Enhance syncback process by integrating serialization of service children

- Introduced `SerializationService` to serialize child instances during syncback, improving data handling.
- Updated `performSyncback` to include serialized children data in the syncback request.
- Refactored `ServiceChunk` structure to store child count instead of serialized data, optimizing memory usage.
- Adjusted related functions and tests to accommodate the new data structure, ensuring consistency and accuracy in syncback operations.

These changes significantly enhance the efficiency and clarity of the syncback process, allowing for better management of service data.

plugin/src/App/init.lua

@@ -1,5 +1,6 @@
 local ChangeHistoryService = game:GetService("ChangeHistoryService")
 local Players = game:GetService("Players")
+local SerializationService = game:GetService("SerializationService")
 local ServerStorage = game:GetService("ServerStorage")
 local RunService = game:GetService("RunService")
 
@@ -640,11 +641,21 @@ function App:performSyncback()
 	end
 
 	local services = {}
+	local allChildren = {}
 	for _, className in SYNCBACK_SERVICES do
 		local ok, service = pcall(game.FindService, game, className)
 		if ok and service then
-			table.insert(services, encodeService(service))
+			local chunk = encodeService(service)
+			for _, child in service:GetChildren() do
+				table.insert(allChildren, child)
 			end
+			table.insert(services, chunk)
+		end
+	end
+
+	local data = buffer.create(0)
+	if #allChildren > 0 then
+		data = SerializationService:SerializeInstancesAsync(allChildren)
 	end
 
 	local url = ("http://%s:%s/api/syncback"):format(host, port)
@@ -652,6 +663,7 @@ function App:performSyncback()
 		protocolVersion = Config.protocolVersion,
 		serverVersion = Config.expectedServerVersionString,
 		placeId = game.PlaceId,
+		data = data,
 		services = services,
 	})
 

plugin/src/ChangeBatcher/encodeService.lua

@@ -1,5 +1,3 @@
-local SerializationService = game:GetService("SerializationService")
-
 local Packages = script.Parent.Parent.Parent.Packages
 local Log = require(Packages.Log)
 local RbxDom = require(Packages.RbxDom)
@@ -24,7 +22,8 @@ return function(service: Instance)
 				continue
 			end
 
-			local isReadable = propertyMeta.scriptability == "ReadWrite" or propertyMeta.scriptability == "Read"
+			local isReadable = propertyMeta.scriptability == "ReadWrite"
+				or propertyMeta.scriptability == "Read"
 			local doesSerialize = propertyMeta.serialization ~= "DoesNotSerialize"
 
 			if isReadable and doesSerialize then
@@ -54,20 +53,9 @@ return function(service: Instance)
 		end
 	end
 
-	local children = service:GetChildren()
-	local data = buffer.create(0)
-	if #children > 0 then
-		local serializeOk, result = pcall(SerializationService.SerializeInstancesAsync, SerializationService, children)
-		if serializeOk then
-			data = result
-		else
-			Log.warn("Failed to serialize children of {}: {}", service.ClassName, tostring(result))
-		end
-	end
-
 	local chunk = {
 		className = service.ClassName,
-		data = data,
+		childCount = #service:GetChildren(),
 	}
 	if next(properties) then
 		chunk.properties = properties

src/cli/serve.rs

@@ -142,43 +142,47 @@ fn build_dom_from_chunks(payload: SyncbackPayload) -> anyhow::Result<WeakDom> {
 
     let mut dom = WeakDom::new(InstanceBuilder::new("DataModel"));
     let root_ref = dom.root_ref();
-
     let mut global_ref_map: HashMap<Ref, Ref> = HashMap::new();
     let mut created_services: std::collections::HashSet<String> = std::collections::HashSet::new();
 
+    let cloned_children: Vec<Ref> = if !payload.data.is_empty() {
+        let chunk_dom = rbx_binary::from_reader(Cursor::new(&payload.data))
+            .context("Failed to parse rbxm data blob")?;
+
+        let mut cloned = Vec::new();
+        for &child_ref in chunk_dom.root().children() {
+            deep_clone_into(&chunk_dom, &mut dom, child_ref, root_ref, &mut global_ref_map);
+            let new_ref = *global_ref_map.get(&child_ref).unwrap();
+            cloned.push(new_ref);
+        }
+        cloned
+    } else {
+        Vec::new()
+    };
+
+    let mut cursor = 0usize;
     for chunk in &payload.services {
         let mut builder = InstanceBuilder::new(&chunk.class_name);
-
         for (key, value) in &chunk.properties {
             builder = builder.with_property(key.as_str(), value.clone());
         }
-
         let service_ref = dom.insert(root_ref, builder);
         created_services.insert(chunk.class_name.clone());
 
