Implement basic DNS parsing

3 files changed, 237 insertions, 46 deletions

diff --git a/backends/rtpmidi.c b/backends/rtpmidi.c
index 2eec871..97364cf 100644
--- a/backends/rtpmidi.c
+++ b/backends/rtpmidi.c
@@ -11,9 +11,9 @@
 #include "rtpmidi.h"
 
 //TODO learn peer ssrcs
-//TODO default session join?
 //TODO default mode?
 //TODO internal loop mode
+//FIXME what qualifies an instance to be announced via mdns?
 
 static struct /*_rtpmidi_global*/ {
 	int mdns_fd;
@@ -41,6 +41,7 @@ MM_PLUGIN_API int init(){
 		.conf_instance = rtpmidi_configure_instance,
 		.channel = rtpmidi_channel,
 		.handle = rtpmidi_set,
+		.interval = rtpmidi_interval,
 		.process = rtpmidi_handle,
 		.start = rtpmidi_start,
 		.shutdown = rtpmidi_shutdown
@@ -59,38 +60,90 @@ MM_PLUGIN_API int init(){
 	return 0;
 }
 
-static int rtpmidi_configure(char* option, char* value){
-	char* host = NULL, *port = NULL;
+static int dns_decode_name(uint8_t* buffer, size_t len, size_t start, dns_name* out){
+	size_t offset = 0, output_offset = 0;
+	uint8_t current_label = 0;
+	uint16_t ptr_target = 0;
 
-	if(!strcmp(option, "mdns-name")){
-		if(cfg.mdns_name){
-			LOG("Duplicate mdns-name assignment");
-			return 1;
+	//reset output data length and terminate null name
+	out->length = 0;
+	if(out->name){
+		out->name[0] = 0;
+	}
+
+	while(start + offset < len){
+		current_label = buffer[start + offset];
+
+		//if we're at a pointer, move there and stop counting data length
+		if(DNS_POINTER(current_label)){
+			if(start + offset + 1 >= len){
+				LOG("mDNS internal pointer out of bounds");
+				return 1;
+			}
+
+			//do this before setting the target
+			if(!ptr_target){
+				out->length += 2;
+			}
+
+			//calculate pointer target
+			ptr_target = DNS_LABEL_LENGTH(current_label) << 8 | buffer[start + offset + 1];
+
+			if(ptr_target >= len){
+				LOG("mDNS internal pointer target out of bounds");
+				return 1;
+			}
+			start = ptr_target;
+			offset = 0;
 		}
+		else{
+			if(DNS_LABEL_LENGTH(current_label) == 0){
+				if(!ptr_target){
+					out->length++;
+				}
+				break;
+			}
 
-		cfg.mdns_name = strdup(value);
-		if(!cfg.mdns_name){
-			LOG("Failed to allocate memory");
-			return 1;
+			//check whether we have the bytes we need
+			if(start + offset + DNS_LABEL_LENGTH(current_label) > len){
+				LOG("mDNS bytes missing");
+				return 1;
+			}
+
+			//check whether we have space in the output
+			if(output_offset + DNS_LABEL_LENGTH(current_label) > out->alloc){
+				out->name = realloc(out->name, (output_offset + DNS_LABEL_LENGTH(current_label) + 2) * sizeof(uint8_t));
+				out->alloc = output_offset + DNS_LABEL_LENGTH(current_label);
+			}
+
+			//copy data from this label to output buffer
+			memcpy(out->name + output_offset, buffer + start + offset + 1, DNS_LABEL_LENGTH(current_label));
+			output_offset += DNS_LABEL_LENGTH(current_label) + 1;
+			offset += DNS_LABEL_LENGTH(current_label) + 1;
+			out->name[output_offset - 1] = '.';
+			out->name[output_offset] = 0;
+			if(!ptr_target){
+				out->length = offset;
+			}
 		}
-		return 0;
 	}
-	else if(!strcmp(option, "mdns-bind")){
-		if(cfg.mdns_fd >= 0){
-			LOG( "Only one mDNS discovery bind is supported");
-			return 1;
-		}
+	return 0;
+}
 
-		mmbackend_parse_hostspec(value, &host, &port, NULL);
+static uint32_t rtpmidi_interval(){
+	return max(0, RTPMIDI_SERVICE_INTERVAL - (mm_timestamp() - cfg.last_service));
+}
 
-		if(!host){
-			LOGPF("Not a valid mDNS bind address: %s", value);
+static int rtpmidi_configure(char* option, char* value){
+	if(!strcmp(option, "mdns-name")){
+		if(cfg.mdns_name){
+			LOG("Duplicate mdns-name assignment");
 			return 1;
 		}
 
