From 18541786e1c7484fa108f1197de5c4dcabe4046c Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Tue, 25 Feb 2025 18:17:30 +0000
Subject: [PATCH] Add support for CHOICE to client DER encode/decode logic

---
 client/src/der.vala         | 24 ++++++++++++++++++++++
 client/tests/der_tests.vala | 40 ++++++++++++++++++++++++++++++++++---
 2 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/client/src/der.vala b/client/src/der.vala
index bfdcfd9..968a0e7 100644
--- a/client/src/der.vala
+++ b/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);
+		}
+	}
 }
diff --git a/client/tests/der_tests.vala b/client/tests/der_tests.vala
index ec9433a..da564a0 100644
--- a/client/tests/der_tests.vala
+++ b/client/tests/der_tests.vala
@@ -172,6 +172,14 @@ void main(string[] args) {
 			test_encode(sequence, expected);
 		});
 
+	Test.add_func("/encode/choice/1:foo", () => {
+			var choice = new Der.Choice(1, new Utf8String("foo"));
+			var expected = new uint8[] {
+				0x81, 0x05, 0x0c, 0x03, 0x66, 0x6f, 0x6f
+			};
+			test_encode(choice, expected);
+		});
+
 	/*
 	 * Decoding
 	 */
@@ -227,10 +235,10 @@ void main(string[] args) {
 		});
 
 	Test.add_func("/decode/sequence/foo,42", () => {
+			var expected_len = 2;
 			var bytes = new uint8[] {
 				0x30, 0x08, 0x0c, 0x03, 0x66, 0x6f, 0x6f, 0x02, 0x01, 0x2a
 			};
-			var expected = 2;
 			Der.Sequence sequence;
 			try {
 				sequence = decode(bytes) as Der.Sequence;
@@ -245,9 +253,9 @@ void main(string[] args) {
 				return;
 			}
 			Datum[] elems = sequence.value;
-			if (elems.length != expected) {
+			if (elems.length != expected_len) {
 				Test.message(
-					@"Expected $expected elements, got $(elems.length)");
+					@"Expected $expected_len elements, got $(elems.length)");
 				Test.fail();
 				return;
 			}
@@ -255,5 +263,31 @@ void main(string[] args) {
 			test_integer_value(42, elems[1]);
 		});
 
+	Test.add_func("/decode/choice/1:foo", () => {
+			var expected_id = 1;
+			var bytes = new uint8[] {
+				0x81, 0x05, 0x0c, 0x03, 0x66, 0x6f, 0x6f
+			};
+			Der.Choice choice;
+			try {
+				choice = decode(bytes) as Der.Choice;
+			} catch (DecodeError err) {
+				Test.message("Decoding failed: %s", err.message);
+				Test.fail();
+				return;
+			}
+			if (choice == null) {
+				Test.message("Bytes were not decoded as a CHOICE");
+				Test.fail();
+				return;
+			}
+			if (choice.id != expected_id) {
+				Test.message(@"Expected ID $expected_id, got $(choice.id)");
+				Test.fail();
+				return;
+			}
+			test_utf8string_value("foo", choice.value);
+		});
+
 	Test.run();
 }