-        if !chunk.data.is_empty() {
+        let count = chunk.child_count as usize;
-            let chunk_dom =
+        let end = (cursor + count).min(cloned_children.len());
-                rbx_binary::from_reader(Cursor::new(&chunk.data)).with_context(|| {
+        for &child_ref in &cloned_children[cursor..end] {
-                    format!("Failed to parse rbxm for service {}", chunk.class_name)
+            dom.transfer_within(child_ref, service_ref);
-                })?;
-
-            for &child_ref in chunk_dom.root().children() {
-                deep_clone_into(
-                    &chunk_dom,
-                    &mut dom,
-                    child_ref,
-                    service_ref,
-                    &mut global_ref_map,
-                );
-            }
         }
+        cursor = end;
 
         if !chunk.refs.is_empty() {
             let children: Vec<Ref> = dom.get_by_ref(service_ref).unwrap().children().to_vec();
             for (prop_name, target) in &chunk.refs {
                 let found = children.iter().find(|&&child_ref| {
                     let child = dom.get_by_ref(child_ref).unwrap();
-                    child.name.as_str() == target.name && child.class.as_str() == target.class_name
+                    child.name.as_str() == target.name
+                        && child.class.as_str() == target.class_name
                 });
                 if let Some(&child_ref) = found {
                     let service = dom.get_by_ref_mut(service_ref).unwrap();

src/web/api.rs

@@ -247,11 +247,13 @@ async fn handle_api_syncback(
     }
 
     log::info!(
-        "Live syncback requested with {} service chunks",
+        "Live syncback requested with {} service chunks, {} bytes of rbxm data",
-        syncback_request.services.len()
+        syncback_request.services.len(),
+        syncback_request.data.len()
     );
 
     let payload = SyncbackPayload {
+        data: syncback_request.data,
         services: syncback_request.services,
     };
     syncback_signal.fire(payload);

src/web/interface.rs

@@ -27,18 +27,21 @@ pub(crate) const SERVER_VERSION: &str = env!("CARGO_PKG_VERSION");
 /// Current protocol version, which is required to match.
 pub const PROTOCOL_VERSION: u64 = 6;
 
-/// A single service's children serialized as rbxm binary data, plus the
+/// Metadata for a single service in the live syncback request.
-/// service's own properties and Ref property hints.
 ///
-/// Attributes and Tags are included in the `properties` map as
+/// Children are NOT stored here — they live in the top-level `data` blob
-/// `Variant::Attributes(...)` and `Variant::Tags(...)` respectively,
+/// (a single rbxm containing all children from all services). `child_count`
-/// matching the encoding used by the existing `/api/write` path.
+/// tells the server how many consecutive children in that blob belong to
+/// this service.
+///
+/// Attributes and Tags are included in `properties` as
+/// `Variant::Attributes(...)` / `Variant::Tags(...)`.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct ServiceChunk {
     pub class_name: String,
-    #[serde(with = "serde_bytes")]
+    #[serde(default)]
-    pub data: Vec<u8>,
+    pub child_count: u32,
     #[serde(default)]
     pub properties: HashMap<String, Variant>,
     #[serde(default)]
@@ -64,12 +67,15 @@ pub struct SyncbackRequest {
     pub protocol_version: f64,
     pub server_version: String,
     pub place_id: Option<f64>,
+    #[serde(with = "serde_bytes", default)]
+    pub data: Vec<u8>,
     pub services: Vec<ServiceChunk>,
 }
 
