Added more debugging, a package filter, a mode to only verify metadata, and more help output

[sure-fire]

Having spent the past 72 hours struggling to recover a CalyxOS backup onto a GrapheneOS phone, this tool was invaluable. Thank you for creating it!

To troubleshoot issues and generally learn how Seedvault is supposed to work, I added more debugging messages. Eventually, I started adding some convenient features and decided it was worth offering up.

Since I was searching across multiple backups, trying to test mnemonic phrases and find certain app data, I added a "--check" flag to verify when I had the right mnemonic and a "--package" flag to extract only the needed package.

While I was at it, I added "--debug" so it can be either an environment variable or a command-line option. Plus a "--help" flag and detailed output.

Let it be known that this is the first time I've written Golang and had it actually compile. So please be gentle. 😅

[sure-fire]

Here's an example / test run: (possibly also a mini-tutorial if anyone else is trying to salvage their text messages):

$ ./extract --help
usage: extract [PATH] [MNEMONIC] [optional]
    PATH      should be a 13-digit folder name (inside .SeedVaultAndroidBackup)
    MNEMONIC  should be a twelve word phrase

    Optional arguments include:
       --check    confirms that the backup metadata is valid, but does not extract the data
       --list     lists the package names only, but does not extract the data
       --debug    enables excessive amounts of output *INCLUDING SENSITIVE DATA, LIKE KEYS AND PHRASES*
       --package  specifies a Android package name -- all others will be skipped

    Example usage:
         extract my_backups/.SeedVaultAndroidBackup/1708344900209 'buzz float culture lake paper season amused rain marine promote coyote mechanic' --list
         extract my_backups/.SeedVaultAndroidBackup/1708344900209 'buzz float culture lake paper season amused rain marine promote coyote mechanic' --check
         extract my_backups/.SeedVaultAndroidBackup/1708344900209 'buzz float culture lake paper season amused rain marine promote coyote mechanic' --package com.android.contacts

$ export PHRASE="buzz float culture lake paper season amused rain marine promote coyote mechanic"

$ export BACKUPS="/mnt/backups/pixel"

$ ./extract $BACKUPS/.SeedVaultAndroidBackup/1708344900209 "$PHRASE" --check
CHECK-MODE ENABLED: extract on '1708344900209' stopped before deploying 179 packages

$ ./extract $BACKUPS/.SeedVaultAndroidBackup/1708344900209 "$PHRASE" --list --package com.android.providers.telephony
    com.android.providers.telephony

$ ./extract $BACKUPS/.SeedVaultAndroidBackup/1708344900209 "$PHRASE" --package com.android.providers.telephony
    extracting com.android.providers.telephony.tar

$ ls *.tar
com.android.providers.telephony.tar

$ tar xvf com.android.providers.telephony.tar
apps/com.android.providers.telephony/_manifest
apps/com.android.providers.telephony/d_f/000000_sms_backup
apps/com.android.providers.telephony/d_f/000001_mms_backup

$ cd apps/com.android.providers.telephony/d_f

$ python3 -c "import zlib; print(zlib.decompress(open('000000_sms_backup','rb').read()))" > 000000_sms_backup.json

(Note: filenames and mnemonic phrases have been changed to protect the innocent)