Rudimentary streaming of raw MIDI over multicast UDP

1 files changed, 153 insertions, 0 deletions

diff --git a/midimcast-server.c b/midimcast-server.c
new file mode 100644
index 0000000..a731668
--- /dev/null
+++ b/midimcast-server.c
@@ -0,0 +1,153 @@
+#include <alsa/asoundlib.h>
+#include <arpa/inet.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/socket.h>
+#include <unistd.h>
+
+#include "midimcast.h"
+
+bool midimcast_debug;
+
+int snd_rawmidi_virtual_open(snd_rawmidi_t **inputp,
+			     snd_rawmidi_t **outputp,
+			     const char *name,
+			     snd_seq_t *seq_handle,
+			     int port,
+			     int merge,
+			     int mode);
+
+static void env_read_server(const char **const midi_in)
+{
+	*midi_in = getenv("MIDI_IN");
+	if (!*midi_in)
+		err("`MIDI_IN` unset");
+	debug("Using MIDI input %s", *midi_in);
+}
+
+// TODO: Debug messages
+// TODO: Const stuff
+static void midi_open(const char *const midi_in,
+		      snd_seq_t **seq,
+		      snd_rawmidi_t **input)
+{
+	err_snd(snd_seq_open, seq, "default", SND_SEQ_OPEN_INPUT, 0);
+	err_snd(snd_seq_set_client_name, *seq, "MIDI Broadcaster");
+
+	const int port = snd_seq_create_simple_port(*seq,
+		"MIDI Broadcaster Input",
+		SND_SEQ_PORT_CAP_WRITE
+		| SND_SEQ_PORT_CAP_SYNC_WRITE
+		| SND_SEQ_PORT_CAP_SUBS_WRITE,
+		SND_SEQ_PORT_TYPE_MIDI_GENERIC);
+
+	err_snd(snd_rawmidi_virtual_open,
+		input,
+		NULL,
+		"MIDI Broadcaster",
+		*seq,
+		port,
+		true,
+		SND_RAWMIDI_READ_STANDARD);
+
+	snd_seq_client_info_t *client_info;
+	snd_seq_client_info_alloca(&client_info);
+	snd_seq_client_info_set_client(client_info, -1);
+	snd_seq_addr_t src, dst;
+	for (;;) {
+		if (snd_seq_query_next_client(*seq, client_info))
+			err("Input '%s' absent", midi_in);
+
+		if (strcmp(snd_seq_client_info_get_name(client_info), midi_in) == 0) {
+			src.client = snd_seq_client_info_get_client(client_info);
+
+			snd_seq_port_info_t *port_info;
+			snd_seq_port_info_alloca(&port_info);
+			snd_seq_port_info_set_client(port_info, src.client);
+			snd_seq_port_info_set_port(port_info, -1);
+			if (snd_seq_query_next_port(*seq, port_info))
+				err("Input '%s' has no ports", midi_in);
+			src.port = snd_seq_port_info_get_port(port_info);
+
+			break;
+		}
+	}
+
+	dst.client = snd_seq_client_id(*seq);
+	dst.port = port;
+
+	snd_seq_port_subscribe_t *sub;
+	snd_seq_port_subscribe_alloca(&sub);
+	snd_seq_port_subscribe_set_sender(sub, &src);
+	snd_seq_port_subscribe_set_dest(sub, &dst);
+	err_snd(snd_seq_subscribe_port, *seq, sub);
+}
+
+// TODO: Naming
+static int sock_init(struct sockaddr_in *addr,
+		     const char *const mcast_group,
+		     const uint16_t mcast_port)
+{
+	memset(addr, 0, sizeof(*addr));
+	addr->sin_family = AF_INET;
+	addr->sin_addr.s_addr = inet_addr(mcast_group);
+	addr->sin_port = htons(mcast_port);
+
+	return err_std_neg(socket, AF_INET, SOCK_DGRAM, 0);
+}
+
+static void msg_write(struct msg *const msg,
+		      const size_t midi_size,
+		      const int out_sock,
+		      struct sockaddr_in *addr)
+{
+	msg->ts = htole64(msg->ts);
+	const size_t header_size = (void *)&msg->midi - (void *)&msg->ts;
+	const size_t msg_size = header_size + midi_size;
+	err_std_neg(sendto,
+		    out_sock,
+		    msg,
+		    msg_size,
+		    0,
+		    (struct sockaddr *)addr,
+		    sizeof(*addr));
+	// TODO: Check enough written?
+}
+
+int main()
+{
+	const char *mcast_group;
+	uint16_t mcast_port;
+	const char *midi_in;
+	env_read_common(&mcast_group, &mcast_port);
+	env_read_server(&midi_in);
+
+	snd_seq_t *seq;
+	snd_rawmidi_t *input;
+	midi_open(midi_in, &seq, &input);
+
+	struct sockaddr_in addr;
+	const int sock = sock_init(&addr, mcast_group, mcast_port);
+
+	for (;;) {
+		struct msg msg;
+
+		ssize_t nread = err_snd_neg(snd_rawmidi_read,
+					    input,
+					    &msg.midi,
+					    sizeof(msg.midi));
+		debug("Read %ld bytes", nread);
+
+		msg.ts = now();
+		msg_write(&msg, nread, sock, &addr);
+	}
+
+	// TODO: Make these run
+	err_snd(snd_rawmidi_close, input);
+	err_snd(snd_seq_close, seq);
+	err_std(close, sock);
+
+	return EXIT_SUCCESS;
+}