 /// Payload passed from the API handler to the serve loop after validation.
 #[derive(Debug)]
 pub struct SyncbackPayload {
+    pub data: Vec<u8>,
     pub services: Vec<ServiceChunk>,
 }
 

tests/rojo_test/serve_util.rs

@@ -523,37 +523,30 @@ fn get_port_number() -> usize {
     port
 }
 
-/// Build a ServiceChunk by serializing child instances into rbxm format.
+/// A service entry plus its children (before serialization into the shared
+/// rbxm blob). Use `build_syncback_request` to finalize.
+pub struct ServiceEntry {
+    pub chunk: librojo::web_api::ServiceChunk,
+    pub children: Vec<rbx_dom_weak::InstanceBuilder>,
+}
+
+/// Build a ServiceEntry with children and no extra properties.
 pub fn make_service_chunk(
     class_name: &str,
     children: Vec<rbx_dom_weak::InstanceBuilder>,
-) -> librojo::web_api::ServiceChunk {
+) -> ServiceEntry {
     make_service_chunk_full(class_name, vec![], vec![], children)
 }
 
-/// Build a ServiceChunk with explicit service-level properties and ref hints
+/// Build a ServiceEntry with explicit service-level properties and ref hints.
-/// alongside the serialized children. Attributes and Tags should be included
-/// in the `properties` vec as `Variant::Attributes(...)` / `Variant::Tags(...)`.
 pub fn make_service_chunk_full(
     class_name: &str,
     properties: Vec<(&str, rbx_dom_weak::types::Variant)>,
     refs: Vec<(&str, &str, &str)>,
     children: Vec<rbx_dom_weak::InstanceBuilder>,
-) -> librojo::web_api::ServiceChunk {
+) -> ServiceEntry {
-    use rbx_dom_weak::WeakDom;
     use std::collections::HashMap;
 
-    let mut dom = WeakDom::new(rbx_dom_weak::InstanceBuilder::new("DataModel"));
-    let root = dom.root_ref();
-    for child in children {
-        dom.insert(root, child);
-    }
-    let child_refs: Vec<Ref> = dom.root().children().to_vec();
-    let mut buf = Vec::new();
-    if !child_refs.is_empty() {
-        rbx_binary::to_writer(&mut buf, &dom, &child_refs).unwrap();
-    }
-
     let props_map: HashMap<String, rbx_dom_weak::types::Variant> = properties
         .into_iter()
         .map(|(k, v)| (k.to_string(), v))
@@ -571,17 +564,50 @@ pub fn make_service_chunk_full(
         })
         .collect();
 
-    librojo::web_api::ServiceChunk {
+    ServiceEntry {
+        chunk: librojo::web_api::ServiceChunk {
             class_name: class_name.to_string(),
-        data: buf,
+            child_count: children.len() as u32,
             properties: props_map,
             refs: refs_map,
+        },
+        children,
     }
 }
 
-/// Build a complete rbxl file from service chunks, mirroring the same data
+/// Serialize all ServiceEntries into the final wire format: a single rbxm
-/// that live syncback receives. Used for CLI parity testing.
+/// data blob and a Vec of ServiceChunks (metadata only).
-pub fn make_rbxl_from_chunks(chunks: &[librojo::web_api::ServiceChunk]) -> Vec<u8> {
+pub fn build_syncback_request(
+    entries: Vec<ServiceEntry>,
+) -> (Vec<u8>, Vec<librojo::web_api::ServiceChunk>) {
+    use rbx_dom_weak::WeakDom;
+
+    let mut dom = WeakDom::new(rbx_dom_weak::InstanceBuilder::new("DataModel"));
+    let root = dom.root_ref();
+
+    let mut chunks = Vec::new();
+    for entry in entries {
+        for child in entry.children {
+            dom.insert(root, child);
+        }
+        chunks.push(entry.chunk);
+    }
+
+    let all_refs: Vec<Ref> = dom.root().children().to_vec();
+    let mut data = Vec::new();
+    if !all_refs.is_empty() {
+        rbx_binary::to_writer(&mut data, &dom, &all_refs).unwrap();
+    }
+
+    (data, chunks)
+}
+
+/// Build a complete rbxl file from the single-rbxm data blob + service
+/// chunks, mirroring the same data that live syncback receives.
+pub fn make_rbxl_from_chunks(
+    data: &[u8],
+    chunks: &[librojo::web_api::ServiceChunk],
+) -> Vec<u8> {
     use rbx_dom_weak::types::Variant;
     use rbx_dom_weak::WeakDom;
     use std::collections::HashMap;
@@ -590,22 +616,15 @@ pub fn make_rbxl_from_chunks(chunks: &[librojo::web_api::ServiceChunk]) -> Vec<u
     let mut dom = WeakDom::new(rbx_dom_weak::InstanceBuilder::new("DataModel"));
     let root_ref = dom.root_ref();
 
