feat(vhd-lib): createContentStream (#3086)

Export the raw content of the VHD as a stream.

This features is exposed in CLI: `vhd-cli raw input.vhd output.raw`

Related to #3083

Perf comparison between qemu-img and our vhd-cli to convert a 10GiB VHD file to raw:

```
> time qemu-img convert -f vpc -O raw origin.vhd expected.raw
1.40user 15.19system 1:01.88elapsed 26%CPU (0avgtext+0avgdata 24264maxresident)k
20979008inputs+20971520outputs (12major+4648minor)pagefaults 0swaps
> time vhd-cli raw origin.vhd actual.raw
21.97user 16.03system 1:09.11elapsed 54%CPU (0avgtext+0avgdata 65208maxresident)k
20956008inputs+20972448outputs (1major+754101minor)pagefaults 0swaps

> md5sum *.raw
b55ec6924be750edd2423e4a7aa262c3  actual.raw
b55ec6924be750edd2423e4a7aa262c3  expected.raw
```

packages/vhd-cli/src/_utils.js

@@ -0,0 +1,23 @@
+const { createWriteStream } = require('fs')
+const { PassThrough } = require('stream')
+
+const createOutputStream = path => {
+  if (path !== undefined && path !== '-') {
+    return createWriteStream(path)
+  }
+
+  // introduce a through stream because stdout is not a normal stream!
+  const stream = new PassThrough()
+  stream.pipe(process.stdout)
+  return stream
+}
+
+export const writeStream = (input, path) => {
+  const output = createOutputStream(path)
+
+  return new Promise((resolve, reject) =>
+    input
+      .on('error', reject)
+      .pipe(output.on('error', reject).on('finish', resolve))
+  )
+}

packages/vhd-cli/src/commands/raw.js

@@ -0,0 +1,16 @@
+import { createContentStream } from 'vhd-lib'
+import { getHandler } from '@xen-orchestra/fs'
+import { resolve } from 'path'
+
+import { writeStream } from '../_utils'
+
+export default async args => {
+  if (args.length < 2 || args.some(_ => _ === '-h' || _ === '--help')) {
+    return `Usage: ${this.command} <input VHD> [<output raw>]`
+  }
+
+  await writeStream(
+    createContentStream(getHandler({ url: 'file:///' }), resolve(args[0])),
+    args[1]
+  )
+}

packages/vhd-lib/src/createContentStream.js

@@ -0,0 +1,31 @@
+import asyncIteratorToStream from 'async-iterator-to-stream'
+
+import Vhd from './vhd'
+
+export default asyncIteratorToStream(async function * (handler, path) {
+  const fd = await handler.openFile(path, 'r')
+  try {
+    const vhd = new Vhd(handler, fd)
+    await vhd.readHeaderAndFooter()
+    await vhd.readBlockAllocationTable()
+    const {
+      footer: { currentSize },
+      header: { blockSize },
+    } = vhd
+    const nFullBlocks = Math.floor(currentSize / blockSize)
+    const nLeftoverBytes = currentSize % blockSize
+
+    const emptyBlock = Buffer.alloc(blockSize)
+    for (let i = 0; i < nFullBlocks; ++i) {
+      yield vhd.containsBlock(i) ? (await vhd._readBlock(i)).data : emptyBlock
+    }
+    if (nLeftoverBytes !== 0) {
+      yield (vhd.containsBlock(nFullBlocks)
+        ? (await vhd._readBlock(nFullBlocks)).data
+        : emptyBlock
+      ).slice(0, nLeftoverBytes)
+    }
+  } finally {
+    await handler.closeFile(fd)
+  }
+})

packages/vhd-lib/src/index.js

@@ -1,5 +1,6 @@
 export { default } from './vhd'
 export { default as chainVhd } from './chain'
+export { default as createContentStream } from './createContentStream'
 export { default as createReadableRawStream } from './createReadableRawStream'
 export {
   default as createReadableSparseStream,