feat(desktop): open attachments in active project (#31192)

packages/desktop/src/main/attachment-picker.ts

@@ -0,0 +1,54 @@
+import { randomUUID } from "node:crypto"
+import { open } from "node:fs/promises"
+
+export const MAX_ATTACHMENT_BYTES = 20 * 1024 * 1024
+
+export function createPickedFileAuthorizations(
+  read: (path: string, maxBytes: number) => Promise<ArrayBuffer> = readAttachment,
+  budget = MAX_ATTACHMENT_BYTES,
+) {
+  const selections = new Map<string, { sender: number; paths: Set<string>; remaining: number }>()
+
+  return {
+    add(sender: number, paths: string[]) {
+      const token = randomUUID()
+      selections.set(token, { sender, paths: new Set(paths), remaining: budget })
+      return token
+    },
+    async read(sender: number, token: string, path: string) {
+      const selection = selections.get(token)
+      if (selection?.sender !== sender || !selection.paths.delete(path)) throw new Error("File was not selected by the picker")
+      const bytes = await read(path, selection.remaining)
+      selection.remaining -= bytes.byteLength
+      if (selection.paths.size === 0) selections.delete(token)
+      return bytes
+    },
+    release(sender: number, token: string) {
+      if (selections.get(token)?.sender === sender) selections.delete(token)
+    },
+  }
+}
+
+export function assertAttachmentBudget(files: { size: number }[]) {
+  const total = files.reduce((sum, file) => sum + file.size, 0)
+  if (total <= MAX_ATTACHMENT_BYTES) return
+  throw new Error(`Selected attachments exceed the ${MAX_ATTACHMENT_BYTES / 1024 / 1024} MB limit`)
+}
+
+export async function readAttachment(filePath: string, maxBytes = MAX_ATTACHMENT_BYTES) {
+  const file = await open(filePath, "r")
+  try {
+    const info = await file.stat()
+    if (info.size > maxBytes) throw new Error(`Selected attachments exceed the ${MAX_ATTACHMENT_BYTES / 1024 / 1024} MB limit`)
+    const bytes = Buffer.allocUnsafe(info.size)
+    let offset = 0
+    while (offset < info.size) {
+      const result = await file.read(bytes, offset, info.size - offset, offset)
+      if (result.bytesRead === 0) break
+      offset += result.bytesRead
+    }
+    return bytes.buffer.slice(bytes.byteOffset, bytes.byteOffset + offset) as ArrayBuffer
+  } finally {
+    await file.close()
+  }
+}