-    for chunk in chunks {
+    let cloned_children: Vec<Ref> = if !data.is_empty() {
-        let mut builder = rbx_dom_weak::InstanceBuilder::new(&chunk.class_name);
+        let chunk_dom = rbx_binary::from_reader(Cursor::new(data))
-
+            .unwrap_or_else(|e| panic!("Failed to parse rbxm data blob: {e}"));
-        for (key, value) in &chunk.properties {
-            builder = builder.with_property(key.as_str(), value.clone());
-        }
-
-        let service_ref = dom.insert(root_ref, builder);
-
-        if !chunk.data.is_empty() {
-            let chunk_dom = rbx_binary::from_reader(Cursor::new(&chunk.data))
-                .unwrap_or_else(|e| panic!("Failed to parse rbxm for {}: {e}", chunk.class_name));
 
         let mut ref_map: HashMap<Ref, Ref> = HashMap::new();
+        let mut cloned = Vec::new();
         for &child_ref in chunk_dom.root().children() {
-                deep_clone_into_test(&chunk_dom, &mut dom, child_ref, service_ref, &mut ref_map);
+            deep_clone_into_test(&chunk_dom, &mut dom, child_ref, root_ref, &mut ref_map);
+            cloned.push(*ref_map.get(&child_ref).unwrap());
         }
 
         let all_refs: Vec<Ref> = ref_map.values().copied().collect();
@@ -630,14 +649,33 @@ pub fn make_rbxl_from_chunks(chunks: &[librojo::web_api::ServiceChunk]) -> Vec<u
                 }
             }
         }
+        cloned
+    } else {
+        Vec::new()
+    };
+
+    let mut cursor = 0usize;
+    for chunk in chunks {
+        let mut builder = rbx_dom_weak::InstanceBuilder::new(&chunk.class_name);
+        for (key, value) in &chunk.properties {
+            builder = builder.with_property(key.as_str(), value.clone());
         }
+        let service_ref = dom.insert(root_ref, builder);
+
+        let count = chunk.child_count as usize;
+        let end = (cursor + count).min(cloned_children.len());
+        for &child_ref in &cloned_children[cursor..end] {
+            dom.transfer_within(child_ref, service_ref);
+        }
+        cursor = end;
 
         if !chunk.refs.is_empty() {
             let children: Vec<Ref> = dom.get_by_ref(service_ref).unwrap().children().to_vec();
             for (prop_name, target) in &chunk.refs {
                 let found = children.iter().find(|&&child_ref| {
                     let child = dom.get_by_ref(child_ref).unwrap();
-                    child.name.as_str() == target.name && child.class.as_str() == target.class_name
+                    child.name.as_str() == target.name
+                        && child.class.as_str() == target.class_name
                 });
                 if let Some(&child_ref) = found {
                     let service = dom.get_by_ref_mut(service_ref).unwrap();
@@ -691,6 +729,7 @@ fn deep_clone_into_test(
 /// project path.
 pub fn run_cli_syncback_on_chunks(
     fixture_name: &str,
+    data: &[u8],
     chunks: &[librojo::web_api::ServiceChunk],
 ) -> (TempDir, PathBuf) {
     use crate::rojo_test::io_util::{copy_recursive, ROJO_PATH, SERVE_TESTS_PATH};
@@ -701,7 +740,7 @@ pub fn run_cli_syncback_on_chunks(
     fs::create_dir(&project_path).expect("Couldn't create project subdirectory");
     copy_recursive(&source_path, &project_path).expect("Couldn't copy fixture");
 
-    let rbxl_data = make_rbxl_from_chunks(chunks);
+    let rbxl_data = make_rbxl_from_chunks(data, chunks);
     let rbxl_path = dir.path().join("input.rbxl");
     fs::write(&rbxl_path, rbxl_data).expect("Failed to write rbxl");
 
