Add unrooted Android example - #830

Using LibUsb on non rooted Android devices is explained in this PullRequest.
Should there eventually added a seperate C sample in the example folder for non rooted devices too?

If you can, please have another pull request to add the example for non root device. Thanks.

So this is my Android Sample for Libusb.

The Sample shows how to create an Shared Object with the NDK which can be accessed over JNI or JNA from Java or Kotlin. --> with Granted Permissions on Java/Kotlin and obtained FileDescriptor.

The approach of including the full source of LibUsb to an Android Studio project is quite complicated. It is only possible over NDK for now I think. (eventually it's enough for only applying the precombiled LibUsb lib to an android device and accessing it over the unrooted sample ...)

I only skimmed it, but it looks to be correct. I haven't been using libusb with android directly, but rather with the Rust FFI wrapper. I made a sample project that definitely worked and ran in CI here, in case that is useful to compare.

II'm working on porting a library to android. Here are my notes working off of this readme; I'll edit as I bump into things:

• Given most devices are unrooted, it would make sense for LIBUSB_OPTION_WEAK_AUTHORITY to be the default behavior on android if permissions are not present to enumerate devices.
• This example code casually references a field called mPermissionIntent. It looks like this is not hard to construct but responding to it might require subclassing BroadcastReceiver: https://developer.android.com/guide/topics/connectivity/usb/host#permission-d
• It's notable from that same page that permission can also be acquired by registering to respond to a usb connection event, and it sounds like then no request need be made; worth mentioning.

All these things are just things I noticed, nothing serious. I would merge this simply because it helps people more than what is already there.

See also my android pr #874 which provides for automating the java if the user can provide a jnienv pointer.

The new file examples/unRootedAndroid.c is specific to Android. As such I'd prefer it to live in the android directory. However, since it is just a modified copy of examples/testlibusb.c then you can use preprocessor macros to build the same file for both.

Please also note the naming conventions used in the project. We do not use Camel Case so please find a more suitable name for the file.

Adding preprocessor macros for Android in the original examples files would effect then the functionality for rooted devices, because here we have a different approach of initializing LibUsb.
To guarantee booth ways to work, we need different files I think.

Peter

Just wondering whether we should merge just the improved Readme for 1.0.25RC1 and leave the examples for next release.

If we do pass a pointer (to a pointer) to a context, like so libusb_init(&ctx), then ctx in libusb_init is not NULL, so default_context_options[LIBUSB_OPTION_WEAK_AUTHORITY] that was set before doesn't seem actually used at all, is it?

phew, for my understanding libusb_set_option to LIBUSB_OPTION_WEAK_AUTHORITY skipps the device enumeration. I must admit, I don't know how the internal way of libusb works.

I think the following patch would make LIBUSB_OPTION_WEAK_AUTHORITY have an effect, and it also fixes the app crash problems I was mentioning at first:

diff --git a/libusb/core.c b/libusb/core.c
index 054bc6a..90a1339 100644
--- a/libusb/core.c
+++ b/libusb/core.c
@@ -2205,14 +2205,11 @@ int API_EXPORTED libusb_set_option(libusb_context *ctx,
        }

        ctx = usbi_get_context(ctx);
-       if (NULL == ctx) {
-               return LIBUSB_SUCCESS;
-       }

        switch (option) {
        case LIBUSB_OPTION_LOG_LEVEL:
 #if defined(ENABLE_LOGGING) && !defined(ENABLE_DEBUG_LOGGING)
-               if (!ctx->debug_fixed)
+               if (ctx && !ctx->debug_fixed)
                        ctx->debug = (enum libusb_log_level)arg;
 #endif
                break;
@@ -2230,6 +2227,10 @@ int API_EXPORTED libusb_set_option(libusb_context *ctx,
        default:
                return LIBUSB_ERROR_INVALID_PARAM;
        }
+
+       if (NULL == ctx) {
+               return LIBUSB_SUCCESS;
+       }

        return LIBUSB_SUCCESS;;
 }

The purpose of that patch is to call usbi_backend.set_option(...) (which is what actually uses LIBUSB_OPTION_WEAK_AUTHORITY in linux_usbfs.c) when there is no default context initialised.

Please let me know if you'd like me to create a PR for this.

Please let me know if you'd like me to create a PR for this.

ok, try to create the PR. Eventually add #ifdef __ANDROID__ to not influence the regular way of other platforms.

I extracted the README change here and fixed up formatting, in #996, so that that part can be merged while we wait for the example to be finalized.

The PR has been updated and the libusb_set_option method has been changed.

Only that it doesn't work... due to #942. I can push this as soon as 942 has been sorted out.

Only that it doesn't work... due to #942. I can push this as soon as 942 has been sorted out.

#942 seems to be okay based on my limited understanding of libusb internals. Probably we can merge that first.

If that helps, I've added a sample app that tests #942 here: https://github.com/harbulot/LibUsbAndroidIssue942

(I've put it under MIT license there, but I'd certainly be happy to give to to the libusb project if there's a good place for it.)

Please confirm that this builds and runs fine from git master now.

Hello tormodvolden,

I can confirm that the last build compiles and runs fine.
I have tested the build with following Android Studio Project: https://github.com/Peter-St/unRootedSample

Thanks, Peter

@Peter-St, thanks a lot for verifying and, of course, for contributing this example.