add helper functions for async spawning of processes

src/util/process.ts

@@ -1,5 +1,6 @@
+import assert from 'assert'
+import child_process, { exec as execCb } from 'child_process'
 import util from 'util'
-import { exec as execCb } from 'child_process'
 
 const exec = util.promisify(execCb)
 
@@ -12,3 +13,60 @@ export async function run(command: string) {
 export async function aapt2(path: string, ...args: Array<string>) {
   return await run(`${path} ${args.join(' ')}`)
 }
+
+export async function spawnAsyncNoOut(
+  command: string,
+  args: ReadonlyArray<string>,
+  isStderrLineAllowed?: (s: string) => boolean,
+) {
+  let stdout = await spawnAsync(command, args, isStderrLineAllowed)
+  assert(stdout.length === 0, `unexpected stdout for ${command} ${args}: ${stdout}`)
+}
+
+// Returns stdout. If there's stderr output, all lines of it should pass the isStderrLineAllowed check
+export async function spawnAsync(
+  command: string,
+  args: ReadonlyArray<string>,
+  isStderrLineAllowed?: (s: string) => boolean,
+  allowedExitCodes: number[] = [0],
+) {
+  let proc = child_process.spawn(command, args)
+  let promise = new Promise((resolve, reject) => {
+    let stdoutBufs: Buffer[] = []
+    let stderrBufs: Buffer[] = []
+
+    proc.stdout.on('data', data => {
+      stdoutBufs.push(data)
+    })
+    proc.stderr.on('data', data => {
+      stderrBufs.push(data)
+    })
+
+    proc.on('close', code => {
+      let stderr = ''
+
+      if (stderrBufs.length > 0) {
+        stderr = Buffer.concat(stderrBufs).toString()
+      }
+
+      if (code !== null && allowedExitCodes.includes(code)) {
+        if (stderr.length > 0) {
+          if (isStderrLineAllowed === undefined) {
+            reject(new Error('unexpected stderr ' + stderr))
+          } else {
+            for (let line of stderr.split('\n')) {
+              if (!isStderrLineAllowed(line)) {
+                reject(new Error('unexpected stderr line ' + line))
+              }
+            }
+          }
+        }
+        resolve(Buffer.concat(stdoutBufs).toString())
+      } else {
+        reject(new Error(proc.spawnargs + ' returned ' + code + (stderr.length > 0 ? ', stderr: ' + stderr : '')))
+      }
+    })
+  })
+
+  return promise as Promise<string>
+}