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83 lines
2.8 KiB
Plaintext
83 lines
2.8 KiB
Plaintext
December 6, 2014.
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The idea is to make a proper ssh implementation for Android. Important
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features:
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* it should run happily without root (on a non-root port)
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* it should be a regular android app requiring no special permissions,
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and not requiring any 'magic' executable files
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* should not rely on busybox
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* preferably support sftp
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* open source
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The existing apps are either expensive, don't work, need root, or too
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complicated, or a mix of all of the above. And none of them are open
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source.
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I figure I'll start with dropbear, which I will run through JNI instead
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of putting it in its own binary (because making such a binary executable
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is a bit of a hack).
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So that's the plan........
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December 14, 2014.
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I got dropbear to compile under the Android NDK, so now it's time to work
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on the Android side of it.
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I need:
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* a Service that can be started, stopped, and queried for whether it's
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running or not
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* a Thread to implement the Service's work (by calling into dropbear's
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main()), which can also be stopped.
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* a config UI with at least these choices:
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- bool: start on boot (def: false)
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- number: port number (def: 2222)
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- string: path to authorized_keys file (def: /sdcard/ssh)
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- string: name of default shell (def: /system/bin/sh -l)
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- string: default path for HOME (def: /sdcard/ssh)
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- button: start or (if it's running) stop
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December 15, 2014.
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Getting to the fun part. Process management...
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To start sshd, it seems like I can startService(). Then in the Service's
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onStartCommand(), call startForeground() so it won't be killed (return
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START_STICKY too?).
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The question is if dropbear's main() should run under a separate Thread,
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or a separate Process. The trouble with a Thread is that it might be
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hard to kill. The trouble with a process is that there is no way to
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report back status (such as a failure to start sshd).
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Connectbot starts a new process for its shell -- it really doesn't have a
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choice because the shell binary isn't linked with Connectbot, and exec()
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in a thread stinks. To stop it, it just closes stdin/stdout!!! So
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zombies can (and do) linger.
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I suppose dropbear could be in its own process if it had something like
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stdin/stdout to communicate failure? Or it could just write error
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messages to (i.e.) /sdcard/ssh/log. To stop the service, it would just
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use kill().
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I am curious how the main waiting-for-connections loop looks, but even if
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it uses select(), I'm not sure how I would honor Thread.interrupt() or
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whatever. It's not guaranteed to interrupt select(), and I'm not keen on
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adding an arbitrary timeout/polling feature to it.
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XXX - disable utmp/wtmp
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XXX - visit XXX in jni/interface.c
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XXX - allow user to specify parameters for dropbear
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XXX - convert UI to use proper preferences templates, and have ...->settings instead of putting it on the home screen
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XXX - scp
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XXX - zlib
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XXX - rsync
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