From 6c94102afc70ce28eee3d17aad997a056aaf9195 Mon Sep 17 00:00:00 2001
From: Silas Bartha <silas@exvacuum.dev>
Date: Fri, 11 Oct 2024 19:01:52 -0400
Subject: gltf, wav, and binary codecs

---
 src/binary/mod.rs              |  2 ++
 src/binary/reverse_appendix.rs | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100644 src/binary/mod.rs
 create mode 100644 src/binary/reverse_appendix.rs

(limited to 'src/binary')

diff --git a/src/binary/mod.rs b/src/binary/mod.rs
new file mode 100644
index 0000000..66f6c30
--- /dev/null
+++ b/src/binary/mod.rs
@@ -0,0 +1,2 @@
+mod reverse_appendix;
+pub use reverse_appendix::*;
diff --git a/src/binary/reverse_appendix.rs b/src/binary/reverse_appendix.rs
new file mode 100644
index 0000000..d131526
--- /dev/null
+++ b/src/binary/reverse_appendix.rs
@@ -0,0 +1,35 @@
+use crate::{Codec, Error};
+
+/// Reverses payload binary data and writes it ass-first past the end of the original data. A
+/// length marker is also prepended to the payload *before reversing* so the decoder knows how long
+/// the payload is.
+pub struct BinaryReverseAppendixCodec;
+
+impl Codec for BinaryReverseAppendixCodec {
+    fn encode(&self, carrier: &[u8], payload: &[u8]) -> Result<Vec<u8>, crate::Error> {
+        let mut encoded = Vec::<u8>::new();
+        encoded.extend(carrier.iter());
+        let payload_len = (payload.len() as u64 + 8).to_le_bytes();
+        encoded.extend(payload_len.iter().chain(payload.iter()).rev());
+        Ok(encoded)
+    }
+
+    fn decode(&self, encoded: &[u8]) -> Result<(Vec<u8>, Vec<u8>), crate::Error> {
+        if encoded.len() < 8 {
+            return Err(Error::DataNotEncoded);
+        }
+
+        let encoded_len = encoded.len();
+        let payload_len = u64::from_le_bytes(encoded.iter().rev().take(8).cloned().collect::<Vec<_>>().try_into().unwrap()) as usize;
+        if encoded_len < payload_len + 8 || payload_len < 8 {
+            return Err(Error::DataNotEncoded);
+        }
+
+        let carrier_len = encoded_len - payload_len;
+
+        let carrier = encoded[..carrier_len].to_vec();
+        let payload = encoded.iter().rev().skip(8).take(payload_len - 8).cloned().collect::<Vec<_>>();
+
+        Ok((carrier, payload))
+    }
+}
-- 
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