Add some real messages to ASN.1 and handle pings on server

server/asn1/StudySystemProtocol.asn1

@@ -1,11 +1,40 @@
 StudySystemProtocol DEFINITIONS EXPLICIT TAGS ::= BEGIN
 
+ActivityType ::= ENUMERATED {
+	reading(0),
+	exercises(1)
+}
+
+Session ::= SEQUENCE {
+	subjectId INTEGER,
+	type ActivityType,
+	timestamp INTEGER,
+	minutes INTEGER
+}
+
 Request ::= CHOICE {
-	foo [0] NULL
+	ping [0] NULL,
+	listPrioritizedActivities [1] NULL,
+	logSession [2] Session
+}
+
+PrioritizedActivity ::= SEQUENCE {
+	subjectId INTEGER,
+	subjectName UTF8String,
+	type ActivityType,
+	priority INTEGER
+}
+
+Error ::= ENUMERATED {
+	invalidRequest(0),
+	invalidArguments(1),
+	serverError(2)
 }
 
 Response ::= CHOICE {
-	msg [0] UTF8String
+	error [0] Error,
+	ack [1] NULL,
+	prioritizedActivities [2] SEQUENCE OF PrioritizedActivity
 }
 
 END