Possible to use multiple authorities with FileProvider?

android android-manifest android-contentprovider manifest-merging
stkent picture stkent · Apr 3, 2017 · Viewed 17.5k times · Source

Background

I maintain a library whose core functionality involves sharing programmatically-captured screenshots to external email applications.

I use a FileProvider to accomplish this, which means my library's manifest contains a <provider> tag:

<provider
    android:name="android.support.v4.content.FileProvider"
    android:authorities="${applicationId}.bugshaker.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/filepaths" />
</provider>

filepaths.xml is defined as follows:

<paths>
    <files-path path="bug-reports/" name="bug-reports" />
</paths>

A consumer of my library has an application which itself uses a FileProvider to share files. My expectation was that it should be possible to allow both providers to share files if the consuming application used the following manifest <provider> tag:

<provider
    android:authorities="${applicationId}.fileprovider;${applicationId}.bugshaker.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true"
    android:name="android.support.v4.content.FileProvider"
    tools:replace="android:authorities">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/file_paths"
        tools:replace="android:resource" />
</provider>

This manifest entry:

  • specifies two Provider authorities, ${applicationId}.fileprovider (for application file sharing) and ${applicationId}.bugshaker.fileprovider (for library file sharing);
  • references an updated filepaths.xml, which contains separate directory definitions for application-generated files and library-generated files:
<paths>
    <external-path
        name="redacted"
        path="" />
    <files-path
        name="bug-reports"
        path="bug-reports/" />
</paths>

After building the application, we have confirmed that the generated manifest has had the correct nodes replaced with these updated values.

However, when the application using this configuration is assembled (successfully) and run, we see a crash on launch:

E: FATAL EXCEPTION: main
   Process: com.stkent.bugshakertest, PID: 11636
   java.lang.RuntimeException: Unable to get provider android.support.v4.content.FileProvider: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.XmlResourceParser android.content.pm.PackageItemInfo.loadXmlMetaData(android.content.pm.PackageManager, java.lang.String)' on a null object reference
       at android.app.ActivityThread.installProvider(ActivityThread.java:5856)
       at android.app.ActivityThread.installContentProviders(ActivityThread.java:5445)
       at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5384)
       at android.app.ActivityThread.-wrap2(ActivityThread.java)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1545)
       at android.os.Handler.dispatchMessage(Handler.java:102)
       at android.os.Looper.loop(Looper.java:154)
       at android.app.ActivityThread.main(ActivityThread.java:6119)
       at java.lang.reflect.Method.invoke(Native Method)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
    Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.XmlResourceParser android.content.pm.PackageItemInfo.loadXmlMetaData(android.content.pm.PackageManager, java.lang.String)' on a null object reference
       at android.support.v4.content.FileProvider.parsePathStrategy(FileProvider.java:583)
       at android.support.v4.content.FileProvider.getPathStrategy(FileProvider.java:557)
       at android.support.v4.content.FileProvider.attachInfo(FileProvider.java:375)
       at android.app.ActivityThread.installProvider(ActivityThread.java:5853)
       at android.app.ActivityThread.installContentProviders(ActivityThread.java:5445) 
       at android.app.ActivityThread.handleBindApplication(ActivityThread.java:5384) 
       at android.app.ActivityThread.-wrap2(ActivityThread.java) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1545) 
       at android.os.Handler.dispatchMessage(Handler.java:102) 
       at android.os.Looper.loop(Looper.java:154) 
       at android.app.ActivityThread.main(ActivityThread.java:6119) 
       at java.lang.reflect.Method.invoke(Native Method) 
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

Using the debugger, I am able to see that the method FileProvider.parsePathStrategy invokes PackageManager.resolveContentProvider with the authority string "${applicationId}.fileprovider;${applicationId}.bugshaker.fileprovider". resolveContentProvider then returns null, leading to this NPE.

If I manually call resolveContentProvider while paused at this instruction and pass either "${applicationId}.fileprovider" or "${applicationId}.bugshaker.fileprovider", resolveContentProvider instead returns a non-null ProviderInfo instance (which would seem to be the expected result).

This difference confuses me because the <provider> element documentation states that multiple authorities are supported:

A list of one or more URI authorities that identify data offered by the content provider. Multiple authorities are listed by separating their names with a semicolon. To avoid conflicts, authority names should use a Java-style naming convention (such as com.example.provider.cartoonprovider). Typically, it's the name of the ContentProvider subclass that implements the provider

There is no default. At least one authority must be specified.

Questions

  • Is it possible to have a single application expose a FileProvider with multiple authorities and file paths?
    • If so, what do I need to change to make that work?
    • If not, are there other ways to configure file sharing within my library that avoid conflicts such as this one?

Answer

stkent picture stkent · Apr 17, 2017

My solution to this problem has actually been to avoid relying on a single FileProvider parsing multiple authorities. While this doesn't directly address the question as stated, I'm posting it for posterity.

I updated my library to leverage an empty subclass of FileProvider, so that the library's updated manifest provider entry is now:

<provider
    android:name=".flow.email.screenshot.BugShakerFileProvider"
    android:authorities="${applicationId}.bugshaker.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true">
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/library_file_paths" />
</provider>

The merged manifest of an application that (1) uses a stock FileProvider and (2) consumes my library will now contain both of the entries shown below (no collision!):

<provider
    android:name="android.support.v4.content.FileProvider"
    android:authorities="com.consuming.application.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true" >
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/application_file_paths" />
</provider>

<provider
    android:name="com.github.stkent.bugshaker.flow.email.screenshot.BugShakerFileProvider"
    android:authorities="com.consuming.application.bugshaker.fileprovider"
    android:exported="false"
    android:grantUriPermissions="true" >
    <meta-data
        android:name="android.support.FILE_PROVIDER_PATHS"
        android:resource="@xml/library_file_paths" />
</provider>

I didn't realize that this was a potential solution until a coworker pointed it out. My assumption had previously (and incorrectly) been that all FileProviders in the manifest must set

android:name="android.support.v4.content.FileProvider"

but a quick check of the documentation revealed my error:

The name of the class that implements the content provider, a subclass of ContentProvider. This should be a fully qualified class name (such as, "com.example.project.TransportationProvider"). [...]

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