Build .fig ZIP in Rust instead of fflate

fflate's zipSync produces ZIP files that Figma rejects. Move the entire
fig-kiwi container + Zstd compression + ZIP packaging into a single
Rust command (build_fig_file). Zstd now includes content size via
set_pledged_src_size. Web fallback still uses fflate/deflate.

desktop/Cargo.lock

@@ -47,6 +47,15 @@ version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7f202df86484c868dbad7eaa557ef785d5c66295e41b460ef922eca0723b842c"
 
+[[package]]
+name = "arbitrary"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c3d036a3c4ab069c7b410a2ce876bd74808d2d0888a82667669f8e783a898bf1"
+dependencies = [
+ "derive_arbitrary",
+]
+
 [[package]]
 name = "async-broadcast"
 version = "0.7.2"
@@ -643,6 +652,17 @@ dependencies = [
  "serde_core",
 ]
 
+[[package]]
+name = "derive_arbitrary"
+version = "1.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e567bd82dcff979e4b03460c307b3cdc9e96fde3d73bed1496d2bc75d9dd62a"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.117",
+]
+
 [[package]]
 name = "derive_more"
 version = "0.99.20"
@@ -2346,6 +2366,7 @@ dependencies = [
  "tauri-plugin-dialog",
  "tauri-plugin-fs",
  "tauri-plugin-opener",
+ "zip",
  "zstd",
 ]
 
@@ -5340,6 +5361,21 @@ dependencies = [
  "syn 2.0.117",
 ]
 
+[[package]]
+name = "zip"
+version = "2.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fabe6324e908f85a1c52063ce7aa26b68dcb7eb6dbc83a2d148403c9bc3eba50"
+dependencies = [
+ "arbitrary",
+ "crc32fast",
+ "crossbeam-utils",
+ "displaydoc",
+ "indexmap 2.13.0",
+ "memchr",
+ "thiserror 2.0.18",
+]
+
 [[package]]
 name = "zmij"
 version = "1.0.21"

desktop/Cargo.toml

@@ -25,4 +25,5 @@ serde_json = "1"
 tauri-plugin-dialog = "2.6.0"
 tauri-plugin-fs = "2.4.5"
 zstd = "0.13"
+zip = { version = "2", default-features = false }
 

desktop/src/lib.rs

@@ -4,20 +4,66 @@ use tauri::{
 };
 
 #[tauri::command]
-fn zstd_compress(data: Vec<u8>) -> Result<Vec<u8>, String> {
-    use std::io::Write;
+fn build_fig_file(
+    schema_deflated: Vec<u8>,
+    kiwi_data: Vec<u8>,
+    thumbnail_png: Vec<u8>,
+    meta_json: String,
+) -> Result<Vec<u8>, String> {
+    use std::io::{Cursor, Write};
+
+    // Zstd-compress kiwi data with content size in frame header
     let mut encoder = zstd::Encoder::new(Vec::new(), 3).map_err(|e| e.to_string())?;
     encoder
         .include_contentsize(true)
         .map_err(|e| e.to_string())?;
-    encoder.write_all(&data).map_err(|e| e.to_string())?;
-    encoder.finish().map_err(|e| e.to_string())
+    encoder
+        .set_pledged_src_size(Some(kiwi_data.len() as u64))
+        .map_err(|e| e.to_string())?;
+    encoder.write_all(&kiwi_data).map_err(|e| e.to_string())?;
+    let zstd_data = encoder.finish().map_err(|e| e.to_string())?;
+
+    // Build fig-kiwi container
+    let version: u32 = 106;
+    let fig_kiwi_len = 8 + 4 + 4 + schema_deflated.len() + 4 + zstd_data.len();
+    let mut fig_kiwi = Vec::with_capacity(fig_kiwi_len);
+    fig_kiwi.extend_from_slice(b"fig-kiwi");
+    fig_kiwi.extend_from_slice(&version.to_le_bytes());
+    fig_kiwi.extend_from_slice(&(schema_deflated.len() as u32).to_le_bytes());
+    fig_kiwi.extend_from_slice(&schema_deflated);
+    fig_kiwi.extend_from_slice(&(zstd_data.len() as u32).to_le_bytes());
+    fig_kiwi.extend_from_slice(&zstd_data);
+
+    // Deflate-compress the schema for verification it's already deflated
+    // (schema_deflated is already deflated, we just pass it through)
+
+    // Build ZIP with canvas.fig + thumbnail.png + meta.json (all STORED)
+    let buf = Cursor::new(Vec::new());
+    let mut zip = zip::ZipWriter::new(buf);
+    let options =
+        zip::write::SimpleFileOptions::default().compression_method(zip::CompressionMethod::Stored);
+
+    zip.start_file("canvas.fig", options)
+        .map_err(|e| e.to_string())?;
+    zip.write_all(&fig_kiwi).map_err(|e| e.to_string())?;
+
+    zip.start_file("thumbnail.png", options)
+        .map_err(|e| e.to_string())?;
+    zip.write_all(&thumbnail_png).map_err(|e| e.to_string())?;
+
+    zip.start_file("meta.json", options)
+        .map_err(|e| e.to_string())?;
+    zip.write_all(meta_json.as_bytes())
+        .map_err(|e| e.to_string())?;
+
+    let result = zip.finish().map_err(|e| e.to_string())?;
+    Ok(result.into_inner())
 }
 
