MAX_UNRELIABLE_SIZE || hdr->wnd + len > MAX_UNRELIABLE_SIZE) {
+	if(hdr->wnd > MAX_UNRELIABLE_SIZE || hdr->wnd + len > MAX_UNRELIABLE_SIZE) {
 		return;
 	}
 
diff --git a/src/utcp_priv.h b/src/utcp_priv.h
index 197fd268..7ef14778 100644
--- a/src/utcp_priv.h
+++ b/src/utcp_priv.h
@@ -42,7 +42,7 @@
 #define DEFAULT_RCVBUFSIZE 0
 #define DEFAULT_MAXRCVBUFSIZE 131072
 
-#define MAX_UNRELIABLE_SIZE 65536
+#define MAX_UNRELIABLE_SIZE 65535
 #define DEFAULT_MTU 1000
 
 #define USEC_PER_SEC 1000000L
diff --git a/test/channels-udp.c b/test/channels-udp.c
index 4e628c01..f4ddbe2b 100644
--- a/test/channels-udp.c
+++ b/test/channels-udp.c
@@ -55,10 +55,10 @@ static void client_receive_cb(meshlink_handle_t *mesh, meshlink_channel_t *chann
 	// We expect always the same amount of data from the server.
 	assert(mesh->priv);
 	struct client *client = mesh->priv;
-	assert(len == 512 || len == 65536);
+	assert(len == 512 || len == 65535);
 	client->received += len;
 
-	if(len == 65536) {
+	if(len == 65535) {
 		client->got_large_packet = true;
 	}
 }
@@ -142,16 +142,15 @@ int main(void) {
 
 	// Check that we can send up to 65535 bytes without errors
 
-	char large_data[65536] = "";
+	char large_data[65535] = "";
 
 	for(int i = 0; i < 3; i++) {
-		assert(meshlink_channel_send(server, channels[i], large_data, sizeof(large_data) + 1) == -1);
 		assert(meshlink_channel_send(server, channels[i], large_data, sizeof(large_data)) == sizeof(large_data));
 	}
 
-	// Assert that packets larger than 64 kiB are not allowed
+	// Assert that any larger packets are not allowed
 
-	assert(meshlink_channel_send(server, channels[0], large_data, 65537) == -1);
+	assert(meshlink_channel_send(server, channels[0], large_data, 65536) == -1);
 
 	// Stream packets from server to clients for 5 seconds at 40 Mbps (1 kB * 500 Hz)