java.io.FileNotFoundException

E/LogWriter: save: 
 java.io.FileNotFoundException: /data/com.github.piasy.bootstrap/performance/looper-2016-12-11_23-48-25.844.log (No such file or directory)
     at java.io.FileOutputStream.open(Native Method)
     at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
     at java.io.FileOutputStream.<init>(FileOutputStream.java:140)
     at com.github.moduth.blockcanary.LogWriter.save(LogWriter.java:108)
     at com.github.moduth.blockcanary.LogWriter.save(LogWriter.java:56)
     at com.github.moduth.blockcanary.BlockCanaryInternals$1.onBlockEvent(BlockCanaryInternals.java:63)
     at com.github.moduth.blockcanary.LooperMonitor$1.run(LooperMonitor.java:74)
     at android.os.Handler.handleCallback(Handler.java:751)
     at android.os.Handler.dispatchMessage(Handler.java:95)
     at android.os.Looper.loop(Looper.java:154)
     at android.os.HandlerThread.run(HandlerThread.java:61)

[zjupure]

@Piasy this problem is produced when the external storage is not available or not writable. For example, the external storage is unmounted and it is really exist in some devices. When external storage is not exist, the library with choose the /data/{your_provided_dir}, but this directory is not accessible by normal app due to permission limit. the code in BlockCanaryInternals.getPath() have some drawback in design.

static String getPath() {
        String state = Environment.getExternalStorageState();
        String logPath = BlockCanaryInternals.getContext()
                == null ? "" : BlockCanaryInternals.getContext().providePath();

        if (Environment.MEDIA_MOUNTED.equals(state)
                && Environment.getExternalStorageDirectory().canWrite()) {
            return Environment.getExternalStorageDirectory().getPath() + logPath;
        }
        return Environment.getDataDirectory().getAbsolutePath() + BlockCanaryInternals.getContext().providePath();
    }

There is another permission problem, the external storage is not writeable default except the app-specifical directory due to the dynamic permission mechanism since Android 6.0. So i suggest BlockCanary library can modify the implementation of BlockCanaryInternals.getPath(), there are two choice:

1. the path is provided entirely by user through BlockCanaryContext.providePath(), the path validation is decided by user.
2. change the external storage directory to app-specifical directory, when this path is not avaiable, use the internal storage directory instead.

App-specifical directory usually locates in external storage /Android/data/{pacakage_name}, you can use Context.getExternalCacheDir() or Context.getExternalFilesDir() to obtain a cache directory(/cache) or a files directory(/files). Those directory do not need to declare permission in Android Mainifest since Kitkat. If abvoe path is not avaiable (external storage is unmount), use Context.getCacheDir() or Context.getFilesDir() instead. The result are usually located in /data/data/{pacakage_name} in internal storage and always available to normal app.

A reference implementation for choice 2

static String getPath() {
        String state = Environment.getExternalStorageState();
        String logPath = BlockCanaryInternals.getContext()
                == null ? "" : BlockCanaryInternals.getContext().providePath();

        Context context = BlockCanaryInternals.getContext().provideContext();
        File appCache = context.getExternalCacheDir();
        if (appCache != null && Environment.MEDIA_MOUNTED.equals(state)) {
            return  appCache.getAbsolutePath() + logPath;
        }
        return context.getCacheDir() + logPath;
    }

[markzhai]

@initialjie @zjupure thanks, I adopt that the path should be provided entirely by user, the library itself should not do any magic to it.