@@ -743,20 +782,34 @@ impl TestServeSession {
     }
 
     /// Post to /api/syncback with correct version/protocol info.
+    /// `data` is the single rbxm blob; `services` are the metadata chunks.
     /// Panics if the response is not 200.
     pub fn post_api_syncback(
         &self,
         place_id: Option<u64>,
+        data: Vec<u8>,
         services: Vec<librojo::web_api::ServiceChunk>,
     ) {
         use serde::Serialize;
 
-        let request = serde_json::json!({
+        #[derive(Serialize)]
-            "protocolVersion": librojo::web_api::PROTOCOL_VERSION,
+        #[serde(rename_all = "camelCase")]
-            "serverVersion": env!("CARGO_PKG_VERSION"),
+        struct Req {
-            "placeId": place_id,
+            protocol_version: u64,
-            "services": services,
+            server_version: String,
-        });
+            place_id: Option<u64>,
+            #[serde(with = "serde_bytes")]
+            data: Vec<u8>,
+            services: Vec<librojo::web_api::ServiceChunk>,
+        }
+
+        let request = Req {
+            protocol_version: librojo::web_api::PROTOCOL_VERSION,
+            server_version: env!("CARGO_PKG_VERSION").to_string(),
+            place_id,
+            data,
+            services,
+        };
 
         let mut body = Vec::new();
         let mut serializer = rmp_serde::Serializer::new(&mut body)

tests/tests/live_syncback.rs

@@ -5,18 +5,24 @@ use rbx_dom_weak::InstanceBuilder;
 use crate::rojo_test::{
     roundtrip_util::assert_dirs_equal,
     serve_util::{
-        make_service_chunk, make_service_chunk_full, run_cli_syncback_on_chunks, run_serve_test,
+        build_syncback_request, make_service_chunk, make_service_chunk_full,
+        run_cli_syncback_on_chunks, run_serve_test, ServiceEntry,
     },
 };
 
-use librojo::web_api::{ServiceChunk, SocketPacketType, PROTOCOL_VERSION};
+use librojo::web_api::{SocketPacketType, PROTOCOL_VERSION};
 
-fn assert_live_matches_cli(fixture_name: &str, chunks: &[ServiceChunk], place_id: Option<u64>) {
+fn assert_live_matches_cli(
+    fixture_name: &str,
+    entries: Vec<ServiceEntry>,
+    place_id: Option<u64>,
+) {
+    let (data, chunks) = build_syncback_request(entries);
     run_serve_test(fixture_name, |session, _| {
-        session.post_api_syncback(place_id, chunks.to_vec());
+        session.post_api_syncback(place_id, data.clone(), chunks.clone());
         session.wait_to_come_back_online();
 
-        let (_cli_dir, cli_path) = run_cli_syncback_on_chunks(fixture_name, chunks);
+        let (_cli_dir, cli_path) = run_cli_syncback_on_chunks(fixture_name, &data, &chunks);
         assert_dirs_equal(session.path(), &cli_path);
     });
 }
@@ -46,7 +52,7 @@ fn parity_scripts() {
                 ),
         ],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -63,7 +69,7 @@ fn parity_models_with_properties() {
                 )),
             )],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -76,7 +82,7 @@ fn parity_special_names() {
             InstanceBuilder::new("Folder").with_name("A/B"),
         ],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -89,7 +95,7 @@ fn parity_duplicate_names() {
             InstanceBuilder::new("Folder").with_name("Data"),
         ],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -111,7 +117,7 @@ fn parity_deep_hierarchy() {
                                 rbx_dom_weak::types::Variant::String("return true".into()),
                             )])])])])],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -134,7 +140,7 @@ fn parity_mixed_file_types() {
                 ),
         ],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -169,7 +175,7 @@ fn parity_multi_service() {
                 .with_property("Anchored", rbx_dom_weak::types::Variant::Bool(true))],
         ),
     ];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -181,7 +187,7 @@ fn parity_empty_services_mixed() {
         ),
         make_service_chunk("ServerScriptService", vec![]),
     ];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 // ── Service property parity tests ────────────────────────────────
@@ -200,7 +206,7 @@ fn parity_lighting_properties() {
         vec![],
         vec![InstanceBuilder::new("PointLight").with_name("TestLight")],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -219,7 +225,7 @@ fn parity_soundservice_properties() {
         vec![],
         vec![],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -232,7 +238,7 @@ fn parity_starterplayer_properties() {
         vec![],
         vec![],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -248,7 +254,7 @@ fn parity_textchatservice_properties() {
         vec![],
         vec![],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -264,7 +270,7 @@ fn parity_childless_service_with_properties() {
         vec![],
         vec![],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -285,7 +291,7 @@ fn parity_service_properties_with_children() {
                 .with_property("Source", Variant::String("return {}".into())),
         ],
     )];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
@@ -310,13 +316,37 @@ fn parity_multiple_services_with_properties() {
             vec![InstanceBuilder::new("Folder").with_name("Assets")],
         ),
     ];
-    assert_live_matches_cli("live_syncback", &chunks, None);
+    assert_live_matches_cli("live_syncback", chunks, None);
+}
+
+#[test]
+fn parity_cross_service_refs() {
+    use rbx_dom_weak::types::Variant;
+
+    let target_part = InstanceBuilder::new("Part")
+        .with_name("TargetPart")
+        .with_property("Anchored", Variant::Bool(true));
+
+    let obj_value = InstanceBuilder::new("ObjectValue")
+        .with_name("Pointer")
+        .with_property("Value", Variant::Ref(target_part.referent()));
+
+    let chunks = vec![
+        make_service_chunk("Workspace", vec![target_part]),
+        make_service_chunk(
+            "ReplicatedStorage",
+            vec![InstanceBuilder::new("Folder")
+                .with_name("Refs")
+                .with_child(obj_value)],
+        ),
+    ];
+    assert_live_matches_cli("live_syncback", chunks, None);
 }
 
