feat: Add in overlay

lib/util/Overlay.ts

@@ -0,0 +1,92 @@
+import fs from "fs/promises"
+import * as T from "../types"
+import cp from "child_process"
+import { promisify } from "util"
+import { Buffer } from "node:buffer"
+export const execFile = promisify(cp.execFile)
+
+export class Overlay {
+  private constructor(readonly effects: T.Effects, readonly rootfs: string) {}
+  static async of(effects: T.Effects, imageId: string) {
+    const rootfs = await effects.createOverlayedImage({ imageId })
+
+    for (const dirPart of ["dev", "sys", "proc", "run"] as const) {
+      const dir = await fs.mkdir(`${rootfs}/${dirPart}`, { recursive: true })
+      if (!dir) break
+      await execFile("mount", ["--bind", `/${dirPart}`, dir])
+    }
+
+    return new Overlay(effects, rootfs)
+  }
+
+  async mount(options: MountOptions, path: string): Promise<Overlay> {
+    path = path.startsWith("/")
+      ? `${this.rootfs}${path}`
+      : `${this.rootfs}/${path}`
+    if (options.type === "volume") {
+      await execFile("mount", [
+        "--bind",
+        `/media/startos/volumes/${options.id}`,
+        path,
+      ])
+    } else if (options.type === "assets") {
+      await execFile("mount", [
+        "--bind",
+        `/media/startos/assets/${options.id}`,
+        path,
+      ])
+    } else if (options.type === "pointer") {
+      await this.effects.mount({ location: path, target: options })
+    } else {
+      throw new Error(`unknown type ${(options as any).type}`)
+    }
+    return this
+  }
+
+  async destroy() {
+    await execFile("umount", ["-R", this.rootfs])
+    await fs.rm(this.rootfs, { recursive: true, force: true })
+  }
+
+  async exec(
+    command: string[],
+    options?: CommandOptions,
+  ): Promise<{ stdout: string | Buffer; stderr: string | Buffer }> {
+    return await execFile("chroot", [this.rootfs, ...command], options)
+  }
+
+  spawn(
+    command: string[],
+    options?: CommandOptions,
+  ): cp.ChildProcessWithoutNullStreams {
+    return cp.spawn("chroot", [this.rootfs, ...command], options)
+  }
+}
+
+export type CommandOptions = {
+  env?: { [variable: string]: string }
+  cwd?: string
+}
+
+export type MountOptions =
+  | MountOptionsVolume
+  | MountOptionsAssets
+  | MountOptionsPointer
+
+export type MountOptionsVolume = {
+  type: "volume"
+  id: string
+}
+
+export type MountOptionsAssets = {
+  type: "assets"
+  id: string
+}
+
+export type MountOptionsPointer = {
+  type: "pointer"
+  packageId: string
+  volumeId: string
+  path: string
+  readonly: boolean
+}