delete done parts during assembly to prevent needing double the stream size as available disk space

src/lib/streamCache.svelte.ts

@@ -67,8 +67,6 @@ export async function download(stream: StreamSummary) {
 export async function remove(streamId: string) {
     cached.delete(streamId);
     await discard(streamId);
-    const root = await navigator.storage.getDirectory();
-    await root.removeEntry(streamId).catch(() => {});
 }
 
 export async function getUrl(streamId: string): Promise<string | null> {
@@ -140,10 +138,15 @@ async function assemble(streamId: string, total: number) {
     const root = await navigator.storage.getDirectory();
     const dir = await partsDir(streamId, true);
     const handle = await root.getFileHandle(streamId, { create: true });
-    const writable = await handle.createWritable();
+
+    // track size from previous assembling attempt if there was one
+    const done = (await handle.getFile()).size;
+
+    const writable = await handle.createWritable({ keepExistingData: done > 0 });
+    await writable.seek(done);
 
     // check at each step the chunk names (ranges) are coherent
-    let written = 0;
+    let written = done;
     while (written < total) {
         const name = String(written);
         const part = await dir.getFileHandle(name).catch(() => null);
@@ -156,7 +159,8 @@ async function assemble(streamId: string, total: number) {
     }
     await writable.close();
 
-    await discard(streamId);
+    partials.delete(streamId);
+    await sweep(streamId);
     // chunks went missing, shit's fucked...
     if (written !== total) throw new Error(`Assembled ${written} of ${total} bytes`);
 }
@@ -168,9 +172,11 @@ async function partsDir(streamId: string, create = false) {
     return parts.getDirectoryHandle(streamId, { create });
 }
 
-/** discard stream's partial download state and run a sweep of leftover parts files */
+/** discard everything on disk for a stream that is not fully downloaded */
 async function discard(streamId: string) {
     partials.delete(streamId);
+    const root = await navigator.storage.getDirectory();
+    await root.removeEntry(streamId).catch(() => {});
     await sweep(streamId);
 }