Document dependency on and check existence of zip and unzipon Linux

Closes #57

README.md

@@ -51,7 +51,7 @@ You can now install the `example-patched.apk` file on your Android device and us
 
 ### Patching App Bundles
 
-You can also patch apps using [Android App Bundle](android-app-bundle) with `apk-mitm` by providing it with a `*.xapk` file (for example from [APKPure][apkpure]) or a `*.apks` file (which you can export yourself using [SAI][sai]).
+You can also patch apps using [Android App Bundle](android-app-bundle) with `apk-mitm` by providing it with a `*.xapk` file (for example from [APKPure][apkpure]) or a `*.apks` file (which you can export yourself using [SAI][sai]). If you're doing this on Linux, make sure that both `zip` and `unzip` are installed.
 
 ### Making manual changes
 

src/cli.ts

@@ -19,6 +19,7 @@ export type TaskOptions = {
   uberApkSigner: UberApkSigner
   tmpDir: string
   wait: boolean
+  isAppBundle: boolean
   debuggable: boolean
 }
 
@@ -55,17 +56,20 @@ async function main() {
   const outputName = `${baseName}-patched${fileExtension}`
   const outputPath = path.resolve(path.dirname(inputPath), outputName)
 
+  let isAppBundle = false
   let taskFunction: (options: TaskOptions) => Listr
 
   switch (fileExtension) {
     case '.apk':
       taskFunction = patchApk
       break
     case '.xapk':
+      isAppBundle = true
       taskFunction = patchXapkBundle
       break
     case '.apks':
     case '.zip':
+      isAppBundle = true
       taskFunction = patchApksBundle
       break
     default:
@@ -92,6 +96,7 @@ async function main() {
     uberApkSigner,
     wait: args.wait,
     skipPatches: args.skipPatches,
+    isAppBundle,
     debuggable: args.debuggable,
   })
     .run()

src/tasks/check-prerequisites.ts

@@ -1,3 +1,4 @@
+import execa = require('execa')
 import Listr = require('listr')
 
 import { TaskOptions } from '../cli'
@@ -25,13 +26,36 @@ export default function checkPrerequisites(options: TaskOptions) {
           throw new VersionError('Java', MIN_JAVA_VERSION, majorVersion)
       },
     },
+    {
+      title: 'Checking additional tools',
+      task: async () => {
+        if (options.isAppBundle && process.platform !== 'win32')
+          await ensureZipUlitiesAvailable()
+      },
+    },
     {
       title: 'Downloading tools',
       task: () => downloadTools(options),
     },
   ])
 }
 
+/**
+ * Ensure that `zip` and `unzip` are installed on Linux or macOS. Both are used
+ * (through the `cross-zip` package) when patching App Bundles.
+ */
+async function ensureZipUlitiesAvailable() {
+  try {
+    await execa('unzip', ['-v'])
+    await execa('zip', ['-v'])
+  } catch {
+    throw new Error(
+      'apk-mitm requires the commands "unzip" and "zip" to be installed when patching App Bundles.' +
+        " Make sure they're both installed and try again!",
+    )
+  }
+}
+
 class VersionError extends Error {
   constructor(tool: string, minVersion: number, currentVersion: number) {
     super(