event-httpd: add event httpd support

Add event httpd, which is a small and basic http server designed to
provide server sent events to clients. The server accepts updates
through a simple "UPDATE" method which are then broadcast to clients
listening using the "GET" method.

Signed-off-by: Russell King <rmk@armlinux.org.uk>

1 files changed, 105 insertions, 0 deletions

diff --git a/resource.c b/resource.c
new file mode 100644
index 0000000..c1473e7
--- /dev/null
+++ b/resource.c
@@ -0,0 +1,105 @@
+// Copyright (C) 2021 Russell King.
+// Licensed under GPL version 2. See COPYING.
+#include <gio/gio.h>
+#include "event-httpd.h"
+#include "resource.h"
+
+struct resource_object {
+	GList *client_list;
+	char *str;
+};
+
+static struct resource_object position_object;
+static struct resource_object signal_object;
+
+static void object_v1_send(struct client *c, struct resource_object *obj)
+{
+	const char *str = obj->str;
+	GString *s;
+
+	if (!str)
+		return;
+
+	// Format the text/event-stream response
+	// The double newline terminates this event
+	// See https://www.html5rocks.com/en/tutorials/eventsource/basics/
+	s = g_string_sized_new(1024);
+	g_string_printf(s, "data:%s\n", str);
+	g_string_append_c(s, '\n');
+
+	respond_chunk(c, s);
+	g_string_free(s, TRUE);
+}
+
+static int object_v1_get(struct client *c, struct resource *r)
+{
+	struct resource_object *obj = r->data;
+
+	respond_header(c, 200, "OK",
+		       "Cache-Control: no-cache\r\n"
+		       "Connection: keep-alive\r\n"
+		       "Content-Type: text/event-stream; charset=UTF-8\r\n"
+		       "Transfer-Encoding: chunked\r\n");
+
+	object_v1_send(c, obj);
+
+	// Add this client to the object list so it receives updates
+	obj->client_list = g_list_append(obj->client_list, c);
+
+	return 1;
+}
+
+// Update this client with the new resource object data
+static void object_v1_client_update(gpointer data, gpointer user_data)
+{
+	struct resource_object *obj = user_data;
+	struct client *c = data;
+
+	object_v1_send(c, obj);
+}
+
+// Update all attached clients with the new resource object data
+static int object_v1_update(struct client *c, struct resource *r, const char *m)
+{
+	struct resource_object *obj = r->data;
+	char *n, *o;
+
+	n = g_strdup(m);
+	g_strchomp(n);
+	o = obj->str;
+	obj->str = n;
+	if (o)
+		g_free(o);
+
+	g_list_foreach(obj->client_list, object_v1_client_update, obj);
+
+	return 0;
+}
+
+static void object_v1_close(struct client *c, struct resource *r)
+{
+	struct resource_object *obj = r->data;
+
+	// Remove this client from the object list
+	obj->client_list = g_list_remove(obj->client_list, c);
+}
+
+static struct resource resource_position1 = {
+	.get = object_v1_get,
+	.update = object_v1_update,
+	.close = object_v1_close,
+	.data = &position_object,
+};
+
+static struct resource resource_signal1 = {
+	.get = object_v1_get,
+	.update = object_v1_update,
+	.close = object_v1_close,
+	.data = &signal_object,
+};
+
+void resource_init(GHashTable *hash)
+{
+	g_hash_table_insert(hash, "/api/1/position", &resource_position1);
+	g_hash_table_insert(hash, "/api/1/signal", &resource_signal1);
+}