-		cfg.mdns_fd = mmbackend_socket(host, (port ? port : RTPMIDI_MDNS_PORT), SOCK_DGRAM, 1, 1);
-		if(cfg.mdns_fd < 0){
-			LOGPF("Failed to bind mDNS interface: %s", value);
+		cfg.mdns_name = strdup(value);
+		if(!cfg.mdns_name){
+			LOG("Failed to allocate memory");
 			return 1;
 		}
 		return 0;
@@ -925,6 +978,79 @@ static int rtpmidi_service(){
 	return 0;
 }
 
+static int rtpmidi_handle_mdns(){
+	uint8_t buffer[RTPMIDI_PACKET_BUFFER];
+	dns_header* hdr = (dns_header*) buffer;
+	dns_rr* rr = NULL;
+	dns_name name = {
+		.alloc = 0
+	};
+	ssize_t bytes = 0;
+	size_t u = 0, offset = sizeof(dns_header);
+
+	for(bytes = recv(cfg.mdns_fd, buffer, sizeof(buffer), 0); bytes > 0; bytes = recv(cfg.mdns_fd, buffer, sizeof(buffer), 0)){
+		if(bytes < sizeof(dns_header)){
+			continue;
+		}
+		LOGPF("%" PRIsize_t " bytes of mDNS data", bytes);
+
+		hdr->id = be16toh(hdr->id);
+		hdr->questions = be16toh(hdr->questions);
+		hdr->answers = be16toh(hdr->answers);
+		hdr->servers = be16toh(hdr->servers);
+		hdr->additional = be16toh(hdr->additional);
+
+		//TODO Check for ._apple-midi._udp.local.
+		LOGPF("ID %d, Opcode %d, %s, %d questions, %d answers, %d servers, %d additional", hdr->id, DNS_OPCODE(hdr->flags[0]), DNS_RESPONSE(hdr->flags[0]) ? "response" : "query", hdr->questions, hdr->answers, hdr->servers, hdr->additional);
+		for(u = 0; u < hdr->questions; u++){
+			dns_decode_name(buffer, bytes, offset, &name);
+			offset += name.length;
+			offset += sizeof(dns_question);
+
+			LOGPF("Question: %s", name.name);
+		}
+
+		for(u = 0; u < hdr->answers; u++){
+			dns_decode_name(buffer, bytes, offset, &name);
+			offset += name.length;
+			rr = (dns_rr*) (buffer + offset);
+			offset += sizeof(dns_rr) + be16toh(rr->data);
+
+			LOGPF("Answer (%d): %s, %d bytes of data", be16toh(rr->rtype), name.name, be16toh(rr->data));
+		}
+
+		for(u = 0; u < hdr->servers; u++){
+			dns_decode_name(buffer, bytes, offset, &name);
+			offset += name.length;
+			rr = (dns_rr*) (buffer + offset);
+			offset += sizeof(dns_rr) + be16toh(rr->data);
+
+			LOGPF("Authority (%d): %s, %d bytes of data", be16toh(rr->rtype), name.name, be16toh(rr->data));
+		}
+
+		for(u = 0; u < hdr->additional; u++){
+			dns_decode_name(buffer, bytes, offset, &name);
+			offset += name.length;
+			rr = (dns_rr*) (buffer + offset);
+			offset += sizeof(dns_rr) + be16toh(rr->data);
+
+			LOGPF("Additional (%d): %s, %d bytes of data", be16toh(rr->rtype), name.name, be16toh(rr->data));
+		}
+	}
+
+	free(name.name);
+	if(bytes <= 0){
+		if(errno == EAGAIN){
+			return 0;
+		}
+
+		LOGPF("Error reading from mDNS descriptor: %s", strerror(errno));
+		return 1;
+	}
+
+	return 0;
+}
+
 static int rtpmidi_handle(size_t num, managed_fd* fds){
 	size_t u;
 	int rv = 0;
@@ -933,7 +1059,7 @@ static int rtpmidi_handle(size_t num, managed_fd* fds){
 
 	//handle service tasks (mdns, clock sync, peer connections)
 	if(mm_timestamp() - cfg.last_service > RTPMIDI_SERVICE_INTERVAL){
-		DBGPF("Performing service tasks, delta %" PRIu64, mm_timestamp() - cfg.last_service);
+		//DBGPF("Performing service tasks, delta %" PRIu64, mm_timestamp() - cfg.last_service);
 		if(rtpmidi_service()){
 			return 1;
 		}
@@ -942,7 +1068,8 @@ static int rtpmidi_handle(size_t num, managed_fd* fds){
 
 	for(u = 0; u < num; u++){
 		if(!fds[u].impl){
-			//TODO handle mDNS discovery input
+			//handle mDNS discovery input
+			rtpmidi_handle_mdns();
 		}
 		else{
 			//handle rtp/control input
@@ -963,30 +1090,53 @@ static int rtpmidi_handle(size_t num, managed_fd* fds){
 	return rv;
 }
 
