Add support for CHOICE to client DER encode/decode logic

client/src/der.vala

@@ -48,6 +48,8 @@ namespace StudySystemClient.Der {
 
 	private static Datum decode_datum(uint8 type, uint8[] content)
 			throws DecodeError {
+		if ((type & 0xc0) == Choice.BASE_TYPE)
+			return new Choice.from_content(type, content);
 		switch (type) {
 		case Boolean.TYPE:
 			return new Boolean.from_content(content);
@@ -262,4 +264,26 @@ namespace StudySystemClient.Der {
 			return elems.data;
 		}
 	}
+
+	public class Choice : Datum {
+		internal const uint8 BASE_TYPE = 0x80;
+
+		public int id { get; private set; }
+		public Datum value { get; private set; }
+
+		public Choice(int id, Datum val) {
+			type = BASE_TYPE | id;
+			content = val.encode();
+			this.id = id;
+			value = val;
+		}
+
+		internal Choice.from_content(uint8 type, uint8[] bytes)
+			throws DecodeError {
+			this.type = type;
+			content = bytes;
+			id = type & 0x3f;
+			value = decode(bytes);
+		}
+	}
 }