1 files changed, 91 insertions, 0 deletions
diff --git a/src/gltf/extras.rs b/src/gltf/extras.rs
new file mode 100644
index 0000000..eade453
--- /dev/null
+++ b/src/gltf/extras.rs
@@ -0,0 +1,91 @@
+use std::borrow::Cow;
+
+use base64::Engine;
+use gltf::Gltf;
+use serde_json::{json, value::to_raw_value, Value};
+
+use crate::{Codec, Error};
+
+/// Codec for embedding data in a GLTF file "extras" entry. It uses the extras entry in the first
+/// scene in the file and stores the data as base64.
+#[derive(Default)]
+pub struct ExtrasEntryCodec;
+
+impl Codec for ExtrasEntryCodec {
+    fn encode(&self, carrier: &[u8], payload: &[u8]) -> Result<Vec<u8>, crate::Error> {
+        let gltf = match Gltf::from_slice(carrier) {
+            Ok(gltf) => gltf,
+            Err(e) => return Err(Error::DependencyError(e.to_string())),
+        };
+
+        let mut json = gltf.document.into_json();
+        let mut scene = json.scenes.remove(0);
+        let mut extras = match serde_json::from_str::<Value>(scene.extras.clone().unwrap_or(to_raw_value(&json!({})).unwrap()).get()) {
+            Ok(extras) => extras,
+            Err(e) => return Err(Error::DependencyError(e.to_string())),
+        };
+        match &mut extras {
+            Value::Object(object) => {
+                let base64_payload = base64::engine::general_purpose::STANDARD.encode(payload);
+                object.insert("occule".into(), Value::String(base64_payload));
+            },
+            _ => return Err(Error::DataInvalid("Carrier has extras in non-object format, not gonna mess with that.".into()))
+        }
+        let extras = match to_raw_value(&extras) {
+            Ok(raw) => Some(raw),
+            Err(e) => return Err(Error::DependencyError(e.to_string())),
+        };
+        scene.extras = extras;
+        json.scenes.insert(0, scene);
+        let json_string = match gltf_json::serialize::to_string(&json) {
+            Ok(json_string) => json_string,
+            Err(e) => return Err(Error::DependencyError(e.to_string())),
+        };
+
+        let mut glb = match gltf::binary::Glb::from_slice(carrier) {
+            Ok(glb) => glb,
+            Err(e) => return Err(Error::DependencyError(e.to_string())),
+        };
+        glb.header.length = (glb.header.length as usize - glb.json.len() + align_to_multiple_of_four(json_string.len())) as u32;
+        glb.json = Cow::Owned(json_string.into_bytes());        
+
+        Ok(match glb.to_vec() {
+            Ok(vec) => vec,
+            Err(e) => return Err(Error::DependencyError(e.to_string()))
+        })
+    }
+
+    fn decode(&self, encoded: &[u8]) -> Result<(Vec<u8>, Vec<u8>), crate::Error> {
+        let gltf = match Gltf::from_slice(encoded) {
+            Ok(gltf) => gltf,
+            Err(e) => return Err(Error::DependencyError(e.to_string())),
+        };
+        let mut json = gltf.document.into_json();
+        let mut extras = match &json.scenes[0].extras {
+            Some(extras) => match serde_json::from_str::<Value>(extras.get()) {
+                Ok(Value::Object(value)) => value,
+                _ => return Err(Error::DataNotEncoded),
+            },
+            None => return Err(Error::DataNotEncoded),
+        };
+        let payload = match extras.remove("occule".into()) {
+            Some(Value::String(payload)) => match base64::engine::general_purpose::STANDARD.decode(payload) {
+                Ok(payload) => payload,
+                Err(e) => return Err(Error::DependencyError(e.to_string())),
+            },
+            _ => return Err(Error::DataNotEncoded),
+        };
+
+        json.scenes[0].extras = match to_raw_value(&Value::Object(extras)) {
+            Ok(extras) => Some(extras),
+            Err(e) => return Err(Error::DependencyError(e.to_string()))
+        };
+
+        // TODO: remove payload from carrier
+        Ok((encoded.to_vec(), payload))      
+    }
+}
+
+fn align_to_multiple_of_four(n: usize) -> usize {
+    (n + 3) & !3
+}