-static int rtpmidi_start(size_t n, instance** inst){
-	size_t u, p, fds = 0;
-	rtpmidi_instance_data* data = NULL;
+static int rtpmidi_start_mdns(){
+	struct ip_mreq mcast_req = {
+		.imr_multiaddr.s_addr = htobe32(((uint32_t) 0xe00000fb)),
+		.imr_interface.s_addr = INADDR_ANY
+	};
 
-	//if mdns name defined and no socket, bind default values
-	if(cfg.mdns_name && cfg.mdns_fd < 0){
-		cfg.mdns_fd = mmbackend_socket(RTPMIDI_DEFAULT_HOST, RTPMIDI_MDNS_PORT, SOCK_DGRAM, 1, 1);
-		if(cfg.mdns_fd < 0){
-			return 1;
-		}
+	struct ipv6_mreq mcast6_req = {
+		.ipv6mr_multiaddr.s6_addr = {0xff, 0x02, 0x00, 0x00,
+						0x00, 0x00, 0x00, 0x00,
+						0x00, 0x00, 0x00, 0x00,
+						0x00, 0x00, 0x00, 0xfb},
+		.ipv6mr_interface = 0
+	};
+
+	if(!cfg.mdns_name){
+		LOG("No mDNS name set, disabling AppleMIDI discovery");
+		return 0;
 	}
 
-	//register mdns fd to core
-	if(cfg.mdns_fd >= 0){
-		if(mm_manage_fd(cfg.mdns_fd, BACKEND_NAME, 1, NULL)){
-			LOG("Failed to register mDNS socket with core");
-			return 1;
-		}
-		fds++;
+	//FIXME might try passing NULL as host here to work around possible windows ipv6 handicaps
+	cfg.mdns_fd = mmbackend_socket(RTPMIDI_DEFAULT_HOST, RTPMIDI_MDNS_PORT, SOCK_DGRAM, 1, 1);
+	if(cfg.mdns_fd < 0){
+		LOG("Failed to create requested mDNS descriptor");
+		return 1;
 	}
-	else{
-		LOG("No mDNS discovery interface bound, AppleMIDI session discovery disabled");
+
+	//join ipv4 multicast group
+	if(setsockopt(cfg.mdns_fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (uint8_t*) &mcast_req, sizeof(mcast_req))){
+		LOGPF("Failed to join IPv4 multicast group for mDNS: %s", strerror(errno));
+		return 1;
+	}
+
+	//join ipv6 multicast group
+	if(setsockopt(cfg.mdns_fd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, (uint8_t*) &mcast6_req, sizeof(mcast6_req))){
+		LOGPF("Failed to join IPv6 multicast group for mDNS: %s", strerror(errno));
+		return 1;
 	}
 
+	//register mdns fd to core
+	return mm_manage_fd(cfg.mdns_fd, BACKEND_NAME, 1, NULL);
+}
+
+static int rtpmidi_start(size_t n, instance** inst){
+	size_t u, p, fds = 0;
+	rtpmidi_instance_data* data = NULL;
+	uint8_t mdns_required = 0;
+
 	for(u = 0; u < n; u++){
 		data = (rtpmidi_instance_data*) inst[u]->impl;
 		//check whether instances are explicitly configured to a mode
@@ -1013,6 +1163,9 @@ static int rtpmidi_start(size_t n, instance** inst){
 				data->peer[p].connected = 1;
 			}
 		}
+		else if(data->mode == apple){
+			mdns_required = 1;
+		}
 
 		//register fds to core
 		if(mm_manage_fd(data->fd, BACKEND_NAME, 1, inst[u]) || (data->control_fd >= 0 && mm_manage_fd(data->control_fd, BACKEND_NAME, 1, inst[u]))){
@@ -1022,6 +1175,13 @@ static int rtpmidi_start(size_t n, instance** inst){
 		fds += (data->control_fd >= 0) ? 2 : 1;
 	}
 
