Show proper error message from libimobiledevice

[Noisyfox]

Currently when something goes wrong in libimobiledevice, it simply print out a generic error message like

Failed to get debug server (debug_server_error_t returned -256)

It will be better to show the error detail from libimobiledevice.

[Berstanio]

I had a small look into it and I think there are theoretical just a few things to tweak.

1. Add the --enable-debug flag as option to the autogen.sh script.

https://github.com/multi-os-engine/moe-prebuilts/blob/moe-master/external/libimobiledevice/libimobiledevice/moe-prebuild-macos.sh#L26-L36

2. Set a few variables like here (I think only "idevice_set_debug_level" is needed):

https://github.com/libimobiledevice/libimobiledevice/blob/master/tools/idevicedebugserverproxy.c#L205-L209

But then everything will be written in stderr and therefor will be always logged into the console I think. But this would be extremly spamming and annoying. The only fix/workaround I see here is to edit the following lines to print to a specific file.
https://github.com/multi-os-engine/libimobiledevice/blob/f1f05dcc9db7e3132e2b6da4a09e4d87394f1dcc/common/debug.c#L68-L73
Then, on error, read the file and print the content of the file? But this seems a bit complicated and not clean. Am I missing something?

https://github.com/libimobiledevice/libimobiledevice/blob/master/common/debug.c#L78-L96

//EDIT: Why isn't it previewing the lines of code? Does this only work in the same repo?

[Noisyfox]

I don't think these debugging output provides any useful information though... Most of the debug outputs are simply just "xxx bytes sent/received", but doesn't really tell you the actual error and how to resolve it.

[Berstanio]

I would partially agree. Yes, most of the debug output isn't really useful, but sometimes I think it provides relevant information.
e.g.: https://github.com/libimobiledevice/libimobiledevice/blob/master/src/idevice.c (nearly every error gets mapped to just "IDEVICE_E_UNKNOWN_ERROR")
or
https://github.com/libimobiledevice/libimobiledevice/blob/master/src/lockdown.c#L756-L768

Also the more useless debug logs can help to search for others having the same error (see e.g. idevice above). But I would agree that it is really just a low priority feature.