Warn on MTU mismatchv0.1-rc3

2 files changed, 40 insertions, 2 deletions

diff --git a/src/handshake.c b/src/handshake.c
index a17fd2b..2359af4 100644
--- a/src/handshake.c
+++ b/src/handshake.c
@@ -44,6 +44,7 @@ static const char const *RECORD_TYPES[RECORD_MAX] = {
 	"(protocol specific 3)",
 	"(protocol specific 4)",
 	"(protocol specific 5)",
+	"MTU",
 };
 
 static const char const *REPLY_TYPES[REPLY_MAX] = {
@@ -53,13 +54,15 @@ static const char const *REPLY_TYPES[REPLY_MAX] = {
 };
 
 #define AS_UINT8(ptr) (*(uint8_t*)(ptr).data)
+#define AS_UINT16(ptr) ((*(uint8_t*)(ptr).data) + (*((uint8_t*)(ptr).data+1) << 8))
 
 
 fastd_buffer fastd_handshake_new_init(fastd_context *ctx, fastd_peer *peer, size_t tail_space) {
 	size_t protocol_len = strlen(ctx->conf->protocol->name);
 	fastd_buffer buffer = fastd_buffer_alloc(sizeof(fastd_packet), 0,
-						 2*5 +           /* handshake type, mode */
-						 4+protocol_len+ /* protocol name */
+						 2*5 +            /* handshake type, mode */
+						 6 +		  /* MTU */
+						 4+protocol_len + /* protocol name */
 						 tail_space
 						 );
 	fastd_packet *request = buffer.data;
@@ -69,6 +72,7 @@ fastd_buffer fastd_handshake_new_init(fastd_context *ctx, fastd_peer *peer, size
 
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_HANDSHAKE_TYPE, 1);
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_MODE, ctx->conf->mode);
+	fastd_handshake_add_uint16(ctx, &buffer, RECORD_MTU, ctx->conf->mtu);
 
 	fastd_handshake_add(ctx, &buffer, RECORD_PROTOCOL_NAME, protocol_len, ctx->conf->protocol->name);
 
@@ -76,8 +80,15 @@ fastd_buffer fastd_handshake_new_init(fastd_context *ctx, fastd_peer *peer, size
 }
 
 fastd_buffer fastd_handshake_new_reply(fastd_context *ctx, fastd_peer *peer, const fastd_handshake *handshake, size_t tail_space) {
+	bool first = (AS_UINT8(handshake->records[RECORD_HANDSHAKE_TYPE]) == 1);
+	size_t mtu_size = 0;
+
+	if (first)
+		mtu_size = 6;
+
 	fastd_buffer buffer = fastd_buffer_alloc(sizeof(fastd_packet), 0,
 						 2*5 +           /* handshake type, reply code */
+						 mtu_size +
 						 tail_space
 						 );
 	fastd_packet *request = buffer.data;
@@ -88,6 +99,9 @@ fastd_buffer fastd_handshake_new_reply(fastd_context *ctx, fastd_peer *peer, con
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_HANDSHAKE_TYPE, AS_UINT8(handshake->records[RECORD_HANDSHAKE_TYPE])+1);
 	fastd_handshake_add_uint8(ctx, &buffer, RECORD_REPLY_CODE, 0);
 
+	if (first)
+		fastd_handshake_add_uint16(ctx, &buffer, RECORD_MTU, ctx->conf->mtu);
+
 	return buffer;
 }
 
@@ -129,6 +143,13 @@ void fastd_handshake_handle(fastd_context *ctx, fastd_peer *peer, fastd_buffer b
 
 	handshake.type = AS_UINT8(handshake.records[RECORD_HANDSHAKE_TYPE]);
 
+	if (handshake.records[RECORD_MTU].length == 2) {
+		if (AS_UINT16(handshake.records[RECORD_MTU]) != ctx->conf->mtu) {
+			pr_warn(ctx, "MTU configuration differs with peer %P: local MTU is %u, remote MTU is %u",
+				 peer, ctx->conf->mtu, AS_UINT16(handshake.records[RECORD_MTU]));
+		}
+	}
+
 	if (handshake.type == 1) {
 		uint8_t reply_code = REPLY_SUCCESS;
 		uint8_t error_detail = 0;
diff --git a/src/handshake.h b/src/handshake.h
index d540de0..a5b861e 100644
--- a/src/handshake.h
+++ b/src/handshake.h
@@ -42,6 +42,7 @@ typedef enum _fastd_handshake_record_type {
 	RECORD_PROTOCOL3,
 	RECORD_PROTOCOL4,
 	RECORD_PROTOCOL5,
+	RECORD_MTU,
 	RECORD_MAX,
 } fastd_handshake_record_type;
 
@@ -101,5 +102,21 @@ static inline void fastd_handshake_add_uint8(fastd_context *ctx, fastd_buffer *b
 	buffer->len += 5;
 }
 
+static inline void fastd_handshake_add_uint16(fastd_context *ctx, fastd_buffer *buffer, fastd_handshake_record_type type, uint16_t value) {
+	if ((uint8_t*)buffer->data + buffer->len + 6 > (uint8_t*)buffer->base + buffer->base_len)
+		exit_bug(ctx, "not enough buffer allocated for handshake");
+
+	uint8_t *dst = (uint8_t*)buffer->data + buffer->len;
+
+	dst[0] = type;
+	dst[1] = type >> 8;
+	dst[2] = 2;
+	dst[3] = 0;
+	dst[4] = value;
+	dst[5] = value >> 8;
+
+	buffer->len += 6;
+}
+
 
 #endif /* _FASTD_HANDSHAKE_H_ */