+	if(mdns_required && rtpmidi_start_mdns()){
+		return 1;
+	}
+	else{
+		fds++;
+	}
+
 	LOGPF("Registered %" PRIsize_t " descriptors to core", fds);
 	return 0;
 }
diff --git a/backends/rtpmidi.h b/backends/rtpmidi.h
index a08cf0f..b1fe26a 100644
--- a/backends/rtpmidi.h
+++ b/backends/rtpmidi.h
@@ -8,6 +8,7 @@ static int rtpmidi_configure(char* option, char* value);
 static int rtpmidi_configure_instance(instance* instance, char* option, char* value);
 static int rtpmidi_instance(instance* inst);
 static channel* rtpmidi_channel(instance* instance, char* spec, uint8_t flags);
+static uint32_t rtpmidi_interval();
 static int rtpmidi_set(instance* inst, size_t num, channel** c, channel_value* v);
 static int rtpmidi_handle(size_t num, managed_fd* fds);
 static int rtpmidi_start(size_t n, instance** inst);
@@ -22,6 +23,11 @@ static int rtpmidi_shutdown(size_t n, instance** inst);
 #define RTPMIDI_DEFAULT_NAME "MIDIMonster"
 #define RTPMIDI_SERVICE_INTERVAL 1000
 
+#define DNS_POINTER(a) (((a) & 0xC0) == 0xC0)
+#define DNS_LABEL_LENGTH(a) ((a) & 0x3F)
+#define DNS_OPCODE(a) (((a) & 0x78) >> 3)
+#define DNS_RESPONSE(a) ((a) & 0x80)
+
 enum /*_rtpmidi_channel_type*/ {
 	none = 0,
 	note = 0x90,
@@ -90,6 +96,12 @@ enum applemidi_command {
 	apple_feedback = 0x5253 //RS
 };
 
+typedef struct /*_dns_name*/ {
+	size_t alloc;
+	char* name;
+	size_t length;
+} dns_name;
+
 #pragma pack(push, 1)
 typedef struct /*_apple_session_command*/ {
 	uint16_t res1;
@@ -128,4 +140,25 @@ typedef struct /*_rtp_midi_command*/ {
 	uint8_t flags;
 	uint8_t length;
 } rtpmidi_command_header;
+
+typedef struct /*_dns_header*/ {
+	uint16_t id;
+	uint8_t flags[2];
+	uint16_t questions;
+	uint16_t answers;
+	uint16_t servers;
+	uint16_t additional;
+} dns_header;
+
+typedef struct /*_dns_question*/ {
+	uint16_t qtype;
+	uint16_t qclass;
+} dns_question;
+
+typedef struct /*_dns_rr*/ {
+	uint16_t rtype;
+	uint16_t rclass;
+	uint32_t ttl;
+	uint16_t data;
+} dns_rr;
 #pragma pack(pop)
diff --git a/backends/rtpmidi.md b/backends/rtpmidi.md
index e857a5a..c188039 100644
--- a/backends/rtpmidi.md
+++ b/backends/rtpmidi.md
@@ -25,7 +25,6 @@ stream, which may lead to inconsistencies during playback.
 | Option	| Example value		| Default value 	| Description		|
 |---------------|-----------------------|-----------------------|-----------------------|
 | `detect`      | `on`                  | `off`                 | Output channel specifications for any events coming in on configured instances to help with configuration |
-| `mdns-bind`	| `10.1.2.1 5353`	| `:: 5353`		| Bind host for the mDNS discovery server |
 | `mdns-name`	| `computer1`		| none			| mDNS hostname to announce, also used as AppleMIDI peer name |
 
 #### Instance configuration
@@ -51,9 +50,8 @@ Common instance configuration parameters
 |---------------|-----------------------|-----------------------|-----------------------|
 | `bind`	| `10.1.2.1 9001`	| `:: <random>`		| Local network address to bind to (note that AppleMIDI requires two consecutive port numbers to be allocated) |
 | `session`	| `Just Jamming`	| `MIDIMonster`		| Session name to announce via mDNS |
-| `invite`	| `pad`			| none			| Devices to send invitations to when discovered (the special value `*` invites all discovered peers). Setting this option makes the instance a session initiator. May be specified multiple times |
+| `invite`	| `pad`			| none			| Devices to send invitations to when discovered (the special value `*` invites all discovered peers). Setting this option makes the instance a session initiator. May be specified multiple times. |
 | `join`	| `Just Jamming`	| none			| Session for which to accept invitations (the special value `*` accepts the first invitation seen). Setting this option makes the instance a session participant |
-| `peer`	| `10.1.2.3 9001`	| none			| Configure a direct session peer, bypassing AppleMIDI discovery. May be specified multiple times |
 
 Note that AppleMIDI session discovery requires mDNS functionality, thus the `mdns-name` global parameter
 (and, depending on your setup, the `mdns-bind` parameter) need to be configured properly.