 #[test]
 fn parity_camera_not_synced() {
     let camera_child = InstanceBuilder::new("Camera").with_name("Camera");
-    let chunks = [make_service_chunk_full(
+    let entries = vec![make_service_chunk_full(
         "Workspace",
         vec![],
         vec![("CurrentCamera", "Camera", "Camera")],
@@ -327,9 +357,10 @@ fn parity_camera_not_synced() {
                 .with_property("Anchored", rbx_dom_weak::types::Variant::Bool(true)),
         ],
     )];
+    let (data, chunks) = build_syncback_request(entries);
 
     run_serve_test("live_syncback", |session, _| {
-        session.post_api_syncback(None, chunks.to_vec());
+        session.post_api_syncback(None, data.clone(), chunks.clone());
         session.wait_to_come_back_online();
 
         let workspace_dir = session.path().join("src/workspace");
@@ -485,12 +516,12 @@ fn rejects_unlisted_place() {
 
 #[test]
 fn allows_whitelisted_place() {
-    let chunks = vec![make_service_chunk(
+    let (data, chunks) = build_syncback_request(vec![make_service_chunk(
         "ReplicatedStorage",
         vec![InstanceBuilder::new("Folder").with_name("Allowed")],
-    )];
+    )]);
     run_serve_test("live_syncback_place_ids", |session, _| {
-        session.post_api_syncback(Some(123), chunks);
+        session.post_api_syncback(Some(123), data, chunks);
         let new_info = session.wait_to_come_back_online();
         assert!(
             !new_info.project_name.is_empty(),
@@ -501,12 +532,12 @@ fn allows_whitelisted_place() {
 
 #[test]
 fn allows_any_place_when_unrestricted() {
-    let chunks = vec![make_service_chunk(
+    let (data, chunks) = build_syncback_request(vec![make_service_chunk(
         "ReplicatedStorage",
         vec![InstanceBuilder::new("Folder").with_name("Any")],
-    )];
+    )]);
     run_serve_test("live_syncback", |session, _| {
-        session.post_api_syncback(Some(99999), chunks);
+        session.post_api_syncback(Some(99999), data, chunks);
         session.wait_to_come_back_online();
     });
 }
@@ -515,7 +546,7 @@ fn allows_any_place_when_unrestricted() {
 
 #[test]
 fn server_comes_back_functional() {
-    let chunks = vec![make_service_chunk(
+    let (data, chunks) = build_syncback_request(vec![make_service_chunk(
         "ReplicatedStorage",
         vec![InstanceBuilder::new("ModuleScript")
             .with_name("TestModule")
@@ -523,10 +554,10 @@ fn server_comes_back_functional() {
                 "Source",
                 rbx_dom_weak::types::Variant::String("return 42".into()),
             )],
-    )];
+    )]);
 
     run_serve_test("live_syncback", |session, _| {
-        session.post_api_syncback(None, chunks);
+        session.post_api_syncback(None, data, chunks);
         let new_info = session.wait_to_come_back_online();
 
         let read = session.get_api_read(new_info.root_instance_id).unwrap();
@@ -548,17 +579,17 @@ fn server_comes_back_functional() {
 