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
     tauri::Builder::default()
-        .invoke_handler(tauri::generate_handler![zstd_compress])
+        .invoke_handler(tauri::generate_handler![build_fig_file])
         .plugin(tauri_plugin_opener::init())
         .plugin(tauri_plugin_dialog::init())
         .plugin(tauri_plugin_fs::init())

src/engine/fig-export.ts

@@ -7,6 +7,10 @@ import type { CanvasKit } from 'canvaskit-wasm'
 import type { SceneGraph, SceneNode, Color } from './scene-graph'
 import type { SkiaRenderer } from './renderer'
 
+const THUMBNAIL_1X1 = Uint8Array.from(atob(
+  'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8/5+hHgAHggJ/PchI7wAAAABJRU5ErkJggg=='
+), (c) => c.charCodeAt(0))
+
 interface KiwiNodeChange {
   guid: { sessionID: number; localID: number }
   parentIndex?: { guid: { sessionID: number; localID: number }; position: string }
@@ -194,24 +198,13 @@ function sceneNodeToKiwi(
   return result
 }
 
-async function compressData(data: Uint8Array): Promise<Uint8Array> {
-  if (IS_TAURI) {
-    const { invoke } = await import('@tauri-apps/api/core')
-    return new Uint8Array(await invoke<number[]>('zstd_compress', { data: Array.from(data) }))
-  }
-  return deflateSync(data)
-}
-
-async function buildFigKiwi(schemaDeflated: Uint8Array, dataRaw: Uint8Array): Promise<Uint8Array> {
-  const dataCompressed = await compressData(dataRaw)
+function buildFigKiwi(schemaDeflated: Uint8Array, dataCompressed: Uint8Array): Uint8Array {
   const FIG_KIWI_VERSION = 106
-
   const total = 8 + 4 + 4 + schemaDeflated.length + 4 + dataCompressed.length
   const out = new Uint8Array(total)
   const view = new DataView(out.buffer)
 
-  const magic = new TextEncoder().encode('fig-kiwi')
-  out.set(magic, 0)
+  out.set(new TextEncoder().encode('fig-kiwi'), 0)
   view.setUint32(8, FIG_KIWI_VERSION, true)
 
   let offset = 12
@@ -351,27 +344,33 @@ export async function exportFigFile(
     msg.blobs = blobs.map((bytes) => ({ bytes }))
   }
 
-  const dataRaw = compiled.encodeMessage(msg)
-  const canvasData = await buildFigKiwi(schemaDeflated, dataRaw)
+  const kiwiData = compiled.encodeMessage(msg)
 
   const currentPageId = pageId ?? pages[0]?.id
-  const thumbnail = ck && renderer && currentPageId
+  const thumbnailPng = (ck && renderer && currentPageId
     ? generateThumbnail(ck, renderer, graph, currentPageId)
-    : null
+    : null) ?? THUMBNAIL_1X1
 
-  const THUMBNAIL_1X1 = Uint8Array.from(atob(
-    'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8/5+hHgAHggJ/PchI7wAAAABJRU5ErkJggg=='
-  ), (c) => c.charCodeAt(0))
-
-  const meta = JSON.stringify({
+  const metaJson = JSON.stringify({
     version: 1,
     app: 'OpenPencil',
     createdAt: new Date().toISOString()
   })
 
+  if (IS_TAURI) {
+    const { invoke } = await import('@tauri-apps/api/core')
+    return new Uint8Array(await invoke<number[]>('build_fig_file', {
+      schemaDeflated: Array.from(schemaDeflated),
+      kiwiData: Array.from(kiwiData),
+      thumbnailPng: Array.from(thumbnailPng),
+      metaJson
+    }))
+  }
+
+  const canvasData = buildFigKiwi(schemaDeflated, deflateSync(kiwiData))
   return zipSync({
     'canvas.fig': [canvasData, { level: 0 }],
-    'thumbnail.png': [thumbnail ?? THUMBNAIL_1X1, { level: 0 }],
-    'meta.json': new TextEncoder().encode(meta)
+    'thumbnail.png': [thumbnailPng, { level: 0 }],
+    'meta.json': new TextEncoder().encode(metaJson)
   })
 }