Android `withDocumentPicker` may crash on real devices due to `URL.appendingPathComponent` NPE

[guoshao-dev]

Body

We are seeing a real-device Android crash when importing files with SkipKit's withDocumentPicker.

Symptoms

After selecting a file from the system picker, the app immediately crashes on the main thread before our own import/validation logic runs.

This is reproducible for us with PDF files from Downloads on a real Android device. We did not reliably reproduce it on emulator.

Stack trace

java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1062580886, result=-1, data=Intent { dat=content://com.android.providers.downloads.documents/document/msf:146 flg=0x43 }} to activity {app.coutto.jade/jade.module.MainActivity}: java.lang.NullPointerException。整体的log：04-16 23:46:58.618 W/HwActivityTaskManagerServiceEx( 1387): appSwitch from: com.android.documentsui to: app.coutto.jade
04-16 23:46:58.674 E/AndroidRuntime(10066): FATAL EXCEPTION: main
04-16 23:46:58.674 E/AndroidRuntime(10066): Process: app.coutto.jade, PID: 10066
04-16 23:46:58.674 E/AndroidRuntime(10066): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1062580886, result=-1, data=Intent { dat=content://com.android.providers.downloads.documents/document/msf:146 flg=0x43 }} to activity {app.coutto.jade/jade.module.MainActivity}: java.lang.NullPointerException
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.ActivityThread.deliverResults(ActivityThread.java:6027)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.ActivityThread.handleSendResult(ActivityThread.java:6068)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:51)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2706)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.os.Handler.dispatchMessage(Handler.java:109)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.os.Looper.loop(Looper.java:228)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.ActivityThread.main(ActivityThread.java:9105)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at java.lang.reflect.Method.invoke(Native Method)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:614)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1129)
04-16 23:46:58.674 E/AndroidRuntime(10066): Caused by: java.lang.NullPointerException
04-16 23:46:58.674 E/AndroidRuntime(10066):     at skip.foundation.URL._appendingPathComponent(URL.kt:322)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at skip.foundation.URL.appendingPathComponent(URL.kt:325)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at jade.ui.View_JadeDocumentPickerKt.withJadeDocumentPicker$lambda$0$0$0(View+JadeDocumentPicker.kt:63)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at jade.ui.View_JadeDocumentPickerKt.$r8$lambda$0XlgswPBrP8Xoc9uug2MGsF6uXQ(Unknown Source:0)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at jade.ui.View_JadeDocumentPickerKt$$ExternalSyntheticLambda0.invoke(D8$$SyntheticClass:0)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at androidx.activity.compose.ActivityResultRegistryKt.rememberLauncherForActivityResult$lambda$4$0$0(ActivityResultRegistry.kt:104)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at androidx.activity.compose.ActivityResultRegistryKt.$r8$lambda$3CvmGOvkwZLY6ksF4ULs20ma2UE(Unknown Source:0)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at androidx.activity.compose.ActivityResultRegistryKt$$ExternalSyntheticLambda2.onActivityResult(D8$$SyntheticClass:0)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at androidx.activity.result.ActivityResultRegistry.doDispatch(ActivityResultRegistry.kt:350)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at androidx.activity.result.ActivityResultRegistry.dispatchResult(ActivityResultRegistry.kt:311)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at androidx.activity.ComponentActivity.onActivityResult(ComponentActivity.kt:788)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at androidx.fragment.app.FragmentActivity.onActivityResult(FragmentActivity.java:152)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.Activity.dispatchActivityResult(Activity.java:8735)
04-16 23:46:58.674 E/AndroidRuntime(10066):     at android.app.ActivityThread.deliverResults(ActivityThread.java:6020)
04-16 23:46:58.674 E/AndroidRuntime(10066):     ... 11 more
04-16 23:46:58.679 W/ActivityTaskManager( 1387): finishTopCrashedActivityLocked Force finishing activity app.coutto.jade/jade.module.MainActivity
04-16 23:46:58.680 W/HwActivityTaskManagerServiceEx( 1387): setResumedActivityUncheckLocked start call, from: ActivityRecord{cd771ce u0 app.coutto.jade/jade.module.MainActivity t392 f}}, to: ActivityRecord{f5a29a7 u0 com.huawei.android.launcher/.unihome.UniHomeLauncher t2}
04-16 23:46:58.680 W/HwActivityTaskManagerServiceEx( 1387): appSwitch from: app.coutto.jade to: com.huawei.android.launcher
04-16 23:46:58.716 W/InputDispatcher( 1387): Attempted to unregister already unregistered input channel '8df915f app.coutto.jade/jade.module.MainActivity (server)'
04-16 23:46:59.181 W/ActivityTaskManager( 1387): Activity top resumed state loss timeout for ActivityRecord{cd771ce u0 app.coutto.jade/jade.module.MainActivity t-1 f}}
04-16 23:47:04.700 E/SWAP_AppModel( 1387): getAppNowScore, app not exist: app.coutto.jade

Likely cause

The Android implementation of withDocumentPicker copies the selected document into cache and builds the destination path with URL.appendingPathComponent(...).

That eventually reaches:

return components_0.url(relativeTo = baseURL)!!

in SkipFoundation.URL._appendingPathComponent, which can return null on Android and then crash with NPE.

So this looks like an Android path construction issue inside SkipKit / SkipFoundation, not an app-level file parsing issue.

Minimal fix suggestion

In the Android cache-copy path, avoid URL.appendingPathComponent(...) entirely and use JVM file APIs instead:

let safeFilename = selectedFilename.wrappedValue ?? "imported_file"
let outputFile = java.io.File(storageDir, safeFilename)
let destinationFileURL = URL(platformValue: outputFile.toURI())

This avoids the problematic SkipFoundation.URL path construction on Android.

Additional hardening that would help

• avoid selectedFilename.wrappedValue!
• avoid getColumnIndexOrThrow(...)
• fall back to resolver.getType(uri)
• fall back to uri.lastPathSegment when DISPLAY_NAME is missing
• handle openInputStream(uri) returning null

[marcprux]

Is that diagnosis from an LLM? I'm not sure it is accurate (although it may be right that we should do more hardening, if only to be able to report errors better).

Can you check the AndroidManifest.xml and ensure that you have the android.permission.WRITE_EXTERNAL_STORAGE and android.permission.READ_EXTERNAL_STORAGE permission set? E.g., see https://github.com/skiptools/skipapp-showcase-fuse/blob/main/Android/app/src/main/AndroidManifest.xml#L26

[guoshao-dev]

Quick note: the diagnosis above was actually suggested by an LLM, which also proposed a workaround that bypasses the crash in withDocumentPicker.

Unfortunately, the issue still persists even after adding both android.permission.WRITE_EXTERNAL_STORAGE and android.permission.READ_EXTERNAL_STORAGE to AndroidManifest.xml. Some files can be imported successfully, while others consistently cause the app to crash. So it's not about permission.

After some investigation, I've confirmed that the crash is triggered by file names containing whitespace — renaming the files to remove the spaces allows them to be imported correctly. Hope this helps narrow down the root cause.