 #[test]
 fn syncback_twice_different_data() {
-    let chunks_a = vec![make_service_chunk(
+    let (data_a, chunks_a) = build_syncback_request(vec![make_service_chunk(
         "ReplicatedStorage",
         vec![InstanceBuilder::new("Folder").with_name("DataA")],
-    )];
+    )]);
-    let chunks_b = vec![make_service_chunk(
+    let (data_b, chunks_b) = build_syncback_request(vec![make_service_chunk(
         "ReplicatedStorage",
         vec![InstanceBuilder::new("Folder").with_name("DataB")],
-    )];
+    )]);
 
     run_serve_test("live_syncback", |session, _| {
-        session.post_api_syncback(None, chunks_a);
+        session.post_api_syncback(None, data_a, chunks_a);
         session.wait_to_come_back_online();
 
         assert!(
@@ -566,7 +597,7 @@ fn syncback_twice_different_data() {
             "First syncback should create DataA"
         );
 
-        session.post_api_syncback(None, chunks_b);
+        session.post_api_syncback(None, data_b, chunks_b);
         session.wait_to_come_back_online();
 
         assert!(
@@ -582,7 +613,7 @@ fn syncback_twice_different_data() {
 
 #[test]
 fn syncback_replaces_all_old_files() {
-    let chunks = vec![make_service_chunk(
+    let (data, chunks) = build_syncback_request(vec![make_service_chunk(
         "ReplicatedStorage",
         vec![InstanceBuilder::new("ModuleScript")
             .with_name("NewFile")
@@ -590,7 +621,7 @@ fn syncback_replaces_all_old_files() {
                 "Source",
                 rbx_dom_weak::types::Variant::String("return 'new'".into()),
             )],
-    )];
+    )]);
 
     run_serve_test("live_syncback", |session, _| {
         assert!(
@@ -598,7 +629,7 @@ fn syncback_replaces_all_old_files() {
             "OldModule should exist before syncback"
         );
 
-        session.post_api_syncback(None, chunks);
+        session.post_api_syncback(None, data, chunks);
         session.wait_to_come_back_online();
 
         assert!(
@@ -624,16 +655,12 @@ fn roundtrip_build_syncback_rebuild() {
         let rbxl_data_a = fs::read(&rbxl_path_a).unwrap();
 
         let dom_a = rbx_binary::from_reader(Cursor::new(&rbxl_data_a)).unwrap();
+        let mut all_child_refs = Vec::new();
         let mut chunks = Vec::new();
         for &service_ref in dom_a.root().children() {
             let service = dom_a.get_by_ref(service_ref).unwrap();
             let child_refs: Vec<rbx_dom_weak::types::Ref> = service.children().to_vec();
 
-            let mut data = Vec::new();
-            if !child_refs.is_empty() {
-                rbx_binary::to_writer(&mut data, &dom_a, &child_refs).unwrap();
-            }
-
             let mut properties = std::collections::HashMap::new();
             let mut refs_map = std::collections::HashMap::new();
             for (key, value) in &service.properties {
@@ -655,15 +682,21 @@ fn roundtrip_build_syncback_rebuild() {
                 }
             }
 
-            chunks.push(ServiceChunk {
+            chunks.push(librojo::web_api::ServiceChunk {
                 class_name: service.class.to_string(),
-                data,
+                child_count: child_refs.len() as u32,
                 properties,
                 refs: refs_map,
             });
+            all_child_refs.extend(child_refs);
         }
 
-        session.post_api_syncback(None, chunks);
+        let mut data = Vec::new();
+        if !all_child_refs.is_empty() {
+            rbx_binary::to_writer(&mut data, &dom_a, &all_child_refs).unwrap();
+        }
+
+        session.post_api_syncback(None, data, chunks);
         session.wait_to_come_back_online();
 
         thread::sleep(Duration::from_millis(500));