Implement loopback backend

4 files changed, 175 insertions, 25 deletions

diff --git a/README.md b/README.md
index 7c62452..8a79d1f 100644
--- a/README.md
+++ b/README.md
@@ -115,6 +115,33 @@ NRPNs are not yet fully implemented, though rudimentary support is in the codeba
 
 The channel specification syntax is currently a bit clunky.
 
+### The `loopback` backend
+
+This backend allows the user to create logical mapping channels, for example to exchange triggering
+channels easier later. All events that are input are immediately output again on the same channel.
+
+#### Global configuration
+
+All global configuration is ignored.
+
+#### Instance configuration
+
+All instance configuration is ignored
+
+#### Channel specification
+
+A channel may have any string for a name.
+
+Example mapping:
+```
+loop.foo = loop.bar123
+```
+
+#### Known bugs / problems
+
+It is possible to configure loops using this backend. Triggering a loop
+will create a deadlock, preventing any other backends from generating events.
+
 ### The `osc` backend
 
 TBD
diff --git a/loopback.c b/loopback.c
new file mode 100644
index 0000000..56e8759
--- /dev/null
+++ b/loopback.c
@@ -0,0 +1,120 @@
+#include <string.h>
+#include "loopback.h"
+
+#define BACKEND_NAME "loopback"
+
+int init(){
+	backend loopback = {
+		.name = BACKEND_NAME,
+		.conf = backend_configure,
+		.create = backend_instance,
+		.conf_instance = backend_configure_instance,
+		.channel = backend_channel,
+		.handle = backend_set,
+		.process = backend_handle,
+		.start = backend_start,
+		.shutdown = backend_shutdown
+	};
+
+	//register backend
+	if(mm_backend_register(loopback)){
+		fprintf(stderr, "Failed to register loopback backend\n");
+		return 1;
+	}
+	return 0;
+}
+
+static int backend_configure(char* option, char* value){
+	//intentionally ignored
+	return 0;
+}
+
+static int backend_configure_instance(instance* instance, char* option, char* value){
+	//intentionally ignored
+	return 0;
+}
+
+static instance* backend_instance(){
+	instance* i = mm_instance();
+	if(!i){
+		return NULL;
+	}
+
+	i->impl = calloc(1, sizeof(loopback_instance));
+	if(!i->impl){
+		fprintf(stderr, "Failed to allocate memory\n");
+		return NULL;
+	}
+
+	return i;
+}
+
+static channel* backend_channel(instance* inst, char* spec){
+	size_t u;
+	loopback_instance* data = (loopback_instance*) inst->impl;
+
+	//find matching channel
+	for(u = 0; u < data->n; u++){
+		if(!strcmp(spec, data->name[u])){
+			break;
+		}
+	}
+
+	//allocate new channel
+	if(u == data->n){
+		data->name = realloc(data->name, (u + 1) * sizeof(char*));
+		if(!data->name){
+			fprintf(stderr, "Failed to allocate memory\n");
+			return NULL;
+		}
+
+		data->name[u] = strdup(spec);
+		if(!data->name[u]){
+			fprintf(stderr, "Failed to allocate memory\n");
+			return NULL;
+		}
+		data->n++;
+	}
+
+	return mm_channel(inst, u, 1);
+}
+
+static int backend_set(instance* inst, size_t num, channel** c, channel_value* v){
+	size_t n;
+	for(n = 0; n < num; n++){
+		mm_channel_event(c[n], v[n]);
+	}
+	return 0;
+}
+
+static int backend_handle(size_t num, managed_fd* fds){
+	//no events generated here
+	return 0;
+}
+
+static int backend_start(){
+	return 0;
+}
+
+static int backend_shutdown(){
+	size_t n, u, p;
+	instance** inst = NULL;
+	loopback_instance* data = NULL;
+
+	if(mm_backend_instances(BACKEND_NAME, &n, &inst)){
+		fprintf(stderr, "Failed to fetch instance list\n");
+		return 1;
+	}
+
+	for(u = 0; u < n; u++){
+		data = (loopback_instance*) inst[u]->impl;
+		for(p = 0; p < data->n; p++){
+			free(data->name[p]);
+		}
+		free(data->name);
+		free(inst[u]->impl);
+	}
+
+	free(inst);
+	return 0;
+}
diff --git a/loopback.h b/loopback.h
new file mode 100644
index 0000000..fe44e91
--- /dev/null
+++ b/loopback.h
@@ -0,0 +1,16 @@
+#include "midimonster.h"
+
+int init();
+static int backend_configure(char* option, char* value);
+static int backend_configure_instance(instance* instance, char* option, char* value);
+static instance* backend_instance();
+static channel* backend_channel(instance* instance, char* spec);
+static int backend_set(instance* inst, size_t num, channel** c, channel_value* v);
+static int backend_handle(size_t num, managed_fd* fds);
+static int backend_start();
+static int backend_shutdown();
+
+typedef struct /*_loopback_instance_data*/ {
+	size_t n;
+	char** name;
+} loopback_instance;
diff --git a/monster.cfg b/monster.cfg
index 194b115..f1caf87 100644
--- a/monster.cfg
+++ b/monster.cfg
@@ -5,31 +5,18 @@ name = MIDIMonster
 bind = * 6454
 net = 0
 
-;[backend osc]
+[midi pad]
+read = Launchpad
+write = Launchpad
 
-[midi bcf]
-read = BCF
-write = BCF
-
-[midi lc1]
-read = Launch Control
-write = Launch Control
-
-[midi xlate]
-
-[artnet net1]
-net = 0
-uni = 1
-output = true
+[loopback loop]
 
 [map]
-bcf.cc0.81 = lc1.cc0.1
-bcf.cc0.82 = lc1.note0.1
-bcf.cc0.83 = lc1.cc0.9
-net1.15 = lc1.cc0.1
-bcf.cc0.1 = net1.1
-bcf.cc0.2 = net1.3
-;net1.257 = bcf.cc0.81
-;net1.231 = foo.1
-;net1.255 = lc1.cc0.1
-;net1.231 = osc.f/channel5/ toggle=127
+loop.test = pad.note0.0
+
+pad.note0.1 = loop.test
+pad.note0.2 = loop.test
+pad.note0.3 = loop.test
+pad.note0.4 = loop.test
+pad.note0.5 = loop.test
+pad.note0.6 = loop.test