From adf66538075417ba3a3ca24ce4cad019434e358c Mon Sep 17 00:00:00 2001
From: Aaron Hill <aa1ronham@gmail.com>
Date: Sun, 14 Aug 2022 21:32:00 -0500
Subject: [PATCH] swf: Write a non-zero 'index' value for
 true/false/undefined/null default values

A zero 'index' does not have a subsequent 'kind' field in the
written SWF. The 'index' field is not actually used for
true/false/undefined/null, so it can be anything as long
as it's non-zero.
---
 swf/src/avm2/read.rs                |  18 ++++++++++++++++++
 swf/src/avm2/write.rs               |  16 +++++++++-------
 swf/tests/swfs/Avm2DefaultValue.as  |   8 ++++++++
 swf/tests/swfs/Avm2DefaultValue.swf | Bin 0 -> 580 bytes
 4 files changed, 35 insertions(+), 7 deletions(-)
 create mode 100644 swf/tests/swfs/Avm2DefaultValue.as
 create mode 100644 swf/tests/swfs/Avm2DefaultValue.swf

diff --git a/swf/src/avm2/read.rs b/swf/src/avm2/read.rs
index 441819966..ac66a84cb 100644
--- a/swf/src/avm2/read.rs
+++ b/swf/src/avm2/read.rs
@@ -904,6 +904,24 @@ pub mod tests {
         }
     }
 
+    #[test]
+    fn test_round_trip_default_value() {
+        use crate::avm2::write::Writer;
+
+        let orig_bytes = read_abc_from_file("tests/swfs/Avm2DefaultValue.swf");
+        let mut reader = Reader::new(&orig_bytes[..]);
+        let parsed = reader.read().unwrap();
+
+        let mut out = vec![];
+        let mut writer = Writer::new(&mut out);
+        writer.write(parsed).unwrap();
+
+        assert_eq!(
+            orig_bytes, out,
+            "Incorrectly written Avm2DefaultValue class"
+        );
+    }
+
     #[test]
     fn read_u30() {
         let read = |data: &[u8]| Reader::new(data).read_u30().unwrap();
diff --git a/swf/src/avm2/write.rs b/swf/src/avm2/write.rs
index e4e82fb3d..225c23c4f 100644
--- a/swf/src/avm2/write.rs
+++ b/swf/src/avm2/write.rs
@@ -373,9 +373,9 @@ impl<W: Write> Writer<W> {
             DefaultValue::Private(ref i) => (i.as_u30(), 0x05),
             DefaultValue::Double(ref i) => (i.as_u30(), 0x06),
             DefaultValue::Namespace(ref i) => (i.as_u30(), 0x08),
-            DefaultValue::False => (0, 0x0a),
-            DefaultValue::True => (0, 0x0b),
-            DefaultValue::Null => (0, 0x0c),
+            DefaultValue::False => (0x0a, 0x0a),
+            DefaultValue::True => (0x0b, 0x0b),
+            DefaultValue::Null => (0x0c, 0x0c),
             DefaultValue::Package(ref i) => (i.as_u30(), 0x16),
             DefaultValue::PackageInternal(ref i) => (i.as_u30(), 0x17),
             DefaultValue::Protected(ref i) => (i.as_u30(), 0x18),
@@ -392,16 +392,18 @@ impl<W: Write> Writer<W> {
             None => self.write_u30(0)?,
             Some(ref value) => {
                 let (index, kind) = match *value {
-                    DefaultValue::Undefined => (0, 0x00),
+                    // Just write out a non-zero 'index' field - it's unused,
+                    // so it doesn't matter what it is.
+                    DefaultValue::Undefined => (0x01, 0x00),
                     DefaultValue::String(ref i) => (i.as_u30(), 0x01),
                     DefaultValue::Int(ref i) => (i.as_u30(), 0x03),
                     DefaultValue::Uint(ref i) => (i.as_u30(), 0x04),
                     DefaultValue::Private(ref i) => (i.as_u30(), 0x05),
                     DefaultValue::Double(ref i) => (i.as_u30(), 0x06),
                     DefaultValue::Namespace(ref i) => (i.as_u30(), 0x08),
-                    DefaultValue::False => (0, 0x0a),
-                    DefaultValue::True => (0, 0x0b),
-                    DefaultValue::Null => (0, 0x0c),
+                    DefaultValue::False => (0x0a, 0x0a),
+                    DefaultValue::True => (0x0b, 0x0b),
+                    DefaultValue::Null => (0x0c, 0x0c),
                     DefaultValue::Package(ref i) => (i.as_u30(), 0x16),
                     DefaultValue::PackageInternal(ref i) => (i.as_u30(), 0x17),
                     DefaultValue::Protected(ref i) => (i.as_u30(), 0x18),
diff --git a/swf/tests/swfs/Avm2DefaultValue.as b/swf/tests/swfs/Avm2DefaultValue.as
new file mode 100644
index 000000000..f413bb8d5
--- /dev/null
+++ b/swf/tests/swfs/Avm2DefaultValue.as
@@ -0,0 +1,8 @@
+package {
+	public class Avm2DefaultValue {
+		public static var defaultTrue:Boolean = true;
+		public static var defaultFalse:Boolean = false;
+		public static var defaultNull:String = null;
+		public static var defaultUndefined:* = undefined;
+	}
+}
diff --git a/swf/tests/swfs/Avm2DefaultValue.swf b/swf/tests/swfs/Avm2DefaultValue.swf
new file mode 100644
index 0000000000000000000000000000000000000000..67bd81344c18d43d5345f095dc2b2c5cc3eac8c7
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