use single fd for all operations

src/NodeFileSystemWriteableFileStream.ts

@@ -1,5 +1,4 @@
 import * as fs from 'node:fs'
-import * as asyncfs from 'node:fs/promises'
 import * as path from 'node:path'
 import { Writable } from 'node:stream'
 import type {
@@ -11,35 +10,51 @@ import type {
 
 export default class NodeFileSystemWritableFileStream extends WritableStream implements FileSystemWritableFileStream {
     #seek_position = 0
-    #name: string
+    #fd: number
     constructor(name: string, options: FileSystemCreateWritableOptions = {}) {
         name = path.normalize(name)
-        super(Writable.toWeb(fs.createWriteStream(name)))
-        this.#name = name
-        if(!options.keepExistingData) this.truncate(0)
+        let flags = 'w'
+        if (!options.keepExistingData) flags = 'r+'
+        const fd = fs.openSync(name, flags)
+        super(Writable.toWeb(fs.createWriteStream(name, { "fd": fd })))
+        this.#fd = fd
     }
     async seek(position: number): Promise<void> {
+        if (this.locked) throw new Error("stream is locked")
         this.#seek_position = position
     }
-    truncate(size: number): Promise<void> {
-        return asyncfs.truncate(this.#name, size)
+    async truncate(size: number): Promise<void> {
+        if (this.locked) throw new Error("stream is locked")
+        return fs.ftruncateSync(this.#fd, size)
     }
     async write(wdata: FileSystemWriteChunkType): Promise<void> {
+        if (this.locked) throw new Error("stream is locked")
         if (wdata instanceof Blob) wdata = await wdata.bytes()
         if (typeof wdata === 'string') wdata = new TextEncoder().encode(wdata)
         let wsize: number = null
         let pseek_position = this.#seek_position
         if ((wdata as WriteParams).type) {
             const { type, position, size, data } = (wdata as WriteParams)
-            if (type === 'truncate') return asyncfs.truncate(this.#name, size)
+            if (type === 'truncate') return this.truncate(size)
             if (position) this.#seek_position = position
             if (type === 'seek') return
             if (size) wsize = size
             wdata = data
         }
-        const file = await asyncfs.open(this.#name,'r+')
-        await file.write((wdata as Uint8Array), null, wsize, this.#seek_position)
-        await file.close()
+        fs.writeSync(this.#fd, (wdata as Uint8Array), null, wsize, this.#seek_position)
         this.#seek_position = pseek_position
     }
+    async #_close() {
+        try {
+            fs.closeSync(this.#fd)
+        } catch { }
+    }
+    async close(): Promise<void> {
+        await super.close()
+        await this.#_close()
+    }
+    async abort(reason?: any): Promise<void> {
+        await super.abort(reason)
+        await this.#_close()
+    }
 }